System, bag and method for purifying water

Abstract

The disclosure relates to a purification system and a purification bag (6) for use therein, configured for (solar) heat-driven water purification of contaminated water. The purification bag (6) comprises a distillation assembly (601,..60n), comprising: - a contaminated water chamber (30) for collecting contaminated water, the contaminated water chamber (30) comprising a top sheet configured for absorbing heat; - a purified water chamber (50) for collecting purified water, the purified water chamber (50) comprising a condensation sheet configured for collecting condensed purified water; - a membrane (40) arranged between the top sheet and condensation sheet, the membrane dividing the distillation assembly into the contaminated water chamber (30) and the purified water chamber (50), wherein the membrane (40) comprises a membrane sheet configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet; wherein the top sheet and the membrane sheet are polymeric sheets that are bonded to each other by welding according to a welding pattern.

Description

[0001] SYSTEM, BAG AND METHOD FOR PURIFYING WATER

[0002] The present invention relates to a purification system for heat-driven water purification of contaminated water and to a purification bag configured to be used in a purification system. The invention also relates to the use of a purification bag or purification system, to a method of heat- driven water purification of contaminated water in a purification system and to a method of manufacturing a purification bag.

[0003] In the course of times many different types of systems for purifying contaminated water have been developed. Various disadvantages in view of manufacturing cost, operational costs (maintenance, fouling, cleaning, refilling, repairs), expected lifetime, and environmentally friendly and sustainable disposal are associated with at least some of these known purification systems. Furthermore, there is a need for purification systems that may operate without any externally generated electrical energy or fossil fuels.

[0004] According to a first aspect a purification bag for use in a purification system for heat- driven water purification of contaminated water is provided, the purification bag comprising a distillation assembly or a stack of distillation assemblies, wherein each distillation assembly is configured to receive a part of the contaminated water and separate a purified water portion from the received part of the contaminated water, and wherein a distillation assembly comprises:

[0005] - a contaminated water chamber for collecting contaminated water, the contaminated water chamber comprising a top sheet configured for absorbing heat;

[0006] - a purified water chamber for collecting purified water, the purified water comprising a condensation sheet configured for collecting condensed purified water;

[0007] - a membrane arranged between the top sheet and condensation sheet, the membrane dividing the distillation assembly into the contaminated water chamber and the purified water chamber, wherein the membrane comprises a membrane sheet configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet; wherein the top sheet and the membrane sheet are polymeric sheets that are bonded to each other by welding according to a welding pattern, wherein the top sheet and membrane sheet, preferably also the condensation sheet, are thin films.

[0008] Reference is made to “sheets” which are stated to be “thin films”. Throughout the present disclosure these sheet may equally be referred to as “thin film sheets”. The thickness of the (thin film) sheets typically is smaller than 1 mm, for instance in the range of 20 micrometers to 1000 micrometers, preferably between 50 and 500 micrometers, and / or the density (when referring to the characteristics of the sheets, the term density may be used to refer to mass per unit area, i.e. g / m2) of the (thin film) sheets may be in the range of 10 to 1000 g / m2, preferably between 30 and 300 g / m2, for example between 50-150 m2. Furthermore, the sheets or thin films (i.e. the thin film sheets) used in the water purification bag are flexible to the extent that the bag, and preferably the contaminated water chambers, is / are inflatable when filled with fluid. Preferably the top sheet, the condensation sheet and at least the membrane sheet of the membrane are configured to be connected or bonded to each other by welding. In further embodiments the top sheet, the condensation sheet, the membrane sheet (and a reinforcement sheet of the membrane, if present) are configured to be bonded to each other by welding. The purified water chamber may also be referred to as condensation chamber.

[0009] In embodiments of the present disclosure, at least one of the top sheet, condensation sheet and membrane sheet are flexible sheets, preferably configured to be flexible to form one or more channels when used, more preferably configured to be inflatable from an essentially flat state to an expanded state. The inflation takes place when the bag is filled with fluid (i.e. water) at the usual operating conditions, for instance at a slight overpressure relative to the ambient air pressure.

[0010] In embodiments of the present disclosure, the top sheet and the membrane (i.e. the membrane sheet and / or an optional reinforcement sheet) are solely connected by welding, wherein preferably the top sheet, condensation sheet and membrane sheet are mutually solely bonded by thermal welding. In this manner strengthening constructions, for instance comprising stiff elements like plates and / or frames, can be dispensed with, making the overall construction of the bag less complex and expensive. Hence, in embodiments of the present disclosure, the purification bag does not comprise a plate and / or frame construction and / or, in similar embodiments, the bag is configured to operate without comprising plates or frames.

[0011] By absorbing heat (for instance, solar heat impinging on the top surface of the distillation assembly) the temperature in the first, uppermost contaminated water chamber is raised (typically to temperatures between 50 and 90 degrees Celsius). This temperature rise causes (not- contaminated) water and / or water vapor in the contaminated water chamber (i.e. water in liquid and / or vapor phase) to pass the membrane into the purified water chamber. In the purified water chamber the water that has passed the membrane is in the vapor phase and starts to condense in the chamber (the condensation sheet having a temperature generally below the temperature of the water vapor arriving in the purified water chamber) so as to generate purified water in the liquid phase. During this condensation on the condensation sheet heat is generated that may be used to raise the temperature in a second contaminated water chamber (if present) that is arranged below the first purified water chamber. This is repeated for all the distillation assemblies.

[0012] An advantage of using a polymeric membrane and polymeric sheets is that (solar) heat- powered membrane distillation or evaporation can be achieved using materials that are significantly more cost-effective and / or cheaper than known membranes in similar applications of water purification. The membrane and sheets can be easily produced by manufacturers and have proven to be effective in the purification of water in the present system. The concept is based on the insight that the present heat-driven purification system is a low-throughput system meaning that the regular flow velocities of the contaminated water in the contaminated water chamber(s) are relatively low and / or that the regular static pressure inside the purification bag is relatively low compared to the ambient pressure. Due to these low velocities and pressures, materials can be used in the purification system that would normally be considered to be unsuited for the purpose. Furthermore, similar advantages in view of costs, ease of manufacturing and effectiveness can be realized by simply welding the sheets and membrane to each other. The welding is made possible since the materials used are all polymeric materials (preferably polymeric materials of the same type, as will be discussed later). By welding the materials together, purification bags may be realized that do not need any external frames, plate constructions or similar means to provide the necessary constructional strength: just welding of the polymeric materials according to a predefined welding pattern to form (channels in) the chambers in the purification bag is sufficient. In fact, in certain embodiments of the present disclosure, the top sheet and the membrane sheet are solely bonded to each other by the welds of said welding pattern.

[0013] Contaminants could be in liquid and / or solid phase. An example of a contaminant in contaminated water (saline water) is salt (saline water = water with a relatively high concentration of dissolved salts). The contamination of the contaminated water could also be salt in combination with a toxic compound (for instance, toxic ions dissolved in water), in which case in the saline water one or more potentially toxic compounds have been dissolved, etc. In the latter case both the salt and toxic compound are not present in purified water (while they remain present (in a higher concentration) in the contaminated water chamber).

[0014] As mentioned above, the transport (flow) of water inside the water purification module involves relatively low flow velocities. In embodiments of the present disclosure the water flow is a quasi-static flow in order to ensure a suitable thermo-halocline stratification. More in general, the distribution of the hydrostatic pressure in the (channels of the) water purification module should be such that this pressure is larger than pressure variations caused by the flow of water in the water purification module (i.e. the local varying hydrodynamic pressure). When the purification for instance is used to purify saline water, more specifically sea water, the velocity of the water inside the water purification module should be in order of magnitude of several centimeters per second (maximum), for instance in the order of centimeters per second, for instance about 1 cm / s or lower.

[0015] The required hydrostatic pressure may be achieved by positioning a feed water tank at a height position above the top end portion of each of the purification bags in the purification system. A residual water tank may be positioned downstream of the water purification module(s). The tank may be fitted with thermal insulation to keep the water purification modules at the desired higher temperature (i.e. desired from the point of view of an effective distillation and therefore of the purified water capacity of the system).

[0016] Tests in an outdoor environment have proven that a yield of purified water from a saline water (sea water) feed per day (a day with an average amount of sunshine) and per m2irradiated area of the purification system may be 3-5 liter for a single distillation assembly and 6-9 liter for a stack of three distillation assemblies in a purification bag.

[0017] In embodiments of the present disclosure the membrane sheet is a microporous membrane sheet. The transfer of water towards the purified water chamber primarily takes place by distillation through the pores of this membrane sheet. In embodiments (to be described later) wherein the membrane comprises a membrane sheet and a coating provided on the membrane sheet, distillation and pervaporation take places through the pores of the microporous membrane sheet and through the coating. Membrane distillation in these embodiments may be defined as a process in which water in liquid form present on top of a membrane evaporates through the pores of the (polyolefin) membrane sheet and condenses on the cooler (polyolefin) condensation sheet. If a (silicone) thin coating on top of the porous membrane sheet is present, water molecules diffuse through the silicone coating and similarly evaporate through the pores in the membrane sheet. The mass transport of the water molecules is driven by the temperature difference in the top compartment or contaminated water chamber (including the (optionally coated) membrane sheet) and the (cooler) condensation sheet of the lower compartment or purified water chamber.

[0018] In embodiments of the present disclosure the polymeric top sheet, polymeric membrane sheet and polymeric condensation sheet are made of polyolefin material, for instance LDPE, HDPE, polypropylene (PP), or polymethylpentene.

[0019] In other embodiments of the present disclosure, the top sheet and condensation sheet are made of a polyamide polymer, for instance Nylon, and the membrane sheet is hydrophilic, for instance (partly) made of a polyetheramide block-copolymer which can be welded to the polyamide. In further embodiments of the present disclosure the top sheet and condensation sheet are made of a polyester polymer and the hydrophilic membrane sheet is a polyether ester blockcopolymer which can be welded to the polyester.

[0020] In these embodiments of the present disclosure the membrane sheet is an essentially non- porous sheet, in the sense that the sheet essentially does not comprise (micro) pores. The transfer of water towards the purified water chamber primarily takes place by pervaporation through the non- porous sheet and / or by swelling of the polyetheramide sheet. It has been shown that water evaporation takes place on the side facing the condensation sheet and driven by concentration gradients the dissolved contaminants that pass through the membrane are driven back towards the bulk in the feed water chamber formed by top sheet and the hydrophilic membrane sheet. In embodiments of the present disclosure the condensation sheet is a polymeric sheet that is bonded to at least one of the top sheet and the membrane sheet by welding according to a further welding pattern. The bonding strength of the welds is sufficient to cope with the relatively high pressure in the (channels of the) chambers, especially in the contaminated water chamber, so that in use no further attachment means, such as an external plate and frame construction for pressing individual sheets against each other, are needed. The purification bag is configured to operate in a stand-alone manner.

[0021] Furthermore, the (further) welding pattern may be formed by a number of point patterns, for instance point-shaped welds distributed over the respective bonded sheets, for instance distributed evenly over the area of the bonded sheets. The (further) welding pattern may also be formed by a plurality of consecutive point-shaped welds forming a line or line like-welding pattern (i.e. a dotted line). In other embodiments the welding pattern is formed by one more essentially uninterrupted welds extending essentially without interruptions along a line.

[0022] In embodiments of the present disclosure the welding pattern and the further welding pattern are respectively formed by one or more first welding lines and one or more second welding lines. Welding lines may be substantially uninterrupted lines or interrupted lines, including interrupted lines comprising point welds arranged to as to form one or more dotted lines. The welding lines tend to provide for a reduced amount of tension when the respective chamber is filled with water. Especially in case of the contaminated water chamber, a relatively high pressure may be built at inflation or in an inflated state (i.e. filling the (channels of the) chamber with contaminated water) so that an uninterrupted welding line or a welding with a relatively small number and / or size of interruptions may be preferred.

[0023] In embodiments of the present disclosure the microporous membrane sheet and the condensation sheet are made of the same type of material, preferably materials comprising the same polymer. In other words, polymers being welded (the polymers comprised in the microporous membrane sheet and the top sheet and potentially other sheets in the water purification bag) should ideally be miscible, meaning they can mix and dissolve in each other to form strong joints when welded together as sheets.

[0024] In embodiments of the present disclosure the welding of two polymeric sheets comprises heating material of both polymeric sheets, melting the polymeric sheets together and then allowing the polymeric sheets to cool causing fusion. This way of bonding is preferred (over, for instance, solvent welding or solid-state welding). In the preferred welding process, the welding is achieved using only the material of sheets involved. This implies that in principle no filler material or similar other material needed in certain types of welding process and / or bonding adhesives are needed to properly connect the sheets to each other. In embodiments of the present disclosure at least one of the welding pattern and further welding pattern is formed in one welding step, preferably using a thermal welding stamp. This has the advantage of an easy and accurate manufacturing. The term thermal welding is used to refer to any kind of welding effectively using heat, irrespective of how the heat is generated. For instance, the heat required to connect the sheets of the bag to each other may be generated by subjecting the sheets with ultrasound (ultrasonic welding).

[0025] In embodiments of the present disclosure the membrane comprises a hydrophobic membrane sheet, for instance a polyolefin sheet with micropores. A surface of a material (sheet) may be “hydrophobic” when the static water contact angle 0 is > 90° and a material is hydrophilic when this angle 0 is < 90° (see definition https: / / pubs.acs.org / doi / pdf / 10.1021 / jz402762h | J. Phys. Chem. Lett. 2014, 5, 686-688). Generally, liquid water has a large contact angle when brought into contact with hydrophobic surfaces due to their water repelling nature compared to the small contact angle that occurs when water is brought into contact with hydrophilic surfaces.

[0026] In embodiments of the present disclosure the membrane (further) comprises an uncoated microporous sheet. The uncoated microporous film holds back liquid water with dissolved salts and allows evaporation from the water surface of a meniscus supported by surface tension at the circumference of the micropores. For purifying feedwater with relatively low content of salt (low salinity) this type of membrane has been shown to have a relatively long lifetime before pore plugging by crystallization (scale), plugging with debris particles or biofouling decreases the productivity. However, for purifying feedwater with relatively high content of salt (high salinity) or for numerous other purification mixtures, one side of the microporous membrane sheet, preferably the side facing the contaminated water chamber, may be provided with a coating. The coating is at least one of a flexible, macromolecular chained, thin non-porous hydrophobic coating. Such coating may create a smooth surface and covers up the micropores of a microporous sheet to improve its anti-fouling, and anti-scale properties.

[0027] A disadvantage of the use of a microporous polymeric membrane (i.e. a hydrophobic microporous polymeric membrane or a hydrophilic microporous polymeric membrane) is that it is prone to fouling and therefore can only function properly under restrictive operating conditions. However, whereas most saline water membrane distillation processes use hydrophilic membranes and / or hydrophilic membrane coatings and these processes are optimized for high flux and high rejection of salts, it was surprisingly found that silicone (organic) coating can be used for the present low flux (passive and / or solar driven) membrane distillation systems. The ability to use silicone is remarkable since it is a hydrophobic material and the use of a hydrophobic material would not appear to be sensible in applications wherein water (in liquid and / or vapor form) is to pass the material for distillation purposes. Nevertheless it was found that for low water flux applications, a silicone coating applied to a microporous polymeric (polyolefin) membrane on the one hand still makes a distillation process possible since some of the water (vapor) will still pass the microporous membrane and coating, while on the other hand, a significant advantage against scaling and biofouling is given. Furthermore, due to the hydrophobic nature of the coating, it may also give a high selectivity for rejection of salts. More specifically, the silicone coating may form a barrier by allowing water to pass but leave salt or other contaminations behind. The silicone coating covers the micropores. Its viscosity is selected to avoid filling or clogging the micropores. The silicone coating provides a smooth surface facing the contaminated water chamber, thereby helping to avoid biofouling.

[0028] Additionally, as discussed earlier, embodiments wherein the micropores of the microporous sheet are covered by a silicone coating allow for suitable distillation: In case an air gap is present at the side of the membrane facing the purified water chamber, water in vapor form leaves the membrane and enters the air gap. This water in vapor form may condense into (purified) water in liquid form at the bottom of the purified water chamber. In embodiments wherein the membrane sheet is provided with a hydrophobic coating, solid or low-volatile organic impurities cannot pass. Furthermore, dissolved aqueous salt ions are rejected by the hydrophobic silicone coating, and thus remain for a large part in solution.

[0029] As discussed earlier, in membrane distillation, feed liquid is evaporated on the feed side of the membrane sheet and the resulting vapor then passes through the membrane sheet. Another mechanism is pervaporation wherein the feed liquid (for instance, a saline solution) may flow into the membrane (for instance, a hydrophilic membrane like a membrane made of polyetheramide), essentially not into the purified water chamber. The liquid that has entered the membrane is separated by evaporation on the membrane surface facing the purified water chamber (filled with mostly air).

[0030] In further embodiments of the present disclosure the coating is a silicone coating with a thickness of 10 micrometers or less, preferably less than 5 micrometers. The coating may be a silicone coating applied as (or comprising) a reactive silicone liquid. In general, reactive silicones are characterized by the presence of functional groups that serve to allow curing after shaping and often allow reaction with functional groups in materials to be bonded to the silicone, such as in coatings that impart anti-adhesive properties to the coated substrates. Common reactive groups include vinyl, epoxy, amino, acetoxy and hydrosilane functionality. The reactive silicone (reactive silicone liquid) preferably has a viscosity in a range of 1.000 to 15.000 mPa.s, preferably in a range of 2.000 to 5.000 mPa.s. The viscosity should be high enough to limit penetration into the micropores but still allow for a closed and homogenous silicone coating on the surface the material.

