Water treatment system and method for water treatment

Abstract

The invention, which relates to a water treatment system (1) and to a method for water treatment, addresses the problem of specifying a water treatment system (1) and a method for water treatment which enable simple and safe water treatment, wherein the costs for the production, maintenance and operation of the water treatment system (1) are reduced. This problem is solved by the disclosed arrangement in that the stage (3) for receiving raw water to be purified comprises a first pump (9), a suction hose (10) and a coarse filter (11); in the filter stage (5) a nanofiltration membrane (6) is arranged; the nanofiltration membrane (6) is arranged in a backflush branch; and the water treatment system (1) has a purification circuit for maintaining specified quality properties of the treated water in which at least the storage container (8), a fifth pipeline (35), a second pump (36), a fourth pipeline (32) and a UV filter element (33) and / or a catalyst (34) for biofilm elimination and reduction of contaminations and deposits are arranged.

Description

[0001] Water treatment plant and water treatment process

[0002] The invention relates to a water treatment plant which, in a flow direction of the water in the water treatment plant, has at least one stage for receiving raw water to be purified from a source, a filter stage for treating the raw water and for producing treated water, and a storage tank for collecting the treated water.

[0003] The invention also relates to a method for water treatment, in which at least one intake of raw water to be purified from a source, a treatment of the taken-up raw water and a production of treated water and a storage of the treated water takes place.

[0004] In particular, the invention relates to a water treatment plant which is used for drinking water treatment or for contaminated wastewater concentration, such as leachate from landfills.

[0005] Furthermore, the invention relates in particular to a mobile water treatment plant which is suitable for decentralized drinking water supply.

[0006] A water treatment plant of this type is understood to be a system that processes water to be treated, for example, from a river or well, to meet specified requirements. Such requirements can be so-called quality characteristics for drinking water or industrial water. In Germany, the quality characteristics for drinking water are regulated by DIN 2000, Guidelines for Central Drinking Water Supplies, and DIN 2001, Guidelines for Individual Drinking Water Supplies. Industrial water is water used for commercial, industrial, agricultural, or similar purposes with various quality characteristics, unless the quality characteristics of drinking water are required.

[0007] Chemical, physical, and mechanical processes are used for this type of water treatment. Such water treatment plants are used to produce fresh water, for example, with drinking water quality characteristics, or to treat wastewater. Depending on the requirements and application, constituents are removed and / or added to the water being treated.

[0008] Water treatment plants usually comprise several components or stages in which process steps for treating freshwater take place. Such process steps can include, for example, mechanical pretreatment for river water, aeration, deacidification, decarbonization, precipitation, flocculation, softening, demineralization, decontamination, and others.

[0009] Various water treatment plants are known from the state of the art.

[0010] DE 10 2015 013 916 B3 discloses a water treatment device. The objective is to create a water treatment device that is simple to manufacture and suitable for meeting local drinking and / or industrial water needs, particularly in developing countries or regions with poor or undeveloped infrastructure.

[0011] The solution is specified that at least one pump of the water treatment device is a piston pump, that the water treatment plant has a filter device and that the filter device for providing process water and / or drinking water, seen in the flow direction of the water to be filtered, has in succession a polypropylene filter, a granulate activated carbon filter, a first block activated carbon filter, a reverse osmosis filter and a second block activated carbon filter.

[0012] DE 197 45 333 A1 discloses a method and device for treating water by reverse osmosis or nanofiltration. The water to be treated is fed to a first osmosis or nanofiltration stage, thereby obtaining permeate and concentrate. To reduce the amount of water used during the process, the process is designed such that the concentrate from the first stage is fed to a second stage. While the first stage is in operation, the second stage is periodically separated from the first, so that the water flows through the second stage in the opposite direction, thereby cleaning its membrane.

[0013] Ceramic filters or ceramic membranes, which are used to filter a flowing medium, are also known. Such filters, also known as ceramic cross-flow filters, usually have a tubular geometry. Typically, a certain number of these tubular geometries, i.e., channels with the same or different diameters, are arranged in a so-called filter element (cross-flow element). Several of these filter elements are arranged in a housing, such as a stainless steel housing, thus forming a so-called filter module according to the state of the art. These filter modules are used in conventional water treatment systems.

[0014] During filtration, the process medium, which is the water to be treated or the raw water to be purified and is also referred to as the feed, flows through such filter modules. The process medium, which is fed into the filter module via an inlet opening, flows through the filter module's channels at a set flow rate. The channels have a membrane layer applied internally, also referred to as the active layer.

[0015] The process medium is pressurized by a suitable means and introduced into the filter module via a first connection such as an inlet opening. This pressure, which is in the range between 3 bar and 5 bar, in particular 4 bar, initiates filtration in the filter module. Due to the pressure, the process medium is split into a so-called permeate and a so-called concentrate. The concentrate consists of components or particles which, due to their size, cannot penetrate the pores of the membrane layer and are thus retained within the channels. This process is known as concentration. This concentrate, also known as retentate, is discharged from the filter module via another connection such as an outlet opening.Small components or particles of the process medium that penetrate the pores of the membrane layer form the purified permeate, which is discharged via another connection such as a second outlet opening of the filter module.

[0016] A disadvantage of other known filter modules, such as an NF membrane system (nanofilter membrane system), is the occurrence of what is known as fouling. This means that the membranes of such NF membrane systems become blocked over time due to the formation of a coating layer of organic and inorganic particles. Causes include particles, organic matter, precipitation, or the formation of a biofilm on the membrane.

