APPARATUS AND METHOD FOR PROVIDING PURIFIED WATER

Abstract

There is described a method of treating potable mains feed water to provide a purified water stream of conductivity <20 μS/cm, comprising at least the steps of: (a) providing the potable mains feed water into a first storage tank; (b) circulating the feed water in the first storage tank one or more times through a first purification re-circulation loop including a first capacitive deionisation module in a charging mode to provide a first purified water stream having a conductivity less than the feed water; (c) circulating the first purified water stream one or more times through a second purification re-circulation loop including a second capacitive deionisation module in a charging mode to provide a second purified water stream having a conductivity less than the first purified water stream.

Claims

1. A method of treating potable mains feed water to provide a purified water stream of conductivity <20 μS/cm, comprising at least the steps of: (a) providing the potable mains feed water into a first storage tank; (b) circulating the feed water in the first storage tank one or more times through a first purification re-circulation loop including a first capacitive deionisation module in a charging mode to provide a first purified water stream having a conductivity less than the feed water; and (c) circulating the first purified water stream one or more times through a second purification re-circulation loop including a second capacitive deionisation module in a charging mode to provide a second purified water stream having a conductivity less than the first purified water stream.

2. The method as claimed in claim 1 wherein the first and second capacitive deionisation modules have a predetermined capacity prior to discharge, and wherein the second capacitive deionisation module is operated to a lower capacity than the first capacitive deionisation module.

3. The method as claimed in claim 2 wherein the first capacitive deionisation module is charged to >70% of its capacity prior to discharge, and the second capacitive deionisation module is charged to <70% of its capacity prior to its discharge.

4. The method as claimed in claim 1 wherein the first purification loop and the second purification loop recirculate from and return to the first storage tank.

5. The method as claimed in claim 1 wherein some of the path of the first purification re-circulation loop is the same as the path of the second purification re-circulation loop.

6. The method as claimed in claim 1 further comprising the steps of: (d) providing water into a second storage tank; (e) circulating the water in the second storage tank one or more times through a first concentration re-circulation loop including the first capacitive deionisation module in a discharging mode to provide a first concentrate water stream; (f) circulating the water in the second storage tank one or more times through a second concentration re-circulation loop including the second capacitive deionisation module in a discharging mode to provide a second concentrate water stream; and (g) passing the first concentrate water stream or the second concentrate water stream or both concentrate water streams, to a drain.

7. The method as claimed in claim 6 wherein first concentration loop and the second concentration loop recirculate from and return to the second storage tank.

8. The method as claimed in claim 6 wherein some of a path of the first concentration re-circulation loop is the same as a path of the second concentration re-circulation loop.

9. The method as claimed in claim 6 further comprising providing a first purified water stream from the first storage tank to the first concentration re-circulation loop having the first capacitive deionisation module in a discharging mode.

10. The method as claimed in claim 6 wherein the water is pumped though the first purification recirculation loop, the first concentration recirculation loop, the second purification recirculation loop, and the second concentration recirculation loop by one pump.

11. The method as claimed in claim 10 wherein the pressure out of the pump and at all points in the recirculation loops is maintained at <1 bar.

12. The method as claimed in claim 6 comprising: running one or more first alternating cycles of a first water purification stage comprising step (b), and of a first water concentrating stage comprising step (e); running one or more second alternating cycles of a second water purification stage comprising step (c), and a second water concentrating stage comprising step (f); and passing the first concentrate water stream and the second concentrate water stream to a drain of step (g).

13. The method as claimed in claim 12 wherein the one or more first alternating cycles provide a purified water stream of conductivity <200 μS/cm.

14. The method as claimed in claim 12 wherein the first and second cycles occur over at least 6 hours.

15. The method as claimed in claim 12 wherein the first and second cycles occur over less than 12 hours.

16. The method as claimed in claim 12 wherein the first alternating cycles occur at least three times each.

17. The method as claimed in claim 1 wherein the purified water stream has conductivity <10 μS/cm.

18. The method as claimed in claim 1 further comprising passing water through an electrodeionisation device or module prior to the dispense.

