WO2021110590A1

WO2021110590A1 - Waste water treatment system and method of treating waste water

Info

Publication number: WO2021110590A1
Application number: PCT/EP2020/083920
Authority: WO
Inventors: Cécile DEKEUWER; Carine MINEAU; Arthur Arash MOFAKHAMI
Original assignee: Weco Sas
Current assignee: Weco Sas
Priority date: 2019-12-05
Filing date: 2020-11-30
Publication date: 2021-06-10
Anticipated expiration: 2022-06-05
Also published as: CN115066401A; EP4069647A1

Abstract

The disclosure relates to waste water treatment. A flow of an aqueous solution comprising a chloride salt is electrolysed between an anode and a cathode of an electrolysis cell. The flow of aqueous solution is separated from the anode by a first ion-exchange structure and from the cathode by a second ion-exchange structure. A first auxiliary flow of liquid is driven through a first auxiliary region between the anode and the first ion-exchange structure during the electrolysis. A second auxiliary flow of liquid is driven through a second auxiliary region between the cathode and the second ion-exchange structure during the electrolysis. The first auxiliary flow, or liquid from the first auxiliary flow, is used to treat waste water.

Description

WASTE WATER TREATMENT SYSTEM AND METHOD OF TREATING

WASTE WATER

The present disclosure relates to treating waste water, such as waste water from toilet, bathroom or kitchen facilities. The disclosure is particularly applicable to providing mobile or temporary facilities where access to power and/or fresh water may be limited.

Various approaches for treating waste water from toilets are known.

US6523186 B2, for example, discloses a recycling system that can completely decompose human or animal wastewater, as well as biodegradable solid or liquid by products in water. The disclosed system relies on a series of bioreactors to decompose waste water. Forced aeration is used to boost the decomposition but the process is still relatively slow, requiring more than 30 hours to provide effective treatment. Furthermore, the required apparatus is heavy and bulky, requiring many large tanks to implement.

IKEMATSU, M. et al. Electrolytic Treatment of Human Urine to Remove Nitrogen and Phosphorus. Chemistry letters, 2006, vol. 35, no 6, p. 576-577 discloses an alternative approach in which electrolysis is used to treat urine. The electrolysis decreases levels of nitrogen and phosphorus levels in domestic wastewater.

KIM et al. “Electrolysis of urea and urine for solar hydrogen.” Catalysis Today, 2013, vol. 199, p. 2-7, discloses electrolysis of urine mixed with salt, which was found to produce chorine species that promote effective treatment of water. The chorine species disinfect and oxidize organic and inorganic materials. Parasitic chemical reactions reduce the efficiency of the electrochlorination and can cause degradation (e.g. scaling) of electrodes. The electrolysis also produces mixtures of gases that need to be managed to ensure safety.

It is an object of the invention to provide an alternative approach for treating waste water that at least partially addresses one or more shortcomings in the prior art.

According to an aspect of the invention, there is provided a waste water treatment system, comprising: an electrolysis unit comprising at least one electrolysis cell, the electrolysis unit being configured to apply a voltage between an anode and a cathode of each electrolysis cell to electrolyse a flow of an aqueous solution comprising a chloride salt through the electrolysis cell, wherein the flow of the aqueous solution is separated from the anode in each electrolysis cell by a first ion- exchange structure in the electrolysis cell and is separated from the cathode in each electrolysis cell by a second ion-exchange structure in the electrolysis cell; and a flow management system configured, for each electrolysis cell, to: drive the flow of aqueous solution through a primary region of the electrolysis cell; drive a first auxiliary flow of liquid through a first auxiliary region of the electrolysis cell between the anode and the first ion-exchange structure during the electrolysis; drive a second auxiliary flow of liquid through a second auxiliary region of the electrolysis cell between the cathode and the second ion-exchange structure during the electrolysis; and use the first auxiliary flow, or liquid from the first auxiliary flow, to treat waste water received by the system.