[0031] In embodiments of the present disclosure the micropores of the microporous membrane sheet are symmetrically distributed over the area facing the contaminated water chamber and / or wherein the micropores of the microporous membrane are asymmetrically distributed over its thickness, wherein the average pore size of the micropores in a first area facing the contaminated water chamber is smaller than the average pore size of the micropores in a second area facing the purified water chamber.

[0032] Furthermore, the pores in the membrane sheet should be sized (and shaped) to allow only vapor to pass, and not water in liquid form droplets of the feed liquid (water). In specific embodiments the pores are micropores having a diameter smaller than 2.0 pm, preferably smaller than 0.5 pm or even smaller than 0.2 pm. In embodiments wherein the pore diameter increases from a first side facing the contaminated water chamber to a second side facing the purified water chamber (asymmetric membrane) the preferred diameter of the micropores refers to the diameter of the pores in the area close to the first side of the membrane sheet facing the contaminated water chamber. The micropores closer to the second side of the membrane sheet may have a larger pore diameter.

[0033] In embodiments of the present disclosure the microporous sheet has a density (mass per unit area) in the range of 5 to 250 g / m2, preferably between 30 and 100 g / m2, and / or a thickness between 10 and 500 micrometer, preferably between 50 and 200 micrometer. In embodiments of the disclosure the top sheet and / or condensation sheet has a density (mass per unit area) in the range of 20 to 1000 g / m2, preferably between 50 and 300 g / m2, and / or a thickness of 20-1000 micrometer, preferably between 50 and 300 micrometer.

[0034] In embodiments of the present disclosure the membrane comprises a vapor-permeable reinforcement sheet attached to the side of the microporous membrane sheet facing the purified water chamber. In case of the presence of an air gap, the vapor-permeable reinforcement sheet may be attached to the side bordering the air gap. The attachment could be realized by lamination or by any other suitable attachment technique.

[0035] In embodiments of the present disclosure the reinforcement sheet is a fibrous polyolefin sheet, preferably having a density of about 10-1000 g / m2, and / or a thickness of 100-1000 pm, for example using a polymer adhesive web and / or preferably a hydro-entangled non-woven polyolefin. This may allow its welding onto the purification system in the same step together with the top sheet and the membrane.

[0036] In embodiments of the present disclosure the purification bag comprises a stack of multiple distillation assemblies arranged one on top of the other. The purification bag may comprise a first distillation assembly arranged on top of a second distillation assembly, wherein the condensation sheet of the first distillation assembly is formed by the top sheet of the second distillation assembly. In this manner less sheet material is needed. Furthermore, in these embodiments, condensation heat of the first distillation assembly is regenerated (reused) for evaporation purposes in the second distillation assembly, condensation heat of the second distillation assembly is regenerated (reused) for evaporation purposes in the third distillation assembly, etc.

[0037] In embodiments of the present disclosure the welding pattern comprises first welding lines (i.e. essentially uninterrupted lines or lines formed by arrays of welding points) arranged to form inner welding lines to define a plurality of interconnected channels for receiving and holding contaminated water and / or wherein the further pattern comprises second welding lines arranged to form outer welding lines to define at least one channel for receiving and holding purified water.

[0038] As mentioned above, in embodiments of the present disclosure the contaminated water chamber is arranged above the purified water chamber. Furthermore, the purified water chamber may be configured to form an air gap below the membrane so as to allow for air gap membrane distillation of the contaminated water. This air gap may be provided by the use of one or more spacers, for instance a spacer sheet / layer / material made of mesh material arranged inside a purified water chamber, to maintain an air gap below the membrane. In preferred embodiments, the spacer sheet or -material is bendable, or foldable at certain points, such that the water purification bag may be folded, for example transported or stored, in a folded configuration.

[0039] A spacer may be arranged inside a purified water chamber to provide a predefined minimum height of the purified water chamber. The spacer increases the likelihood of the presence of a sufficiently large air gap at the bottom side of the membrane (i.e. membrane borders an air gap at its lower side). In this manner a proper air gap distillation process through the membrane may be stimulated. It also creates enough space so that droplets can form on the condensation sheet without these droplets touching the membrane (which is preferable), thus ensuring easy roll of off the droplets to the bottom. This also prevents droplets touching the membrane sheet, especially in case the membrane sheet is microporous, in order to avoid contamination of clean water with polluted water, In specific embodiments the predefined minimum height of the purified water chamber (and therefore of the spacer arranged therein) is 2- 12 mm. In this manner contact between water droplets on the condensation sheet and the membrane are avoided.

[0040] In embodiments of the present disclosure the spacer is comprised of polymeric, for instance polyolefin, material. This is especially beneficial in embodiments wherein the spacer is bonded to any of the sheets by welding. In other embodiments, however, the spacer is made from any other type of material (preferably an environmentally friendly material). In these embodiments the spacer may be simply placed in the purified water chamber, without any bonding to a sheet. The spacer may further be configured to define an open structure allowing water to pass so that the water vapor can condense on the condensation sheet of the purified water chamber, thereby releasing its latent heat of condensation to heat up the contaminated water inside a further contaminated water chamber. The final distillation assembly may also be supported by a spacer to allow water from all distillation assemblies to be collected at the bottom of a housing (for instance a steel casing and a transparent top) in which the purification bag has been placed, so that it can be discharged as purified water.

[0041] In embodiments of the present disclosure the purification bag comprises a common inlet and outlet for feeding-in contaminated water to at least one of the contaminated water chambers, preferably to all contaminated water chambers and for feeding-out contaminated water and the residual water parts from at least one of the contaminated water chambers, preferably from all of the contaminated water chambers. It has been found by the inventors that the concentration of contaminations in the contaminated water chamber (for instance, the salt concentration in saline water) can be kept for a relatively long time period at a relatively low level (compared to embodiments with separate inlets and outlets), so that the purification may be remain effective for a prolonged time and time intervals between cleaning operations or between replacement of purification bags can be relatively long (for instance, in the order of magnitude of weeks or months, in case of sea water). Preferably, the common inlet / outlet is arranged at the bottom end of a purification bag, while an air vent is arranged at the upper end of the purification bag so that gas in the contaminated water chambers, for instance air, can be easily removed.

[0042] In embodiments of the present disclosure the purification bag comprises a connection unit configured to mutually provide a fluid connection between stacked contaminated water chambers. A fluid here is a liquid (for instance contaminated water) and / or a gas (for instance air).

[0043] In embodiments of the present disclosure the connection unit is arranged at an upper end of the water purification bag. In use the content of each contaminated water chamber may be deaerated via this connection unit, for instance using a single air connection or air vent.

[0044] As an example, the connection unit may comprise tubing interconnecting the plurality of contaminated water chambers. In other embodiments the connection unit comprises a connector, the connector preferably extending transversely to the respective contaminated water chambers.

[0045] In embodiments of the present disclosure the connection unit comprises a connector extending through respective openings provided in the upper ends of the respective contaminated water chambers and purified water chambers, while only the contaminated water chambers are in fluid connection with the inner volume of the connector.

[0046] In embodiments of the present disclosure the purification bag comprises a circulation limiter configured to limit the circulation of contaminated water between respective contaminated water chambers. In specific embodiments this circulation limiter is combined with the connector. The connector may comprise a tubular element, the tubular element comprising a number of openings to allow water to flow between the contaminated water chamber, wherein the inner surface of the tubular element is provided with one or more flow limiters, for instance a flow limiting flange, extending radially inward so as to keep the air pockets in place.

[0047] In embodiments of the present disclosure the tubular element is configured to be removably slid into to the openings, wherein the tubular element preferably is configured to mutually space apart the contaminated water chambers at respective predetermined distances while sliding the tubular element into the openings.

[0048] In embodiments of the present disclosure, a connector is provided comprising disks welded into openings of the sheets, wherein the disks comprise openings connecting the contaminated water chambers and forming a sealed passage through the condensation chambers, wherein the openings are preferably alternately shifted with respect to each other such that the openings form a zig-zag shaped passage, that may provide deaeration and circulation limiting functions during use.

[0049] A second aspect of the present disclosure concerns a purification system for heat-driven water purification of contaminated water, the purification system comprising:

[0050] - a housing;

[0051] - a feed water unit for the supply of contaminated water comprising contaminants;

[0052] - a water purification module connected to the feed water unit and configured to receive contaminated water and separate the received contaminated water into a purified water portion and a residual water portion comprising residual water and contaminants;

[0053] - a purified water unit connected to the water purification module and configured for receiving the purified water portion;

[0054] - a residual water unit connected to the water purification module and configured for receiving the residual water portion; wherein the water purification module comprises one or more purification bags removably arranged in the housing; and wherein a purification bag comprises a distillation assembly or a stack of distillation assemblies, wherein each distillation assembly is configured to receive a part of the contaminated water and separate a purified water portion from the received part of the contaminated water into a purified water portion and a residual water portion, the distillation assembly further comprising:

[0055] - a contaminated water chamber for collecting contaminated water, the contaminated water chamber comprising a top sheet configured for absorbing heat;

[0056] - a purified water chamber for collecting purified water, the purified water chamber) comprising a condensation sheet configured for collecting condensed purified water;

[0057] - a membrane arranged between the top sheet and condensation sheet, the membrane dividing the distillation assembly into the contaminated water chamber (30) and the purified water chamber, wherein the membrane is configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation of contaminated water through the membrane.

[0058] In a certain embodiment of the present disclosure the purification bag of the purification system is the purification bag according to the above-mentioned first aspect of the present disclosure. In other embodiments, the water purification module may also comprise other water purification assemblies, such as a plate and frame or bag-box assembly.

[0059] In embodiments of the disclosure the purification system comprises a drive unit, for instance a pump, for actively transporting the water through the water purification module.

[0060] The purification system may be a passive system driven by solar-heat and gravity. In order for gravity to drive the water flows, at least one of the housing and the water purification module is to be arranged at an inclined orientation relative to the direction of gravity. In a specific embodiment, the feed water unit, water purification module, purified water unit and residual water unit are arranged for passively transporting water through the water purification module, wherein the transport of water is gravity- and / or solar-heat-driven, more specifically comprising transporting water by thermohaline circulation. In case of an oblique (inclined) arrangement of the housing and / or water purification module, when the system is in use (i.e. during normal operation), there will be a driving force caused by gravity, and also by (thermohaline circulation caused by) temperature differences and / or contamination concentration differences causing a flow from the water purification modules towards the residual water tank.

[0061] In embodiments of the disclosure the residual water unit is a residual water tank having a tank volume larger than the volume of the combined volume of the contamination water chambers. Preferably (and especially if the feed water is sea water or water with a similar salinity), the ratio of the volume of the residual water unit and the combined volume of the contamination water chamber is at least 2, or even more than 4.

[0062] In use, the residual water portion at least some of the contaminated water chambers is in fluid communication with the residual water tank, preferably in fluid communication with both the residual water tank and the feed water unit. When, in use, the residual water portion in each of the contaminated water chambers of a water purification bag is in fluid communication with both the residual water tank and the feed water unit, especially good results in view of efficiency and lifetime may be achieved.

[0063] It was surprisingly found that when the residual water portion in each of the contaminated water chambers is in (constant) fluid communication with the residual water tank and when the volume of the residual water tank is high relative to the volume of the chambers of the water purification module, the system is hydraulically extended outside only the contaminated water chambers. As will be explained later, the hydraulic extension of the system has the effect that the usual increase in the course of the time of the concentration of contaminations in the contaminated water chambers is reduced or at least is slowed down. This prolongs the operational lifetime of the purification system (for instance, extends the time interval between cleaning operations of the purification system or replacement operations of the purification bags of the purification system). Furthermore, the hydraulic extension may reduce the effect of fouling, scaling and ultimately short circuiting of the membrane. Short circuiting is understood to be the phenomenon that when salt penetrates and passes through a membrane over time, a water bridge may be created across the membrane. Furthermore, in case of saline water (i.e. when the contamination is formed by dissolved salt), the risk of crystallization of salt in the contaminated water chamber (comprising contaminated water and residual water portion) can be reduced as well.

[0064] For all these reasons the increase in the course of time of the concentration of contaminants in the residual water units may be slowed down, resulting in a lower frequency with which the residual water tank needs to be emptied to safeguard a sufficient purification efficiency.

[0065] Should the above-mentioned ratio of the residual water tank volume and the combined contaminated water chamber volume of the water purification module(s) be lower than 2, the system may continue to function although the time interval between necessary flushing operations will be become (too) short. The minimum ratio plays a role in treating highly saline solutions by increasing in the length of time before the pores of the membrane fail due to wetting which subsequently leads to short circuiting and ultimately salt transport across the membrane and in time to the forming of salt crystals on the membrane in the purified water chamber. Is has been discovered that this phenomenon may be retarded as more concentrated saline water gravitates downwards and accumulates in the residual water tank, thereby keeping the saline concentration close to the membrane relatively low compared to the bulk of the contaminated feed water. Thus it is understood that a higher ratio of the residual water tank volume and the combined contaminated water chamber volume of the water purification module(s) is beneficial for purifying feed water with a relatively high salinity. This performance-life prolonging effect will be less relevant for low salinity feed water.

[0066] The above-mentioned feature of the residual water portion in each of the contaminated water chambers being in fluid communication with the residual water tank may mean that each of the contaminated water chambers has an individual conduit (channel, connector, etc.) in fluid connection with the residual water tank (and possibly also the feed water unit). However, in other embodiments the system has one single or several common conduits (e.g. connectors) in fluid communication with the residual water tank. For instance, in an embodiment, a subset of the plurality of purification bags (for instance, one two bags having a common conduit while the further bag(s) has / have an individual conduit) has a single, common conduit providing an essentially permanent fluid communication between all contaminated water chambers and the residual water tank.

[0067] The contaminated water from the feed water unit should be supplied at a sufficient pressure to cause the water purification units(s) to be fully filled. This can be accomplished by arranging the feed water unit, for instance a feed water tank of the feed water unit, at a sufficient height relative to the water purification unit(s) to provide a suitable “static head pressure”. However, the required static pressure can be realized differently as well. Typically, an over pressure of 0.1 - 0.2 bar inside the water purification bag is enough to press contaminated water in the contaminated water chambers, form chambers, optionally channels, in the bag, i.e. inflate the contaminated water chambers, optionally channels, (however) without overstressing the channel joints.

[0068] More specifically, in certain embodiments, a common feed-discharge conduit is provided in fluid communication with the water purification module, the residual water tank and the feed water unit and arranged to both supply contaminated water to the water purification module and discharge residual water portion from the water purification module. In some embodiments, each of the water purification units has one single common feed-discharge conduit. The common feeddischarge conduit may comprise a three-way connector (distributing contaminated feed water from the feed water unit, residual water from water purification unit and residual water and / or contaminated water from the residual water tank). The common feed-discharge conduit works surprisingly well, i.e. with the residual water portion and the contaminated feed water flowing in opposite directions. In case of saline feed water, the lower salinity feed water moves up and the residual water downwards due to difference in density inside the common feed-discharge conduit.

[0069] In embodiments of the disclosure the residual water portion in the water purification module and the residual water portion in the residual water tank are in fluid communication to form one continuous uninterrupted volume of residual water.

[0070] In use the water purification module (which is arranged in an inclined orientation) has an upper end and a lower end. In embodiments of the present disclosure the connection of the feed water unit, the connection of the residual water unit and the connection of the purified water unit are arranged in the lower end of the water purification module. Filling the water purification unit from the bottom end tends to cause air (bubbles) almost inevitably generated in the heating process to be displaced upwards. The air bubbles will accumulate in the upper end of the water purification module. By forcing the air bubbles towards the upper end of the water purification module as a result of the oblique arrangement, there will be less or no air bubbles present in the bulk of the (contaminated water chamber(s) of the water purification module), which has a positive effect on the efficiency of the purification process.

[0071] More and more air bubbles will accumulate in the upper end of the contaminated water chamber(s) in the course of time. Therefore, in a preferred embodiment, the purification bag comprises an air venting unit or gas venting unit arranged in the upper end so that air bubbles may be removed, as will be explained hereafter.

[0072] As mentioned above, the water purification module is arranged in an inclined manner relative to the (horizontal) floor. In the inclined orientation the water purification module extends at an angle (0) relative to the direction of gravity of more than 0 and less than 90 degrees, preferably more than 5 and less than 85 degrees. In specific embodiments, the angle is in the range of 15 - 35 degrees, the lower limit being set to ensure a proper movement of air (bubbles) towards the upper end of the module (so that the module may be easily deaerated).

[0073] The angle is also related to the orientation of the sun (in case of a solar energy driven system). It is selected such that the water to be purified, the purified water and the residual water are automatically displaced under the influence of gravity, without the need for external or internal drive means like one or more pumps. Especially for deaeration purposes the tilt angle should be large enough, for instance more than 15 degrees. The tilt angle may be selected to maximize absorption of solar energy (in case of solar-heat driven systems) and to allow downward gravity flow of stratified feed water and its (solid) contaminants.

[0074] As mentioned above, the water purification module may comprise an air venting unit (suitable for venting any gas), preferably connected to the upper end of the at least one contaminated water chamber and configured to provide an outlet for air bubbles generated in the water purification module.