[0017] Since backwashing to clean the filter surface is not possible with this type of state-of-the-art NF membrane system, which is also known as NF wound membrane modules, the energy required to ensure the desired filtration rate of the process medium increases with increasing operating time. This means that the NF membrane system must be replaced regularly, leading to high operating costs for such water treatment plants.

[0018] One known cleaning method is the so-called "cleaning-in-place" method, in which, for example, a system or filter is cleaned, usually without significant disassembly, on the side of the system or filter that contacts the process medium. This type of cleaning is carried out, for example, using appropriate cleaning agents at a specified pressure and temperature for a specified period of time. This cleaning method, used, for example, in the food and dairy industries, can only remove part of the coating layer that has formed on the surface of a membrane.

[0019] Replacement and the associated costs are unavoidable when using state-of-the-art NF membrane systems in water treatment plants, even with the "cleaning-in-place" cleaning process described above. Therefore, there is a need for an improved water treatment system and an improved water treatment process.

[0020] The object of the invention is to provide a water treatment plant and a method for water treatment which enable simple and safe water treatment, while reducing the costs for the manufacture, maintenance and operation of the water treatment plant.

[0021] Furthermore, the water treated by the water treatment plant must maintain specified quality characteristics over a long period of time. These specified quality characteristics can, for example, be the quality characteristics of drinking water or industrial water.

[0022] In addition, a mobile water treatment plant will be provided that can be used automatically to supply drinking water. The water treatment plant should also be suitable for concentrating contaminated wastewater.

[0023] This problem is solved by a water treatment system having the features according to claim 1 of the independent patent claims. Further developments are specified in the dependent patent claims.

[0024] It is intended that the water treatment plant, viewed in a flow direction of the water in the water treatment plant, has at least one stage for receiving raw water to be purified from a source, a filter stage for treating the raw water and producing treated water, and a storage stage with a storage tank for collecting the treated water.

[0025] The water to be treated in the water treatment plant can, for example, be drawn from a source such as a well, a lake, or a river through the stage for receiving raw water to be treated from the source. Alternatively, such a source is contaminated wastewater collected in a landfill. The raw water to be treated taken from the source is fed to the filter stage, which processes the raw water to be treated using one or more filtration processes, thus producing the treated water.

[0026] This treated water is collected in a storage tank during a storage stage. If the source was a well, a lake, or a river, for example, the treated water, which has been treated to drinking water quality, can be drawn from the storage tank, for example, for drinking water supply.

[0027] In the case of the treatment of contaminated wastewater from a landfill, the treated water from the storage tank is discharged into the sewer system as uncontaminated wastewater, for example.

[0028] According to the invention, the stage for receiving raw water to be purified comprises a first pump, a suction hose and a coarse filter, that a nanofiltration membrane is arranged in the filter stage and that the nanofiltration membrane is arranged in a backwash branch.

[0029] A first pump is located in the stage for receiving the raw water to be treated. A suction hose is connected to the inlet of this first pump. This hose leads to the source and through which the raw water to be treated is drawn from the source via a coarse filter located at the end of the suction hose. Such coarse filters, as is well known, prevent the entry of coarse material such as plant debris and stones, thus preventing damage to the first pump.

[0030] The first pump's outlet is connected to the filter stage via a first pipe. To compensate for the oscillations or pressure fluctuations caused by the first pump, a pulsation dampener is installed between the outlet of the first pump and the filter stage. This ensures that the filter stage is supplied with a constant flow of the raw water to be treated from the source.

[0031] Furthermore, a pressure sensor and a pressure relief valve are provided in the first pipeline between the first pump and the filter stage to protect against overpressure. Such a pressure sensor can, for example, be used to control the power or speed of the first pump in order to maintain a constant pressure in the first pipeline.

[0032] In general, additional elements or assemblies may be installed in all stages of the water treatment system (stage for receiving water to be purified, filter stage, storage stage) that are necessary for the operation of the water treatment system, for example, during filtration, backwashing, and cleaning of the already treated water. Such elements or assemblies include, for example, valves such as shut-off valves, check valves, pressure relief valves, vent valves, as well as pumps, pressure gauges, temperature or pressure sensors, pressure reducers, water meters, pulsation dampers, additional filters, and other elements.

[0033] It is also planned that a nanofiltration membrane be installed in the filter stage to filter the raw water and produce treated water. The nanofiltration membrane is capable of retaining particles larger than 1.3 nm, particularly larger than 0.7 nm. Crossflow filtration, also known as cross-flow filtration, takes place in this nanofiltration membrane. In contrast to conventional filtration processes, the raw water to be purified, also referred to here as the process medium or feed, flows tangentially over the filter surface.

[0034] This tangential flow creates a turbulent flow on the membrane surface of the nanofiltration membrane, which prevents the material being separated from the raw water to be treated from forming a deposit on the filter surface. This at least partially cleans the membrane surface, enabling a more constant flow rate over time, or a more continuous operation of the nanofiltration membrane.

[0035] A portion of the incoming raw water to be treated passes through the channels of the nanofiltration membrane unfiltered and flows out of the nanofiltration membrane as retentate, while the filtered, treated portion of the raw water to be treated leaves the nanofiltration membrane as permeate, or treated water. The retentate, which can also be referred to as concentrated raw water, is returned to the source or the inlet of the first pump via a corresponding line.

[0036] Due to its design, the nanofiltration membrane is capable of retaining fine particles, bacteria, and viruses. The filtration process in the nanofiltration membrane takes place at a raw water pressure to be treated in the range of 2.0 bar to 6.0 bar, particularly at a pressure of 4 bar.