Thus, a waste water treatment system is provided which uses ion-exchange structures to separate products of an electrolysis process performed on an aqueous solution comprising a chloride salt (e.g. brine) and uses these products to improve the efficiency of the treatment. As exemplified below, this action allows subsets of products to be used in separate processes to improve multiple aspects of the performance, as well as reducing some undesirable parasitic chemical reactions between products. The reduction of parasitic chemical reactions enables the liquid from the first auxiliary flow to have more powerful disinfecting properties than is readily possible using alternative approaches based on electrolysis in the absence of ion-exchange structures. Treatment may be performed more quickly and/or using less energy.

In some embodiments, the using of the first auxiliary flow to treat the waste water comprises incorporating at least a portion of the waste water into the first auxiliary flow through the first auxiliary region of the electrolysis cell. Thus, in embodiments of this type a portion of the waste water to be treated passes through the electrolysis unit. This approach allows the waste water to be treated both by the liquid of the first auxiliary flow (including products of the electrolysis process such as HCIO that have beneficial properties) and by the electrolysis process directly (so as to subject contamination in the waste water to electrochemical reactions), which may result in a higher level of treatment of the waste liquid than is possible without subjecting the waste liquid directly to the electrolysis process. The added benefit of subjecting the waste liquid to the electrolysis process directly in this manner may depend on the composition of the waste liquid to be treated and/or on the susceptibility of contaminants in the waste liquid to being broken down or otherwise desirably transformed by the electrolysis process).

In some embodiments, the using of the liquid from the first auxiliary flow to treat the waste water comprises mixing liquid extracted from the first auxiliary flow with the waste water. In embodiments of this type, the liquid extracted from the first auxiliary flow may be mixed with the waste water without allowing the waste water to flow through the first auxiliary region of the electrolysis cell. The arrangement does not therefore require any portion of the waste water itself to pass through the electrolysis unit, thereby obviating the need to add salt directly to the waste water (which could interfere with bacterial pretreatment), as well as reducing the risk of clogging or scale build up in the electrolysis unit.

In an embodiment, the first ion-exchange structure is configured to allow anions to pass through the first ion-exchange structure during the electrolysis and thereby produce HCIO and O2 in the first auxiliary flow. Thus, the first auxiliary flow can be made to contain high levels of HCIO. HCIO is known to be highly effective in treating polluted water (e.g. blackwater or greywater). HCIO provides an acidic environment (typically pH<3.5) having a high efficacy in destroying a wide range of bacteria and fungi, as well as oxidizing a range of inorganic pollutants commonly present in wastewater and providing a decolouring action. HCIO also has a desirable deodorant action partly attributable to its ability to oxidise inorganic odour generating compounds. The use of HCIO also minimises levels of undesirable components such as trihalomethanes (THM) and organochlorine by-products of the disinfection process after the treatment. In alternative approaches based on electrolysis of aqueous salt solution in the absence of ion-exchange structures, parasitic reactions lead to formation of NaCIO at the expense of HCIO. NaCIO has a disinfectant action but is considerably less powerful than HCIO and tends to leave behind high levels of THM and organochlorine by-products.

The use of ion-exchange structures to provide HCIO instead of NaCIO thus allows waste water to be treated more efficiently and quickly.

In an embodiment, O2 liberated in the first auxiliary flow is prevented from mixing with ¾ liberated in the second auxiliary flow. Preventing mixing of the O2 and ¾ gases, which are produced in stoichiometric quantities, avoids any risk of explosion without requiring any special venting or other countermeasures. In an embodiment, the system is further configured to use liquid from the second auxiliary flow to treat the waste water. Using the liquid from the second auxiliary flow provides a further stage of treatment and improves the quality of treatment. The liquid from the second auxiliary flow, which in some embodiments contains NaOH for example, increases the pH of the waste water being treated. Treatment using NaOH at the higher pH (e.g. pH>7) desirably promotes destruction of organochlorine by-products.

In an embodiment, the system is configured to use liquid from the second auxiliary flow to adjust a pH of waste water treated by the first auxiliary flow, or by liquid from the first auxiliary flow, to be in the range of 6.5 < pH < 8.5. The treatment by the liquid from the first auxiliary flow will typically reduce the pH of treated waste waters to levels that are too acidic to be suitable for reuse. The liquid in the second auxiliary flow can be used to raise the pH to a level that is near enough to neutral pH to make the treated waste water (which may at this stage consist of relatively clean water) safe for reuse (e.g. for use in a toilet flush, for hand washing, plant watering, or even for drinking). As mentioned above, this raising of the pH may also have the side effect of promoting destruction of any organochlorine by-products from the treatment by the liquid from the first auxiliary flow.