[0075] The inventors surprisingly found that an improved long term purification efficiency can be achieved if the circulation of contaminated water from a contaminated water to another contaminated water chamber (in case of a stack of distillation assemblies) at the upper end the chambers can be reduced or even avoided. It was furthermore found that the circulation can be reduced or even blocked by making use of the above-discussed gas, for instance air bubbles, that inevitably are generated in the purification process and / or by gas, for instance air, that enters the distillation assemblies in the feeding (filling) phase. If sufficient gas (air) can be captured or accumulated at the upper / top ends of the contaminated water chambers and this gas can be trapped, i.e. captured to stay in a certain area, the gas in this area can prevent the circulation of contaminated water between the various contaminated water chambers. To this end the purification bag may comprise a circulation limiter configured to locally capture gas generated in at least one the respective contaminated water chambers (30) and form at least one local gas pocket in the contaminated water chamber so as to have the at least one gas pocket interrupt the flow of contaminated water between the contaminated water chambers. Details of embodiments of such circulation limiter will become apparent from the discussion hereafter. It may be the case that the circulation limiter limits the circulation between each and every contaminated water chamber. In other embodiments wherein the purification bag comprises a set of (a plurality of) contaminated water chambers, wherein the circulation limiter is configured to only capture gas in a subset of contaminated water chambers for temporarily blocking the flow of contaminated water to or from said subset of contaminated water chambers, while in the remaining contaminated water chambers essentially no gas is captured.

[0076] In embodiments with a lower contaminated water chamber and one or more further contaminated water chambers placed above the lower contaminated water chamber, a circulation limiter may be provided that is configured to only capture gas (for instance air bubbles) from the further contaminated water chambers. An advantage of this embodiment is that a reduced amount of material is needed to manufacture the circulation limiter.

[0077] In embodiments of the disclosure the water purification bags are arranged in a housing. The housing may comprise a protective casing. The protective casing is a mechanical construction element to mount the unit at a tilted angle and has an insulating function and serves as a protection against dust, wind and animal or insect intrusion. In case of solar-heat driven systems, the top can be opaque, or solid, for example black metal to allow heat transfer to the water purification unit (s), and / or transparent, for example glass, to allow solar radiation to pass to the underlying water purification unit(s), through an insulating air layer. In other embodiment the system lacks such casing. These embodiments, however, may be less efficient due to heat loss if used outdoors and / or may be more vulnerable to damage.

[0078] According to a third aspect a method of heat-driven water purification of contaminated water in a purification system is provided. The method comprises:

[0079] - feeding contaminated water into the contamination water chamber or chambers of at least one distillation assembly;

[0080] - separating of a part of a contaminated water portion received by a distillation assembly into a purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet;

[0081] - discharging the purified water from the purified water chamber or chambers.

[0082] In a preferred embodiment the method comprises feeding unpurified contaminated water into one or more contaminated water chambers and at the same time discharging a residual water portion comprising water and contaminants remaining in the contaminated water chamber contaminated water resulting from the purification from the one or more contaminated water chambers, preferably via a common inlet and outlet.

[0083] According to a fourth aspect a method of manufacturing a water purification bag as defined herein is provided, the method comprising: - melting polymeric material of a polymeric membrane sheet and melting polymeric material of the top sheet;

[0084] - merging the melted polymeric materials; and

[0085] - allowing the merged polymeric material to cure, or to cool and solidify.

[0086] In case the membrane comprises a membrane sheet and a coating on top of the membrane sheet, the top sheet and membrane sheet may be ultrasonically welded by:

[0087] - ultrasonically displacing a part of the coating to locally expose a part of the polymeric membrane sheet;

[0088] - ultrasonically melting polymeric material of the exposed part of the polymeric membrane sheet and ultrasonically melting polymeric material of the top sheet;

[0089] - merging the melted polymeric materials; and

[0090] - allowing the merged polymeric material to cure or to cool and solidify.

[0091] In this document, the term sheet is used to refer to a thin film. The sheets used in the water purification bag are flexible (bendable or pliant, sometimes even stretchable) to the extent that the bag, and preferably the contaminated water chamber, more preferably the channels in the contaminated water chamber, are inflatable by applying a (fluid) over pressure, preferably a fluid over pressure of 0,1 - 0,2 bar. In preferred embodiments, the water purification bag is configured such that the contaminated water chambers inflate to at least 50% of their maximum volume at a fluid over pressure of 0,1 - 0,2 bar at 15 degrees Celsius, preferably to more than 60%, for example 80% or 90% or 100%. The sheets contained in the water purification bag according to preferred embodiments of this disclosure are flexible. If one or more spacers are arranged in one or more of the chambers then these spacers may be configured to be flexible (bendable and / or pivotable) to some extent (but not too flexible in view of their spacer function).

[0092] At least one of the thin film sheets (i.e. the top sheet, condensation sheet, membrane sheet, etc.) may be a homogenous sheet, more specifically a sheet of homogenous polymeric material like material consisting of essentially one polymer. In other embodiments the thin film sheets comprise a combination of a non-woven material and a polymeric material. Furthermore, the water purification bag may comprise sheets of thin polymeric textile or non-woven material which have a heterogenous surface compared to homogenous films but have the same range of flexibility and other material properties as homogeneous thin films.

[0093] As a result, the preferred water purification bag as a whole is a substantially flexible, inflatable container, wherein more preferably no plates or frames are comprised. For example, any or all sheets comprised in the water purification bag according to this disclosure may be any of the following: a thin film or foil, and / or flexible as described above, deformable, bendable, non-rigid, skin-like, membranous. In preferred embodiments, the top sheet and the membrane sheet and preferably the condensation sheet comprised in the water purification bag, are less than 2 mm thick, preferably thinner than 1 millimeter.

[0094] The above and / or other aspects of exemplary embodiments will become apparent and more readily appreciated from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying figures.

[0095] Figures 1A-1D are schematic drawings of a water purification system according to an embodiment of the present disclosure, wherein figure 1A is a side view of a purification system with six rows of purification bags arranged in a housing, figure IB is a detailed view of a common inlet to a row of purification bags, and figures 1C and ID are cross-sections of embodiments of a purification system comprising respectively a single distillation assembly (single layer purification bag) and a stack of distillation assemblies (multilayer purification bag), taken along line A-A in figure 1A.

[0096] Figure 2A is a longitudinal cross-section of an embodiment of a water purification system comprising a, a feed water unit 2 for supplying contaminated water to be purified to a water purification module 5, a water purification module 5 comprising at least one multilayer purification bag 6, a residual water unit 3 for collecting the residual water portion, and a purified water unit 4 for collecting purified water, wherein the purification bag further comprises a first embodiment of a circulation limiter, in operation.

[0097] Figure 2B is a detailed view of figure 2A showing in more detail the composition of the distillation membrane of the purification bag 6;

[0098] Figure 2C is a detailed view of figure 2A showing in more detail a first embodiment of a circulation limiter for improving the purification efficiency;

[0099] Figure 2D is a detailed view of figure 2A showing a second embodiment of the circulation limiter;

[0100] Figures 3A-3B show schematic longitudinal cross-sections of the arrangement of figures 2A-2D, with a representative heat distribution in an embodiment without a circulation limiter (figure 3 A) and an embodiment with a circulation limiter (figure 3B);

[0101] Figures 4A-4G correspond to figure 3B, in consecutive stages of operation; two preferred embodiments of the water purification system according to the present application, more specifically a step-by-step filling, refilling and emptying operation of the water purification system.

[0102] Figure 5 is a schematic detailed view in cross-section of the common inlet / outlet;

[0103] Figures 6A-6B are respectively a longitudinal section and a cross-section of a distillation assembly comprising a membrane comprised of an uncoated microporous membrane sheet according to an embodiment of the present disclosure. Figures 7A-7B are respectively a longitudinal section and a cross-section of a distillation assembly comprising a membrane comprised of a coated microporous membrane sheet according to an embodiment of the present disclosure.

[0104] Figure 8 schematically clarifies the solar heat driven distillation / pervaporation of water / water vapor through an uncoated microporous membrane according to the present disclosure

[0105] Figures 9A-9B respectively show a schematic side view and a partly cut-away view of a water purification bag before inflation and after inflation, specifically indicating a specific welding pattern according to the present application.

[0106] Figures 10A-10D show schematic transversal cross-sections of welded, multi-layered water purification bags according to the present application.

[0107] Figures 11 A-l IB schematically show channels of the contaminated water chamber in a water purification bag according to the present invention.

[0108] Figures 12A-12D schematically show various welding patterns of preferred embodiments according to the present application.

[0109] Figures 13A-13B schematically show a longitudinal cross-section of an embodiment of a three-distillation-assembly water purification bag comprising a top and bottom connector according to the present application, respectively in empty condition and in filled condition. figure 13C schematically shows a longitudinal cross-section of another embodiment of a water purification bag having only a single distillation assembly

[0110] Figure 14 schematically shows a partly cut-away side view in perspective of a water purification bag comprising a top and bottom connector according to a further embodiment.

[0111] Figure 15 is a cross-sectional view of the embodiment of the top connector of figure 14,;

[0112] Figure 16 is a cross-sectional view of the bottom connector and purified water oulet of figure 14.

[0113] Figure 17 schematically shows an inner cylinder of a connector according to a preferred embodiment.

[0114] Figure 18 schematically shows a cross-section of the inner cylinder of a connector according to figure 17.

[0115] Figure 19A-19E schematically show a step-by-step mounting of an inner cylinder of a connector to an embodiment of a water purification bag.

[0116] Figure 20 schematically shows a core-less connector in perspective.

[0117] Figure 21 schematically shows a cross-section of a core-less connector welded into the water purification bag.

[0118] Figure 22 schematically shows a cross-section of a core-less connector during use. Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings. That which is encompassed by the claims may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example. Furthermore, like numbers refer to the same or similar elements or components throughout.

[0119] It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

[0120] Membrane distillation here may be defined as a separation process in which water which originally is present in liquid form present on top of a membrane sheet (i.e. on top of the membrane sheet itself if no coating is present and on top of the coating if a coating is present) evaporates and moves in vapor form into and diffusing through the micropores of the membrane sheet. If the membrane comprises a microporous membrane provided with a coating, then water first diffuses through the coating of the membrane (for instance, as a solute in the material of the coating). Once the water has diffused through the coating, then this water evaporates in the micropores and water in vapor form then passes the micropores of the membrane sheet to arrive at the purified water chamber.

[0121] In case of a microporous hydrophobic membrane sheet, the membrane distillation separates two aqueous solutions at different temperatures, i.e. the aqueous solution (contaminated water) in the contaminated water chamber which has a relatively high temperature, and the purified water in the vapor and liquid phase in the purified water-chamber which has a lower temperature. The microporous membrane sheet is hydrophobic which substantially prevents mass transfer of contaminated water, whereby a gas-liquid interface is created. The temperature gradient on the membrane sheet results in a vapor pressure difference, whereby a part of the contaminated water in the contaminated water chamber evaporates through the micropores of the membrane. More specifically, a relatively high vapor pressure of the contaminated water in the contaminated water chamber causes transport via diffusion and / or convection from the chamber of high vapor pressure to the chamber of low vapor pressure.

[0122] In embodiments the purified water in the purified water chamber may be in direct contact with the membrane (for instance, with the membrane sheet) (direct contact membrane distillation, DCMD). In other (preferred) embodiments, the membrane distillation involves air gap distillation (AGMDA) which means that there is an air gap at the purified water chamber side of the membrane sheet. In other words, in these embodiments the evaporated water is collected on the condensation sheet that is separated from the membrane sheet via an air gap. In embodiments the membrane comprises a membrane sheet that has been provided (at its contaminated water chamber side) with a hydrophobic coating. This coating may be essentially non-porous for water vapor. In these embodiments water in liquid phase diffuses in the essentially non-porous hydrophobic coating until it reaches the micropores of the membrane sheet. Then the above-described membrane distillation takes over and allows water vapor to be transferred to the side of the purified water chamber.

[0123] Referring to the side view of figure 1A and the longitudinal section of figure 2A, an embodiment of a water purification system 100 is shown. The purification system 100 is configured to separate contaminated water from a feed water unit 2, for instance a feed water tank or a feed water supply line, into a purified water portion and a residual water portion to be collected in a purified water unit 4 and a residual water unit 3 (for instance, a residual water tank), respectively. The purified water portion is separated from the contaminated water by means of one or more distillation membranes in a number of water purification bags 6 of the water purification module 5 and then discharged to the purified water unit 4. The water purification bags 6 are arranged side-by-side in neighboring elongated compartments of a housing 8 and discharged to a purified water unit 4. The number of compartments of the shown embodiment is six, in other embodiments this number could be smaller or larger. Furthermore, in the figure is shown that each compartments comprises three purification bags serially arranged in fluid communication, forming as if it were one combined purification bag. In other embodiments there is only one purification bag in a compartment, extending from its bottom end up to the upper end of the compartment. In the following description reference may be made only to the term “purification bag”, irrespective of whether there is only one actual bag or whether in fact a series of multiple bags in mutual fluid connection forming one combined purification bag is provided. In other preferred embodiments, the water purification module 5 may also comprise other water purification assemblies, such as a plate and frame or bag-box assembly.

[0124] Generally, a feed water tank of the feeding water unit 2 is arranged at a position higher than the top end 20 of the water purification module 5, such that the water in the tank provides a static pressure (herein also referred to as the static head) sufficient to press the contaminated water in direction 15 (figure 1A) all the way into the water purification module 5.

[0125] The housing 8 is supported on a number of supports (not shown) and generally extends in a generally oblique orientation (angle 3) relative to the floor / ground, although embodiments with a horizontal arrangement (i.e. perpendicular to the direction of gravity) are possible as well. In the inclined orientation each water purification module 5 defines a top end 20 and a bottom end 21.

[0126] An advantage of the inclined position of the housing 8 and the water purification module 5 therein is that water has entered the water purification module 5 under the static head of the water supply unit 2 (arranged at a heigh position above the upper end 20 of the water purification module 5) may be discharged passively, i.e. without the need of any drive means like pumps and the like. This means the purification can function autonomously, without any pump.

[0127] At the upper / top end 20 the water purification module 5 has an air vent 22 to de-aerate the module from time to time, as air (bubbles) will inevitably be generated in the purification process.

[0128] In embodiments of the present disclosure, feed water unit 2 comprises an inlet 13 to refill the water tank from time to time. Each of the contaminated water chambers of the water distillation assemblies comprises at least one inlet / outlet opening (and preferably only one single inlet / outlet opening). In embodiments wherein a (combined) water purification bag 6 has multiple contaminated water chambers in a series of water purification bags and / or multiple purified water chambers in a series of water purification bags, the contaminated water chambers may be in fluid connection with each other and / or the multiple purified water chambers may be in fluid connection with each other by suitable tubing or connecting channels. Additionally, the contaminated water chambers of the purification bag at its top end 20 are interconnected, for instance by a suitable connector device 9.

[0129] Water chambers of a multi-layered water purification bag may be connected to each other inside or outside the water purification bag. A common supply line 17 and a feed / discharge conduit 19 connect the feed water unit 2 to the inlet / outlet opening of the (combined) purification bag 6 in a compartment. The feed / discharge conduit 19 is also in fluid connection with the residual water tank 3. The common supply line 17 and a feed / discharge conduit 19 leading to a purification bag 6 make it possible to fill (direction 15, figure 1A) each of the water purification modules 5 with contaminated water from the feed water unit 2. Each feed / discharge conduit 19 is provided with a valve 14 for selectively closing or opening the feed / discharge line 19. As will be explained later, the feed / discharge conduit 19 is configured to both supply contaminated water from the feed water supply 2 to the water purification module(s) 5 in direction 25 and receive a residual portion from the water purification module 5 in an opposite direction 26 (cf. figure IB). The residual portion arriving through the feed / discharge conduit 19 is discharged to the residual water unit 3 (in this embodiment also referred to as residual water tank or brine tank 3). In the shown embodiment all compartments of the purification system 100 are connected to a single residual water tank. However, in other embodiments a larger number of residual water tanks may be used. Periodically the residual water unit 3 may be emptied by opening a valve 12 arranged at the bottom side of the residual water unit 3. The purified water from the water purification module(s) 5 arrives via a number of purified water discharge conduits 27 and common purified water discharge line 23 (direction 16, figure 1A). The purified water is collected and temporarily stored in the purified water tank 4. The purified water tank 4 may have a valve 11 (or 11’, cf. fig. 13 A) to allow discharge of the collected purified water. The shown arrangement allows for an essentially continuous and uninterrupted fluid connection between feed water unit 2, water purification module 5 and residual water unit 3.

[0130] Water in the purification system can flow along line 19 upwards in the direction of the water purification module, i.e. direction 25, and downwards, in the direction of the residual water tank 3, as indicated by arrow 26, as indicated in figure IB. The system is preferably configured such that a continuous, uninterrupted liquid connection is provided between the feed water tank, the water purification module, i.e. the water chambers 30 in the water purification bags 6, and the residual water tank 3. Thus, in operation according to a preferred use, the water inside the water purification module, the lines 19, pipe 17 and tanks 2 and 3, form one uninterrupted, continuous body of water. In operation, when purified water starts to pass through the membranes 40 in the water purification bag’s 6, contamination stays behind in the contaminated water chamber and the concentration of the brine increases. However, when the water in the chamber 30 and the water in the residual water tank are in liquid connection with each other, the (relatively heavy) contamination / salt / brine in the contaminated water chambers may be moving downward towards the residual water tank as a result of local concentration variations (figure 5) before the contamination / salt / brine would be mixed over the total volume. This may result in a lower concentration of contamination / salt / brine in the contaminated water chamber 30 and therefore may increase the efficiency of the water purification and / or increase the operational lifespan of the membrane 40 (in view of a reduced fouling rate of the membrane).

[0131] Water purification module 5 may be configured for passive, heat-driven separation of a contaminated water portion into a purified water portion and a residual contaminated water portion. In the embodiment shown in figure 1A the purification system 100 is solar driven meaning that the source for providing heat to at least the upper part of the water purification module 5 is the sun. To this end the cover of the housing 8 is made of generally transparent material. More specifically, in embodiments of the present disclosure, the housing may be made of metal or plastic trays with glass or plastic transparent tops, such that solar rays may easily enter the water purification module 5 and heat at least the top sheet 31 of the first distillation assembly in the water purification bag 6.