[0037] In particular, the nanofiltration membrane is intended to be manufactured using a so-called layer-by-layer process, in which a layer-by-layer buildup of oppositely charged polymers, so-called polyelectrolytes, occurs on a filter surface. In this process, a charged surface of the filter is brought into contact with an aqueous polyelectrolyte solution, whereupon the polymers adhere. This results in a complete recharge of the surface until no more polymers can be adsorbed (self-limitation). After removing unbound polymers, the next layer with the opposite charge can then be applied.

[0038] A nanofiltration membrane with such a surface, or filter membrane, enables the safe treatment of even difficult-to-treat water resources, such as river water, wastewater, or rainwater, in a single treatment step. Particles such as microplastics, bacteria, and viruses, as well as dissolved water constituents (organic matter, salts), are retained by this filter membrane.

[0039] The advantages of nanofiltration membranes manufactured using layer-by-layer technology are significantly higher purification performance and an individually scalable coating of the filter membrane surface. Furthermore, the pore size can be individually adjusted or specified using this technology. Furthermore, the energy requirement when using such filters is significantly lower than with conventional reverse osmosis membrane filters, as such filters have lower flow resistance. According to the invention, the nanofiltration membrane is arranged in a backwash branch. The nanofiltration membrane manufactured using layer-by-layer technology can be backwashed, meaning that deposits on the surfaces of the nanofiltration membrane are removed during backwashing of the water treatment plant.This extends the service life of the nanofiltration membrane and reduces the energy required to filter the process medium while maintaining consistent quality. This ensures high-quality water treatment over a long operating life without significantly increasing the energy consumption of the water treatment plant and without significantly reducing the amount of treated water produced by the water treatment plant.

[0040] In one embodiment, such a backwash branch comprises the storage tank, a second pump, optionally a third check valve, a second shut-off valve, the nanofiltration membrane and a return line in which optionally a third shut-off valve and a first control valve are arranged, wherein the return line runs to the source.

[0041] Optionally, the backwash branch can also include at least one pressure gauge and / or sensors for measuring pressure, temperature or water quantity.

[0042] According to the invention, it is further provided that the water treatment system has a purification circuit for maintaining predetermined quality properties of the treated water, in which at least the storage tank, a fifth pipeline, a second pump, a fourth pipeline, and a UV filter element and / or a catalyst for biofilm elimination and the reduction of contamination and deposits are arranged. The predetermined quality properties are, for example, the quality properties of drinking water or industrial water.

[0043] The water treated in the water treatment plant is collected in a storage tank from which it can be withdrawn as needed. If the treated water remains in the storage tank for an extended period of time, biological contaminants, particularly bacteria, can develop in the treated water. To prevent or eliminate such biological contaminants, particularly bacteria, the water in the storage tank is cleaned at intervals to remove any resulting biological contaminants, particularly bacteria. For this cleaning operation of the water treatment plant, the treated water is withdrawn from the storage tank by a second pump and fed to a filter, such as a UV filter element, before the thus cleaned water flows back into the storage tank.In addition, a catalyst can be used to eliminate biofilm and reduce contamination and deposits.

[0044] In one embodiment, such a cleaning circuit comprises, in addition to appropriate pipe sections and branch pipes, a second pump, at least one check valve, a shut-off valve, and a UV filter element. Optionally, the cleaning circuit also includes a catalyst for biofilm elimination and reducing contamination and deposits.

[0045] According to the invention, it is further provided that the nanofiltration membrane has a first connection which is at least indirectly connected to the first pump, that the nanofiltration membrane has a second connection for a permeate as treated water, which is at least indirectly connected to the storage container and that the nanofiltration membrane has a third connection for a retentate, which is at least indirectly connected to the first pump or the source via a return line.

[0046] The nanofiltration membrane has a first connection through which the raw water to be cleaned or the process medium is fed to the nanofiltration membrane. For this purpose, the first connection is at least indirectly connected to the first pump. This means that further elements or assemblies can be arranged between the first connection of the nanofiltration membrane and the first pump. In one embodiment, a pulsation damper, a pressure relief valve, a vent valve, a first check valve and a first pressure gauge are arranged between the first pump and the first connection of the nanofiltration membrane. Furthermore, the nanofiltration membrane has a second connection through which water treated in a filtration operation of the water treatment plant, which water is referred to as permeate, is discharged.This second connection for discharging the permeate is at least indirectly connected to the storage tank. This means that further elements or assemblies can be arranged between the second connection of the nanofiltration membrane and the storage tank. In one embodiment, at least a first shut-off valve and a further filter, such as a UV filter element, are arranged between the second connection of the nanofiltration membrane and the storage tank. This UV filter element is used to further treat or purify the water treated by the nanofiltration membrane. This disinfection of the water occurs to ensure the microbiological quality of the treated water. The UV light generated in the UV filter element kills bacteria and viruses by destroying their DNA, so that they can no longer reproduce or die.

[0047] In another embodiment, a catalyst for biofilm elimination and the reduction of contamination and deposits is also installed in this area. This catalyst enables biocide-free structural treatment of water, whereby contamination and deposits on surfaces are removed without leaving any residue. The core of this technology is a catalyst in the form of mineral-metal foils. The special feature of the process lies in the structural treatment of the water, whereby the natural processes of the water are accelerated and dissolved substances remain in solution, even when the water is subjected to technical stress. This means, for example, that limescale does not precipitate, thus providing no basis for biological settlement. By improving solubility, the risk of deposits decreases and fouling is reduced.

