Apparatus and method for providing purified water

Abstract

A method is disclosed for treating a potable water supply to provide a purified water stream having a conductivity of less than 20 μS / cm, the method comprising at least the steps of: (a) providing a potable water supply to a first storage tank; (b) circulating the supply water in the first storage tank one or more times through a first purified recirculation loop including a first capacitive deionization module in a charging mode to provide a first purified water stream having a lower conductivity than the supply water; and (c) circulating the first purified water stream one or more times through a second purified recirculation loop including a second capacitive deionization module in a charging mode to provide a second purified water stream having a lower conductivity than the first purified water stream.

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for providing ultrapure water, particularly but not exclusively for providing ultrapure water for medical and laboratory purposes. [Background technology]

[0002] Water purification devices used in laboratories and medical facilities are known. Generally, they involve reducing and / or removing contaminants and impurities to very low levels from the water source as well as removing any impurities originating from within the device itself. They usually use a variety of techniques to remove particles, colloids, bacteria, ionic species, organic matter and / or molecules. These techniques usually include reverse osmosis, microfiltration, ion exchange, ultrafiltration, adsorption, UV irradiation.

[0003] A typical water purification system has an inlet for providing water to a first purification stage, usually involving reverse osmosis, which provides partially purified water to a storage tank. A recirculation loop from the storage tank passes through a second purification stage, usually ion exchange, and the water exiting the second purification stage is either removed from the water purification system as product water or, in some cases, passes through a third purification stage, usually a bacterial filter, at the point of distribution, or the water exiting the second purification stage returns to the storage tank. Recirculation of the water helps to maintain the required high level of purity.

[0004] The deionization technique used in the first purification stage is typically reverse osmosis. Reverse osmosis uses membranes with pores on the scale of 0.001 to 0.0001 microns. This scale is orders of magnitude smaller than bacteria and viruses, and similar to the ionic radius of dissolved and hydrated salts. Reverse osmosis requires high pressure to be applied to the feed side of the membrane, and it is costly to pump the feed water to the required pressure. Typically, small laboratory water purifiers have a reverse osmosis feed pressure of 4 to 6 bar, and larger laboratory water purifiers have a feed pressure of 8 to 12 bar.

[0005] Larger industrial reverse osmosis membranes can operate at high recovery rates; that is, about 70% of the feed water can be recovered as product water. This can be achieved by softening the feed water to the reverse osmosis membrane to exchange hardness-forming ions such as calcium and magnesium for more soluble ions such as sodium. This reduces the possibility of problematic precipitate formation from salts in the water, which can coat surfaces in the equipment and impede flow or prevent the purification technology from functioning efficiently. This potential is often referred to as the scaling potential and can be listed as the Langelier Saturation Index (LSI).

[0006] This method of softening feedwater is rarely practical in small-scale units used in laboratories due to the size of the softener and the need for salt to regenerate the resin. In laboratory water purification systems, to keep the potential for scaling low, reverse osmosis modules are typically operated at about 15% recovery, up to six times the amount of water passing down the drain to pass on for further purification. By passing the concentrate from the first reverse osmosis module through a second and sometimes a third reverse osmosis module, water recovery can be increased to about 40%, but the pressure requirements and concentration of the feed to the modules mean that the latter modules are less efficient and the permeate quality is reduced. Summary of the Invention

[0007] It is an object of the present invention to provide an improved method for purifying water in a laboratory scale water purification device which reduces the pressure required within the device and increases the water recovery rate.

[0008] According to one aspect of the invention, there is provided a method for treating a potable water supply to provide a purified water stream having a conductivity of less than 20 μS / cm, comprising the steps of: (a) providing a potable water supply to a first storage tank; (b) circulating the feed water in the first storage tank one or more times through a first purified recirculation loop including a first capacitive deionization module in a charging mode to provide a first purified water stream having a lower conductivity than the feed water; (c) circulating the first purified water stream one or more times through a second purified recirculation loop including a second capacitive deionization module in a charging mode to provide a second purified water stream having a lower conductivity than the first purified water stream; The present invention provides a method comprising at least the steps of:

[0009] Potable mains feed water is water delivered by a jurisdiction, usually municipal or private, to domestic and industrial locations to make it suitable for human consumption. It may be taken from a river, a storage tank or an underground aquifer and may be partially purified in a municipal water treatment facility before being pumped to domestic and industrial locations. It usually has a conductivity of 50-1000 μS / cm. Groundwater usually has higher levels of dissolved "hardness-forming ions" than surface water.

[0010] Water purification methods and equipment have been developed that remove all dissolved ions from drinking water supplies, so that the conductivity of "ultrapure water" is the sole result of the dissociation of water molecules into hydronium and hydroxide ions. The level of dissociation varies with temperature, and the conductivity of the ions also varies with temperature, but a standard is usually taken at 25°C, where the conductivity limit for purified water is 0.055 μS / cm. This value can also be expressed as the reciprocal of the resistivity; thus, a conductivity of 0.055 μS / cm corresponds to a resistivity of 18.2 MΩ.cm.

[0011] As the level of desired purity increases, so does the cost of purified water, and the actual purity a user requires for their operation can be very important. There are national and international organizations, such as the International Organization for Standardization (ISO), that issue standards with various purity requirements. As a result, for example, "ISO3696 Grade 1 water" requires a resistivity of 10 MΩ.cm at 25°C, which corresponds to 0.1 μS / cm, "Grade 2 water" requires a resistivity of 1 MΩ.cm, which corresponds to 1 μS / cm, and "Grade 3 water" requires a resistivity of 0.2 MΩ.cm, which corresponds to 5 μS / cm.

[0012] The term "feed water" as used herein relates to the stream of water that is intended to be provided to the method and apparatus of the present invention.

[0013] As used herein, the term "feedwater" refers to any flow of water supplied to a module, unit, or the like.

[0014] The present invention employs capacitive deionization in a first and second capacitive deionization module, the first capacitive deionization module providing a first purification of the feed water and the second capacitive deionization module providing further purification.

[0015] Capacitive deionisation (CDI) is a process in which a stream of water is passed through one or more pairs of spaced apart electrodes located within a housing forming a CDI module. The electrodes have a large surface area and low electrical resistance between them. CDI is able to remove ions from water by "capturing" the ions from the water using electrical attraction and adsorption to the surfaces of the electrodes.

[0016] Examples of CDIs are known in the art, such as those described in US Patent No. 5,192,432 and US Patent No. 5,425,858. The inlet water to a CDI module generally flows between electrodes, through the electrodes themselves, or between or around multiple electrodes located in either a single or multiple chamber module within the CDI module. These configurations have various advantages, all related to providing a purified water stream with ions removed.

[0017] The operation of removing ions, including "hardness-forming ions," from the water in a CDI module is generally referred to as "charging," and therefore its operating time is generally referred to as the "charge time." Similarly, the subsequent operation of removing those same ions from the CDI electrodes (allowing them to be collected elsewhere) is typically referred to as "discharging," and therefore its operating time is typically referred to as the "discharge time."

[0018] Compared to "charging", the electrodes can be discharged relatively quickly by shorting or reversing the direction of the current, discharging the ions so collected from the electrodes with additional water flow between the electrodes into the water where they can then be eluted from the module as a concentrate stream. There may also be a short period between charging and discharging to allow for flushing of the ions. The total time of both charging and discharging is usually referred to as the "operating time" (of the CDI or CDI module).