[0132] In this document, the term sheet is used to refer to a thin film. The sheets used in the water purification bag are flexible to the extent that the bag, and preferably the contaminated water chamber, more preferably the channels in the contaminated water chamber, are inflatable by applying a (fluid) over pressure, preferably a fluid over pressure of 0,1 - 0,2 bar. The sheets contained in the water purification bag according to preferred embodiments of this disclosure are flexible. As a result, the preferred water purification bag is a substantially flexible, inflatable container, wherein more preferably no plates or frames are comprised. In preferred embodiments, some relatively rigid or non-flexible material may be used in the water purification bag to provide the spacer material in the condensation chamber or the connector for example. In preferred embodiments however, the spacer material is bendable or at least foldable at certain points, for instance for transportation or storage.

[0133] Figure 1C shows a schematic cross section of a water purification module 5 comprising a housing 8 and a set of single-layer water purification bags 6, i.e. comprising one distillation assembly, according to a preferred embodiment. In the embodiment of this figure the distillation assembly comprises a contaminated water chamber 30 and a purified water chamber 50, separated by a membrane 40. Figures ID and 2A show a schematic cross-section of a water purification module 5 comprising a set (six) of multi-layer (three layer) water purification bags 6, each purification bag comprising multiple distillation assemblies stacked on top of each other, is arranged inside casing 8. In the embodiment wherein the purification bag 6 has a stack of three distillation assemblies, the first distillation assembly 601comprises a first contaminated water chamber 301and a first purified water chamber 501, separated by a membrane 401, a second distillation assembly 602comprising a second contaminated water chamber 302and a second purified water chamber 502, separated by a second membrane 402, and a third distillation assembly 603comprising a third contaminated water chamber 303and a third purified water chamber 503, separated by a third membrane 403.

[0134] Figure 2A and, in more detail figure 2B, show an example of a distillation assembly 60. The distillation assembly 60 comprises a contaminated water chamber 30 for collecting contaminated water arriving from the feed / discharge conduit 19, the contaminated water chamber 30 being defined by a top sheet 31 configured for absorbing heat and a membrane 40. Heat may be generated by solar radiation (R) impinging on the transparent cover top of the housing 8. The distillation assembly 60 further comprises a purified water chamber 50 for collecting purified water through the membrane 40, the purified water being discharged via purified water discharge conduit 27 and purified water discharge line 23. The purified water chamber 50 is defined by the above- mentioned membrane 40 and a condensation sheet 51. The condensation sheet 51 is configured to allow condensation of water vapor and for collecting and then discharging the condensed purified water droplets (D). In embodiments wherein multiple distillation assemblies are stacked upon each other, the upper distillation assembly 60 has the above -described composition, while the next (second) distillation assembly right below the upper distillation assembly has a contaminated water chamber 302of which the top sheet is the condensation sheet 51 of the upper distillation assembly.

[0135] In principle a membrane 40 is arranged between the top sheet 31 and condensation sheet 51 and thereby divides the associated distillation assembly into a contaminated water chamber 30 and a purified water chamber 50. As will be further explained later, the membrane 40 may comprise a microporous membrane sheet 41 (cf. figures 2B) configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet. In some embodiments the microporous sheet is uncoated, while in other embodiment a (non-porous) coating layer is applied on the microporous sheet (cf. figures 6A. 6B). Furthermore, in some embodiments, the membrane sheet 41 is attached to a reinforcement sheet 42 (see figures 7A, 7B).

[0136] Contaminated water directly arriving from the feed / discharge conduit 19 is fed into each of the purification modules 5 at the bottom end 21 of a purification bag 6. Under the static pressure provided by the feed water supply 2 the contaminated water fills all contaminated water chambers 30, 30'-303. This is indicated in figure 2A by the hatching. At the top end 21 a circulation limiter (unit) 90 may be provided to limit the circulation of contaminated water between the contaminated water chambers 30, 30'-303by the provision of certain bent portions 91 '-912in feed water chambers (see also figures 2C and 2D showing two different embodiments of a circulation limiter 90, wherein in the embodiment of figure 2D the circulation limiter is configured to prevent circulation from all contaminated water chambers while in the embodiment of figure 2C circulation from the lowermost contaminated water chamber 303remains possible in order to be able to remove any excess air (see air bubbles forming an air pocket at the left hand side of figure 2C) from the other contaminated water chambers 301, 302). These bent portions form gas locks in each of the contaminated water chambers in the embodiment of figure 2D and in each of the contaminated water chambers in the embodiment of figure 2C except the lowermost one. Hereafter the operation and advantages of having a purification system with a circulation limiter will be explained in more detail. Finally, an air venting unit 22 is in fluid communication with the contaminated water chambers to allow excess gas (air) 93 which would otherwise reduce the purification efficiency, to be safely removed and discharged to the environment. Air venting unit 22 is suitable for venting any gas.

[0137] In other embodiments, for instance the embodiment shown in figure 3A, no circulation limiter is provided and fluids from any one of the contaminated water chamber may flow to a neighboring contaminated water chamber.

[0138] Referring to figure 2A, each of the membranes 40-403is configured to, under the influence of heat, let pass water or water vapor, by membrane distillation or pervaporation whilst nonvolatile contaminations such as salts are blocked and remain in the respective contaminated water chamber. Water vapor in the purified water chamber 50 starts to condense and forms water droplets (D, figure 2B). The water droplets in each of the distillation assemblies move downward under the influence of gravity, are collected at the bottom end 21 of the purification module 5 and then discharged via water discharge conduit 27 and common purified water discharge line 23 towards the purified water unit (tank) 4. Heat for the uppermost distillation assembly 60 is primarily provided by solar energy radiated through a transparent cover of the housing, while heat for each of the subsequent distillation assembly is (also) provided by the condensation energy that is freed when the water vapor in the contaminated water chamber above starts to condense.

[0139] More specifically, in embodiments wherein a water purification bag 6 comprises multiple water distillation assemblies stacked on top of each other, the term condensation sheet of the first assembly refers to the same sheet as the term top sheet of the second assembly. The condensation heat released when water vapor in the first purified water chamber condenses on the first condensation sheet, i.e. second top sheet, is transferred to the second contaminated water chamber via said sheet. This multi-layered arrangement therefore advantageously uses the waste heat of an n-th water distillation assembly to purify water in an n+lth water distillation assembly. Figures ID, 2 A to 5, 9B to 10C and 13A to 16 all show embodiments employing a multi-layered water purification bag.

[0140] In solar heat driven purification systems the temperature in the uppermost contaminated water chamber can typically rise to 70-80 degrees Celsius. The temperature in the second distillation assembly right below the firsts one will generally be slightly lower (about 20 degrees Celsius lower), the temperature in the third distillation assembly typically ranges from 40 to 50 degrees Celsius. The water production (i.e. the amount of purified water per unit of time) of embodiments having three stacked distillation assemblies generally is twice as large as an embodiment with only one distillation assembly. This production can even be increased in purification systems wherein a purification module 5 has four or five stacked distillation assemblies. Water production of at least 6-8 l / m2per day for a purification module with uncoated membranes with a solar radiation of 6.5 kWh / m2per day can be achieved. When coated membranes are used, the water production will generally be about 30% smaller. However, due to the reduced fouling of coated membranes, the maximum lifetime and / or the time intervals between replacement or cleaning operations is much larger. Typically the water production in the first distillation assembly is about 50% of the total water production, in the second distillation assembly about 33% and in the third distillation assembly about 17%.

[0141] Figures 3A and 3B show representative heat distributions in an embodiment of a solarheat driven purification system without a circulation limiter (figure 3A) and with a circulation limiter (figure 3B). The arrows in the figures schematically indicate the liquid flow inside each of the contaminated water chambers and between the contaminated water chambers. In figure 3A is indicated that as a result of solar energy heating primarily the uppermost contaminated water chamber, the temperature inside this chamber will be higher than the temperature in the contaminated water chamber right below. The temperature in the further two contaminated water chambers will be even lower, in a stepwise manner. Furthermore, as a result of the possibility of fluid flow between the contaminated water chambers, the temperature distribution will be such that instead of a more or less uniform temperature within in each of the contaminated water chambers (with a stepwise diminishing temperature from top to bottom), the temperature distribution will become such that at the lower portion of each of the water chambers the water will be at a reduced temperature while at the higher portions of the contaminated water chambers the water will be at an increased temperature relative to a uniform temperature distribution.

[0142] Figure 3B shows the effect of the presence of gas bubbles 93 in a circulation limiter 90 (see also figure 2C): the distribution of the temperature in each of the contaminated water chambers is more uniform. This ensures a more optimal operation of the purification system and has a positive effect on the water production that can be reached with the purification system.

[0143] Figures 4A-4G show various stages of a method of purifying contaminated water using a water purification system as described herein. Figure 4A shows the purification system in an initial, empty stage. In figure 2 is shown that the water supply unit 2, more specifically the water supply tank and the suppl line 17, is filled with contaminated water (hatched), such as sea water (saline water). The contaminated water from the supply unit 2 may enter the residual water tank 3 as well through the supply line 17 and feed / discharge conduit 19. Once the residual water tank 3 is sufficiently filled (cf. figure 4C), contaminated water will start to flow upward (under influence of the hydrostatic head, cf. figure 4E) via the same common feed / discharge conduit 19 with which the contaminated water has flown downward to the residual water tank 3, into the respective contaminated water chambers 301, 302, 303,304(in the shown embodiment the water purification module has a stack of four distillation assemblies while in other embodiments this number may be smaller (for instance 3, 2, or 1) or larger) until the water purification module is fully filled with contaminated water.

[0144] Once the sun has heated the water purification module to an extent sufficiently to at least partially evaporate the water in the contaminated water chambers (directly in the uppermost contaminated water chamber 301or indirectly in the other contaminated water chambers 302-303), water vapor will move through the membrane and enter the respectively purified water chambers. Water vapor in the purified water chambers will condense and the resulting purified water droplets will be discharged towards the purified water tank 4. In the course of the heating process gas bubbles will inevitably be generated and these gas bubbles will travel upwards to the upper end of the purification modules. Figure 4F shows the gas bubbles 93 are accumulated in the bent portions of the contamination chambers 30'-304. Once in a while the supply tank of the water supply unit 2 is refilled with contaminated water (cf. figure 4F) and a part of the residual water accumulated at the bottom of the residual water tank 3 may be discharged by opening the outlet 12 of the tank 3. This process of refilling the water supply tank and removing a part of the residual water from the residual water tank 3 may be repeated several times until purification capacity of the purification module starts deteriorating. Once this happens the purification module should be cleaned to bolster the purification capacity again. Reference is made to figure 5. As water / water vapor leaves a contaminated water chamber 30 upon passing the membrane 40, the volume of contaminated water in chamber 30 is replenished under influence of the static force provided by the water in feed water tank of the feed unit 2 (see direction 25). However, at low flow rates according to a preferred, passive, solar driven operation mode of the embodiment according to figure 1A, i.e. when the dynamic forces in the system are at least an order magnitude smaller that the static forces in the system, surprisingly, stratification between the relatively heavy brine in the contaminated water chamber and the relatively lightweight contaminated water in feed tank 2 and pipe 17 arises. As a result, relatively heavy and relatively lightweight contaminated water moves substantially separately without mixing, under the influence of gravity: relatively heavy contaminated water with a high contamination concentration flows downwards along chamber 30 and feed / discharge conduits 19, in the direction indicated by arrow 26, whilst relatively lightweight contaminated water moves upwards along line 19 and chamber 30, as indicated by arrow 25. In figure 5, the dotted hatching represents a mixture with a relatively heavy / high concentration of contaminants (brine), and the lined hatching represents a mixture with a relatively lightweight / low concentration of contaminants. Thus, according to a preferred embodiment shown in figure 1A and figure 5 for example, the residual water tank is arranged lower than the water purification module, and the feed / discharge conduit 19 connecting the water purification module and the residual water tank is substantially straight and vertical. As such, the relatively / highly concentrated mixture may flow out of the contaminated water chamber 30 and into the residual water tank 3 easily. Furthermore, according to preferred embodiments, the volume of residual water tank 3 is relatively large compared to the volume of the (inflated) contaminated water chambers 30nin the water purification module. As the volume of the residual water tank 3 increases, the concentration of the contamination in the contaminated water chambers may decrease. Furthermore, a large residual water tank may increase the time it takes before the concentration of the contaminants inside the contaminated water chamber 30 reaches a certain undesirable level, and therefore may decrease the frequency with which the user needs to empty the residual water tank 3. For example, in a preferred embodiment, the volume of the residual water tank 3 is at least as large as the volume of all contaminated water chambers 30nin the water purification module 5, more preferably at least two times larger, most preferably at least three times larger.

[0145] A system according to an embodiment as described above with reference to figure 1A may advantageously increase the production of purified water, increase the life span of the membranes in the water purification module, and decrease the burden of maintenance on the user.

[0146] Figures 6A-6B, 7A-7B and 8 show various embodiments of the membrane 40 used in the present purification system. Each water purification bag 6 according to the present disclosure comprises at least one water distillation assembly 60. A water distillation assembly 60 may comprise a top sheet 31 and a membrane 40 comprising a permeable or microporous membrane sheet 41 (see figure 6B depicting a schematic drawing of a cross-section of a microporous sheet). The term sheet is used to refer to a thin film. The sheets used in the water purification bag are flexible to the extent that the bag as such, and preferably also the contaminated water chamber, more preferably the individual channels in the contaminated water chamber as well, are inflatable (i.e. are inflated to an expanded state when a fluid is allowed to enter at the slight overpressure, preferably a fluid overpressure, of 0,1 - 0,2 bar relative to the surrounding air pressure. In preferred embodiments, the water purification bag is configured such that the contaminated water chambers inflate to at least 50% of their maximum volume at a fluid over pressure of 0,1 - 0,2 bar at 15 degrees Celsius, preferably to more than 60%, for example 80% or 90% or 100%.

[0147] The space between / defined by the top sheet 31 and the membrane 40 is inflatable (with fluid, i.e. a liquid and / or gas) and forms the contaminated water chamber 30. The microporous or permeable sheet 41 will be shortly referred to as the microporous sheet (41) in the following. The microporous sheet and the top sheet are comprised of the same weldable material. Furthermore, the membrane may comprise a permeable sheet comprising a copolymer, for instance polyetheramide, which is weldable to nylon, and the top sheet also comprises nylon, for instance polyamide-6. Or, the membrane comprises a microporous sheet 41 containing a polymeric material such as polyolefin material, for instance LDPE, HDPE, polypropylene (PP), or polymethyl pentene, and the top sheet also comprises a polymeric material.

[0148] In a purification bag 6 according to a preferred embodiment, the top sheet and the membrane (or, in some embodiments, all sheets of the bag) are solely connected to each other (so that no connection with a constructional element like a stiff plate or a frame construction, is needed). In further embodiments the sheets (including the membrane) are solely connected to each other by welding. In embodiments wherein the membrane comprises both a membrane sheet and a (non-woven) reinforcement sheet, at least one of the membrane sheet and reinforcement sheet, preferably both the membrane sheet and reinforcement sheet, are welded to one or more of the other sheets. As indicated above, preferably the purification bag does not comprise a plate and / or frame construction. Preferably, purification bag 6 is configured to be expanded to the expanded state (inflated state) and operate as intended without the purification comprising plates or frames.

[0149] In the embodiment according to figures 6A-7B, the top sheet 31 is a weldable, preferably polyolefin, sheet preferably having a black color as to increase heat absorbance. For example, top sheet 31 may comprise a carbon black to create a black color. Furthermore, the embodiment according to figures 6A-7B, sheet 41 is a microporous polyolefin sheet. Sheets comprised in the water purification bag 6 according to the present description have a weight per square meter in the order of magnitude of 100 g / m2.

[0150] The microporous sheet facilitates separation of contaminated water into a purified water portion and a residual water portion / brine portion. Figure 8 shows a schematic drawing of water or water vapor (from the contaminated water chamber 30) passing through a microporous sheet 41 (thus entering purified water chamber 50). Under the influence of heat, for example sunrays 200, top sheet 31 heats up and transfers the heat to the contaminated water in the contaminated water chamber 30, see figure 2B and figure 8. As a result, water or water vapor passes through the microporous sheet 41 via at least one of distillation or pervaporation, see figure 8. Contaminations such as non-volatile contaminations and salt cannot pass through microporous sheet 41 and stay behind in the contaminated water chamber 30. Purified water or water vapor enters the purified water chamber on the other side of membrane 40.

[0151] In preferred embodiments, a water distillation assembly further comprises a condensation sheet 51 arranged at the other side of the membrane. The space between / defined by the membrane

[0152] 40 and the condensation sheet is inflatable and forms the purified water chamber 50. The condensation sheet 51 and purified water chamber 50 are configured to facilitate condensation of water vapor and collect / hold purified water that has passed through the membrane 40. In preferred embodiments, condensation sheet 51 comprises the same weldable material as top sheet 31 and microporous sheet 41.

[0153] In some preferred embodiments, a spacer material 45 is arranged inside the purified water chamber 50, see for example figure 6A and 7A. The spacer 45 is configured to space apart the membrane 40 and the condensation sheet 51 , i.e. to create an airgap on the purified water chamberside of the membrane 40. Accordingly and advantageously, the spacer may ensure that membrane- air-gap distillation of water from the contaminated water chamber 30, through membrane 40 and into the purified water chamber 50 is possible. According to preferred embodiments, spacer material 45 may be a mesh material, preferably having an open structure.