19. The method as claimed in claim 18 wherein the purified water stream has a conductivity <0.2 μS/cm.

20. The method as claimed in claim 19 wherein the electrodeionisation module is located in a third purification re-circulation loop formed or extending from the first storage tank.

21. The method as claimed in claim 1 further comprising passing the water through a degassing membrane prior to dispense.

22. The method as claimed in claim 21 wherein the degassing membrane is located in the second purification re-circulation loop, a third purification re-circulation loop, or a combined section of the two.

23. The method as claimed in claim 1 wherein the volume of purified water having a conductivity <20 82 S/cm is >50% of the volume of the potable mains feed water provided into the first storage tank.

24. A water purification apparatus for providing a purified water stream with conductivity <20 μS/cm from a potable main feed water, comprising: an inlet for potable water; a first storage tank; a pump; a first purification recirculation loop from the first storage tank through a first capacitive deionisation module in a charging mode and returning to the first storage tank; a second storage tank; a first concentration recirculation loop from the second storage tank through the first capacitive deionisation module in a discharging mode and returning to the second storage tank; a second purification recirculation loop from the first storage tank through a second capacitive deionisation module in a charging mode and returning to the first storage tank; a second concentration loop from the second storage tank through the second capacitive deionisation module in a discharging mode and returning to the second storage tank; and an outlet for purified water.

25. The water purification apparatus as claimed in claim 24 constructed in a single chassis, frame or housing.

26. The water purification apparatus as claimed in claim 24 wherein the apparatus is configured to fit on or under a laboratory bench or to be mounted on a laboratory wall.

27. The water purification apparatus as claimed in claim 24 wherein the working volume of the second storage tank is equal to or less than 10% of the first storage tank.

28. The water purification apparatus as claimed in claim 27 wherein the total working volume for water of the first storage tank is less than 20 litres, while the total working volume for water of the second storage tank is less than 2 litres.

29. The water purification apparatus as claimed in claim 24 further comprising an electrodeionisation device or module located to receive the water stream prior to the dispense from the water purification apparatus.

30. The water purification apparatus as claimed in claim 24 further comprising a degassing membrane.

31. The water purification apparatus as claimed in claim 24 further comprising one or more sensors to measure the conductivity of water in the first purification recirculation loop, or in the an outlet for purified water, or both.

32. The water purification apparatus as claimed in claim 24 further comprising one or more control modules to control the flow of water in one or more of the group comprising: the first purification recirculation loop, the second purification recirculation loop, the first concentration recirculation loop, and the second concentration recirculation loop.

Description

[0139] Embodiments of the present invention will now be described by way of example only, and with reference to the accompany drawings in which:

[0140] FIG. 1 is a schematic of a first embodiment of the invention;

[0141] FIGS. 2a-d are a series of schematics showing operation of the first embodiment of the invention:

[0142] FIG. 2a being a first purification stage based on the first capacitive deionisation module in a charging mode,

[0143] FIG. 2b being a first concentrating stage based on the first capacitive deionisation module in a discharging mode,

[0144] FIG. 2c being a second purification stage based on the second capacitive deionisation module in a charging mode; and

[0145] FIG. 2d being a second concentrating stage based on the second capacitive deionisation module in a discharging mode;

[0146] FIG. 3 is a schematic of the first embodiment of the invention with the addition of a degassing membrane in the feed to the second capacitive deionisation module;

[0147] FIG. 4 is a schematic of a second embodiment of the invention;

[0148] FIG. 5 is a schematic of a third embodiment of the invention, and

[0149] FIGS. 6, 7 and 8 are graphical representations of changes in water purity with repeating cycles of the present invention.

[0150] 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 deionisation (CDI) module 18 and a second capacitive deionisation module 20.

[0151] The storage tanks, pumps and CDI modules are connected by tubes, pipes or conduits as known in the art, and indicated by the lines in the accompanying FIGS. 1-5. Operation of the water purification apparatus 10, takes place by a controller such as a microprocessor or programmable logic controller (PLC, not shown). The controller is connected to the pump 16 and such 2-way or 3-way valves as required to cause the water to flow in the tubes, pipes and conduits as necessary to allow the processes described hereafter to take place.