[0019] CDIs can purify water without the need for a redox reaction to occur because the electrode electrostatically adsorbs and desorbs contaminants, usually within the macro- and mesopores of the electrode. During the charge or adsorption portion of the cycle, ions are transferred to the electrode and water is purified, while during the discharge or desorption portion, ions are transferred from the electrode and the water becomes more concentrated.

[0020] One particular form of CDI is described in US Pat. No. 6,709,560, which describes the combination of a CDI electrode with a charge barrier, such as an ion exchange membrane, placed in front of one or both of the electrodes, usually in front of both electrodes. The ion exchange membrane has a high internal charge because it has binding groups such as sulfonic acid or quaternary amines. This allows easy access for ions of the opposite charge to the binding group (counterions), either positive or negative, and blocks access for ions of the same charge type (co-ions). They then prevent ions from entering the electrode during discharge. This form of capacitive deionization is now commonly referred to as "membrane capacitive deionization" (MCDI).

[0021] The use of ion exchange membranes can significantly improve the performance in terms of salt adsorption charge efficiency and energy consumption of a CDI module or CDI process, depending on the ions being removed.

[0022] Traditionally, CDI is provided by large-scale CDI "plants," where the amount of water produced by the CDI plant is several times greater than the amount of water used in a laboratory. In these instances, multiple CDI units are used in a bank of parallel operation, so that some are operated in a charging mode and some are operated in a discharging mode to form a system with a steady flow of feed water and product water with a certain level of impurities therefrom, from which electrical energy can be recovered. However, this method of operation is not suitable for laboratory scale.

[0023] CDI electrodes have an ionic capacitance that can be expressed in terms of the ionic equivalent charge, i.e., moles of charge removed, so that the electrodes of a capacitive deionization module have a capacitance of x charge equivalents per meter squared (eq / m 2 ), and Ym 2 A module with electrodes of 0.4 m has a total capacitance of XY. For example, a small CDI module has a total capacitance of 0.4 m 2 Membrane area, 0.05eq / m 2 of electrode capacitance and a total capacitance of 0.02eq.

[0024] CDI units therefore have a limit or "capacity" on the amount of ions or ionic charge they can remove before they can no longer remove ions. When their capacity reaches full, the force holding the ions in the electrodes decreases and they become less efficient at trapping ions. It is therefore preferable to set CDI units to discharge before reaching 100% capacity. However, it is also important not to switch to discharging too early, as this will cause water to go down the drain and reduce the water recovery rate of the purification process. So a balance must be struck between the charge time and the capacity used for each charge.

[0025] Also, to achieve the highest purity at the end of the purification cycle, the amount of ions retained in the electrodes should be limited to maximize removal of low level ions in solution. Thus, if desired, the second CDI module will operate at a lower capacitance than the first CDI module, so that the second CDI module maintains the ability to reduce its inlet water to a lower conductivity outlet, allowing purer water to be dispensed from the device when desired by the user.

[0026] In particular, the first and second capacitive deionization modules may have a predetermined capacitance prior to discharge, with the second capacitive deionization module operating at a lower capacitance than the first capacitive deionization module.

[0027] Preferably, the first CDI module is charged to more than 70% of its capacity before discharging and the second CDI module is charged to less than 70% of its capacity before discharging.

[0028] Because immediately after switching from charge to discharge there is a time that water in the CDI unit and in the lines between the CDI unit and the valves must be moved before the effects of the discharge increase the ion content, it may also be advantageous to operate one or more valves to direct such water to drain for a short period of time after switching to discharge. Similarly, when changing from discharging to charging from the CDI unit, a delay in valve operation allows ions in the CDI unit and between the CDI unit and the valves to move to drain.

[0029] Optionally, the first purification loop and the second purification loop recirculate from and back to the first storage tank.

[0030] Optionally, a portion of the path of the first purified recirculation loop is the same as the path of the second purified recirculation loop. In this manner, the first purified recirculation loop and the second purified recirculation loop may use the same storage tanks, pumps, sensors and valves while using different capacitive deionization modules and other components.

[0031] In one embodiment of the invention, the method comprises: (d) providing water to a second storage tank; (e) circulating the water in the second storage tank one or more times through a first concentrate recirculation loop including the first capacitive deionization module in a discharging mode to provide a first concentrate stream; (f) circulating the water in the second storage tank one or more times through a second concentrate recirculation loop including a second capacitive deionization module in a discharging mode to provide a second concentrate stream; (g) passing the first concentrate stream or the second concentrate stream, or both concentrate streams, to a drain; Further includes:

[0032] Optionally, the first concentrate loop and the second concentrate loop recirculate from and back to the second storage tank.

[0033] Optionally, a portion of the path of the first concentrate recirculation loop is the same as the path of the second concentrate recirculation loop. In this manner, the first concentrate recirculation loop and the second concentrate recirculation loop may use the same storage tanks, pumps, sensors and valves while using different capacitive deionization modules and other components.

[0034] Optionally, the method further includes providing a first purified water stream from the first storage tank to a first concentrate recirculation loop having a first capacitive deionization module in a discharging mode.

[0035] Preferably, the first storage tank serves as a reservoir of water as water is purified by the first and / or second CDI modules during a CDI charging phase, while the second storage tank serves as a reservoir of water that is concentrated during a CDI discharging phase of the first and / or second CDI modules.

[0036] Optionally, the water flows in the first purified recirculation loop, the first concentrated recirculation loop, the second purified recirculation loop and the second concentrated recirculation loop are provided by one pump.

[0037] If necessary, the pressure from the pump and at all points in the recirculation loop is kept below 2 bar, if necessary below 1 bar.

[0038] Optionally, the device includes sanitation means for regularly or intermittently disinfecting or otherwise cleaning all or at least part of the device, for example with a disinfecting solution such as citric acid.

[0039] It can be seen that the present invention is based on providing or carrying out one or more sets of a first alternating cycle of a first water purification stage comprising step (b) as defined above and a first water concentrating stage comprising step (e) as defined above and providing or carrying out one or more sets of a second alternating cycle of a second water purification stage comprising step (c) as defined above and a second water concentrating stage comprising step (f) as defined above.

[0040] Preferably, step (a) is carried out only prior to the first alternating cycle.

[0041] The water in the water concentration stage can be feed water or water removed from the first storage tank.

[0042] After one, each, some or all of the water concentration stages, the concentrated water stream may be passed to a drain.

[0043] After one or several water concentration stages, the concentrate water stream may be retained in a second storage tank for use in the next water concentration stage.

[0044] In this manner, the first alternating cycle provides an initial purification of the feed water to a first level of conductivity, and the second alternating cycle provides further purification of the purified water of the first alternating cycle to provide final water having a lower conductivity. Thus, the second alternating cycle further purifies or purifies the purified water provided by the first alternating cycle.

[0045] The first alternating cycle includes a first water purification stage through a first CDI module that reduces the conductivity of the feed water supplied thereto, followed by a "cleaning" of the first CDI module after each purification stage with a first water concentration stage. The first alternating cycle may include one or more sets of first water purification stages and one or more first water concentration stages, preferably at least 3-8 times each stage, and possibly more.