[0048] The nanofiltration membrane also has a third connection, through which concentrated raw water, referred to as retentate, is discharged during a filtration process of the water treatment plant. This third connection of the nanofiltration membrane is connected, at least indirectly, to an inlet of the first pump or source via a return line. This means that additional elements or assemblies can be arranged between the third connection of the nanofiltration membrane and the inlet of the first pump or source. In one embodiment, a second pressure gauge, a third shut-off valve, and a first control valve are arranged between the third connection of the nanofiltration membrane and the inlet of the first pump or source.

[0049] It is also provided that the nanofiltration membrane is arranged in a backwash branch which comprises at least the storage tank, a second pump connected at least indirectly to the second connection of the nanofiltration membrane via a fifth pipeline for withdrawing treated water from the storage tank, the nanofiltration membrane and a return line connected to the third connection of the nanofiltration membrane.

[0050] While raw water is treated in a filtration operation of the water treatment plant, deposits on the surface of the nanofiltration membrane are at least partially removed in a backwash operation of the water treatment plant.

[0051] For this purpose, previously treated water is fed to the nanofiltration membrane via the second port. This water penetrates the nanofiltration membrane and dissolves deposits on the surface or filter surface of the nanofiltration membrane. These dissolved deposits are then removed from the nanofiltration membrane via the third port.

[0052] To supply the treated water to the nanofiltration membrane, the second port of the nanofiltration membrane is connected at least indirectly to the storage tank via a first line path, a second pipe and a fifth pipe. This first line path, which represents a first part of the backwash branch, also contains, for example, a second pump, a third check valve, and a second shut-off valve.

[0053] In order to remove the dissolved deposits from the nanofiltration membrane via the third connection, the latter is connected at least indirectly to the source and the inlet of the first pump by means of a second line path, which is essentially formed by the return line.

[0054] In this second line path, which represents a second part of the backwash branch, a second pressure gauge, a third shut-off valve and a first control valve are also arranged.

[0055] The arrangement of various elements or assemblies in the water treatment plant enables the water treatment plant to operate in different modes, such as filtration, backwash, and purification. Pipeline sections, pipe branches, or elements or assemblies are used in different modes. The elements or assemblies in the water treatment plant are controlled by a central control system (not described in detail). This central control system generates corresponding control signals for the elements or assemblies in the water treatment plant, depending on the selected operating mode.The central control system is also connected to sensors that measure pressure, temperature, concentration or various other parameters of the raw water and / or treated water at various points in the water treatment plant.

[0056] It is further provided that at least one sieve filter is arranged in the stage for receiving raw water to be purified.

[0057] To pre-treat the raw water drawn from the source via the suction line before the raw water to be treated is fed to the nanofiltration membrane, at least one sieve filter, such as a stainless steel sieve filter, is installed. Depending on the design of the sieve filter, this sieve filter allows for the retention of particles of a specific size. The advantage of one or more such sieve filters is that the mesh sizes, such as those of a stainless steel sieve filter, retain sediment in a size range between 5 pm and 500 pm, thus relieving the load on the downstream nanofiltration membrane.

[0058] It is particularly advantageous that three sieve filters are arranged in the stage for receiving raw water to be purified, the first sieve filter having openings in the range between 90 pm and 110 pm, the second sieve filter having openings in the range between 45 pm and 55 pm and the third sieve filter having openings in the range between 4 pm and 6 pm.

[0059] Such an arrangement of three sieve filters in a supply line to the nanofiltration membrane enables a step-by-step pre-treatment of the raw water taken from the source.

[0060] It is planned to arrange a first sieve filter with openings in the range between 90 pm and 110 pm as the first filter stage, a second sieve filter with openings in the range between 45 pm and 55 pm as the second filter stage and a third sieve filter with openings in the range between 4 pm and 6 pm as the third filter stage in succession in order to ensure optimal pre-cleaning of the raw water to be cleaned.

[0061] The problem is also solved by a method having the features according to claim 6 of the independent patent claims. Further developments are specified in the dependent patent claims.

[0062] In general, a water treatment process involves at least a small amount of raw water to be purified from a source, such as a lake or river, into the water treatment plant. This raw water to be purified is then processed in the water treatment plant, producing treated water, which is typically stored in a treated water storage tank. This makes the treated water available for consumption, such as drinking water.

[0063] According to the invention, a backwashable nanofiltration membrane is provided for treating the raw water taken in, the raw water to be cleaned is fed to the backwashable nanofiltration membrane in a filtration operation via a first connection, a permeate as treated water is discharged from the nanofiltration membrane via a second connection and a retentate is discharged via a third connection, and treated water stored in the form of a second connection is fed to the backwashable nanofiltration membrane in a backwash operation in order to remove deposits on the surfaces of the nanofiltration membrane, and deposits removed from the surface are discharged via the third connection.

[0064] The use of a backwashable nanofiltration membrane in the water treatment plant enables the water treatment plant to operate in several modes, such as filtration and backwash.

[0065] During filtration, the backwashable nanofiltration membrane is fed with the raw water to be treated via the first connection. This raw water to be treated flows through the nanofiltration membrane according to crossflow filtration in the longitudinal direction of the nanofiltration membrane channels. The pressurized raw water or process medium penetrates the nanofiltration membrane in a filtering direction due to the filter function of the nanofiltration membrane, producing treated water or permeate. The raw water that does not penetrate the nanofiltration membrane in the filtering direction remains in the nanofiltration membrane channels and forms the concentrated retentate.

[0066] The permeate is removed from the nanofiltration membrane via the second port and stored in a storage tank. The retentate, after passing through the nanofiltration membrane channels, is removed from the nanofiltration membrane via the third port and returned to the source, for example, via a return line.