[0152] The water purification apparatus has a feed water inlet conduit 22, which can be connected to any suitable potable mains source of water to be purified, preferably a potable source as supplied by a local water authority. The apparatus also has a product water outlet conduit 24 for the dispense of the purified water at a suitable point of use by a use, and a concentrate water outlet conduit 26 for the removal of wastewater (containing the ions removed) from the apparatus 10.

[0153] FIGS. 2a-d show the operation of the apparatus based on different stages and cycles of a method of the present invention. Those water pathways and components of FIG. 1 used in each stage or cycle are retained in full for clarity. FIG. 2a shows a charging stage of the first CDI 18 as part of a first purification re-circulation loop; FIG. 2b shows a discharging stage of the first CDI 18 as part of a first concentrating re-circulation loop; FIG. 2c shows a charging stage of the second CDI 20 as part of a second purification recirculation loop; and FIG. 2d shows a discharging stage of the second CDI 20 as part of a second concentrating re-circulation loop.

[0154] FIG. 2a shows the steps of providing the potable mains feed water into a first storage tank 12, and circulating the feed water in the first storage tank one or more times through a first purification re-circulation loop including a first capacitive deionisation module 18 in a charging mode to provide a first purified water stream having a conductivity less than the feed water. The feed water enters the storage tank 12 such that there is a volume of water 28 in first storage tank 12. The amount of water in first storage tank 12 may be determined by a level sensor, mass or pressure measurements or determined by flow measurements in the conduit(s), all as known in the art.

[0155] The water 28 then passes from first storage tank 12 into pump 16 via pump feed conduit and suitable valving, and into first CDI module 18 via first CDI module feed conduit 32 and suitable valving. In the first CDI module 18 voltage is applied across the electrodes and ions are drawn into the electrodes such that the water leaving the first CDI module 18 has less ions therein than were in the water entering it, i.e. that it has become partially purified. This partially purified water is then returned to the first storage tank 12 via recirculation conduit 34 and suitable valving to complete the first purification re-circulation loop (12, 30, 16, 32, 18, 34), and to complete one circulation of multiple circulations as a first purification stage. As the recirculation from the first storage tank 12 through the first CDI module 18 in a charging mode proceeds, some of the ions that were in the volume of water 28 in first storage tank 12 are taken up by the electrodes of the first CDI module 18, and the conductivity of the water 28 in the first storage tank 12 reduces.

[0156] The first purification stage can continue for a pre-determined time, or until the water reaches a pre-determined purity. Alternatively or additionally, as the capacity of the electrodes of the first CDI module 18 for ions is limited, there may be a point when no further ions can be taken up on the electrodes, or the efficiency of that take up becomes reduced.

[0157] The apparatus then initiates a first concentrating stage, circulating water in the second storage tank 14 one or more times through a first concentration re-circulation loop including the first capacitive deionisation module 18 in a discharging mode, to provide a first concentrate water stream which can be passed to a drain 26 as shown in FIG. 2b.

[0158] In FIG. 2b, water in the recirculation conduit 34 can be temporarily diverted by suitable valving to the second storage tank 14, until the amount of water 36 in the second storage tank 14 reaches a desired quantity. Desirably, the amount of water 36 in second storage tank 14 is much smaller than the amount of water 28 in first storage tank 12. Alternatively or additionally, a fresh quantity of feedwater is passed directly into second storage tank 14 from the feed water inlet conduit 22. This arrangement can be preferable while operating the first alternating cycles of the present invention.

[0159] Once the second storage tank 14 has the desired amount of water 36 therein, the feed to the pump 16 is changed such that it comes from the second storage tank 14. The water 36 in the second storage tank is passed by pump 16 into the first CDI module 18 and back to the second storage tank by conduits 30, 32 and 34a forming a first concentrating loop (14, 30, 16, 32, 18, 34a) with suitable valving, and to complete one circulation of multiple circulations as a water concentrating stage. The first CDI module 18 is operated in discharge mode. The discharge mode is usually a reversal of the direction of current that was used during the charging mode. Ions on the electrodes pass into the water as it passes through the first CDI module 18 such that the ionic content of the water leaving the first CDI module is greater than that entering the first CDI module 18. As the water 36 in the second storage tank 14 is recirculated in this manner, its ionic content and conductivity increase.