In an embodiment, the system further comprises a bioreactor unit configured to use bacteria to treat waste water received by the system. The bioreactor uses bacteria to biodegrade components of the waste water.

In an embodiment, the system is configured to direct O2 produced in the first auxiliary flow by the electrolysis to the bioreactor unit. Thus, O2 produced in the first auxiliary flow as a side effect of the electrolysis can be used to boost aerobic activity of bacteria in the bioreactor unit. Performance of the bioreactor unit can thus be improved without having to provide separate apparatus or energy consumption to provide O2 from a different source.

In an embodiment, the system is configured to direct ¾ produced in the second auxiliary flow by the electrolysis to an energy storage system. Thus, ¾ produced in the second auxiliary flow as a side effect of the electrolysis can be used as an energy source, allowing reuse of energy and thereby reducing the overall energy consumption of the system.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 depicts example integration of a waste water treatment system with a reservoir containing treated water and a toilet generating waste water to be treated;

Figure 2 schematically depicts an electrolysis unit of a waste water treatment system;

Figure 3 is a schematic side sectional view of an electrolysis cell depicting flows through different regions of the electrolysis cell;

Figure 4 schematically depicts an example first flow management unit for use in the system of Figure 2, the first flow management unit being configured in this example to extract liquid from the first auxiliary flow and mix the extracted liquid with waste water to treat the waste water;

Figure 5 schematically depicts an alternative first flow management unit for use in the system of Figure 2, the first flow management unit being configured in this example to treat the waste water by incorporating at least a portion of the waste water into the first auxiliary flow;

Figure 6 is a schematic side sectional view depicting two electrolysis cells connected together in series; and

Figure 7 is a schematic side sectional view depicting three electrolysis cells connected together electrically in parallel.

The present disclosure relates to an improved waste water treatment system 100. Figure 1 depicts an example context in which the waste water treatment system 100 may be used (i.e. to receive waste water from a toilet facility in this case). The waste water treatment system 100 may also be used in other similar contexts, such as where waste water is generated from bathroom and/or kitchen facilities.

In an embodiment, as depicted in Figure 1, waste water from a toilet facility 2 is fed from the toilet facility 2 to waste water treatment system 100 (flow 101). The waste water treatment system 100 treats the waste water and outputs treated water (flow 103). In the embodiment shown, the treated water is fed to a reservoir 8. The reservoir 8 stores treated water until it is needed. In an embodiment, the treated water is fed from the reservoir 8 back to the toilet facility 2 (flow 104). The treated water may be used as flushing water for a toilet and/or as water for cleaning hands in a wash basin).

The waste water comprises polluted water from a toilet (sometimes referred to as blackwater or wastewater). In an embodiment, as depicted in Figure 1, the waste water treatment system 100 comprises a bioreactor unit 4. The bioreactor unit 4 uses bacteria to treat waste water received by the waste water treatment system 100. The bioreactor biodegrades unwanted components within the waste water, thereby providing a first step towards providing treated water that can be reused. In an embodiment, the bioreactor unit 4 comprises a filtration system for separating solid matter from liquid matter. An output from the bioreactor unit 4 is fed (flow 102) to an electrolysis unit 6. The bioreactor unit 4 is thus upstream from the electrolysis unit 6 and thereby provides a pre-treatment of the waste water.

An example configuration for the electrolysis unit 6 is depicted in Figure 2. In embodiments of this type, the electrolysis unit 6 comprises at least one electrolysis cell 25. The electrolysis unit applies a voltage between an anode 10 and a cathode 11/12 of each electrolysis cell 25. The voltage is applied by voltage source 54. A flow 14 of a solution comprising a chloride salt (e.g. water containing a high concentration of NaCl, also known as brine) is provided through each electrolysis cell 25. The voltage between the anode 10 and the cathode 11/12 electrolyses the flow 14 of aqueous solution. In the example of Figure 2, the flow 14 of aqueous solution flows through a central region 40 where the electrolysis occurs.