[0046] Similarly, the second alternating cycle includes a second water purification stage passing through a second CDI module that further reduces the conductivity of the feed water supplied thereto, followed by "washing" the second CDI module after each water purification stage with a second water concentrating stage. The second alternating cycle may include one or more sets of second water purification stages and one or more second water concentrating stages, preferably at least 3-6 times each stage, and possibly more.

[0047] Since the first purification stage and the first concentration stage may alternate, the first alternating cycle may occur over a period of time when the provision of a purified water stream is not required. Typically, this may be during off-peak hours or during periods of no demand, such as "overnight," which typically occur during periods of demand for water during "working hours" or "working days." In particular, the first and second alternating cycles may occur "overnight" to provide a volume of a purified water stream having a predetermined conductivity that is ready for use at the start of the next "working day," typically in the morning hours.

[0048] One skilled in the art will appreciate that the present invention allows for automatic repeated application overnight or during other non-use periods to provide a purified stream of the required conductivity that is ready for the next operational requirement.

[0049] The first alternating cycle may provide a purified water stream having a target conductivity, which may be a predetermined conductivity or a conductivity that is a percentage of the conductivity of the potable water supply, and the second alternating cycle may provide further purified water having a target conductivity, which is a second predetermined conductivity, for example, less than 20 μS / cm.

[0050] The present invention allows for the first and / or second target conductivities or algorithms to generate them and are set by either a service engineer or a user, or both. That is, the number of cycles within the first alternating cycle or the second alternating cycle or both, and the timing therebetween, can be organized to achieve any desired level of conductivity. Sensors or means for sensing conductivity levels and determining the achievement of a predetermined conductivity in any portion of the present invention are known in the art and will not be described further herein.

[0051] The present invention also has the versatility to tailor the timing, number of cycles, component sizes, etc. to suit the purity and / or volume of the final purified water stream provided by the present invention.

[0052] In one embodiment of the invention, the method of the invention comprises the steps of: supplying potable water supply to the first storage tank of step (a); performing one or more first alternating cycles of a first water purification stage comprising step (b) and a first water concentration stage comprising step (e); passing the first concentrate stream to a drain; Optionally, before one or both of the first and second water concentration stages, supplying water in the first storage tank to a second storage tank; performing one or more second alternating cycles of a second water purification stage comprising step (c) and a second water concentration stage comprising step (f); and passing the second concentrate stream to the drain of step (g).

[0053] Optionally, one or more of the first alternating cycles provide a purified water stream with a conductivity of less than 400 μS / cm, or less than 300 μS / cm, or less than 200 μS / cm, or less than 100 μS / cm, or less than 50 μS / cm.

[0054] Optionally, the one or more first alternating cycles provide a purified water stream with a conductivity of less than 40%, less than 30%, less than 20% or less than 10% of the conductivity of the potable supply water to the water purification device.

[0055] One skilled in the art will appreciate that the conductivity of the first purified water stream can be adjusted to any suitable predetermined value or percentage, as needed, within the first purified recirculation loop or first storage tank based on appropriate measurements of the conductivity of the first purified water.

[0056] Optionally, the first and second cycles occur over a period of at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or more hours. This may occur over an "overnight" or other period that does not require purified water flow.

[0057] Optionally, the first and second cycles occur over less than 12, 11, 10, 9, 8, 7, 6 hours.

[0058] Optionally, the first alternating cycles occur at least three times each.

[0059] Optionally, the methods of the present invention may provide a purified water stream with a conductivity of less than 10 μS / cm, or less than 5 μS / cm, or less than 1 μS / cm, or even lower.

[0060] Optionally, the invention further includes passing the water through an electrodeionization device or module prior to distribution. Electrodeionization (EDI) applies an electric field across an ion exchange resin bed and uses ion selective membranes to remove ionized and ionizable species from the water. The water passes through one or more chambers filled with ion exchange resin held between cation and anion selective membranes. Ions in the solution are exchanged for hydroxide or hydrogen ions on the resin, producing deionized water. Unwanted ions then migrate under the influence of an electric field through the ion exchange resin and ion selective membrane to separate concentration chambers from which they can be washed out and exit the electrodeionization device.

[0061] Typically, the EDI chamber is arranged in the form of a "stack" between two main electrodes. The amount of ions that can be removed can be a function of the applied current, so the stack can easily become overloaded if there are high levels of salt or other ionic or ionizable species in the water stream. Particulate and organic fouling can also degrade the performance of the stack. EDI stacks are particularly susceptible to the formation of hardness scale on the membrane, formed by the precipitation of poorly soluble salts of "hardness forming ions" such as calcium or magnesium. This requires that the feed water to the EDI must have very low levels of such dissolved hardness forming ions to maintain proper function. The typical specification requirement for EDI units such as the Evoqua Ionpure LX is less than 1 ppm as CaCO3, which corresponds to 0.4 ppm calcium at the feed water inlet to the EDI.

[0062] Therefore, water intended to be purified to the highest level achievable by EDI is typically "preconditioned" or "pretreated". Traditionally, this pretreatment has included at least reverse osmosis to remove most of the ionic contaminants. Softening treatments before or after reverse osmosis with conventional sodium form ion exchange materials have been used to remove more or remaining hardness forming ions.

[0063] Because the feed water to the EDI module of the present invention is already highly pure, the EDI module of the present invention may have only three or five chambers in the stack, such that the EDI module of the present invention has only one chamber for removing anions using an anion exchange resin, one for removing cations using a cation exchange resin or one for removing both anions and cations in a mixed resin chamber.

[0064] Optionally, the EDI module may be located in a third purified water recirculation loop formed from or extending from the first storage tank, thereby purifying the water stored in the first storage tank by recirculating the water in the first storage tank through the EDI module. The third purified water recirculation loop may share a majority of the loop with the second purified water recirculation loop. Alternatively, the EDI module may be located in the distribution line from the purification device using the method of the present invention.

[0065] The EDI module may be powered continuously or intermittently during purification, thereby transferring ions removed by the ion exchange resin to the concentrate chamber, and may be continuously or intermittently flushed with a concentrate stream generating a concentrate stream. Alternatively, the EDI module may be powered during a specific regeneration mode that may operate periodically after a number of operating cycles. In the latter case, concentrate is produced from the EDI module only during this specific regeneration cycle.

[0066] Optionally, the use of an EDI module in the present invention can provide a purified water stream with a conductivity of less than 0.5 μS / cm, or less than 0.2 μS / cm, or less than 0.1 μS / cm.

[0067] Silica may also be present in drinking water supplies. However, silica has a very small dissociation constant, resulting in very poor removal by the use of CDI. Therefore, the additional involvement of an EDI module may ionize and remove the amount of silica in the final purified distribution water stream, so that the amount of silica in the distribution stream may be less than 5% by weight, and preferably the weight percent of the amount of silica in the drinking water supply may be less than 1% by weight or less than 0.1% by weight.

[0068] Optionally, the method further comprises passing the water through a degassing membrane. Carbon dioxide removal can be assisted by the use of a degassing membrane, optionally placed in the second clean water recirculation loop, the third clean water recirculation loop, or the junction of the two. Degassing membranes are known in the art and use a vacuum, gas, or air flow on one side of a membrane through which carbon dioxide or other gases can pass, so that gas passes from the liquid flowing on the other side of the membrane to the vacuum or gas flow. Degassing membranes have a large membrane area and usually reduce the amount of carbon dioxide in the liquid, but do not remove all of it. This reduces the amount of carbon dioxide that needs to be removed by other processes, but these processes require water purification to a conductivity of less than 0.5 μS / cm or a resistivity of more than 2 MΩ.cm.