[0067] During backwash operation, in which no raw water treatment takes place in the water treatment plant, stored treated water is fed to the backwashable nanofiltration membrane via the second connection to remove deposits on the surfaces of the nanofiltration membrane. This treated water, supplied under pressure via the second connection, penetrates the nanofiltration membrane in the opposite direction to the filtering direction and loosens deposits from the surfaces of the nanofiltration membrane tubes. These dissolved deposits are removed from the nanofiltration membrane via the third connection. In one embodiment, the backwash operation, or the removal of dissolved deposits from the nanofiltration membrane via the third connection, is supported by a metered supply of raw water via the first connection.Here, the metered supply is a supply of raw water which is carried out in smaller quantities and at lower pressure than in the filtration operation and thus supports the removal of dissolved deposits, whereby the backwash operation opposite to the filter direction is not affected.

[0068] According to the invention, it is further provided that in order to maintain predetermined quality properties of the treated water, such as the quality properties of drinking water or process water, the treated water is periodically removed from the storage tank in a cleaning operation and fed to a UV filter element and / or a catalyst, whereby biofilm elimination, a reduction of soiling, deposits and biological contaminants, in particular bacteria, takes place before the water thus purified flows back into the storage tank.

[0069] To prevent or reduce biological contamination, especially bacteria, in the treated water, it is periodically cleaned using a UV filter element. For this purpose, the treated water is circulated in a cleaning circuit, which includes at least the storage tank and the UV filter element. A pump, such as the second pump, is provided to generate a flow of the treated water to be cleaned in the cleaning circuit.

[0070] Optionally, a catalyst is used in addition to the UV filter element to purify the treated water in the cleaning circuit.

[0071] It is also planned that the deposits removed during backwashing will be returned to the source.

[0072] The dissolved deposits are removed from the nanofiltration membrane via the third connection and returned to the source via a corresponding return line. In this way, the deposits are removed from the nanofiltration membrane and the water treatment system during backwashing. It has proven very advantageous to perform backwashing at set times or via sensor control, with the sensor analyzing the purity level of the treated water.

[0073] The filtration operation of the water treatment plant is initiated by control signals generated by the central control unit for the elements or assemblies of the water treatment plant. This occurs after the water treatment plant has been commissioned or if the treated water level in the storage tank falls below a specified level. If the treated water level in the storage tank reaches or exceeds a specified level, the control signals generated by the central control unit for the elements or assemblies of the water treatment plant temporarily stop the water treatment in the water treatment plant.Due to the fixed fill level in the storage tank, a certain amount of treated water is always available in the water treatment plant's storage tank, which can be used, for example, as drinking water. To determine the current fill level of the treated water in the storage tank, a fill level sensor is installed in the storage tank, which transmits its measurement data to the central control unit.

[0074] During backwash operation of the water treatment plant, the central control system also generates corresponding control signals for the elements or assemblies of the water treatment plant, which enable backwash operation in the manner described above.

[0075] The backwash operation of the water treatment plant is started after a specified time.

[0076] Alternatively, backwash operation is started after a specified number of operating hours of the water treatment plant in filtration mode.

[0077] Alternatively, backwash operation can be started by sensor control. For this purpose, one version monitors the energy required for filtration and / or the amount of treated water produced per unit of time during filtration. Both parameters allow conclusions to be drawn about the condition of the nanofiltration membrane. As deposits on the surface of the nanofiltration membrane increase, the energy requirement rises and the amount of treated water produced per unit of time decreases. In this way, backwash operation is started as needed.

[0078] It is also planned that the treated water will be fed to the nanofiltration membrane during backwash operation with a pressure that varies in intensity.

[0079] The treated water is fed to the nanofiltration membrane in backwash mode via its second connection under pressure in order to flow through the nanofiltration membrane in the opposite direction to the filtering direction and thus to dissolve or remove deposits on the surface of the nanofiltration membrane.

[0080] To improve the cleaning intensity of the nanofiltration membrane during backwashing, the pressure of the treated water is pulsed. These pressure pulses enable improved detachment of deposits from the surface of the nanofiltration membrane.

[0081] In a very advantageous embodiment of the invention, it is provided that the pressure of the treated water supplied to the nanofiltration membrane changes in a pulse-like manner in a range between 2.0 bar and 6.0 bar.

[0082] During backwash operation, the treated water is fed to the nanofiltration membrane via the backwash branch with pulse-shaped, alternating pressure. These pressure pulses can be generated by compressing the treated water using the second pump and pushing it against a check valve. When a minimum pressure is reached, the check valve opens, allowing the pressurized treated water to reach the nanofiltration membrane. When the compressed water is released with the check valve open, the pressure of the treated water decreases, causing the check valve to close. Because the second pump continues to run continuously, the pressure upstream of the check valve increases again, which opens again when the minimum pressure is reached. This process occurs periodically, generating the pulse-shaped pressure surges.These pulse-shaped pressure surges lead to a change in the pressure of the treated water fed to the nanofiltration membrane in a range between 2.0 bar and 6.0 bar.

[0083] The above-explained features and advantages of this invention will be better understood and appreciated after careful study of the following detailed description of the preferred, non-limiting exemplary embodiments of the invention with the accompanying drawings, which show:

[0084] Fig. 1 : a schematic diagram of an embodiment of the inventive

[0085] water treatment plant,

[0086] Fig. 2: a schematic diagram of the water treatment plant in a

[0087] filtration operation,

[0088] Fig. 3: a schematic diagram of the water treatment plant in a

[0089] Backwash operation,

[0090] Fig. 4: a schematic diagram of the water treatment plant in a

[0091] Cleaning operation and

[0092] Fig. 5: part of the first pipeline of the water treatment plant with additional filters arranged.