The chloride salt comprises a choride anion. The chloride salt further comprises one or more cations. Each cation may be any suitable cation but typically the one or more cations are selected from alkali metal cations and alkaline earth metal cations. Typically, the one or more cations comprise sodium cations. The aqueous solution may therefore comprise at least NaCl. NaCl is widely available and provides an efficient implementation of the water treatment mechanisms described below.

The flow 14 of the aqueous solution is separated from the anode 10 in each electrolysis cell 25 by a first ion-exchange structure 21 in the electrolysis cell 25. The flow 14 of aqueous solution is separated from the cathode 11/12 in each electrolysis cell 25 by a second ion-exchange structure 22 in the electrolysis cell 25.

A flow management system is provided to drive flows of liquid through different regions of each electrolysis cell 25. The flow management system may comprise any combination of pumps, valves, filters, conduits, reservoirs and/or controllers suitable for performing the functionalities described below.

In an embodiment, the flow management system drives the flow 14 of aqueous solution through the central region 40 (which may be referred to also as a primary region herein) of each electrolysis cell 25. In an embodiment, as depicted in Figure 2, the flow 14 of aqueous solution is provided as a circulatory flow in a flow circuit (so that the aqueous solution is recirculated through the central region 40 repeatedly). In an embodiment, the flow circuit is connected to a salt reservoir unit 51. A controller 200 may be provided that controls a concentration of salt in the flow 14 of aqueous solution by controlling addition of salt from the salt reservoir unit 51 to the flow 14 of aqueous solution. A salt sensor may be provided for measuring a concentration of the salt and an output from the salt sensor may be provided to the controller 200.

In an embodiment, the flow management system drives a first auxiliary flow 31 of liquid (comprising water for example) through a first auxiliary region 41 of the electrolysis cell 25 during the electrolysis. The first auxiliary region 41 is between (e.g. delimited by) the anode 10 and the first ion-exchange structure 21. In an embodiment, as depicted in Figure 2, the first auxiliary flow 31 is provided as a circulatory flow in a flow circuit (so that the liquid is recirculated through the first auxiliary region 41 repeatedly). In an embodiment, the flow circuit is connected to, and managed by, a first flow management unit 52. Two example configurations for the first flow management unit 52 are depicted in Figures 4 and 5 and discussed further below.

In an embodiment, the flow management system also drives a second auxiliary flow 32 of liquid (comprising water for example) through a second auxiliary region 42 of the electrolysis cell 25 during the electrolysis. The second auxiliary region 42 is between (e.g. delimited by) the cathode 11/12 and the second ion-exchange structure 22. In an embodiment, as depicted in Figure 2, the second auxiliary flow 32 is provided as a circulatory flow in a flow circuit (so that the liquid is recirculated through the second auxiliary region 42 repeatedly). In an embodiment, the flow circuit is connected to, and managed by, a second flow management unit 53.

In some embodiments, as exemplified schematically in Figures 2, 3, 6 and 7, the anode 10, cathode 11/12, first ion-exchange structure 21, and second ion exchange structure 22 are substantially planar and parallel with each other. The regions 40-42 through which flow is driven are formed by spaces between the planar and parallel elements (which may be sealed around the peripheral edges to form respective chambers, with openings to allow entry and exit of the flows 14/31/32 into the chambers). The respective flows 14/31/32 through the different regions 40-42 (chambers) are separated from each other by the first and second ion-exchange structures 21 and 22 except for certain ions that are allowed to pass through the structures 21 and 22. Ion-exchange structures are well known in the art. Any type of ion-exchange structure which is suitable for providing the functionality described herein, in particular for allowing the ions discussed below to pass through them with little or no passage of water, could be used. Each of the first ion-exchange structure 21 and the second ion-exchange structure 22 may, for example, comprise an ion-exchange membrane or an ion-exchange separator. For example, either or both of a Nation^® ion-exchange membrane or a Zirfon ion-exchange separator could be used.

Figure 3 schematically depicts flow of ions between the different regions 40- 42 during electrolysis in an electrolysis cell 25 of the type described above.

The first ion-exchange structure 21 is configured to allow Cl ions and OH ions to pass through the first ion-exchange structure 21 during the electrolysis and thereby produce HCIO and O2 in the first auxiliary flow 31 of liquid.