[0069] If necessary, the water purification device may contain complementary purification technologies to remove non-ionic contaminants such as chlorine, bacteria, and particles. Chlorine may be removed, for example, by activated carbon, as known in the art. Bacteria may be inactivated using an ultraviolet light irradiation device, preferably a UV LED disinfection device, installed in one or more recirculation loops or distribution conduits. Large particles may be removed with an inlet strainer or filter. Smaller particles, including bacteria, may be removed by a point-of-use device installed where the purified water is dispensed from the device.

[0070] Optionally, the degassing membrane may be located in the second purified recirculation loop, the third purified recirculation loop or at the junction of the two.

[0071] It has been found that the present invention can produce a volume of purified water with a conductivity of less than 20 μS / cm that is more than 50%, preferably more than 70% or more than 80% of the volume of the potable water supply supplied to the first storage tank.

[0072] This level of water "recovery" (the purified water product produced compared to the potable water supply input) is a dramatic increase for a lab-scale water purification unit and is higher than what is typically achievable with lab-scale reverse osmosis, avoiding the need for a reverse osmosis module and its associated high pressures, CAPEX and OPEX.

[0073] According to a second aspect of the present invention, Drinking water inlet, A first storage tank; A pump, a first purification recirculation loop from the first storage tank through the first capacitive deionization module in a charging mode and back to the first storage tank; a second storage tank; a first concentrate recirculation loop from the second storage tank through the first capacitive deionization module in a discharge mode and back to the second storage tank; a second purification recirculation loop from the first storage tank through a second capacitive deionization module in a charging mode and back to the first storage tank; a second concentrating loop from the second storage tank through a second capacitive deionization module in a discharging mode and back to the second storage tank; A purified water outlet; A water purification device capable of providing a purified water stream having a conductivity of less than 20 μS / cm from a potable water supply is provided, comprising:

[0074] Optionally, the water purification device may be constructed in a single chassis or frame with a housing or cover so that it appears as one complete unit which may be located on or under a laboratory bench or mounted on a laboratory wall and require only connection to a source of potable water, a drain and a power source.

[0075] Preferably, the first storage tank serves as a reservoir of water to be purified by the first and / or second CDI modules during the charging phase, while the second storage tank serves as a reservoir of water to be concentrated during the discharging phase of the first and / or second CDI modules.

[0076] Optionally, the first storage tank is designed to hold, during purification, preferably overnight, the amount of water used in the laboratory during a normal working day and the amount of water that is transferred to the second storage tank during the purification process.

[0077] Optionally, the working volume of the second storage tank should be no more than 10% of the first storage tank, for example, the total working volume of water in the first storage tank may be less than 25 liters, preferably less than 20 liters, and the total working volume of water in the second storage tank may be less than 2 liters, preferably less than 1 liter.

[0078] Preferably, the potable water supply to be purified enters the water purification device, either directly or indirectly, into a first storage tank where it is recirculated through the first capacitive deionization module in charging mode until the utilized capacity of the first capacitive deionization module is greater than 70%, and the conductivity of this first purified water decreases by a proportional amount as indicated by the mass balance of ions in the system.

[0079] At an appropriate stage, the potable water supply is also taken into a second tank as a "retentate stream" and such water is recirculated through the first capacitive deionization module as a retentate stream during discharge mode, so that ions collected in the first capacitive deionization module during charging enter the retentate and increase its conductivity to accommodate the ionic mass balance in the recirculation loop. When most or nearly all of the ions have been removed from the first capacitive deionization module, the retentate stream may be diverted to drain and discharged from the water purification system.

[0080] The first capacitive deionization module is ready to accept more charge from the first purified water in the first storage tank, and this water is recirculated again through the first capacitive deionization module in the charging mode, further reducing the ionic content and conductivity of the first purified water.

[0081] This charging and discharging phase may be repeated as a "first alternating cycle" until the conductivity of the first purified water reaches a desired conductivity or ion content. During this period, the concentrate stream in the second storage tank preferably includes a fresh amount of potable water supply or a portion of the potable water supply for each discharge cycle, but as the purity of the first purified water becomes higher, it may be possible to additionally or alternatively use a quantity of the first purified water as the water used in the concentrate stream. In this case, water may be removed from the first storage tank, passed through the first capacitive deionization module, and diverted to the second storage tank before passing through and being recirculated from the first capacitive deionization module in the discharge mode.

[0082] Starting with a lower conductivity in the concentrate allows the concentrate to operate with less water and the same concentration at the end of the discharge process. Alternatively, if the same amount of concentrate is used, a lower concentration, and therefore a lower potential for scaling, can be achieved in the concentrate.

[0083] If there is a high probability of scaling in the concentrate water at the end of discharge, a suitable solution such as citric acid may be initiated to remove scale from the concentrate loop on a regular or irregular basis.

[0084] After a certain amount of charge and discharge cycles or after the first purified water reaches a desired conductivity or ion content or percentage of the initial feedwater conductivity, appropriate selectors, valves, or other valving can cause the first purified water to pass to and through a second capacitive deionization module for increased purity. The second capacitive deionization module can be operated in the same manner as the first capacitive deionization module for charge and discharge cycles and passes the purified water to the first storage tank as second purified water.

[0085] Optionally, during operation of the second capacitive deionization module, the capacitance of the second capacitive deionization module is preferably used to a lesser extent than was used during operation of the first capacitive deionization module, such that, for example, less than 70% of the capacitance is used in each charging cycle.

[0086] The second capacitive deionization module can be the same size as the first capacitive deionization module, or it can be smaller than the first capacitive deionization module, such as having 50% of the electrode area of ​​the first capacitive deionization module, because it needs to remove fewer ions.

[0087] Optionally, during operation of the second capacitive deionization module, new or fresh municipal supply water is not drawn into the water purification apparatus, and water for the discharge cycle is drawn from a portion of the second purified water into the second storage tank as a concentrate stream.

[0088] As purification goes through cycles, the amount of ions removed in each purification or charge stage or cycle decreases, reducing the concentration of water during the concentrate or discharge stage or cycle, making it possible to operate two or more discharge cycles with the same concentrate, thereby reducing water passing through the drain and increasing the water recovery rate of the purification system.

[0089] By repeated charge / discharge cycles, the second purified water is continually purified until the conductivity of the second purified water reaches a desired conductivity or ion content, typically less than 10 μS / cm, although higher limits may be used if desired by the operator.

[0090] Thus, even with high conductivity potable water supplies, the amount of water passing through the drain during the purification process of the present invention can be less than 50% of the amount of water entering the device, and water recovery is therefore greater than 50%, significantly higher than occurs in conventional reverse osmosis-based laboratory water purification units.

[0091] If the conductivity of the potable water supply is relatively low, the amount of purification cycles that may be required may be further reduced, so that the amount of water that may go down the drain during the purification process of the present invention may be less than 30% or less than 20% of the amount of water entering the device, and thus water recovery is greater than 70% or greater than 80%.