[0093] Figure 1 shows a schematic diagram of an embodiment of the water treatment plant 1 according to the invention.

[0094] The water treatment plant 1 comprises, in a flow direction 2 of the water in the water treatment plant 1, a stage 3 for receiving raw water to be purified from a source 4, a filter stage 5 with a nanofiltration membrane 6 and a storage stage 7 with a storage tank 8.

[0095] In stage 3, a first pump 9 is arranged for taking in raw water to be cleaned. At the inlet of this first pump 9, a suction hose 10 is arranged, the first end of which is connected to the pump 9. The second end of the suction hose 10 is arranged in the source 4, from which the raw water to be cleaned is taken. In Figure 1, the source 4 is indicated by a dash-dash line. At the second end of the suction hose 10, a coarse filter 11 like a sieve basket is arranged, which prevents the entry of coarse material such as plant parts and stones and thus damage to the first pump 9.

[0096] To compensate for the vibrations or pressure fluctuations caused by the first pump 9 in the associated first pipeline 12 between the first pump 9 and the filter stage 5, a pulsation damper 13 is arranged at the outlet of the first pump 9. This ensures that the filter stage 5 is supplied with a constant flow of the raw water to be purified from the source.

[0097] Furthermore, in the first pipeline 12, viewed in the flow direction 2, a pressure relief valve 14 is arranged behind the pulsation damper 13, which opens when a predetermined pressure for the first pipeline 12 is exceeded. A vent valve 15 is also arranged in the first pipeline 12.

[0098] The raw water to be purified, which is taken from the source 4, is pumped by the first pump 9 via the first pipeline 12 in the flow direction 2 to the filter stage 5.

[0099] The nanofiltration membrane 6 is arranged in the filter stage 5. The nanofiltration membrane 6 has a first connection 16, which is connected to the first pipe 12. In an area upstream of the first connection 16, a first check valve 17 and a first pressure gauge 18 are arranged in the first pipe 12. The first check valve 17 prevents the raw water to be cleaned from flowing back from the filter stage 5 to stage 3. The pressure of the raw water to be cleaned at the inlet of the nanofiltration membrane 6 can be read on the first pressure gauge 18. For proper operation of the nanofiltration membrane 6, a pressure in the range between 2.0 bar and 6.0 bar, in particular 4.0 bar, is set. The first pressure gauge 18, as well as other pressure gauges in the water treatment plant 1, can be replaced by a pressure sensor (not shown), which transmits its data to the central control system (also not shown).The central control system, which controls all processes and operating modes of the water treatment plant 1, can, for example, control or regulate the operation of the first pump 9 using pressure measurement data from the first connection 16 and thus maintain a constant prescribed pressure at the first connection 16 of the nanofiltration membrane 6. This ensures continuous and quality-appropriate filtration or treatment of the supplied raw water by the nanofiltration membrane 6.

[0100] The nanofiltration membrane 6 has a second connection 19, at which a second pipe 20 is arranged. The second pipe 20 is connected in the flow direction 2 to an inlet of a first shut-off valve 21. Furthermore, the second pipe 20 is connected to an outlet of a second shut-off valve 22, which belongs to a backwash branch, as will be explained later.

[0101] The nanofiltration membrane 6 further comprises a third connection 23, at which a return line 24 is arranged. A second pressure gauge 25 or a corresponding sensor is arranged in the return line 24 in the region of the third connection 23.

[0102] In a further flow direction 26 of the retentate in the return line 24, a third shut-off valve 27 for closing the return line 24 and a first control valve 28 for influencing the cross-section of the return line 24 are arranged in the return line 24. The return line 24 ends either at the inlet of the first pump 9, as shown in the example in Figure 1, or in the source 4.

[0103] At the outlet of the first shut-off valve 21, a third pipe 29 is arranged, which runs in the flow direction 2 to the inlet of a fourth shut-off valve 30. Furthermore, the third pipe 29 is also connected to an outlet of a second check valve 31.

[0104] The outlet of the fourth shut-off valve 30 is connected to a fourth pipeline 32, through which the treated water flows from the filter stage 5 to the storage tank 8 located in the storage stage 7. A UV filter element 33 is arranged in this fourth pipeline 32 to remove biological contaminants, particularly bacteria, from the treated water. Furthermore, a catalyst for biofilm elimination and the reduction of contamination and deposits, such as a catalyst 34, can be arranged in the fourth pipeline 32. This catalyst enables biocide-free structural treatment of water, removing contamination and deposits on surfaces without leaving any residue.

[0105] A fifth pipe 35 is arranged at an outlet of the storage tank 8 and runs to an inlet of the second shut-off valve 22. A second pump 36 and a third check valve 37 are arranged in this fifth pipe 35 as components of a cleaning circuit, which will be explained in more detail later. The fifth pipe 35 is also connected to the outlet of the second check valve 31.

[0106] To determine the current fill level of the treated water in the storage tank 8, a fill level sensor 38 is arranged in the storage tank 8, which transmits its measurement data to the central control unit (not shown).

[0107] Figure 2 shows a schematic diagram of the water treatment plant 1 in a filtration plant.

[0108] During filtration operation of the water treatment plant 1, raw water to be purified is sucked in by the first pump 9 from the source 4 via the coarse filter 11 and the suction hose 10. The first pump 9 conveys the raw water to be purified via the first pipe 12 in the flow direction 2 to the nanofiltration membrane 6. In the flow direction 2, the elements pulsation damper 13, pressure relief valve 14, vent valve 15, the first check valve 17, and the first pressure gauge 18 are arranged on or in the first pipe 12.