[0154] In preferred embodiments, the membrane 40 comprises a reinforcement sheet 42 arranged adjacent to microporous sheet 41, see figures 6A and 7A. Reinforcement sheet 42 is configured to mechanically support / reenforce the microporous sheet 41, i.e. absorb weight / forces / pressure acting on the microporous sheet 41. Reinforcement sheet 42 may be configured to minimize stretching of the microporous sheet 41. The microporous sheet 41 may be a relatively vulnerable sheet. Therefore, to prevent leakages, the distribution of the forces around contaminated water chamber 30 can be advantageous The reinforcement sheet is preferably configured to have minimal interaction with the water or water vapor passing through the microporous sheet. Reinforcement sheet 42 preferably comprises the same weldable material as top sheet 31 and microporous sheet

[0155] 41 and is for example a non-woven polymeric sheet. In some preferred embodiments, the microporous sheet 41 is provided with a coating 44 on the side of the contaminated water chamber 30, see figures 7A and 7B. The coating is configured to create a smooth surface and cover up the pores of the microporous sheet, to improve the antifouling properties of the microporous film, for example preventing especially salt from getting into the pores of the microporous sheet 41. Therefore, a coating may help to prevent clogging of the pores and leakage of the membrane due to salt channels, and thereby increase the lifespan of the membrane and water purification bag. The coating furthermore facilitates the passing of water / water molecules / water vapor. The coating may also be provided to the membrane 40 on the side of the condensation chamber 50.

[0156] It was surprisingly found that silicone (organic) coating can be used for the present low flux (passive and / or solar driven) membrane distillation systems. More specifically, the inventors found that silicone (organic) coatings can be used in the present water purification bag even though the sheets of the bag need to be configured to be mutually connectable through welding (to form welding patterns defining chambers and optionally channels). The coating may be made of a hydrophobic material, such as silicone. A hydrophobic silicone coating would normally not be considered to be used in membrane distillation because of the fact that such coating would make the membrane poorly permeable to water vapor and seriously complicates the subsequent welding of sheets. Nevertheless, it was found that for low flux applications like the present passive and / or solar driven purification system, a silicone coating applied to a microporous polymeric membrane sheet could give significant advantage against scaling, biofouling and due to its molecular structure, it may also give a relatively high selectivity for rejection of salts and volatile organic molecules.

[0157] According to a preferred embodiment, coating 44 comprises at least one of a flexible, macromolecular chained, thin, non-porous hydrophobic coating. In a preferred embodiment, the coating is a silicone coating. Preferably, the silicone coating is applied to the microporous sheet as a liquid with high viscosity and then cured. Preferably, a reactive silicone liquid is used, the reactive silicone liquid having a viscosity in a range of 1.000 to 15.000 mPa.s, preferably in a range of 2.000 to 5.000 mPa.s. The appropriate viscosity may depend on the microporous sheet and be determined such that the coating does not fully fill the pores at the surface of the microporous sheet. Preferably, the silicone coating in the microporous sheet in the water purification bag according to the present examples has a thickness of 10 micrometers or less, more preferably 5 micrometers or less.

[0158] In embodiments of the present disclosure, water purification bags 6 are made of thermally welded sheets, welded along a welding pattern. More specifically, in order to assemble the sheets and parts comprised in the water distillation assembly (for instance the sheets as shown in figures 6A-7B) into a water purification bag 6, at least some of the sheets 31, 41, 42, 51 are connected by welding. The purpose of welding the sheets is firstly to assemble the sheets into a water purification bag 6 and secondly to provide a water purification bag 6 that requires no further support, i.e. wherein all forces / pressure is taken up by the sheets themselves. Therefore, the welding pattern provides an appropriate distribution of the pressure / balance in forces exerted on the sheets and in the bag. Furthermore, preferably, the welding provides easy deaeration of the contaminated water chamber and modular manufacturing of the water purification bag, i.e. removal of air that has evaporated from the heated contaminated water and forms bubbles inside the contaminated water chambers of the water purification bag.

[0159] In preferred embodiments the thermally welding of sheets of the purification bag involves an ultrasonic type of welding. The method of welding may comprises melting polymeric material of a polymeric membrane sheet, melting polymeric material of the top sheet, merging the melted polymeric materials, and allowing the merged polymeric material to cure or to cool and solidify. If the membrane comprises a membrane sheet and a coating on top of the membrane sheet, the top sheet and membrane sheet may be are ultrasonically welded by ultrasonically displacing part of the coating to locally expose a part of the polymeric membrane sheet (for instance by pushing aside a part of the material of the coating, for instance a part extending along a welding line or pattern), ultrasonically melting polymeric material of the exposed part of the polymeric membrane sheet, ultrasonically melting polymeric material of the top sheet, merging the melted polymeric materials, and then allowing the merged polymeric material to cure or to cool and solidify.

[0160] The displacing of the part of the coating may involve at least one of removing, separating or moving aside material of the coating. A critical pressure is exerted on the sheets surrounding the contaminated water chamber 30, i.e. top sheet 31 and microporous sheet 41 and preferably reinforcement sheet 42.

[0161] In the water purification bag according to embodiments of the present application, top sheet 31 and microporous sheet 41 are connected to each other via welding along a first welding pattern. Preferably, when the membrane 40 in a water purification bag according to a preferred embodiment furthermore comprises a reinforcement sheet 42, reinforcement sheet 42 is also connected to microporous sheet 41 along a first welding pattern. The first welding pattern comprises one or more welds 71 and is configured to distribute the pressure in the contaminated water chamber 30. Optionally, the first welding pattern defines the side borders of the contaminated water chamber. The first welding pattern may comprise, for example, a set of dots, circles and / or lines. The first welding pattern may for example be a dotted pattern defining a plurality of zigzag paths for the contaminated water and air in the water chamber, or a set of welding lines defining a plurality of channels in the water chamber (see for example figures 12A- 12D). Additionally, condensation sheet 51 may be connected to the top sheet via welding along a second welding pattern (defining one or more welds 72), which may also be referred to as the further welding pattern. The second welding pattern thus defines the side borders of the purified water chamber. Optionally, the second welding pattern also defines the outer side boarders of the contaminated water chamber. Preferably, the second welding pattern comprises a contour line extending around the first pattern defining the contour of the water purification bag, see for example figure 9A. Figures 10A-10C show a schematic drawing of a transverse cross-section of a multi-layered water purification bag according to an embodiment of the present disclosure. In a multi-layered water purification bag comprising a plurality of water distillation assemblies, the top sheet of the n+l-th layer functions as the condensation sheet of the n-th layer. Preferably, further welding lines connect the top sheets of all layers and the condensation sheet of the final layer, and defines the borders of the purified water chambers and the contour of the water purification bag 6.

[0162] In the following, the term “welding pattern” may also simply refer to the total set of welding dots / lines connecting the sheets in the water purification bag. In short, the sheets defining the contaminated water chamber are thermally welded along a first welding pattern to form a mattress with the (black) top sheet 31 on top and the microporous membrane sheet 41 and reinforcement layer 42 at the bottom side (cf. figurelOA). A sheet of (polypropylene) structured spacer material 45 is then loosely inserted between the bottom condensation sheet (51) and the reinforcement layer 42. The water condensation sheet is then connected to the top sheet along a third pattern or contour pattern. In a multi-layered embodiment, distillation assemblies may further be connected to each other using the second welding pattern or a further welding pattern, simultaneously or subsequently.

[0163] Welding lines according to the present application may be interrupted or uninterrupted lines, however, are referred to simply as Tines’ and indicated in the figures as uninterrupted lines.

[0164] In embodiments wherein an (unweldable) coating is applied to the microporous sheet on the side on the contaminated water chamber, for example according to the embodiment shown in figures 7A-7B, top sheet 31 and microporous sheet 41 cannot be welded without additional measures. However, it was found, surprisingly, that when the silicone coating is cut or split first, the top sheet 31 and microporous sheet 41 (and optionally reinforcement sheet 42) can be welded through the cut. Surprisingly, a sufficient, homogenously durable weld strength can be achieved even with the silicone coating on the membrane sheet 41. It has also been found that a proper mutual connection by welding can also be achieved without separately cutting or splitting the silicone coating first. It was found that with certain combinations of heat and pressure the same or a similar homogenously durable welding strength could be achieved without first cutting / splitting the silicone coating (in fact without any preprocessing step before the actual welding step), but by cutting / splitting the silicone and welding the sheets in one step / one movement, for instance using a thermal welding stamp.

[0165] For (intermittent) ultrasonic welding of the sheets, the following parameters and / or settings and / or conditions may for instance be applied: a frequency between 15 and 45 kHz, preferably 20 to 35 kHz; a tooling temperature of between 20 and 60 degrees Celsius; an amplitude of between 10-100 um, a pressure of between 1 bar and 10 bar; a resulting weld temperature of between 140 and 240 degrees Celsius,. For thermally welding the sheets, the following parameters and / or settings and / or conditions may for instance be applied: a pressure of between 1 and 10 bar, a weld temperature between 160 and 240 degrees Celsius; a weld time of between 2 seconds and 30 seconds.

[0166] In the embodiments according to figures 9A-9B and 12A-12D, the first welding pattern comprises parallel welding lines defining equally spaced parallel channels in the water chamber, and the second welding pattern comprises a contour line around the first welding pattern.

[0167] In 12A-12D, welding patterns according to preferred embodiments are shown schematically. In figures 12A-D, the first welding pattern comprising welding lines 71, connecting the top sheet 31 and membrane 40, is indicated together with the second welding pattern comprising welding lines 72, connecting the top sheet and the condensation sheet. Contour lines 72 define at least one inlet / outlet opening. Welding lines 71 are arranged to form parallel, evenly spaced channels inside the contaminated water chamber. Welding lines 72 define the contour of the water purification bag. According to a second preferred embodiment, the second welding lines are tapered towards the end. This pattern advantageously facilitates the easy outflow of gas bubbles. Furthermore, according to a third preferred embodiment as shown in figure 12C, the welding lines 71 end in a tear-shaped loop 73. The tear shaped loop 73 advantageously distributes the forces exerted on the end of the welding line along the loop, instead of along the point at the end of the line. Therefore, a first welding pattern according to figure 12C may distribute the forces on the welded part of the sheets more evenly and decrease the chances of ripping, stretching and leakage in the sheets. Furthermore, arced contour line 75 comprised in the second welding pattern facilitates regular folding of the substantially two-dimensional sheets when the chambers, especially the contaminated water chambers, of the water purification bag are inflated to a three- dimensional shaped object. A regular folding of the sheets may further decrease the risk of damage and improve the distribution of forces, thus increasing the lifespan of the water purification bag. In a fourth preferred embodiment according to figure 12D, the first welding pattern comprises parallel welding lines defining channels, wherein the middle line extends along the imaginary line defining the middle of the water purification bag when viewed from above. Furthermore, the middle line ends right next to and in the middle of the opening of the water purification bag defined by contour welding lines 72. Furthermore, the middle welding line comprises a double-tear shaped loop 74 at the end. An embodiment according to figure 12D provides optimal distribution of forces on the welding lines close to the inlet / outlet opening.

[0168] According to a preferred embodiment, the welding pattern comprises two openings, wherein one opening is provided at a first end of the welding pattern and one opening is provided at the second end of the welding pattern, opposing the first end. In preferred embodiments, the welding pattern is contiguous back-to-front, such that, if two water purification bag according to said preferred welding pattern are positioned back-to-front, the first opening of the first water purification bag connects to the second opening of the second water purification bag. Accordingly, multiple patterns may be repeated in juxtaposition to create one, longer, modular water distillation assembly. An example of such a preferred welding pattern is shown in figure 9A. Advantageously, a welding pattern corresponding to figure 9A may be used to create modular water purification bags, as is the case in the embodiment shown in figure 1A, wherein every water purification bag 6 comprises a triple repetition of the same welding pattern in juxtaposition.

[0169] In the spacing between the channels and the width of the welding lines, a balance is sought between dividing the pressure, easy deaeration / removal of gas bubbles inside the water purification bag, and efficiency, i.e. production of purified water per square meter sheet material. In figure 11 A, the forces on the sheets 31, 41, 42 around the contaminated water chamber are indicated with arrows. The forces exerted by the water in the contaminated water chamber on the on the sheets needs to be compensated by the welding lines. If the channels are too broad, the forces on the welding lines become too strong and the material may stretch or rip. However, if the channels become to small, gas bubbles may get stuck, as is shown in figure 1 IB. Preferably, the width of the channels is more than 4 mm, more preferably more than 4 mm. Furthermore, the width of the channels is preferably less than 14 mm, more preferably less than 12 mm. For example, in a preferred embodiment, the width of the channels is in the range between 4 mm and 12 mm, for example 8 mm. Preferably, the width of the welding lines is between 0.2 to 4 millimeters, preferably between 1 and 1.5 millimeters.

[0170] Cross-sections of a water purification bag 6 assembled according to any of the welding patterns of figures 9A-B and 12A-12D is shown schematically in figures 10A-10C. Welding patterns of figure 12B corresponds to the welding patterns shown in figure 9 A. The welding patterns according to the embodiments shown in figures 12A-12D may all correspond to the embodiments shown in figures 10A-11B. Figures 10A and 10B show a schematic drawing of a transverse cross-section (perpendicular to the channels / welding lines 71 of the first welding pattern) of a three-layered water purification bag, respectively deflated and inflated. Welding lines 71 correspond to where the top sheet and the membrane 40 and the top sheet are connected. The channels inside the contaminated water chamber 30 are defined by the first welding pattern. In this respect it is remarked that of the sheets of the purification bag would be non-stretchable (in practice, the sheets may or may not be embodied to be somewhat stretchable), the welding lines delimiting the channels are positioned with a smaller mutual distance when the channels are filled with liquid (inflated condition) than when the channels are (still) deflated. For ease of drawing this difference in mutual distance has not been indicated in figures 10A and 10B (the bag “shrinks” as it were in lateral direction a deflated bag is inflated with water).

[0171] The sheets used in various embodiments of the present disclosure may be thin film sheet having a thickness and density as indicated in table 1 shown below.

[0172] Deaeration

[0173] As discussed earlier, when water is heated, gas (for instance air) dissolved in the water will evaporate. The heating of the contaminated water chambers therefore causes the continuous creation of gas bubbles. These gas bubbles need to be removed regularly from the system because the accumulation of too much gas would reduce the purification efficiency of the purification system. However, it has been found that these gas bubbles also can have a beneficial use since they may temporarily block the flow of contaminated water between the various contaminated water chambers. The blocking of the flow may increase the purification efficiency of the system, as discussed in connection with figure 3A. To remove gas bubbles when the amount of gas tends to become too large, the purification system may be provided with a deaeration system. The deaeration system is configured to selectively let out previously dissolved gas that has evaporated from the water.

[0174] In the embodiments according to figures 2A-4G, 13A-16, and 20-22 , the water chambers are connected to air / the environment (either inside or outside casing 8) using a deaeration element, see for example figures 2 A and 3 A and 3B. The deaeration element provides an connection (for instance via a float valve, not shown in the figures) between the water chamber and the environment. The water purification device in the water purification system is preferably arranged at an angle of 15 degrees or more with respect to the horizontal plane (which is the imaginary plane perpendicular to the direction of gravity). Preferably, the deaeration element is provided at or near the upper end of the contaminated water chamber(s), such that most of the dissolved gas in the contaminated water chamber can flow to the deaeration element. As such, gas bubbles in the contaminated water chamber may rise out of the contaminated water chamber and, via the air connection or gas vent 22, into the environment.

[0175] In figures 2A, 3 A, and 3B, contaminated water chambers are connected to each other at the upper side of the water purification device by the connecting portion of connector 9 (first) and (then) connecting to the environment via a single air connection 22 comprised in connector 9. The connecting portion of connector 9 provides an open connection between the associated water chambers. The term connector usually refers to a device comprising a connecting portion, and optionally a deaeration element and / or a circulation limiter. The term connector may also refer to the connecting portion itself.

[0176] Alternatively, in other embodiments (not shown), each contaminated water chamber of each water purification assembly comprised in the water purification device may be connected to the environment via an air connection separately. An advantage of providing a connector 9 configured to connect all contaminated water chambers in the multi-layered water purification device is that only one air connection may facilitate deaeration of the entire water purification device.

[0177] The connector may be provided externally to the water purification device, see figures 2A- 4G, or internally. Further preferred embodiments of an internal connector device wherein a deaeration element is comprised will be discussed later with respect to figures 13A to 19E.

[0178] For internal connectors, discs with openings may be welded into (openings in) the sheets to create connections / openings between the water chambers and the environment. For external connectors, spouts may be welded between the sheets at an outer edge of the water purification bag to create and opening / connection to the connector or the outer environment. For example, a spout may be welded between the sheets defining a contaminated water chamber 30, for example sheets 31(1) and 40(1) defining contaminated water chamber 30(1). The advantage of this embodiment is that one spout can be welded between two sheets and thus less elements are needed to provide the connector. Furthermore, it may be advantageous to weld the connector elements to the outer edge of the water purification bag in stead of welding elements into (openings in) the sheets.

[0179] Circulation limiter

[0180] Maintaining a temperature gradient across the contaminated water chambers / water purification assemblies increases the productivity of a multi-layered water purification device. However, providing a connector according to the above description may decrease the temperature gradient between the respective water purification assemblies in the water purification device. Figure 3A shows a preferred embodiment according to the present description wherein the contaminated water chambers of the four water purification assemblies 60'-604are connected to each other at the upper end of the water purification bag via connector 9 comprising a deaeration element. In this embodiment according to figure 3A, water in the contaminated water chambers may flow freely between the different layers / water purification assemblies. As a result of the flow of contaminated water between different contaminated water chambers, the temperature gradient in the water purification device may substantially be determined by gravity. For example, as shown in figure 3A using shading, the upper side of the water purification device, i.e. the upper side of each contaminated water chamber in the water purification device, may have a relatively high temperature, whilst the lower side of the water purification device, i.e. the lower side of each contaminated water chamber in the water purification device, may have a relatively low temperature.