[0092] Carbon dioxide dissolves from air into water and must be removed if the water reaches a conductivity of less than 1 μS / cm. Capacitive deionization is an excellent purification method for strongly ionized or dissociated ions in water, but is inadequate for removing weakly ionizable molecules such as silica and carbon dioxide. Alternative processes are capable of removing weakly ionizable molecules, and one such alternative process is electrodeionization.

[0093] In another embodiment of the invention, the second purified water is passed through an electrodeionization device or module before being dispensed from the water purification device.

[0094] Optionally, the apparatus further comprises a recirculation pump for recirculating the water around a recirculation loop within the apparatus.

[0095] Optionally, the device can be placed on or under a laboratory bench or mounted on a laboratory wall.

[0096] Optionally, the apparatus further comprises an electrodeionization device or module prior to dispensing from the water purification device.

[0097] Optionally, the device further comprises a degassing membrane.

[0098] Optionally, the apparatus further comprises one or more sensors for measuring the conductivity of the water in the first purified recirculation loop or the purified water outlet or both.

[0099] Optionally, the apparatus further comprises one or more controls for controlling water flow in one or more of the group including the first purified recirculation loop, the second purified recirculation loop, the first concentrated recirculation loop, and the second concentrated recirculation loop.

[0100] If necessary, the water purification device may include complementary purification technologies to remove non-ionic contaminants such as chlorine, bacteria, and particles. Chlorine may be removed, for example, by activated carbon, as known in the art. Bacteria may be inactivated using an ultraviolet light irradiation device, preferably a UV LED disinfection device, installed in one or more recirculation loops or distribution conduits. Larger particles may be removed with an inlet strainer or filter. Smaller particles, including bacteria, may be removed by a point-of-use device installed where the purified water is dispensed from the device.

[0101] The water purification apparatus includes the electronic controls necessary to operate the apparatus. This typically includes one or more microprocessors located on one or more printed circuit boards, although alternatively a programmable logic controller may be used. The electronic controls may also include inputs and outputs to devices such as sensors, valves, pumps, etc. within the apparatus, and may link to components or management systems external to the water purification apparatus.

[0102] If necessary, level control devices in the storage tanks can be used to stop and start unit operations as well as provide information to operators.

[0103] Optionally, the water treatment method or apparatus includes one or more sensors, such as a flow sensor that monitors one or more parameters, or a water quality sensor, such as a conductivity measuring device or a specific ion determining sensor.

[0104] The present invention may use different sensors at different locations within the device and reference them at different stages of the method.

[0105] Optionally, the present invention employs one or more water quality sensors, typically prior to or after discharge of one or more of the different stages of the process or purification technique in the apparatus, or both.

[0106] In one embodiment, the apparatus and method include one or more water quality sensors, and data from the one or more sensors is used to control the voltage or current applied to the capacitive deionization unit or to initiate a switch from charge to discharge cycle.

[0107] In another embodiment, the apparatus and method include one or more water quality sensors, and data from the one or more sensors is used to control whether the first capacitive deionization module or the second capacitive deionization module is used in that particular cycle.

[0108] Because the water discharged to drain from the latter purification cycle is typically purer than the original potable water being purified, the water or EDI concentrate from the latter CDI discharge cycle can be retained within the device, optionally in a third storage tank, for use as part of the feed water for the next fresh purification run, thereby reducing the amount of feed water required, thereby improving water recovery and reducing the power required for subsequent purification runs.

[0109] Preferably, the apparatus and method include an input device such as a touch screen, buttons or other forms known in the art. A user of the apparatus of the present invention may be able to input application requirements such as the desired water purity, i.e. the required conductivity or resistivity.

[0110] The user may also input environmental requirements, such as a required water "recovery" level (output volume of purified water compared to input volume of feed water), which may be required for facility environmental regulations or reporting. The device may then be able to determine the purity of the water that can be obtained while meeting those environmental limits, or may modify its program, such as concentrating the water while meeting the desired water purity requirements by repeating concentrate recirculation before performing a discharge.

[0111] The user may also input if the potable water supply has low hardness forming ions, such as when there is a softener on site for other uses that may use that supply to feed the water purification device of the present invention. The unit's control system may then modify the cycle to increase the concentration of the retentate, further increasing the water recovery rate of the device.

[0112] Thus, in a further aspect of the present invention, there is provided a method of operating a laboratory water purification apparatus as defined herein and capable of providing water below 10 μS / cm, comprising a step of a user selecting the purity of the water to be provided.

[0113] In this way, a user may specify lower purity water for days when only general laboratory water activities such as glass washing or dilution are performed, but select a higher purity for days when higher purity operations are planned, such as operating analytical equipment. The instrument's control system may then modify its operation so that the number of purification cycles may be reduced, EDI may not be used, and / or water discharge times may be altered.

[0114] The apparatus may also include an electrodeionization module and / or a degassing module and / or a UV LED device.

[0115] The apparatus and method of the present invention is expected to produce batches of water overnight and use that water during daytime laboratory operations, whereby the preparation time of the method and apparatus is less than 12 hours and the use time is typically the remainder of the day.

[0116] If the laboratory is operating 24 hours a day, the apparatus and method may be modified with either a second first storage tank or a second pair of first and second storage tanks to allow for daytime and nighttime purification while keeping the purified water inside the first storage tank available for use. Alternatively, the first storage tank may transfer the purified water to a third tank to hold the final purified water. Thus, the present invention includes embodiments having more than two tanks.

[0117] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0118] [Figure 1] FIG. 1 is a schematic diagram of a first embodiment of the present invention. [Figure 2a] 2a-d are a series of schematic diagrams illustrating the operation of a first embodiment of the present invention, where FIG. 2a shows a first purification stage based on a first capacitive deionization module in charging mode. [Figure 2b] 1 shows a first concentration stage based on a first capacitive deionization module in a discharging mode. [Figure 2c] 4 shows a second purification stage based on a second capacitive deionization module in charging mode. [Figure 2d] 4 shows a second concentration stage based on a second capacitive deionization module in discharging mode. [Diagram 3] FIG. 2 is a schematic diagram of a first embodiment of the present invention with the addition of a degassing membrane in the feed to a second capacitive deionization module. [Figure 4] FIG. 2 is a schematic diagram of a second embodiment of the present invention. [Diagram 5] FIG. 4 is a schematic diagram of a third embodiment of the present invention. [Figure 6] 1 is a graph displaying the change in water purity with repeated cycles of the present invention. [Figure 7] 1 is a graph displaying the change in water purity with repeated cycles of the present invention. [Figure 8] 1 is a graph displaying the change in water purity with repeated cycles of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] Referring to the drawings, FIG. 1 shows a water purification apparatus 10 incorporating a first storage tank 12, a second storage tank 14, a pump 16, a first capacitive deionization (CDI) module 18 and a second capacitive deionization module 20.

[0120] The storage tank, pump and CDI module are connected by tubes, pipes or conduits as known in the art and are shown by lines in accompanying Figures 1-5. Operation of the water purification system 10 is performed by a controller, such as a microprocessor or programmable logic controller (PLC, not shown). The controller is connected to pump 16 and any two-way or three-way valves or the like necessary to cause water to flow through the tubes, pipes and conduits as necessary to enable the execution of the processes described below.