The second ion-exchange structure 22 is configured to allow H⁺ ions and one or more metal cations, selected from alkali metal cations and alkaline earth metal cations, to pass through the second ion-exchange structure 22 during the electrolysis and thereby produce Fh and one or more compounds of the form XOH in the second auxiliary flow, where X is a metal. Figure 3 depicts an example in which the one or more metal cations comprise Na⁺ cations, such that at least Fh and NaOH are produced in the second auxiliary flow 32. This corresponds to the typical case where the aqueous solution comprises at least NaCl (or where NaCl is the only salt present).

The first auxiliary flow 31 , or liquid from the first auxiliary flow 31 , is used to treat waste water received by the waste water treatment system 100. In the embodiment of Figures 1 and 2, waste water is treated by the bioreactor unit 4 before being treated by the liquid from the first auxiliary flow 31. In the embodiment shown in Figure 2, a flow 102 from the bioreactor unit 4 is provided to the first flow management unit 52. The first reservoir management unit 52 either adds liquid from the first auxiliary flow 31 to waste water from flow 102 to provide an output of treated water (flow 103 A), as described below with reference to Figure 4, or incorporates at least a portion of the waste water from flow 102 into the first auxiliary flow 31 to treat the waste water and provide the output of treated water (flow 103 A). In both approaches, the treatment using the first auxiliary flow 31 , or using liquid from the first auxiliary flow 31 , comprises treatment by the powerful disinfecting action of HC10 in (or from) the first auxiliary flow 31.

Figure 4 depicts the first flow management unit 52 in an embodiment in which the waste water is treated using liquid extracted from the first auxiliary flow 31. In this embodiment, the first flow management unit 52 comprises a waste water flow control unit 511 and a first auxiliary flow control unit 512. The waste water flow control unit 511 receives waste water to be treated in flow 102. The first auxiliary flow control unit 512 interacts with the first auxiliary flow 31. The first auxiliary flow 31 may flow through the first auxiliary flow control unit 512. The first auxiliary flow control unit 512 may be additionally configured to drive the first auxiliary flow 31 and/or monitor a composition of liquid in the first auxiliary flow 31. In the present embodiment, the first auxiliary flow control unit 512 is configured to controllably extract liquid from the first auxiliary flow 31. The first auxiliary flow control unit 512 directs liquid extracted from the first auxiliary flow (in flow 521) from the first auxiliary flow control unit 512 to the waste water flow control unit 511. The waste water flow control unit 511 mixes the liquid extracted from the first auxiliary flow 31 with the waste water provided in flow 102. The mixing with the liquid from the first auxiliary flow 31 treats the waste water from flow 102 to provide the treated water (flow 103 A). The waste water flow control unit 511 outputs the treated water in flow 103 A. The liquid extracted from the first auxiliary flow 31 can be mixed with the waste water without allowing the waste water to flow through the first auxiliary region 41 of the electrolysis cell 25.

In embodiments such as that of Figure 4 in which liquid is extracted from the first auxiliary flow 31 without any waste water contaminating the first auxiliary flow 31 itself, the first auxiliary flow control unit 512 may be configured to provide an additional output of liquid (flow 522 in Figure 4) from the first auxiliary flow 31 for uses other that treating the waste water in flow 102. As described above, the liquid from the first auxiliary flow may contain high levels of HC10, which has various beneficial properties. The additional output (flow 522) may be used for example to provide disinfectant for manual cleaning of surfaces in a toilet, bathroom or kitchen facility. A suitable valve such as a tap may be provided for controlling flow 522 in the additional output.

In an embodiment, the treatment may be performed in batches. In such an embodiment, the first auxiliary flow 31 may be driven through the electrolysis cell 25 until a desired concentration of HCIO is achieved in the liquid of the first auxiliary flow 31. A portion of the liquid of the first auxiliary flow 31 may then be directed (flow 521) into a batch (e.g. a predetermined volume) of waste water from flow 102 to treat that batch of waste water. The batch may be temporarily held in a reservoir in the waste water flow control unit 511. Liquid may then be added to the first auxiliary flow 31, the first auxiliary flow 31 may be driven through the electrolysis cell 25 again until a desired concentration of HCIO is again achieved in the liquid of the first auxiliary flow 31 , and a portion of the liquid of the first auxiliary flow 31 may be directed into a new batch of waste water from flow 102. The process can then be repeated to treat multiple batches of waste water, as required.