[0181] However, as explained above, ideally, the temperature gradient extends in the direction perpendicular to the stack of water purification assemblies, i.e. such that the temperature difference between the water purification assemblies is maximized.

[0182] In some preferred embodiments, the water purification device is provided with a circulation limiting unit or circulation limiter 90. The circulation limiter provides one or more gas bubbles 93 between a contaminated water chamber and the connection (for example connector 9) with the other contaminated water chamber(s) comprised in the water purification device, such that the water is prohibited from flowing between two contaminated water chambers via said connection. In preferred embodiments, the circulation limiter comprises at least one bent portion of a tube / connection connecting the respective contaminated water chamber 30nand the connector 9 (connecting the contaminated water chambers of the water purification assemblies in the water purification device). During operation, gas bubble 93 assembles in the bent portion of the tube, formed by air dissolving from said contaminated water (see also figures 4A-4G and the corresponding figure description, especially figures 4E-4F). The gas bubbles 93 in the bent portion prohibits water in said contaminated water chamber 30n. Preferably, the circulation limiter 90 provides enough gas bubbles to prohibit the flow between contaminated all water chambers of the water purification device, for example by comprising at least n-1 bent portions between contaminated water chambers 30'-30n 1and the connecting portion 9.

[0183] In the preferred embodiments shown in figures 2A, 3B-4G, the circulation limiter 90 is provided to the water purification device (externally and) between the contaminated water chambers and the connector 9 at the upper end of the water purification device. Figures 2C and 2D show schematic drawings of preferred embodiments of a circulation limiter and connector and deaeration element combined in one device which is configured to be connected to the contaminated water chambers 30nof the water purification device externally and preferably at their upper end.

[0184] Figure 2C is associated with a three-layered water purification device (comprising a stack of three water purification assemblies). The device shown in figure 2C provides a connection between the contaminated water chambers 30'-303of the respective water purification assemblies in the water purification device. The connecting portion, connecting the contaminated water chambers, of the device as shown is further connected to the environment via an air connection 22. Between the contaminated water chambers 303and 302and the connecting portion, respective bent portions are provided. In the bent portions, gas bubbles 93 accumulate in operation as gas dissolves from the contaminated water. The gas bubbles 93 in the bent portion prohibit water in the contaminated water chambers to flow freely between the respective contaminated water chambers. The size of the gas bubble 93 in a bent portion is limited by the shape of the bent portion. When the gas bubble 93 has reached the maximum size, additional gas bubbles arriving at the bent portion cause overflowing of the gas bubble in the bent portion and some of the gas bubble flows out of the bent portion and into the environment via air connection 22, see figure 2C. Figure 2D shows a schematic of another preferred embodiment of a device comprising a connection between the contaminated water chambers, an air connection (which may be selectively opened or closed) and a circulation limiter between the respective contaminated water chambers and the connecting portion, associated with a four-layered water purification device. The device shown in figure 2D is also configured to be connected to the water purification device externally. The preferred embodiments shown in figures 2C and 2D work according to the same principles. The bent portions may be angular, as shown in figure 2C, or curved, as shown in figure 2D. The preferred embodiment shown in figure 2D comprises a bent portion between the bottom contaminated water chamber 304and the connecting portion, whilst the preferred embodiment according to figure 2C does not comprise a bent portion between the bottom contaminated water chamber 301and the connecting portion. Both embodiments perform equally well, since flow between the contaminated water chambers via the corresponding connecting portion is prohibited by the gas bubbles 93 accumulated in the bent portion(s).

[0185] The multi-layered water purification device according to the present application may comprise at least one connection between the contaminated water chambers of the respective stacked water purification assemblies, which is comprised in or connected to the feed inlet of the water purification device (preferably near the lower end of the water purification device). Furthermore, as discussed above, the contaminated water chambers may be further connected to each other (preferably near the upper end of the water purification device) to provide deaeration of said chambers. Additionally, in preferred embodiments, the respective purified water chambers of the stacked water purification assemblies are connected to each other to provide a single outlet and / or container for purified water.

[0186] These connections may be provided externally or internally, i.e. inside the water purification device or outside the water purification device. For example, figures 2A-4G show embodiments wherein the contaminated water chambers 30nare connected to each other via an external connector 9 comprising a deaeration element (and in some preferred embodiments a circulation limiter). Also, in the embodiments of figures 2A-4G, the respective contaminated water chambers are connected to each other and the feed at the lower end externally. Furthermore, figure 2A shows that the purified water chamber 50'-503are connected to each other internally. When the chambers are connected externally, the chamber may be provided with an opening (see the upper and lower end of the welding pattern in figure 9A) wherein a spout or other connection device is provided. The spout may be connected to tubes or other connection means, for example a connector device as shown in figures 2C and 2D.

[0187] Chambers may also be connected internally using an internal connector 9. Figure 9B shows an example of a multi-layered water purification device wherein disks 951 (corresponding to 951, see figure 15)and 952 (corresponding to 952) (each disk being provided with a central opening or hole) are welded in the top sheet / condensation sheet (31 / 51) and the membrane (40) of every water purification assembly respectively, arranged on top of each other. Respective disks 951and 952may be connected to each other such that, as can be seen in figure 9B, the contaminated water chambers of the respective water purification assemblies are connected via the respective openings in the disks, and, furthermore, the purified water chambers are closed off, i.e. sealed, liquid tight, preferably fluid tight. For example, in figure 9B the disk 952in membrane 40nis connected to the disk 951in condensation sheet 51n / top sheet 31n+1such that the purified water chamber is sealed with respect to the openings connecting the contaminated water chambers. In the embodiment shown in figure 15 use is made of elastic O-rings 88 in order to provide a watertight seal between consecutive disks (for instance 951and 952). In other embodiments O-rings 88 can be left out and the (pairs of) consecutive disks are directly bonded, for instance welded or glued, to each other.

[0188] The resulting connector may be configured for deaeration purposes (preferably near the upper end of the tilted water purification device) or for feed purposes (preferably arranged near the lower end of the water purification device). In an alternative embodiment of the internal connector, the disks may also be provided such that the openings provide a connection between the purified water chambers instead of the contaminated water chambers. However, an internal connection between the purified water chambers 50nmay also be (and usually is) provided by simply providing an opening or cut in the A corresponding connector may facilitate a single outlet for purified water. Furthermore, in some preferred embodiments, the disks may comprise connection portions extending perpendicular to the openings and the sheets, the connection portions configured to be connected to each other. These extending connection portions may advantageously provide spacing between the associated sheets. For example, as shown in figure 9B, the connection portions of the disks provide spacing between the membrane 40nand the condensation sheet 5 ln(which is also top sheet 31n+1). As such, disks welded through the sheets of the respective water purification assemblies may provide an internal connection between the associated chambers of the stacked assemblies in the water purification device and optionally spacing between the membrane and the condensation sheet. Advantageously, the welded disks may provide advantageous connections inside the water purification device. The disks can be flat and light and may thus be easily transported, comprised in the water purification bag. Furthermore, a water purification device wherein internal connections are provided may be more user friendly, since the assembly of the water purification system requires less montage and assembly steps. Furthermore, the water purification system comprising a bag with internal connections may be more robust, since external connectors may be more exposed to the environment or more prone to error or theft or other damage.

[0189] In preferred embodiments according to figures 13A-19E, a connector device comprising welded disks and an internal connector cylinder 88 is provided. In some preferred embodiments, a connector device may comprise disks welded through the respective sheets in the stacked water purification assemblies for providing a liquid connection between the associated chambers (contaminated water chambers or purified water chambers), as described above with respect to figure 9B. Additionally, the connector device may comprise an internal cylinder 88 arranged through the disks. The internal cylinder 88 may serve multiple purposes depending on the function of the respective connector. Two types of connector devices according to preferred embodiments comprising welded disks 95 ', 952and an internal cylinder 88 will be discussed with respect to figures 13A-19E below.

[0190] A connector device arranged at an upper end of the bag 6 is referred to as the upper connector 85. Upper connector 85 is configured for deaeration and comprises a circulation limiter 91. The connector device according to another preferred embodiment is referred to as the lower connector 86. Lower connector 86 is configured for connecting the contaminated water chambers in the water purification bag to the feed.

[0191] Figure 13A schematically shows a longitudinal cross section of a multi-layered water purification bag (from the upper end to the lower end of the water purification bag) according to a preferred embodiment comprising an upper connector 85 and a lower connector 86 in an empty water purification bag (filled with air not with water or other liquid). Figure 13B shows the same cross-section of the same embodiment of the water purification bag in a situation wherein the water purification bag is filled with contaminated water and during operation. Figure 14 shows a schematic drawing of a water purification bag according to a preferred embodiment corresponding to the embodiments of figures 13A and 13B in perspective. Figures 15 and 16 respectively show detailed schematic perspectives of an upper connector 85 and a lower connector 86 according to the preferred embodiments shown in figures 13A-B and 14.

[0192] Figure 13C schematically shows a single layered water purification bag according to a preferred embodiment in operation, comprising an upper connector 85 and a lower connector 86 according to a preferred embodiment.

[0193] Upper connector 85 and lower connector 86 according to the present application both comprise disks 95 welded in the respective sheets of the water purification assemblies and arranged above each other in the direction of the stacked water purification assemblies in the water purification bag. Upper and lower connectors 85 and 86 further comprise tube 88, also referred to as internal cylinder 88, arranged through the disks.

[0194] According to a preferred embodiment (corresponding to figures 13A-19E) disks 951and 952are welded in the top sheet 31 (or condensation sheet 51) and the membrane 40 respectively and are configured to connect to each other, see figures 15 and 16. Disks 951comprise a protruding portion facing the top of the water purification bag and ), disks 952comprise a protruding portion facing the bottom of the water purification bag (in the direction of the stacking of the water purification assemblies in the water purification bag, i.e. substantially perpendicular to the extension of the flat sheets 31 / 41 / 51). The protruding portions are configured to securely connect to each other, preferably with a click mechanism, such that they can be mounted to each other by hand after assembly of the water purification bag. The disks advantageously provide a mounting facility for the inner tube 88 which may be configured according to the purpose of the associated connector device (upper or lower, for example). Tube 88 according to preferred embodiments shown in the figures is a substantially hollow cylindrical tube.

[0195] Figure 15 shows a schematic perspective of an upper connector 85 configured for deaeration according to a preferred embodiment. The embodiment of figure 15 corresponds to the upper connectors 85 in figures 13A-14 and preferably comprises an inner tube 88 according to figures 17 and 18. Connector 85 connects contaminated water chambers 30nvia its hallow inside and openings 87. Substantially hollow tube 88 is arranged though the disks welded in the sheets of the water purification assemblies. Openings 87 are preferably arranged in the wall of tube 88 such that they are adjacent to the contaminated water chambers and face the upper end of the water purification bag (i.e. the end of the water purification bag arranged highest when the water purification bag is tilted in the water purification system). Furthermore, tube 88 of upper connector 85 preferably comprises a circulation limiter 91. In the preferred embodiment according to the figures the circulation limiter inside connector 85 comprises bend portions, also referred to as flanges 89. Flanges 89 are configured to trap one or more gas bubbles 93 at the opening 87 during operation, thereby effectively prohibiting flow of contaminated water between different contaminated water chambers. (See also figure 18 for a cross section of tube 88 in accordance with the preferred embodiment as presently described, comprising a circulation limiter with flanges 89.) The bottom contaminated water chamber may not be provided with a bend portion and may be connected to the hollow inside of the connector by multiple openings 87 and / or openings that do not face the upper end of the water purification bag, since no gas bubble needs to block the opening to prevent flow of contaminated water between chambers when the other openings 87 are already blocked.

[0196] Purified water chambers 50nare closed off from the hollow inside of connector 85 by the protruding portions of the disks and by the wall of the internal tube 88, see figure 15 for example. Furthermore, the hollow inside of the tube 88 is connected with an air connection, also referred to as air vent 22, via opening 110 in tube 88. Air vent 22 is configured as outlet of gas bubbles. In the preferred embodiments according to the figures, gas vent 22 is provided in the top part 99, connected to the upper disk 9511.

[0197] In upper connector 85, tube 88 is arranged with the closed side up, though the disks welded in the sheets of the water purification assemblies. The second end of connector 85 may be closed by closing lid 97 (see figures 15, 16, and 21 for example).

[0198] Figure 13C shows a longitudinal cross-section of a single layered water purification bag comprising an upper connector according to a preferred embodiment. Upper connector 85 (see figure 14) associated with a single-layered water purification bag according to a preferred embodiment may comprise the same structure as upper connector 85 associated with a multilayered water purification bag, i.e. welded disks 951and 952and tube 88 arranged through said disks (see figure 15 for the reference numbers). The hollow inside of tube 88 may be connected to the water chamber 30 via opening 87. The upper connector may furthermore, analogue to the multilayered embodiment, preferably connect water chamber 30 to the environment through an gas vent 22 in top part 99 via an opening in tube 88. The single-layered embodiment of the upper connector may be provided without a circulation limiter.

[0199] Figure 16 shows a schematic perspective of a lower connector 86 configured for connecting the contaminated water chambers to the feed / discharge line 19, also referred to as the feed. The embodiment of figure 16 corresponds to the lower connectors 86 in figures 13A-14. In a preferred embodiment, lower connector 86 comprises an inner tube 88 with grooves 111 according to the tube 88 in figures 17 and 18. (However, preferably, inner tube 88 associated with lower connector 86 does not comprise flanges 89 and may furthermore have two open ends.) In lower connector 86, tube 88 is arranged though the disks welded in the sheets of the water purification assemblies. Connector 86 connects contaminated water chambers 30nvia its hallow inside and openings 87. Substantially hollow tube 88 is arranged though the disks welded in the sheets of the water purification assemblies. Openings 87 are arranged in the wall of tube 88 such that they are adjacent to the contaminated water chambers. In the preferred embodiment of figure 16, lower connector 16 comprises multiple openings 87 for every contaminated water chamber 30n. The openings 87 and hollow inside of the connector 86 are configured to provide an open connection between the contaminated water chambers.

[0200] Purified water chambers 50nare closed off from the hollow inside of connector 86 by the protruding portions of the disks and by the wall of the internal tube 88, see figure 16 for example. Furthermore, the hollow inside of the tube 88 is connected with a feed / discharge conduit 19, via the first open end of the tube and coupler 92. The second end of tube 88 may be closed using closing lid 97, configured for connecting to disk 95 '.

[0201] Figure 13C shows a longitudinal cross-section of a single layered water purification bag comprising a lower connector according to a preferred embodiment. Lower connector 86 (see figure 14) associated with a single-layered water purification bag according to a preferred embodiment may comprise the same structure as lower connector 86 associated with a multilayered water purification bag, i.e. welded disks 951and 952and tube 88 arranged through said disks. The hollow inside of tube 88 may be connected to the contaminated water chamber 30 via openings 87. The lower connector may furthermore, analogue to the multilayered embodiment, preferably connect water chamber 30 to the feed / brine discharge conduit (for example via coupler 92).

[0202] In preferred embodiments, tube 88 is configured to be mounted to the disks welded in the sheets of the water purification bag by screwing the tube into the disks. In a preferred embodiment according to figures 17, tube 88 may therefore comprise grooves 11, also referred to as bayonet couplings 112. Using the bayonet couplings 112, tube 88 may be mounted to the disks and assembled into a connector device 9 according to the steps as shown in figures 19A-19E, by means of screwing. Figure 18 schematically shows a cross section of a tube 88 associated with an upper connector 85 (because of the flanges 89), however, the preferred embodiment of tube 88 as shown in figure 17 may also correspond to a tube associated with the lower connector 86. Advantageously, the water purification bag according to the corresponding preferred embodiment may be transported in a flat state, such that the water purification bag requires less space upon transportation. Furthermore, the mounting of the tube 88, i.e. the assembly of the connector devices according to this embodiment is fool-proof and may be executed by people with no experience or expertise.

[0203] Alternative connector without core

[0204] An alternative embodiment of an internal connector comprising disks welded into the sheets is shown in figures 20-22. In this alternative embodiment, the disks do not form one central opening connecting the water chambers and possibly configured to receive an internal cylinder with a circulation limiter function, but comprise alternately shifted openings connecting the contaminated water chambers and forming a sealed passage (fluid tight) through the condensation chambers, wherein the openings are preferably alternately shifted with respect to each other such that the openings form a zig-zag shaped passage, that may provide a deaeration and circulation limiting functions during use.

[0205] Referring to figures 20-22, in further embodiments, a connector is provided inside the water purification bag that is configured to operate without a core, an internal cylinder or a central opening.

[0206] Figure 20 schematically shows the elements forming the core-less connector in perspective, without the water purification bag.

[0207] Figure 21 schematically shows a cross section of the core-less connector in a water purification bag, wherein no contents of the water purification bag (contaminated water, vapor, purified water) are shown. Disks 96(1) and 96(2) are welded into the top sheets (condensation sheets) and membrane sheets respectively. The top disk 96(1) is configured to be welded into the top sheet and configured to extend upwards, into the condensation chamber above, or into the environment. The bottom disk is configured to be welded into the membrane sheet and to extend downwards, into the condensation chamber below. The top disk 96(1) and bottom disk 96(2) are configured to connect to each other such that a liquid tight, preferably, fluid tight, seal between them is formed (inside the respective condensation chamber 50, i.e. the purified water chamber) enclosing a sealed space. Furthermore, the top disk 96(1) is configured to comprise an opening, preferably arranged at its lower end in use (when welded in the bag), forming an opening / connection between the respective water chamber 30 below and the sealed space on top through which fluid may pass. Additionally, the bottom disk 96(2) is configured to comprise an opening, preferably arranged at its upper end in use (when welded in the bag), forming an opening / connection between the water chamber on top and the sealed space on below through which fluid may pass. On top, the connector is closed with a top part 99 provided with a gas vent 22, at the bottom, the connector is closed using a closing lid 97 configured to seal the connector.