[0121] The water purification apparatus 10 has a feed water inlet conduit 22, which may be connected to any suitable source of potable water to be purified, preferably a source of potable water provided by a local water authority. The apparatus also has a product water outlet conduit 24 for dispensing the purified water at suitable points of use depending on the application, and a retentate outlet conduit 26 for removing waste water (containing the removed ions) from the apparatus 10.

[0122] Figures 2a-d show the operation of the apparatus 10 according to the different stages and cycles of the method of the present invention. The water paths and components of Figure 1 used in each stage or cycle are left intact for clarity. Figure 2a shows the charging stage of the first CDI 18 as part of the first purified recirculation loop, Figure 2b shows the discharging stage of the first CDI 18 as part of the first concentrated recirculation loop, Figure 2c shows the charging stage of the second CDI 20 as part of the second purified recirculation loop, and Figure 2d shows the discharging stage of the second CDI 20 as part of the second purified recirculation loop.

[0123] 2a illustrates providing a potable water supply to a first storage tank 12 and circulating the supply water in the first storage tank one or more times through a first purified recirculation loop including a first capacitive deionization module 18 in a charging mode to provide a first purified water stream having a lower conductivity than the supply water. The supply water enters the storage tank 12 such that there is a volume of water 28 within the first storage tank 12. The amount of water in the first storage tank 12 may be determined by a level sensor, mass or pressure measurement, or by flow measurement in a conduit, all known in the art.

[0124] Water 28 then passes from the first storage tank 12 through the pump 16 via a pump supply conduit 30 and appropriate valving to the first CDI module 18 via a first CDI module supply conduit 32 and appropriate valving. In the first CDI module 18, a voltage is applied across the electrodes and ions are drawn to the electrodes such that the water leaving the first CDI module 18 contains fewer ions than the water entering it, i.e., is partially purified. This partially purified water is then returned to the first storage tank 12 via a recirculation conduit 34 and appropriate valving to complete the first purification recirculation loop (12, 30, 16, 32, 18, 34) and one of multiple cycles as a first purification stage. As recirculation progresses from the first storage tank 12 through the first CDI module 18 in the charging mode, some of the ions that were within the volume of water 28 in the first storage tank 12 are taken up by the electrodes of the first CDI module 18, causing the conductivity of the water 28 in the first storage tank 12 to decrease.

[0125] The first purification stage may continue for a predetermined time or until the water reaches a predetermined purity. Alternatively or additionally, there may be a time when no further ions are loaded onto the electrodes or the loading may become less efficient due to limited capacitance of the electrodes of the first CDI module 18 for ions.

[0126] The apparatus 10 then begins a first concentration stage by circulating the water in the second storage tank 14 one or more times through a first concentration recirculation loop that includes the first capacitive deionization module 18 in a discharge mode, as shown in FIG. 2b, to provide a first concentrated water stream that may be passed through a drain 26.

[0127] 2b, the water in the recirculation conduit 34 may be temporarily diverted to the second storage tank 14 by appropriate valving until the amount of water 36 in the second storage tank 14 reaches a desired amount. Desirably, the amount of water 36 in the second storage tank 14 is much less than the amount of water 28 in the first storage tank 12. Alternatively or additionally, a fresh amount of feed water passes directly from the feed water inlet conduit 22 to the second storage tank 14. This arrangement may be preferred while operating the first alternating cycle of the present invention.

[0128] Once the second storage tank 14 has a desired amount of water 36 in it, the supply to the pump 16 is changed so that it is coming from the second storage tank 14. The water 36 in the second storage tank is passed by the pump 16 through the first CDI module 18 and returned to the second storage tank by the conduits 30, 32 and 34a forming the first concentration loop (14, 30, 16, 32, 18, 34a) and, using appropriate valve operation, completes one of several cycles as a water concentration stage. The first CDI module 18 operates in a discharge mode. The discharge mode is typically the reverse of the direction of the current used during the charge mode. Ions on the electrodes pass through the water as it passes through the first CDI module 18, so that the ion content of the water leaving the first CDI module is greater than the ion content of the water entering the first CDI module 18. When the water 36 in the second storage tank 14 is recirculated in this manner, its ion content and conductivity increase.

[0129] When the electrodes of the first CDI module 18 are depleted of ions, the increase in conductivity, monitored by an appropriate sensor, will decrease or stop. A valve will then direct the water leaving the first CDI module 18 out of the water purification system 10 via the concentrate outlet conduit or drain 26, completing the first concentration stage.

[0130] This charging and discharging mode of the first CDI module 18 constitutes one of the first alternating cycles of the first CDI module 18. Through the first cycle, the ions that were in the water 28 in the first storage tank 12 are ultimately removed from the water purification system 10 as a small amount of concentrate. The remaining water 28 in the first storage tank 12 is purer, i.e., has a lower ion content and conductivity than before the first cycle.

[0131] By repeating the first alternating cycle of the first water purification stage and the first water concentration stage, the ion content of the water 28 in the first storage tank may be progressively decreased. An example pattern of the decrease in the conductivity of the water is shown in Figure 7 and further described below.

[0132] As the purity of the water 28 in the first storage tank increases, the purification quality of the first CDI module 18 becomes limited. To be able to reach a lower conductivity of the final product water, a second CDI module is used.

[0133] 2c and 2d show the operation of the second CDI module 20 in a charge and discharge cycle. In particular, FIG. 2c shows a second water purification stage based on circulating a first purified water stream one or more times through a second purification recirculation loop (12, 30, 16, 32, 20, 34) including the second capacitive deionization module 20 in a charge mode to provide a second purified water stream having a lower conductivity than the first purified water stream. FIG. 2d shows a second concentration stage based on circulating water in the second storage tank 14 one or more times through a second concentration recirculation loop (14, 30, 16, 32, 20, 34a) including the second capacitive deionization module 20 in a discharge mode to provide a second concentrated water stream.

[0134] 2c and 2d together show a second alternating cycle of the present invention. The cycle occurs in a similar manner as described above for the first CDI module 18.

[0135] The second purification stage begins with the recirculation of water 28 from the first storage tank 12 and charging into the second CDI module 20 to remove ions from the water 28. As the charge of the second CDI module 20 decreases or approaches capacity, a small amount of water passes from the first storage tank 12 to the second storage tank 14, and then the water 36 in the second storage tank is recirculated through the second CDI module 20, which is set in a discharge mode, before the so-formed second concentrate stream having ions discharged from the second CDI module 20 is passed out of the water purification device 10 via a discharge conduit or drain 26.

[0136] When the water 28 in the first storage tank 12 is of a predetermined purity quality, the water in the first storage tank 12 is ready for use by a user. The water may be released via product water outlet conduit 24 to a suitable point of use as known in the art.

[0137] 3 illustrates a first embodiment of the invention with the addition of a degassing membrane 42 in the conduit to the second capacitive deionization module 20. Degassing membranes are known in the art and are capable of removing dissolved carbon dioxide from the water passing through them. The carbon dioxide is transported from the water through the membrane to the exhaust gas or vacuum in a manner known in the art.

[0138] Figure 4 shows a second embodiment of the present invention. The second water purification apparatus 110 shares all the features of the first water purification apparatus 10 shown in Figure 1, namely, a first storage tank 112, a second storage tank 114, a pump 116, a first CDI module 118, a second CDI module 120, a water supply conduit 122, a product water conduit 124 and a discharge conduit 126, together with the recirculation conduits defined above.