[0160] As the electrodes of the first CDI module 18 become exhausted of ions, the increase in conductivity, monitored by a suitable sensor, reduces or stops. Operation of valves then cause the water exiting the first CDI module 18 to be passed out of the water purification apparatus 10 via a concentrate outlet conduit or drain 26 to complete the first concentrating stage.

[0161] This charging and discharging modes of the first CDI module 18 constitutes one first alternating cycle of the first CDI module 18. By means of the first cycle, ions that were in the water 28 in the first storage tank 12 are ultimately removed from the water purification apparatus 10 in a small amount of concentrate water. The remaining water 28 in the first storage tank 12 is purer, i.e. of a lower ionic content and conductivity than prior to the first cycle.

[0162] By repeating the first alternating cycles of the first water purification stage and the first water concentrating stage, the ionic content of the water 28 in the first storage tank can be sequentially lowered. An example of the pattern of the lowering of the water conductivity is shown in FIG. 7, discussed further hereafter.

[0163] As the purity of the water 28 in the first storage tank increases, the purification quality of the first CDI module 18 becomes limiting. To be able to reach a lower final product water conductivity a second CDI module is used.

[0164] FIGS. 2c and 2d show operation of a charge and discharge cycle of the second CDI module 20. In particular, FIG. 2c shows a second water purification stage based on circulating the first purified water stream one or more times through a second purification re-circulation loop (12, 30, 16, 32, 20, 34) including the second capacitive deionisation module 20 in a charging mode to provide a second purified water stream having a conductivity less than the first purified water stream. FIG. 2d shows a second concentrating stage based on circulating the water in the second storage tank 14 one or more times through a second concentration re-circulation loop (14, 30, 16, 32, 20, 34a) including the second capacitive deionisation module 20 in a discharging mode to provide a second concentrate water stream.

[0165] Together, FIGS. 2c and 2d show a second alternating cycle of the present invention. The cycles occur in a similar manner to that described above for the first CDI module 18.

[0166] The second purification stage starts with recirculation of water 28 from the first storage tank 12 and charging within the second CDI module 20, removing ions from the water 28. Once the second CDI module 20 charging becomes reduced or the second CDI module is close to capacity, a small amount of water is passed from first storage tank 12 to the second storage tank 14, and the water 36 in the second storage tank is then recirculated through the second CDI module 20 now set to be in a discharging mode, before the so-formed second concentrate stream, having the ions expelled from the second CDI module 20, is passed out of the water purification apparatus via the discharge conduit or drain 26.

[0167] When the water 28 in the first storage tank 12 has become of a pre-determined purity quality, the water in the first storage tank 12 is ready for use by a user. The water can be discharged via a product water outlet conduit 24 to a suitable point of use as known in the art.

[0168] FIG. 3 shows the first embodiment of the invention with the addition of a degassing membrane 42 in the conduit to the second capacitive deionisation module 20. Degassing membranes are known in the art and are able to remove dissolved carbon dioxide from water passing through them. The carbon dioxide is transported from the water across a membrane into an exhaust gas or vacuum in a manner known in the art.

[0169] FIG. 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 FIG. 1, i.e. a first storage tank 112, a second storage tank 114, a pump 116, a first CDI module 118, a second CDI module 120, a feedwater conduit 122, a product water conduit 124, and a discharge conduit 126, along with the recirculation conduits as defined above.

[0170] The second water purification apparatus 110 includes a third water purification device 140 able to remove both strongly ionised impurities and weakly ionised impurities such as dissolved carbon dioxide or silica, so that the water purity can reach a conductivity of <1 μS/cm, preferably <0.1 μS/cm, and possibly approaching the maximum level of ionic purity of water of 0.055 μS/cm. One such water purification device is an electrodeionisation module.