[0208] The openings are thus connected with an outlet for air (gas vent 22), preferably arranged at the top, upper end of the connector, connecting the connector to the environment for deaeration. Additionally this embodiment serves as a circulation limiter because air bubbles 90 separate the contaminated water from the contaminated water chambers in different layers from each other.

[0209] Figure 22 schematically shows a cross section of the core-less connector in the water purification bag during use. This embodiment of the circulation limiter uses the condensation chamber as the area for the air lock position. This makes it possible to weld the end closing lid 97 with a low difference in layer height but without the need for a (hard to injection mold) internal cylinder that needs to have the circulation limiting function. Other benefits are the simplicity of the design. The gaps are preferably only 5 to 10 mm, preferably 7 mm high, but at least 10mm, preferably at least 12mm wide. The closing lid 97 can be identical to the top disk 96(1) except for the opening, which it does not have. The disks may be connected using a sealing element or they may be thermally sealed. Thus, a relatively low amount of different elements may be required to provide a connector according to figures 20-22 and circulation limiter according to embodiment. This might be advantageous to lower the costs in a mass manufactured design. This connector may be welded thermally or ultrasonically. In this embodiment, hot water will rise to the connector, and the energy loss will be be similar , for instance of the same order, to the energy loss in a single layer system. This embodiment of the circulation limiter is preferably used at an angle of 5-50 degrees, more preferably 7-30, most preferably 8-25 degrees, for example 10 degrees, 13 degrees, 15 degrees, or 18 degrees, plus a few extra millimeters of height difference. This height difference is not necessary and can be reduced to make the product shorter; If the minimum angle is 10 degrees, the product can be 5mm shorter. If a minimum angle of 15 degrees is used, the product can be 15mm shorter.

[0210] Inseam connector

[0211] In an alternative embodiment, a connector may be an inseam connector comprising spouts that are welded to the edges between the respective sheets to create an opening and passage to an external connector. Advantageously, in this embodiment, less body parts have to be welded to / in the water purification bag because one spout is welded between two sheets. In an embodiment of an inseam connector, the connector is partly external to the water purification bag.

[0212] It is to be understood that this invention is not limited to particular aspects described, and, as such, may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0213] Other aspects of the present invention are defined in the following numbered examples or clauses.

[0214] CLAUSE 1. Purification bag (6) for use in a purification system (100) for heat-driven water purification of contaminated water, the purification bag (6) comprising a distillation assembly or a stack of distillation assemblies (601, ..60n), wherein each distillation assembly is configured to receive a part of the contaminated water and separate a purified water portion from the received part of the contaminated water, and wherein a distillation assembly (601, ..60n) comprises:

[0215] - a contaminated water chamber (30) for collecting contaminated water, the contaminated water chamber (30) comprising a top sheet configured for absorbing heat;

[0216] - a purified water chamber (50) for collecting purified water, the purified water chamber (50) comprising a condensation sheet configured for collecting condensed purified water; - a membrane (40) arranged between the top sheet and condensation sheet, the membrane dividing the distillation assembly into the contaminated water chamber (30) and the purified water chamber (50), wherein the membrane (40) comprises a membrane sheet configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet; wherein the top sheet and the membrane sheet are polymeric sheets that are bonded to each other by welding according to a welding pattern.

[0217] CLAUSE 2. Purification bag (6) as described in clause 1, wherein the top sheet, the membrane sheet, and condensation sheet are polymeric sheets that are bonded to each other by welding according to a welding pattern.

[0218] CLAUSE 3. Purification bag as described in clause 1 or 2, wherein the membrane sheet is a microporous membrane sheet.

[0219] CLAUSE 4. Purification bag (6) as described in any of the preceding clauses, wherein the polymeric top sheet, polymeric membrane sheet and polymeric condensation sheet are made of polyolefin material, for instance LDPE, HDPE, polypropylene (PP), or polymethyl pentene.

[0220] CLAUSE 5. Purification bag (6) as described in any of clauses 1-3, wherein the polymeric top sheet and the polymeric condensation sheet are made of nylon, and the membrane is a hydrophilic material, for instance polyetheramide.

[0221] CLAUSE 6. Purification bag as described in any of the preceding clauses, wherein the condensation sheet is a polymeric sheet that is bonded to at least one of the top sheet and the membrane sheet by welding according to a further welding pattern.

[0222] CLAUSE 7. Purification bag as described in any of the preceding clauses, wherein the welding pattern and the further welding pattern are respectively formed by one or more first welding lines and one or more second welding lines.

[0223] CLAUSE 8. Purification bag as described in any of the preceding clauses, wherein the microporous membrane sheet and the condensation sheet are made of the same type of material, preferably materials comprising the same polymer.

[0224] CLAUSE 9. Purification bag as described in any of the preceding clauses, wherein the welding of two polymeric sheets comprises heating material of both polymeric sheets, melting the polymeric sheets together and then allowing the polymeric sheets to cool causing fusion.

[0225] CLAUSE 10. Purification bag as described in clause 9, wherein the polymeric sheets are bonded by ultrasonic welding.

[0226] CLAUSE 11. Purification bag as described in clause 9 or 10, wherein if the membrane comprises a membrane sheet and a coating on top of the membrane sheet, the ultrasonic welding of polymeric sheets comprises ultrasonically displacing a part of the coating to locally expose a part of the polymeric membrane sheet, melting polymeric material of the exposed part of the polymeric membrane sheet and melting polymeric material of the top sheet, merging the melted polymeric materials and allowing the merged polymeric material to cure

[0227] CLAUSE 12. Purification bag as described in any of the preceding clauses, wherein at least one of the welding pattern and further welding pattern is formed in one welding step, preferably using a thermal welding stamp.

[0228] CLAUSE 13. Purification bag (6) as described in any of the preceding clauses, wherein the membrane comprises a hydrophobic membrane sheet, for instance a polyolefin sheet with micropores.

[0229] CLAUSE 14. Purification bag (6) as described in any of the preceding clauses, wherein the membrane comprises an uncoated microporous sheet.

[0230] CLAUSE 15. Purification bag (6) as described in any of the preceding clauses, wherein a side of the microporous membrane sheet facing the contaminated water chamber is provided with a coating.

[0231] CLAUSE 16. Purification bag (6) as described in clause 15, wherein the coating is at least one of a flexible, macromolecular chained thin non-porous hydrophobic coating.

[0232] CLAUSE 17. Purification bag (6) as described in clause 15 or 16, wherein the coating is a silicone coating.

[0233] CLAUSE 18. Purification bag (6) as described in any of clauses 15-17, wherein the coating is a silicone coating with a thickness of 10 micrometers or less, preferably less than 5 micrometers or even less than 2 micrometers.

[0234] CLAUSE 19. Purification bag (6) as described in any of clauses 15-18, wherein the coating is a silicone coating made from a reactive silicone liquid, the reactive silicone liquid having a viscosity in a range of 1.000 to 15.000 mPa.s, preferably in a range of 2.000 to 5.000 mPa.s.

[0235] CLAUSE 20. Purification bag (6) as described in any of the preceding clauses, wherein the micropores of the microporous membrane sheet are symmetrically distributed over the area facing the contaminated water chamber and / or wherein the micropores of the microporous membrane are asymmetrically distributed over its thickness, wherein the average pore size of the micropores in a first area facing the contaminated water chamber is smaller than the average pore size of the micropores in a second area facing the purified water chamber.

[0236] CLAUSE 21. Purification bag (6) as described in any of the preceding clauses, wherein the pore diameter of the micropores is smaller than 2.0 pm, preferably smaller than 0.5 pm or even smaller than 0.2 pm.

[0237] CLAUSE 22. Purification bag (6) as described in any of the preceding clauses, wherein the microporous membrane sheet has a density in the range of 10 to 200 g / m2, preferably between 30 and 100 g / m2, more preferably between 40 and 70 g / m2and / or wherein the microporous sheet has a porosity of more than 30%.

[0238] CLAUSE 23. Purification bag (6) as described in any of the preceding clauses, wherein the polymeric membrane comprises a vapor-permeable reinforcement sheet attached to the side of the microporous membrane sheet facing the purified water chamber.

[0239] CLAUSE 24. Purification bag (6) as described in clause 23, wherein the reinforcement sheet is a polymeric sheet, preferably a fibrous polyolefin sheet, for example a hydro-entangled non-woven polyolefin or a polymer adhesive web.

[0240] CLAUSE 25. Purification bag (6) as described in clause 24, wherein the reinforcement sheet has a density of about 30-100 g / m2.

[0241] CLAUSE 26. Purification bag (6) as described in any of the preceding clauses, wherein the purification bag (6) comprises a stack of multiple distillation assemblies arranged one on top of the other.

[0242] CLAUSE 27. Purification bag (6) as described in clause 26, comprising a first distillation assembly arranged on top of a second distillation assembly, wherein the condensation sheet of the first distillation assembly is formed by the top sheet of the second distillation assembly.

[0243] CLAUSE 28. Purification bag (6) as described in any of the preceding clauses, wherein the welding pattern comprises first welding lines arranged to form inner welding lines to define a plurality of interconnected channels to form a contaminated water chamber for receiving and holding contaminated water and / or wherein the further pattern comprises second welding lines arranged to form outer welding lines to define at least one channel to form a purified water chamber for receiving and holding purified water.

[0244] CLAUSE 29. Purification bag (6) as described in any of the preceding clauses, comprising a spacer, for instance a spacer sheet, arranged inside a purified water chamber (50) to provide a predefined minimum height of the purified water chamber (50).

[0245] CLAUSE 30. Purification bag (6) as described in clause 29, wherein the predefined minimum height of the spacer is 2-12 mm.

[0246] CLAUSE 31. Purification bag (6) as described in clause 29 or 30, wherein the spacer is comprised of polymeric, for instance polyolefin material, and / or wherein the spacer defines an open structure allowing water to pass so that the water vapor can condense on the condensation sheet of the purified water chamber, thereby releasing its latent heat of condensation to heat up the contaminated water inside a further contaminated water chamber.

[0247] CLAUSE 32. Purification bag (6) as described in any of the preceding clauses, comprising a common inlet and outlet for feeding-in contaminated water to at least one of the contaminated water chambers, preferably to all contaminated water chambers and for feeding-out contaminated water and the residual water parts from at least one of the contaminated water chambers, preferably from all of the contaminated water chambers.

[0248] CLAUSE 33. Purification bag (6) as described in any of the preceding clauses, comprising a connection unit (9) configured to mutually provide a fluid connection between stacked contaminated water chambers (30), wherein optionally the connection unit (9) is arranged at an upper end of the water purification bag (6) and / or at a lower end of the water purification bag (6).

[0249] CLAUSE 34. Purification bag (6) as described in clause 33, wherein the connection unit (9) comprises tubing (95) interconnecting the plurality of contaminated water chambers (30).

[0250] CLAUSE 35. Purification bag (6) as described in any of clauses 32-34, wherein the connection unit (9) comprises a connector (90), the connector preferably extending transversely to the respective contaminated water chambers (30).

[0251] CLAUSE 36. Purification system as described in any of clauses 32-35, wherein the connection unit (9) comprises a connector (90) extending through respective openings provided in the upper ends of the respective contaminated water chambers (30) and purified water chambers (50), while only the contaminated water chambers (30) are in fluid connection with the inner volume of the connector.

[0252] CLAUSE 37. Purification bag (6) as described in any of clauses 32-36, further comprising a circulation limiter (91) configured to limit the circulation of contaminated water between respective contaminated water chambers (30).

[0253] CLAUSE 38. Purification bag (6) as described in any of clauses 32-37, wherein the circulation limiter (91) is combined with the connector (90).

[0254] CLAUSE 39. Purification bag (6) as described in any of clauses 35-38, wherein the connector (90) comprises a tubular element, the tubular element comprising a number of openings to allow water to flow between the contaminated water chamber, wherein the inner surface of the tubular element is provided with one or more flow limiters, for instance a flow limiting flange, extending radially inward so as to limit the flow of air bubbles between the contaminated water chambers.

[0255] CLAUSE 40. Purification bag (6) as described in clause 39, wherein the tubular element is configured to be removably slid into to the openings, wherein the tubular element preferably is configured to mutually space apart the contaminated water chambers at respective predetermined distances while sliding the tubular element into the openings.

[0256] CLAUSE 41. Purification system (100) for heat-driven water purification of contaminated water, the purification system comprising:

[0257] - a housing (8);

[0258] - a feed water unit (2) for the supply of contaminated water comprising contaminants; - a water purification module (5) connected to the feed water unit (2) and configured to receive contaminated water and separate the received contaminated water into a purified water portion and a residual water portion comprising residual water and contaminants;

[0259] - a purified water unit (4) connected to the water purification module (5) and configured for receiving the purified water portion;

[0260] - a residual water unit (3) connected to the water purification module (5) and configured for receiving the residual water portion; wherein the water purification module (5) comprises one or more purification bags (6) removably arranged in the housing; and wherein a purification bag (6) comprises a distillation assembly or a stack of distillation assemblies (601, ..60n), wherein each distillation assembly is configured to receive a part of the contaminated water and separate a purified water portion from the received part of the contaminated water into a purified water portion and a residual water portion, the distillation assembly (601, ..60n) further comprising:

[0261] - a contaminated water chamber (30) for collecting contaminated water, the contaminated water chamber (30) comprising a top sheet configured for absorbing heat;

[0262] - a purified water chamber (50) for collecting purified water, the purified water chamber (50) comprising a condensation sheet configured for collecting condensed purified water;

[0263] - a membrane (40) arranged between the top sheet and condensation sheet, the membrane dividing the distillation assembly into the contaminated water chamber (30) and the purified water chamber (50), wherein the membrane (40) is configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation of contaminated water through the membrane; and wherein optionally the purification bag is a purification bag as described in any of the preceding clauses.

[0264] CLAUSE 42. Purification system (100) as described in clause 41, comprising a drive unit, for instance a pump, for actively transporting the water through the water purification module (5).

[0265] CLAUSE 43. Purification system (100) as described in clause 42, wherein the purification system is a passive system driven by solar-heat and gravity, wherein preferably at least one of the housing and the water purification module (5) is arranged at an inclined orientation relative to the direction of gravity.

[0266] CLAUSE 44. Purification system (100) as described in any of clauses 41-43, wherein the residual water unit (3) is a residual water tank (13) having a tank volume larger than the volume of the combined volume of the contaminated water chambers (30) and / or wherein, in use, the residual water portion in each of the contaminated water chambers (30) is in fluid communication with the residual water tank (13), preferably in fluid communication with both the residual water tank (13) and the feed water unit (2).

[0267] CLAUSE 45. Purification system as described in any of the clauses 41-44, comprising a common feed-discharge conduit in fluid communication with the water purification module (5), the residual water tank (13) and the feed water unit (2) and arranged to both supply contaminated water to the water purification module (5) and discharge residual water portion from the water purification module (5).

[0268] CLAUSE 46. Purification system as described in any of clauses 43-45, wherein the residual water portion in the water purification module (5) and the residual water portion in the residual water tank (13) are in fluid communication to form one continuous uninterrupted volume of residual water.

[0269] CLAUSE 47. Purification system as described in any of the clauses 33-46, wherein the tank volume of the residual water tank (13) is more than 2 times, preferably more than 4 times, as large as the combined volume of the one or more contaminated water chambers (30).

[0270] CLAUSE 48. Purification system as described in any of clauses 43-47, wherein in use the water purification module (5) has an upper end and a lower end and wherein the connection of the feed water unit (2), the connection of the residual water unit (3) and the connection of the purified water unit (4) are arranged in the lower end of the water purification module (5).

[0271] CLAUSE 49. Purification system as described in any of the clauses 41-48, wherein the water purification module (5) comprises an air venting unit (22), connected to the upper end of the at least one contaminated water chamber (30) and configured to provide an outlet for air bubbles generated in the water purification module (5).

[0272] CLAUSE 50 Purification system as described in any of clauses 43-49, wherein in an inclined orientation the water purification module (5) extends at an angle (0) relative to the direction of gravity of more than 0 and less than 90 degrees, preferably more than 5 and less than 85 degrees or preferably between 10 and 35 degrees.

[0273] CLAUSE 51. Purification system as described in any of clauses 43-50, comprising a circulation limiter (91) configured to locally capture gas generated in at least one contaminated water chamber (30) and form at least one local gas pocket in the contaminated water chamber so as to have the at least one gas pocket interrupt the flow of contaminated water between the contaminated water chambers (30).

[0274] CLAUSE 52. Purification system as described in clause 51, comprising a set of contaminated water chambers (301, . . ., 30n), wherein the circulation limiter is configured to only capture gas in a subset of contaminated water chambers for temporarily blocking the flow of contaminated water to or from said subset of contaminated water chambers, while in the remaining contaminated water chambers essentially no gas is captured.

[0275] CLAUSE 53. Purification system as described in clause 51 or 52, comprising a lower contaminated water chamber (301) and one or more further contaminated water chambers (302..30n), wherein the circulation limiter (91) is configured to only capture air bubbles from the further contaminated water chambers.

[0276] CLAUSE 54. Purification system (100) as described in any of the clauses 41-53, wherein the housing comprises a protective casing in which the water purification unit(s) (5) are arranged. CLAUSE 55. Use of a purification bag (6) or purification system (100) according to any of the preceding clauses.

[0277] CLAUSE 56. Method of heat-driven water purification of contaminated water in a purification system as described in any of clauses 41-55, the method comprising:

[0278] - feeding contaminated water into the contamination water chamber or chambers of at least one distillation assembly;

[0279] - separating of a part of a contaminated water portion received by a distillation assembly into a purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet;

[0280] - discharging the purified water from the purified water chamber or chambers.