[0139] The second water purification apparatus 110 includes a third water purification device 140 capable of removing both strongly ionized impurities and weakly ionized impurities such as dissolved carbon dioxide or silica, so that the purity of the water can reach a conductivity of less than 1 μS / cm, preferably less than 0.1 μS / cm, and in some cases approaching the maximum level of ionic purity of water of 0.055 μS / cm. One such water purification device is an electrodeionization module.

[0140] The second water purification apparatus 110 may further include a degassing membrane 142. The degassing membrane is shown in the combined conduit from the pump 118, but may be located in one or all of the conduits to the first CDI module 118, the second CDI module 120, or the third water purification device 140. The degassing membrane is preferably located in at least one of the conduits for the second CDI module 120 and the third water purification device 140, since the higher the purity of the water, the more effective it is.

[0141] The second water purification device 110 operates with the same first and second alternating water cycles through the first and second CDI modules 118, 120, with the first and second CDI modules 118, 120 operating in the same charge and discharge modes as described above, until the water 128 in the first storage tank 112 reaches a predetermined or desired water purity, preferably a conductivity of less than 10 μS / cm, and more preferably less than 5 μS / cm.

[0142] The water is then recirculated around the third purification device 140 where ions, including weakly ionized molecules, are removed from the recirculated water. In this manner, the water in the first storage tank 112 may further increase the purity of the water to a conductivity of less than 1 μS / cm.

[0143] FIG. 5 illustrates an alternative arrangement of the components of FIG. 4 in which a third water purification device 140 is located in the conduit from the second CDI module 120 to the product water conduit 124 .

[0144] If the third water purification device 140 is an electrodeionization apparatus, it may be operated either with power applied during purification to produce a concentrate stream or in a separate discharge mode, which may be applied after a set time of operation or after a certain amount of ions have been removed or based on a decrease in performance.

[0145] 6, 7, and 8 show conductivity data from the operating method and apparatus shown in FIG. 3, according to the examples below. EXAMPLES

[0146] 3 with first and second capacitive deionization modules 18, 20, each with a capacitance of 17 meq, was operated to purify 19.3 liters of feed water having a conductivity of 1070 μS / cm that was taken up in a first storage tank 12. The water was recirculated at 1 liter per minute by pump 16, the pressure from which was 0.5 bar.

[0147] FIG. 6 illustrates how the conductivity of the water in the first storage tank 12 decreases during operation of the water purification system 10.

[0148] The first purification stage based on the first purification recirculation loop through the first CDI module 18 in charging mode (as shown in FIG. 2a) lasts for ½ hour or 30 minutes, resulting in a decrease in the conductivity of the water in the first storage tank to 923 μS / cm.

[0149] Then there was a first concentration stage based on the first concentration recirculation loop through the first CDI module 18 in discharge mode (as shown in FIG. 2b), lasting 12 minutes (shown as a gap in the conductivity line in FIG. 6), completing a first alternating set of these first stages.

[0150] Another first purification stage or a second first purification stage based on the first purification recirculation loop through the first CDI module 18 in the charging mode continued for another 30 minutes, lowering the conductivity of the water in the first storage tank 12 to 757 μS / cm. This was followed by a second concentration stage (based on the first concentration recirculation loop through the first CDI module 18 in the discharging mode, shown as a second gap in FIG. 6 ) to complete a second alternating set of the first cycle.

[0151] After eight sets of these first alternating cycles, the water in the first water storage tank 12 was purified using the second CDI module 20 in a manner that performed six sets of second alternating cycles of a second purification stage lasting ½ hour or 30 minutes each time based on a second purification recirculation loop through the second CDI module 20 in a charging mode (as shown in FIG. 2c), followed by a second concentration stage lasting 12 minutes each time (each time shown as a gap in the conductive line in FIG. 6) based on a second concentration recirculation loop through the second CDI module 20 in a discharging mode (as shown in FIG. 2d).

[0152] FIG. 6 shows these 14 sets of first and subsequent second alternating cycles reducing the conductivity of the water in the first storage tank to 11 μS / cm (and in the water of 5 μS / cm conductivity leaving the second CDI module 20). For each of the first four first concentration stages, 680 ml of potable water supply was taken into the second storage tank 14 and used for the concentrate flow to the first CDI module 18, while in the other ten (first and second) concentration stages, 680 ml of concentrate 36 was based on using the partially purified water 28 in the first storage tank 12 taken into the second storage tank 14 (from where it was recirculated around the associated capacitive deionization module depending on the cycle).

[0153] At the end of the purification it was possible to dispense 12.5 liters of water, which was 57% of the total water taken up by the device. EXAMPLES

[0154] FIG. 7 shows how the water exiting the first CDI module during three first purification stages and two alternating first concentration stages changed over the first two hours using the present invention with a different feed water.

[0155] The water purification apparatus used was the same as in Example 1 and is shown in Figure 3. The apparatus was operated with an initial feed water of 19.3 liters, which initially had ionic contamination resulting in a conductivity of 610 μS / cm (time A in Figure 7). This feed water was recirculated by pump at 1 liter per minute with a pressure of 0.5 bar from pump 16 in the first purification stage, as shown in Figure 2a.

[0156] As ions in the water 28 were removed by the first CDI module 18 operating in a charging mode, the conductivity of the water 28 recirculating through the first purification loop decreased until the first CDI module 18 was saturated with ions. As a result, at time B in FIG. 7, the first CDI module 18 was changed to a discharging mode to begin the first concentration stage, as shown in FIG. 2b and as described above. Preferably, this change occurs after the first CDI module 20 has reached a high capacitance, e.g., greater than 70%, and most of its capacity is used. This can be initiated on a time basis or as a consolidation of removed ions.

[0157] At time B, 700 ml of feed water was drawn into the unit and used as the concentrate 36 and recirculated through the first CDI module 18. The first CDI module 18 discharged ions captured by the electrodes during charging until time C was reached, at which time the concentrate was discharged from the water purification device 10 via the discharge conduit 26 and the next first purification stage (shown in FIG. 2a and described above) began. As the first purification / charge and concentrate / discharge cycles continued alternating, the ion content of the water 28 in the first storage tank 12 decreased, resulting in a concentration of 515 μS / cm at point B, 446 μS / cm at point D, and 327 μS / cm at point F.

[0158] The cycling continued to decrease the conductivity of the water 28 through each cycle. After the first four cycles, 700 ml of retentate was removed from the first storage tank 12 to the second storage tank 14 as described above. After the eighth charge and discharge cycle using the first CDI module 18, the second CDI module 20 was used.

[0159] FIG. 8 begins with FIG. 7 and shows how the conductivity of the water now exiting the second CDI module changes based on alternating cycles of 10 seconds to 13 seconds between 6.5 hours and 8.8 hours.

[0160] After 6.5 hours of treatment (time G), the water 28 in the first storage tank 12 fed to the second CDI module 20 had ionic contamination resulting in a conductivity of 46 μS / cm. This water underwent another second purification stage (i.e., recirculated as in FIG. 2c) before the second CDI module 20 while passing through a degassing membrane as shown in FIG. 3. As the ions in the water 28 were removed in the second CDI module 20, the conductivity of the water 28 recirculating around the system dropped until time H. At time H in FIG. 8, the second CDI module was switched to a discharge mode and another second concentration stage was initiated. Preferably, this occurs before the second CDI module 20 reaches a high capacitance, e.g., less than 70%, so that it can be effectively discharged and initiated on a time basis or as an integration of the ions removed.