Figure 5 depicts the first flow management unit 52 in an embodiment in which the using of the first auxiliary flow 31 to treat the waste water comprises incorporating at least a portion of the waste water into the first auxiliary flow 31 through the first auxiliary region 41 of the electrolysis cell 25. In this embodiment, the first flow management unit 52 comprises a waste water flow control unit 511 and a first auxiliary flow control unit 512. The waste water flow control unit 511 receives waste water to be treated in flow 102. The first auxiliary flow control unit 512 interacts with the first auxiliary flow 31. The first auxiliary flow 31 may flow through the first auxiliary flow control unit 512. The first auxiliary flow control unit 512 may be additionally configured to drive the first auxiliary flow 31 and/or monitor a composition of liquid in the first auxiliary flow 31. In the present embodiment, the first auxiliary flow control unit 512 is configured to receive waste water (flow 531) from the waste water flow control unit 511 and direct the received waste water into the first auxiliary flow 31 (such that the waste water passes through the first auxiliary region 41 of the electrolysis cell 25). Products from the electrolysis (e.g. HCIO), as well as the electrolysis process itself, treat the waste water while the waste water is circulated through the first auxiliary region 41 of the electrolysis cell 25). When the waste water is sufficiently treated, the waste water is directed back to the waste water flow control unit 511 (flow 532). The waste water flow control unit 511 uses the treated waste water received in flow 532 to provide an output of treated water in flow 103 A (e.g. by redirecting the treated waste water received in flow 532 directly into flow 103 A).

As with the embodiment of Figure 4, the treatment may be performed in batches. In such an embodiment, each batch of waste water to be treated may be circulated in the first auxiliary flow 31 until the batch is sufficiently treated. When the batch is sufficiently treated (determined, for example, by calibration to determine a suitable treatment time or by measurements of composition), the batch is output in flow 103 A and a new batch is incorporated into the first auxiliary flow 31.

In some embodiments, liquid from the second auxiliary flow 32 is also used to treat waste water received by the water treatment system 100. Typically, each volume of waste water (e.g. each batch as discussed above) treated using the first auxiliary flow 31 , or using liquid from the first auxiliary flow 31 , is treated at different respective times using the first auxiliary flow 31 , or using liquid from the first auxiliary flow 31, and by liquid from the second auxiliary flow 32. Typically, each of these volumes of waste water is treated using the first auxiliary flow 31 , or using liquid from the first auxiliary flow 31, before being treated by liquid from the second auxiliary flow 32. In the example shown in Figure 2, a flow 33 of liquid from the second reservoir unit 53 is added to the flow 103 A output from the first flow management unit 52 downstream from the first flow management unit 52 to provide flow 103B. In an embodiment, the treatment by the liquid from the second auxiliary flow 32 comprises treatment by NaOH in the second auxiliary flow 32. In an embodiment, the treatment may be performed in batches (optionally synchronized with the treatment in batches using the first auxiliary flow 31 , or using liquid from the first auxiliary flow 31, described above). In such an embodiment, the second auxiliary flow 32 may be driven through the electrolysis cell 25 until a desired concentration of NaOH is achieved in the liquid of the second auxiliary flow 32. A portion of the liquid of the second auxiliary flow 32 may then be directed into a batch of treated water in flow 103 A to treat that batch of treated water. Liquid may then be added to the second auxiliary flow 32, the second auxiliary flow 32 may be driven through the electrolysis cell 25 again until a desired concentration of NaOH is again achieved in the liquid of the second auxiliary flow 32, and a portion of the liquid of the second auxiliary flow 32 may be directed into a new batch of treated water in flow 103 A. The process can then be repeated to treat multiple batches of treated water in flow 103 A, as required.