[0109] The raw water or process medium to be purified, which is fed under pressure into the nanofiltration membrane 6 via the first connection 16 of the nanofiltration membrane 6, flows through the channels of the nanofiltration membrane 6, forming treated water, i.e., the permeate and the enriched retentate. The enriched retentate is discharged from the nanofiltration membrane 6 via the third connection 23 and, with the third shut-off valve 27 open, returned to the inlet of the first pump 9 via the return line 24 via the first control valve 28. The permeate is discharged via the second outlet 19 of the nanofiltration membrane 6 and, via the second pipe 20, the open first shut-off valve 21, the third pipe 29, the open fourth shut-off valve 30, and the fourth pipe 32, reaches the storage tank 8, in which the permeate is collected as the treated water.In this way, the treated water passes through at least the UV filter element 33.

[0110] During this filtration operation, the second shut-off valve 22, the second check valve 31 and the third check valve 37 are closed and the second pump 36 is not in operation.

[0111] The flow directions of the media in the water treatment plant 1 are shown in Figure 2 for the filtration operation by means of several arrows along the various pipes 12, 20, 29 and 32.

[0112] Figure 3 shows a schematic diagram of the water treatment plant 1 in a backwash operation.

[0113] During backwash operation of the water treatment plant 1, the surface of the nanofiltration membrane 6 is cleaned. For this purpose, the second pump 36 is switched on and pumps treated water from the storage tank 8 via the third check valve 37, which opens under pressure, the fifth pipe 35 and the open second shut-off valve 22 to the nanofiltration membrane 6. The treated water pumped in this way and under pressure is fed to the nanofiltration membrane 6 via the second connection 19 and penetrates the nanofiltration membrane 6 in the opposite direction to the filtering direction, whereby deposits are removed from the surfaces of the tubes of the nanofiltration membrane 6.

[0114] These dissolved deposits are removed from the nanofiltration membrane 6 via the third connection 23 and reach the inlet of the first pump 9 or, alternatively, the source 4 via the return line 24, the open third shut-off valve 27, and the first, at least partially open, control valve 28, which is not shown in Figure 3. The pressure generated by the second pump 36 lies in a range between 2.0 bar and 6.0 bar. In backwash mode, the first pump 9 is not in operation, and the first shut-off valve 21, the fourth shut-off valve 30, the first check valve 17, and the second check valve 31 are closed.

[0115] The flow directions of the media in the water treatment plant 1 are shown in Figure 3 for backwash operation by means of several arrows along the various pipes 35, 20 and 24.

[0116] Figure 4 shows a schematic diagram of the water treatment plant in a cleaning plant.

[0117] During the cleaning operation of the water treatment plant 1, the treated water stored in the storage tank 8 is cleaned or disinfected. If the treated water remains in the storage tank 8 for an extended period of time, contamination such as biological contamination, in particular the formation of bacteria, may occur.

[0118] To remove these contaminants from the treated water, the treated water is periodically cleaned during the cleaning operation of the water treatment plant 1. Alternatively, this cleaning of the treated water can be carried out depending on certain measured values ​​that provide information about the quality of the treated water in the storage tank 8. Such measured values ​​can be, for example, a temperature or a concentration of contaminants in the treated water. To determine such measured values, appropriate sensors or measuring devices are arranged in the water treatment plant 1 or on or in the storage tank 8.

[0119] For cleaning operation, the second pump 36 is switched on and pumps treated water from the storage tank 8 through the third check valve 37, which opens under pressure, into the fifth pipe 35. With the second shut-off valve 22 closed, the pressure generated by the second pump 36 opens the second check valve 31, and the treated water flows to the UV filter element 33 via the open fourth shut-off valve 30 and the fourth pipe 32. The UV filter element 33 removes contaminants such as biological contaminants, particularly bacteria, from the treated water circulating in a cleaning circuit. After this cleaning, the treated water is returned to the storage tank 8 via the fourth pipe 32.

[0120] In cleaning operation, the first pump 9 is not in operation and the first shut-off valve 21, the second shut-off valve 22, the third shut-off valve 27 and the first check valve 17 are closed.

[0121] The flow directions of the media in the water treatment plant 1 are shown in Figure 4 for the cleaning operation by means of several arrows along the pipes 35 and 32.

[0122] Figure 5 shows a part of the first pipeline 12 of the water treatment plant 1 with additional filters arranged therein.

[0123] Optionally, additional filters in the form of sieve filters 39, 40, and 41 are arranged in the first pipeline 12 of the water treatment plant 1 between the vent valve 15 and the first check valve 17. These sieve filters 39, 40, and 41 are used to perform a gradual pre-treatment of the raw water extracted from the source 4.

[0124] In one embodiment of the water treatment plant 1, the first screen filter 39 has openings in the range between 90 pm and 110 pm and forms a first filter stage. The second filter stage is realized by the second screen filter 40, which has openings in the range between 45 pm and 55 pm. A third filter stage is formed by the third screen filter 41 with openings in the range between

[0125] 4 pm and 6 pm.

[0126] In the example of Figure 5, the first sieve filter has 39 openings of 100 pm, the second sieve filter has 40 openings of 50 pm and the third sieve filter has openings of

[0127] 5 pm. This arrangement of the three filter stages ensures optimal pre-treatment of the raw water to be treated in the water treatment plant 1 before the filter stage 5 with the nanofiltration membrane 6.

[0128] In Figure 5, shut-off valves 42, 43, and 44 are arranged on the sieve filters 39, 40, and 41. These valves retain sediment through mesh sizes, for example, in a size range between 5 pm and 500 pm, and thus relieve the downstream nanofiltration membrane 6. By opening a respective shut-off valve 42, 43, 44, water is drained downwards through the filter sump and flows over the filter surface of the respective sieve filter 39, 40, 41, whereby a so-called filter cake is stripped off in the sieve filter 39, 40, 41 and the sieve filter 39, 40, 41 is cleaned.