[0171] The second water purification apparatus 110 may further include a degassing membrane 142. The degassing membrane is shown in a combined conduit from the pump 118, but may be located in one or all of the conduits into the first CDI module 118, the second CDI module 120, or the third water purification device 140. As the degassing membrane has greater effect the higher the water purity, it is preferably located in at least one of the conduit for the second CDI module 120 and the third water purification device 140.

[0172] The second water purification apparatus 110 is operated with the same first and second alternating cycles of water through the first and second CDI modules 118, 120, the first and second CD1 modules 118, 120 being operated in the same charging and discharging modes as discussed above, until the water 128 in the first storage tank 112 has reached a pre-determined or desired water purity, preferably being a conductivity of <10 μS/cm, more preferably <5 μS/cm.

[0173] The water is then recirculated around the third water purification device 140 where the ions, including weakly ionised molecules, are removed from the recirculating water. In this way the water in the first storage tank 112 can further increase the water purity to a conductivity of <1 μS/cm.

[0174] FIG. 5 shows an alternative arrangement of the components in FIG. 4, with the third water purification device 140 located in the conduit from the second CDI module 120 to the product water conduit 124.

[0175] Where the third water purification device 140 is an electrodeionisation device, it may be operated either with power applied during purification to create a concentrate stream, or with a separate discharging mode, which discharging mode may be applied after a set time of operation, or after a set amount of ions have been removed, or based on a decrease in performance.

[0176] FIGS. 6, 7 and 8 show conductivity data from a method of operation and apparatus as shown in FIG. 3 based on the following Examples.

Example 1

[0177] An apparatus as shown in FIG. 3, with first and second capacitive deionisation modules 18, of capacity of 17 meq each, was operated to purify 19.3 litre of feed water of conductivity of 1070 μS/cm taken into the first storage tank 12. Water was recirculated by the pump 16 at 1 litre per minute, and the pressure out of the pump 16 was 0.5 bar.

[0178] FIG. 6 shows how the conductivity of the water in the first storage tank 12 decreased during operation of the water purification apparatus 10.

[0179] The first purification stage based on the first purification recirculation loop through the first CDI module 18 in a charging mode (as shown in FIG. 2a) lasted ½ hour or 30 minutes, and resulted in the conductivity of the water in the first storage tank decreasing to 923 μS/cm.

[0180] There was then a first concentrating stage based on the first concentrating recirculation loop through the first CDI module 18 in a discharging mode (as shown in FIG. 2b) lasting 12 minutes, (and shown as a gap in the conductivity line in FIG. 6), to complete a first alternating set of these first stages.

[0181] Another or a second first purification stage based on the first purification recirculation loop through the first CDI module 18 in a charging mode lasted for another ½ hour period to reduce the conductivity of the water in the first storage tank 12 down to 757 μS/cm. This was followed by a second concentrating stage (based on the first concentrating recirculation loop through the first CDI module 18 in a discharging mode, and shown as a second gap in FIG. 6) to complete a second alternating set of the first cycles.

[0182] After eight sets of these first alternating cycles, the water in the first water storage tank 12 was then purified using the second CDI module 20 in the manner of six sets of second alternating cycles of the second purification stage based on the second purification recirculation loop through the second CDI module 20 in a charging mode (as shown in FIG. 2c) lasting ½ hour or minutes each time, and then a second concentrating stage (based on the second concentrating recirculation loop through the second CDI module in a discharging mode (as shown in FIG. 2d) lasting 12 minutes each time, (and shown each time as a gap in the conductivity line in FIG. 6.

[0183] FIG. 6 shows these fourteen sets of the first and subsequent second alternating cycles, reducing the conductivity of the water in the first storage tank to 11 μS/cm, (and with water of conductivity of 5 μS/cm exiting the second CDI module 20). For each of the first four first concentrating stages, 680 ml of potable feed water was taken into the second storage tank 14 to be used for the concentrate stream to the first CDI module 18, while for the other ten (first and second) concentrating stages, the 680 ml of concentrate water 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 relevant capacitive deionisation module depending on the cycle).