[0161] The retentate 36 was recirculated according to FIG. 2d to release the ions captured by the electrodes from the second CDI module 20 (shown as a conductivity gap in FIG. 8 until time I), at which time the retentate was released from the water purification device 10 via the release conduit 26 and the next purification charging phase (shown in FIG. 2c and described above) was initiated.

[0162] As the charge and discharge cycles continued, the ionic content of the water 28 in the first storage tank 12 decreased, decreasing to 13 μS / cm at point J in FIG. 8, decreasing to 5 μS / cm at point L, and decreasing to 2.5 μS / cm at point N. By time N, the conductivity of the water in the first storage tank was 2.5 μS / cm, and 62% of the total water that entered the water purification system remained.

[0163] Subsequent discharge of the second CDI module 20 caused the conductivity of the retentate to reach 420 μS / cm, which is lower than the original feed water and can be maintained until the first discharge cycle of the next purification session, thereby further improving the water recovery rate of the device over multiple sessions.

Claims

1. 1. A method for treating a potable water supply to provide a purified water stream having a conductivity of less than 20 μS / cm, comprising: (a) providing the potable water supply to a first storage tank; (b) circulating the feed water in the first storage tank one or more times through a first purified recirculation loop including a first capacitive deionization module in a charging mode to provide a first purified water stream having a lower conductivity than the feed water; (c) circulating the first purified water stream one or more times through a second purified recirculation loop including a second capacitive deionization module in a charging mode to provide a second purified water stream having a lower conductivity than the first purified water stream; At least 1. A method for treating a potable water supply to provide a purified water stream having a conductivity of less than 20 μS / cm, wherein the first and second capacitive deionization modules have a predetermined capacitance prior to discharge, and the second capacitive deionization module operates at a lower capacitance than the first capacitive deionization module.

2. 10. The method of claim 1, wherein the first capacitive deionization module is charged to greater than 70% of its capacity before discharging and the second capacitive deionization module is charged to less than 70% of its capacity before discharging.

3. 3. The method of claim 1 or 2, wherein the first purified recirculation loop and the second purified recirculation loop recirculate from the first storage tank and back to the first storage tank.

4. 4. The method according to claim 1, wherein a portion of the path of the first purification recycle loop is the same as a path of the second purification recycle loop.

5. (d) supplying water to a second storage tank; (e) circulating the water in the second storage tank one or more times through a first concentrate recirculation loop including the first capacitive deionization module in a discharging mode to provide a first concentrate stream; (f) circulating the water in the second storage tank one or more times through a second concentrate recirculation loop including the second capacitive deionization module in a discharging mode to provide a second concentrate stream; and, optionally, 5. The method of claim 1, further comprising: (g) passing the first concentrate stream or the second concentrate stream, or both, to a drain.

6. 6. The method of claim 5, wherein the first concentrate recirculation loop and the second concentrate recirculation loop recirculate from and back to the second storage tank.

7. 7. The method of claim 5 or 6, wherein a portion of the path of the first concentration recirculation loop is the same as the path of the second concentration recirculation loop.

8. 8. The method of claim 5, further comprising providing a first purified water stream from the first storage tank to the first concentrate recirculation loop having the first capacitive deionization module in a discharging mode.

9. 9. The method of claim 5, wherein the water flows in the first purified recirculation loop, the first concentrated recirculation loop, the second purified recirculation loop and the second concentrated recirculation loop are provided by a single pump.

10. 10. The method of claim 9, wherein the pressure from the pump and at all points in the first purified recirculation loop, the first concentrate recirculation loop, the second purified recirculation loop and the second concentrate recirculation loop is maintained below 2 bar, optionally below 1 bar.

11. providing the potable water supply to a first storage tank of step (a); carrying out one or more first alternating cycles of a first water purification stage comprising step (b) and a first water concentration stage comprising step (e); performing one or more second alternating cycles of a second water purification stage comprising step (c) and a second water concentration stage comprising step (f); and passing the first concentrate stream and the second concentrate stream to a drain in step (g).

12. 12. The method of claim 11, wherein the one or more first alternating cycles provide a purified water stream with a conductivity of less than 200 μS / cm.

13. 13. The method of claim 11 or claim 12, wherein the first alternating cycle and the second alternating cycle occur over a period of at least 6 hours.

14. 14. The method of any one of claims 11 to 13, wherein the first alternating cycle and the second alternating cycle occur over a period of less than 12 hours.

15. 15. The method of any one of claims 11 to 14, wherein the first alternating cycles occur at least three times each.

16. 16. The method of any one of claims 1 to 15, capable of providing a purified water stream with a conductivity of less than 10 μS / cm.

17. 17. The method of any one of claims 1 to 16, further comprising passing the water through an electrodeionization device or module prior to dispensing.

18. 20. The method of claim 17, capable of providing a purified water stream with a conductivity of less than 0.2 μS / cm.

19. 19. The method of any one of claims 1 to 18, further comprising passing the water through a degassing membrane before dispensing.

20. 1. A water purification device capable of providing a purified water stream having a conductivity of less than 20 μS / cm from a potable water supply, comprising: Drinking water inlet, A first storage tank; A pump, a first purification recirculation loop from the first storage tank through a first capacitive deionization module in a charging mode and back to the first storage tank; a second storage tank; a first concentrate recirculation loop from the second storage tank through the first capacitive deionization module in a discharging mode and back to the second storage tank; a second purification recirculation loop from the first storage tank through a second capacitive deionization module in a charging mode and back to the first storage tank; a second concentrate recirculation loop from the second storage tank through a second capacitive deionization module in a discharging mode and back to the second storage tank; A purified water outlet; Equipped with 1. A water purification apparatus capable of providing a purified water stream having a conductivity of less than 20 μS / cm from a potable primary water supply, wherein the first and second capacitive deionization modules have a predetermined capacitance before discharging, and the second capacitive deionization module operates at a lower capacitance than the first capacitive deionization module.

21. 21. The water purification device of claim 20, constructed within a single chassis or frame.

22. 22. The water purification device of claim 20 or 21, which is positionable on or under a laboratory bench or mounted on a laboratory wall.

23. 23. The water purification apparatus of any one of claims 20 to 22, wherein the working volume of the second storage tank is less than or equal to 10% of the working volume of the first storage tank.

24. 24. The water purification apparatus of claim 23, wherein the total working volume of water in the first storage tank is less than 20 liters and the total working volume of water in the second storage tank is less than 2 liters.

25. 25. The water purification device of any one of claims 20 to 24, further comprising an electrodeionization device or module prior to dispensing from the water purification device.

26. 26. The water purification device of any one of claims 20 to 25, further comprising a deaeration membrane.

27. 27. The water purification device of any one of claims 20 to 26, further comprising one or more sensors for measuring the conductivity of water within the first purified recirculation loop and / or the purified water outlet.

28. 28. The water purification apparatus of any one of claims 20 to 27, further comprising one or more controls for controlling the flow of water in one or more of the group comprising the first purified recirculation loop, the second purified recirculation loop, the first concentrated recirculation loop, and the second concentrated recirculation loop.

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