[0281] CLAUSE 57. Method as described in clause 56, comprising feeding unpurified contaminated water into one or more contaminated water chambers and at the same time discharging a residual water portion comprising water and contaminants remaining in the contaminated water chamber from the one or more contaminated water chambers, preferably via a common inlet and outlet.

[0282] CLAUSE 58. Method of manufacturing a purification bag as described in any of clauses 1- 40, the method comprising:

[0283] - melting polymeric material of a polymeric membrane sheet and melting polymeric material of the top sheet;

[0284] - merging the melted polymeric materials; and

[0285] - allowing the merged polymeric material to cure.

[0286] CLAUSE 59. Method as described in clause 58, wherein if the membrane comprises a membrane sheet and a coating on top of the membrane sheet, the top sheet and membrane sheet are ultrasonically welded by:

[0287] - ultrasonically displacing a part of the coating to locally expose a part of the polymeric membrane sheet; - ultrasonically melting polymeric material of the exposed part of the polymeric membrane sheet and ultrasonically melting polymeric material of the top sheet;

[0288] - merging the melted polymeric materials; and

[0289] - allowing the merged polymeric material to cure.

Claims

CLAIMS1. Purification bag (6) for use in a purification system (100) for heat-driven water purification of contaminated water, the purification bag (6) comprising a distillation assembly or a stack of distillation assemblies (601, ..60n), wherein each distillation assembly is configured to receive a part of the contaminated water and separate a purified water portion from the received part of the contaminated water, and wherein a distillation assembly (601, ..60n) comprises:- a contaminated water chamber (30) for collecting contaminated water, the contaminated water chamber (30) comprising a top sheet configured for absorbing heat;- a purified water chamber (50) for collecting purified water, the purified water chamber (50) comprising a condensation sheet configured for collecting condensed purified water;- a membrane (40) arranged between the top sheet and condensation sheet, the membrane dividing the distillation assembly into the contaminated water chamber (30) and the purified water chamber (50), wherein the membrane (40) comprises a membrane sheet configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet; wherein the top sheet and the membrane sheet are polymeric sheets that are bonded to each other by welding according to a welding pattern; and wherein the top sheet and membrane sheet, preferably also the condensation sheet, are thin films.

2. Purification bag (6) as claimed in claim 1, wherein the welding pattern comprises first welding lines or dots arranged to form inner welding lines configured to define a plurality of interconnected channels for receiving and holding contaminated water, wherein preferably, the interconnected channels have a width of 4 mm to 14 mm.

3. Purification bag (6) as claimed in claim 1, wherein the top sheet, the membrane sheet, and condensation sheet are polymeric sheets that are bonded to each other by welding according to a welding pattern.

4. Purification bag as claimed in claim 1 or 2 or 3, wherein the membrane sheet is a microporous membrane sheet.

5. Purification bag (6) as claimed in any of the preceding claims, wherein the polymeric top sheet, polymeric membrane sheet and polymeric condensation sheet are made of polyolefin material, for instance LDPE, HDPE, polypropylene (PP), or polymethyl pentene.

6. Purification bag (6) as claimed in any of claims 1-4, wherein the polymeric top sheet and the polymeric condensation sheet are made of Nylon, for instance polyamide-6, and the membrane comprises a hydrophilic material, for instance polyetheramide.

7. Purification bag as claimed in any of the preceding claims, wherein the condensation sheet is a polymeric sheet that is bonded to at least one of the top sheet and the membrane sheet by welding according to a further welding pattern.

8. Purification bag as claimed in any of the preceding claims, wherein the welding pattern and the further welding pattern are respectively formed by one or more first welding lines and one or more second welding lines.

9. Purification bag as claimed in any of the preceding claims, wherein the microporous membrane sheet and the condensation sheet are made of the same type of material, preferably materials comprising the same polymer.

10. Purification bag as claimed in any of the preceding claims, wherein the welding of two polymeric sheets comprises heating material of both polymeric sheets, melting the polymeric sheets together and then allowing the polymeric sheets to cool causing fusion.

11. Purification bag as claimed in claim 10, wherein the polymeric sheets are bonded by ultrasonic welding.

12. Purification bag as claimed in claim 10 or 11, wherein if the membrane comprises a membrane sheet and a coating on top of the membrane sheet, the ultrasonic welding of polymeric sheets comprises ultrasonically displacing a part of the coating to locally expose a part of the polymeric membrane sheet, melting polymeric material of the exposed part of the polymeric membrane sheet and melting polymeric material of the top sheet, merging the melted polymeric materials and allowing the merged polymeric material to cure or to cool and solidify.

13. Purification bag as claimed in any of the preceding claims, wherein at least one of the welding pattern and further welding pattern is formed in one welding step, preferably using a thermal welding stamp.

14. Purification bag (6) as claimed in any of the preceding claims, wherein the membrane comprises a hydrophobic membrane sheet, for instance a polyolefin sheet with micropores.

15. Purification bag (6) as claimed in any of the preceding claims, wherein the membrane comprises an uncoated microporous sheet.

16. Purification bag (6) as claimed in any of the preceding claims, wherein a side of the microporous membrane sheet facing the contaminated water chamber is provided with a coating.

17. Purification bag (6) as claimed in claim 16, wherein the coating is at least one of a flexible, macromolecular chained thin non-porous hydrophobic coating.

18. Purification bag (6) as claimed in claim 16 or 17, wherein the coating is a silicone coating.

19. Purification bag (6) as claimed in any of claims 16-18, wherein the coating is a silicone coating with a thickness of 10 micrometers or less, preferably less than 5 micrometers or even less than 2 micrometers.

20. Purification bag (6) as claimed in any of claims 16-19, wherein the coating is a silicone coating comprising a reactive silicone liquid, the reactive silicone liquid having a viscosity in a range of 1.000 to 15.000 mPa.s, preferably in a range of 2.000 to 5.000 mPa.s.

21. Purification bag (6) as claimed in any of the preceding claims, wherein the membrane sheet is a microporous membrane sheet, wherein the micropores of the microporous membrane sheet are symmetrically distributed over the area facing the contaminated water chamber and / or wherein the micropores of the microporous membrane are asymmetrically distributed over its thickness, wherein the average pore size of the micropores in a first area facing the contaminated water chamber is smaller than the average pore size of the micropores in a second area facing the purified water chamber.

22. Purification bag (6) as claimed in any of the preceding claims, wherein the membrane sheet is a microporous membrane sheet, wherein the pore diameter of the micropores is smaller than 2.0 pm, preferably smaller than 0.5 pm or even smaller than 0.2 pm.

23. Purification bag (6) as claimed in any of the preceding claims, wherein the membrane sheet is a microporous membrane sheet, wherein the microporous membrane sheet has a density in the range of 10 to 200 g / m2, preferably between 30 and 100 g / m2, more preferably between 40 and 70 g / m2and / or wherein the microporous sheet has a porosity of more than 30%.

24. Purification bag (6) as claimed in any of the preceding claims, wherein the polymeric membrane comprises a vapor-permeable reinforcement sheet attached to the side of the microporous membrane sheet facing the purified water chamber.

25. Purification bag (6) as claimed in claim 24, wherein the reinforcement sheet is a polymeric sheet, preferably a fibrous polyolefin sheet, for example a hydro-entangled non-woven polyolefin or a polymer adhesive web.

26. Purification bag (6) as claimed in claim 25, wherein the reinforcement sheet has a density of about 30-100 g / m2.

27. Purification bag (6) as claimed in any of the preceding claims, wherein the purification bag (6) comprises a stack of multiple distillation assemblies arranged one on top of the other.

28. Purification bag (6) as claimed in claim 27, comprising a first distillation assembly arranged on top of a second distillation assembly, wherein the condensation sheet of the first distillation assembly is formed by the top sheet of the second distillation assembly.

29. Purification bag (6) as claimed in any of the preceding claims, wherein the welding pattern comprises first welding lines arranged to form inner welding lines to define a plurality of interconnected channels to form a contaminated water chamber for receiving and holding contaminated water and / or wherein the further pattern comprises second welding lines arranged to form outer welding lines to define at least one channel to form a purified water chamber for receiving and holding purified water.

30. Purification bag (6) as claimed in any of the preceding claims, comprising a spacer, for instance a spacer sheet, arranged inside a purified water chamber (50) to provide a predefined minimum height of the purified water chamber (50).

31. Purification bag (6) as claimed in claim 30, wherein the predefined minimum height of the spacer is 2-12 mm.

32. Purification bag (6) as claimed in claim 30 or 31, wherein the spacer is comprised of polymeric, for instance polyolefin material, and / or wherein the spacer defines an open structure allowing water to pass so that the water vapor can condense on the condensation sheet of the purified water chamber, thereby releasing its latent heat of condensation to heat up the contaminated water inside a further contaminated water chamber.

33. Purification bag (6) as claimed in any of the preceding claims, comprising a common inlet and outlet for feeding-in contaminated water to at least one of the contaminated water chambers, preferably to all contaminated water chambers and for feeding-out contaminated water and the residual water parts from at least one of the contaminated water chambers, preferably from all of the contaminated water chambers.

34. Purification bag (6) as claimed in any of the preceding claims, comprising a connection unit (9) configured to mutually provide a fluid connection between stacked contaminated water chambers (30), wherein optionally the connection unit (9) is arranged at an upper end of the water purification bag (6) and / or at a lower end of the water purification bag (6).

35. Purification bag (6) as claimed in claim 34, wherein the connection unit (9) comprises tubing (95) interconnecting the plurality of contaminated water chambers (30).

36. Purification bag (6) as claimed in any of claims 33-35, wherein the connection unit (9) comprises a connector (90), the connector preferably extending transversely to the respective contaminated water chambers (30).

37. Purification system as claimed in any of claims 33-36, wherein the connection unit (9) comprises a connector (90) extending through respective openings provided in the upper ends of the respective contaminated water chambers (30) and purified water chambers (50), while only the contaminated water chambers (30) are in fluid connection with the inner volume of the connector.

38. Purification bag (6) as claimed in any of claims 33-37, further comprising a circulation limiter (91) configured to limit the circulation of contaminated water between respective contaminated water chambers (30).

39. Purification bag (6) as claimed in claim 38, wherein the circulation limiter (91) is combined with the connector (90).

40. Purification bag (6) as claimed in any of claims 36-39, wherein the connector (90) comprises a tubular element, the tubular element comprising a number of openings to allow water to flow between the contaminated water chamber, wherein the inner surface of the tubular element is provided with one or more flow limiters, for instance a flow limiting flange, extending radially inward so as to limit the flow of air bubbles between the contaminated water chambers.

41. Purification bag (6) as claimed in claim 40, wherein the tubular element is configured to be removably slid into to the openings, wherein the tubular element preferably is configured to mutually space apart the contaminated water chambers at respective predetermined distances while sliding the tubular element into the openings.

42. Purification bag (6) as claimed in claim 1, wherein at least one of the top sheet, condensation sheet and membrane sheet are flexible sheets, preferably configured to be flexible to form one or more channels when used, more preferably configured to be inflatable from an essentially flat state to an expanded state.

43. Purification bag (6) as claimed in any of the preceding claims, wherein the top sheet and the membrane are solely connected by welding, wherein preferably the top sheet, condensation sheet and membrane sheet are mutually solely bonded by thermal welding, for instance ultrasonic welding.

44. Purification bag (6) as claimed in any of the preceding claims, wherein the purification bag does not comprise a plate and / or frame construction and / or, wherein the bag is configured to operate without comprising plates or frames.

45. Purification system (100) for heat-driven water purification of contaminated water, the purification system comprising:- a housing (8);- a feed water unit (2) for the supply of contaminated water comprising contaminants;- a water purification module (5) connected to the feed water unit (2) and configured to receive contaminated water and separate the received contaminated water into a purified water portion and a residual water portion comprising residual water and contaminants;- a purified water unit (4) connected to the water purification module (5) and configured for receiving the purified water portion;- a residual water unit (3) connected to the water purification module (5) and configured for receiving the residual water portion; wherein the water purification module (5) comprises one or more purification bags (6) removably arranged in the housing; and wherein a purification bag comprises a distillation assembly or a stack of distillation assemblies (601, ..60n), wherein each distillation assembly is configured to receive a part of the contaminated water and separate a purified water portion from the received part of the contaminated water into a purified water portion and a residual water portion, the distillation assembly (601, ..60n) further comprising:- a contaminated water chamber (30) for collecting contaminated water, the contaminated water chamber (30) comprising a top sheet configured for absorbing heat;- a purified water chamber (50) for collecting purified water, the purified water chamber (50) comprising a condensation sheet configured for collecting condensed purified water;- a membrane (40) arranged between the top sheet and condensation sheet, the membrane dividing the distillation assembly into the contaminated water chamber (30) and the purified water chamber (50), wherein the membrane (40) is configured for separation of the associate part of the contaminated water portion received by the distillation assembly into the purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation of contaminated water through the membrane; and wherein optionally the purification bag is a purification bag as claimed in any of the preceding claims.

46. Purification system (100) as claimed in claim 45, comprising a drive unit, for instance a pump, for actively transporting the water through the water purification module (5).

47. Purification system (100) as claimed in claim 45, wherein the purification system is a passive system driven by solar-heat and gravity, wherein preferably at least one of the housing and the water purification module (5) is arranged at an inclined orientation relative to the direction of gravity.48 Purification system (100) as claimed in any of claims 45-47, wherein the residual water unit (3) is a residual water tank (13) having a tank volume larger than the volume of the combined volume of the contaminated water chambers (30) and / or wherein, in use, the residual water portion in each of the contaminated water chambers (30) is in fluid communication with the residual water tank (13), preferably in fluid communication with both the residual water tank (13) and the feed water unit (2).

49. Purification system as claimed in any of the claims 45-48, comprising a common feeddischarge conduit in fluid communication with the water purification module (5), the residual water tank (13) and the feed water unit (2) and arranged to both supply contaminated water to the water purification module (5) and discharge residual water portion from the water purification module (5).

50. Purification system as claimed in any of claims 47-49, wherein the residual water portion in the water purification module (5) and the residual water portion in the residual water tank (13) are in fluid communication to form one continuous uninterrupted volume of residual water.

51. Purification system as claimed in any of the claims 45-50, wherein the tank volume of the residual water tank (13) is more than 2 times, preferably more than 4 times, as large as the combined volume of the one or more contaminated water chambers (30).

52. Purification system as claimed in any of claims 45-51, wherein in use the water purification module (5) has an upper end and a lower end and wherein the connection of the feed water unit (2), the connection of the residual water unit (3) and the connection of the purified water unit (4) are arranged in the lower end of the water purification module (5).

53. Purification system as claimed in any of the claims 45-52, wherein the water purification module (5) comprises an air venting unit (22), connected to the upper end of the at least one contaminated water chamber (30) and configured to provide an outlet for air bubbles generated in the water purification module (5).

54. Purification system as claimed in any of claims 47-53, wherein in an inclined orientation the water purification module (5) extends at an angle (0) relative to the direction of gravity of more than 0 and less than 90 degrees, preferably more than 5 and less than 85 degrees or preferably between 10 and 35 degrees.

55. Purification system as claimed in any of claims 47-54, comprising a circulation limiter (91) configured to locally capture gas generated in at least one contaminated water chamber (30) and form at least one local gas pocket in the contaminated water chamber so as to have the at least one gas pocket interrupt the flow of contaminated water between the contaminated water chambers (30).

56. Purification system as claimed in claim 55, comprising a set of contaminated water chambers (301, . . ., 30n), wherein the circulation limiter is configured to only capture gas in a subset of contaminated water chambers for temporarily blocking the flow of contaminated water to or from said subset of contaminated water chambers, while in the remaining contaminated water chambers essentially no gas is captured.

57. Purification system as claimed in claim 55 or 56 comprising a lower contaminated water chamber (301) and one or more further contaminated water chambers (302..30n), wherein the circulation limiter (91) is configured to only capture air bubbles from the further contaminated water chambers.

58. Purification system (100) as claimed in any of the claims 45-57, wherein the housing comprises a protective casing in which the water purification unit(s) (5) are arranged.

59. Use of a purification bag (6) or purification system (100) according to any of the preceding claims.

60. Method of heat-driven water purification of contaminated water in a purification system as claimed in any of claims 45-59, the method comprising:- feeding contaminated water into the contamination water chamber or chambers of at least one distillation assembly;- separating of a part of a contaminated water portion received by a distillation assembly into a purified water portion and a residual water portion comprising water and contaminants remaining in the contaminated water chamber by at least one of membrane distillation and pervaporation through the membrane sheet;- discharging the purified water from the purified water chamber or chambers.

61. Method as claimed in claim 60, comprising feeding unpurified contaminated water into one or more contaminated water chambers and at the same time discharging a residual water portion comprising water and contaminants remaining in the contaminated water chamber from the one or more contaminated water chambers, preferably via a common inlet and outlet.

62. Method of manufacturing a purification bag as claimed in any of claims 1-43, the method comprising:- melting polymeric material of a polymeric membrane sheet and melting polymeric material of the top sheet;- merging the melted polymeric materials; and- allowing the merged polymeric material to cure or to cool and solidify.

63. Method as claimed in claim 62, wherein if the membrane comprises a membrane sheet and a coating on top of the membrane sheet, the top sheet and membrane sheet are ultrasonically welded by:- ultrasonically displacing a part of the coating to locally expose a part of the polymeric membrane sheet;- ultrasonically melting polymeric material of the exposed part of the polymeric membrane sheet and ultrasonically melting polymeric material of the top sheet;- merging the melted polymeric materials; and- allowing the merged polymeric material to cure or to cool and solidify.

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