[0184] At the end of purification 12.5 litres of water was available for dispense, being 57% of the total water taken into the apparatus.

Example 2

[0185] FIG. 7 shows how water exiting a first CDI module during three first purification stages and two alternating first concentration stages, varied over a first 2 hours of using the present invention using another feed water.

[0186] The water purification apparatus used was the same as in Example 1 and as shown in FIG. 3. The apparatus was operated with an initial 19.3 litres of feed water, which initially had an ionic contamination which caused a conductivity of 610 μS/cm, (time A in FIG. 7). This feed water was recirculated by a pump in a first purification stage as shown in FIG. 2a at 1 litre per minute, with 0.5 bar pressure from the pump 16.

[0187] As the ions in the water 28 were removed in the first CDI module 18 running in a charging mode, the conductivity of the water 28 recirculating around the first purification loop reduced, until the first CDI module 18 was becoming saturated with ions, such that at time B in FIG. 7, the first CDI module 18 was changed to discharging mode to start the first concentrating stage as shown in 2b and described above. Preferably this change occurs after the first CDI module 20 reaches a high capacity, e.g >70%, so that most of its capacity has been used. It may be initiated on a time basis or as an integration of ions removed.

[0188] At time B, 700 ml of feed water was taken into the unit to use as concentrate water 36, and this was recirculated through the first CDI module 18, and the first CDI module 18 was discharged of the ions taken up on the electrodes during charging to reach time C. At time C, the concentrate water was discharged from the water purification apparatus 10 via the discharge conduit 26, and the next first purification stage (as shown in FIG. 2a and described above), was initiated. As the first purification/charging and concentrating/discharging cycles alternately continued, the ionic content of the water 28 in the first storage tank 12 was reduced, such that it became 515 μS/cm at point B, 446 μS/cm at point D, and 327 μS/cm at point F.

[0189] The cycles continued in this manner reducing the conductivity of the water 28 through each cycle. After the first four cycles, the 700 ml of concentrate water was taken from the first storage tank 12 into the second storage tank 14 as described above. After the eighth charge and discharge cycles using the first CDI module 18, the second CDI module 20 was used.

[0190] FIG. 8 shows how the conductivity of the water starting from FIG. 7 and now exiting the second CDI module varied between the times of 6.5 hours to 8.8 hours, and based on the tenth to thirteenth second alternating cycles.

[0191] After 6.5 hours of treatment, time G, the water 28 in the first storage tank 12 being fed to the second CDI module 20 had an ionic contamination which resulted in a conductivity of 46 μS/cm. This water underwent another second purification stage (i.e. recirculated as in FIG. 2c), whilst also being passed through a degassing membrane as shown in FIG. 3 before the second CDI module 20. 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 reduced to time H. At time H in FIG. 8, the second CDI module was switched to a discharging mode to start another second concentrating stage. Preferably this occurs before the second CDI module 20 reaches a high capacity, e.g <70%, so that it can be discharged effectively and may be initiated on a time basis or as an integration of ions removed.

[0192] Concentrate water 36 was recirculated as per FIG. 2d, and the second CDI module 20 was discharged of the ions taken up on the electrodes (shown as a gap in the conductivity in FIG. 8 until at time I). At time I, the concentrate water was discharged from the water purification apparatus 10 via discharge conduit 26, and the next purification charging stage (as shown in FIG. 2c and described above) was initiated.

[0193] As the charging and discharging cycles continued, the ionic content of the water 28 in the first storage tank 12 was reduced, such that it was reduced to 13 μS/cm at point J in FIGS. 8, to 5 μS/cm at point L, and to 2.5 μS/cm at point N. By time N, the water in the first storage tank had a conductivity of 2.5 μS/cm, and 62% of the total water that had entered the water purification apparatus remained.

[0194] The subsequent discharging of second CDI module caused the concentrate water to reach a conductivity of 420 μS/cm. As this conductivity is less than the initial feed water, this could be retained for the first discharge cycle of the next session of water purification thereby further improving the water recovery of the apparatus over multiple sessions.