[0129] List of reference symbols

[0130] 1 water treatment plant

[0131] 2 Flow direction

[0132] 3rd stage for receiving raw water to be cleaned

[0133] 4 Source

[0134] 5 filter levels

[0135] 6 Nanofiltration membrane

[0136] 7 Stockpiling level

[0137] 8 storage tanks

[0138] 9 first pump

[0139] 10 suction hose

[0140] 11 coarse filters

[0141] 12 first pipeline

[0142] 13 Pulsation damper

[0143] 14 Pressure relief valve

[0144] 15 vent valve

[0145] 16 first connection

[0146] 17 first check valve

[0147] 18 first pressure gauge

[0148] 19 second connection

[0149] 20 second pipeline

[0150] 21 first shut-off valve

[0151] 22 second shut-off valve

[0152] 23 third connection

[0153] 24 Return line

[0154] 25 second pressure gauge

[0155] 26 further flow direction of the retentate

[0156] 27 third shut-off valve

[0157] 28 first control valve third pipe fourth shut-off valve second check valve fourth pipe

[0158] UV filter element

[0159] Catalyst fifth pipe second pump third check valve

[0160] Level sensor first screen filter second screen filter third screen filter fifth shut-off valve sixth shut-off valve seventh shut-off valve

Claims

Patent claims 1. Water treatment plant (1) which, in a flow direction (2) of the water in the water treatment plant (1), has at least one stage (3) for receiving raw water to be purified from a source (4), a filter stage (5) for treating the raw water and for producing treated water, and a storage stage (7) with a storage tank (8) for collecting the treated water, characterized in that the stage (3) for receiving raw water to be purified comprises a first pump (9), a suction hose (10), and a coarse filter (11), that a nanofiltration membrane (6) is arranged in the filter stage (5), that the nanofiltration membrane (6) is arranged in a backwash branch, and that the water treatment plant (1) has a cleaning circuit for maintaining predetermined quality properties of the treated water, in which at least the storage tank (8), a fifth pipeline (35), a second pump (36),a fourth pipeline (32) and a UV filter element (33) and / or a catalyst (34) are arranged for biofilm elimination and reduction of contamination and deposits., 2. Water treatment plant (1) according to claim 1, characterized in that the nanofiltration membrane (6) has a first connection (16) which is at least indirectly connected to the first pump (9), that the nanofiltration membrane (6) has a second connection (19) for a permeate as treated water, which is at least indirectly connected to the storage tank (8) and that the nanofiltration membrane (6) has a third connection (23) for a retentate, which is at least indirectly connected to the first pump (9) or the source (4) via a return line (24).

3. Water treatment plant (1) according to claim 1 or 2, characterized in that the nanofiltration membrane (6) is arranged in a backwash branch which connects at least the storage tank (8), the at least a second pump (36) indirectly connected to the second connection (19) of the nanofiltration membrane (6) via the fifth pipe (35) for withdrawing treated water from the storage tank (8), the nanofiltration membrane (6) and a return line (24) connected to the third connection (23) of the nanofiltration membrane (6).

4. Water treatment plant (1) according to one of claims 1 to 3, characterized in that at least one sieve filter (39, 40, 41) is arranged in the stage (3) for receiving raw water to be purified.

5. Water treatment plant (1) according to one of claims 1 to 4, characterized in that three sieve filters (39, 40, 41) are arranged in the stage (3) for receiving raw water to be purified, the first sieve filter (39) having openings in the range between 90 pm and 110 pm, the second sieve filter (40) having openings in the range between 45 pm and 55 pm and the third sieve filter (41) having openings in the range between 4 pm and 6 pm.

6. A method for water treatment, in which at least one intake of raw water to be purified from a source (4), a treatment of the received raw water and a production of treated water and a storage of the treated water in a storage tank (8) takes place, characterized in that a backwashable nanofiltration membrane (6) is provided for the treatment of the received raw water, that the raw water to be purified is fed to the backwashable nanofiltration membrane (6) in a filtration operation via a first connection (16),wherein a permeate is discharged as treated water via a second connection (19) and a retentate is discharged from the nanofiltration membrane (6) via a third connection (23), and that in a backwash operation, stored treated water is supplied to the backwashable nanofiltration membrane (6) via the second connection (19) to remove deposits on the surfaces of the nanofiltration membrane (6), and deposits removed from the surface are discharged via the third connection (23), and that in order to maintain predetermined quality properties of the treated water in the storage tank (8), the treated water is periodically, is taken from the storage tank (8) and fed to a UV filter element (33) and / or a catalyst (34), whereby biofilm elimination, a reduction of soiling, deposits and biological contaminants, in particular bacteria, takes place before the water thus purified flows back into the storage tank (8).

7. A method for water treatment according to claim 6, characterized in that the deposits removed during backwashing are returned to the source (4).

8. A method for water treatment according to claim 6 or 7, characterized in that the backwash operation takes place at fixed times or is sensor-controlled, wherein the sensor analyzes a cleaning state of the treated water.

9. A method for water treatment according to one of claims 6 to 8, characterized in that the treated water is fed to the nanofiltration membrane (6) in backwash operation with a pressure that varies in intensity.

10. A method for water treatment according to claim 9, characterized in that the pressure of the treated water supplied to the nanofiltration membrane (6) changes in a pulse-like manner in a range between 2.0 bar and 6.0 bar.

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