The treatment using the first auxiliary flow 31 , or using liquid from the first auxiliary flow 31, causes the flow 103 A output from the first flow management unit 52 to have an acidic pH (due to the presence of HCIO). In some embodiments, the system 100 is configured to use liquid from the second auxiliary flow 32 to adjust a pH of waste water treated using the first auxiliary flow 31 , or using liquid from the first auxiliary flow of liquid 31. The adjustment may comprise making the pH in the flow 103 A less acidic to provide a flow 103B that is more suitable for safe reuse. The adjustment may be made before the flow 103 A is provided to the reservoir 8. The liquid from the second auxiliary flow 32 raises the pH due to the presence of NaOH.

In an embodiment, the amount of liquid from the second auxiliary flow 32 and/or the concentration of NaOH in the second auxiliary flow 32 is controlled (e.g. by a controller 200) in order to achieve a desired pH in the flow 103 (e.g. a pH in a safe range 6.5 < pH < 8.5).

As described above, in addition to respectively generating HCIO and NaOH in the first and second auxiliary flows 31 and 32, the electrolysis also respectively generates O2 and ¾ in the regions 41 and 42. The O2 and ¾ are generated in stoichiometric quantities and need to be managed to avoid an explosion risk. In prior art arrangements for electrolysing aqueous solution, the risk of explosion could be avoided by providing suitable venting, but this can add cost or equipment bulk and may not be feasible or safe in all circumstances. In embodiments of the present disclosure, the presence of the first and second ion-exchange structures 21 and 22 allows the gases to be managed more efficiently and even allows the gases to be put to useful effect. In an initial step, the flow management system is configured such that O2 liberated in the first auxiliary flow 31 (e.g. in first auxiliary region 41) is directed out of the electrolysis unit 25 without mixing with ¾ liberated in the second auxiliary flow 32 (e.g. in the second auxiliary region 42). This may be achieved for example by providing suitable ducting to allow gases liberated from the respective first and second auxiliary flows 31 and 32 to be separately channelled away as distinct separate gas flows 105 and 106. Thus, gas flow 105 comprises a high concentration of O2 and a very low concentration of ¾ (or substantially no ¾) and gas flow 106 comprises a high concentration of ¾ and a very low concentration of O2 (or substantially no O2).

In an embodiment, as depicted schematically in Figure 1, an oxygen gas flow system 60 is provided to direct O2 produced in the first auxiliary flow 31 (e.g. in flow 105) to the bioreactor unit 4. The oxygen gas flow system 60 may comprise any suitable combination of pumps, ducting, valves, filters and/or other components to achieve this functionality. Thus, O2 produced in the first auxiliary flow 31 as a side effect of the electrolysis can be used to boost aerobic activity of bacteria in the bioreactor unit 4. Performance of the bioreactor unit 4 can thus be improved without having to provide separate apparatus or energy consumption to provide O2 from a different source. The oxygen gas flow system 60 may also act to keep O2 safely away from Fb generated by the electrolysis. In an embodiment, the bioreactor unit 4 comprises a forced aeration unit 5 configured to bubble the O2 and/or outside air through a region in the bioreactor unit 4 containing bacteria to improve the efficiency of uptake of the gases by the bacteria and maximize the beneficial effects of providing the gases. The bubbling of gases may comprise driving of nanobubbles through the material to maximise exposure of bacteria to the gases.

In an embodiment, as depicted schematically in Figure 1, a hydrogen gas flow system 62 is provided to direct Fb produced in the second auxiliary flow 32 (e.g. in flow 106) to an energy storage system 10. The hydrogen gas flow system 62 may comprise any suitable combination of pumps, ducting, valves, filters and/or other components to achieve this functionality. Thus, Fb produced in the second auxiliary flow 32 as a side effect of the electrolysis can be used as an energy source, allowing reuse of energy and thereby reducing the overall energy consumption of the system.

In an embodiment, the energy storage system 10 comprises a fuel cell. In an embodiment, the energy storage system 10 is used to at least partly drive the forced aeration unit 5 (e.g. to drive a pump of the forced aeration unit 5), as indicated by energy flow 121 in Figure 1. Alternatively or additionally, the energy storage system 10 may be used to at least partly drive the electrolysis unit 6 (e.g. to apply voltages for the electrolysis and/or to pump liquids in one or more of the flows 14/31/32), as indicated by energy flow 122 in Figure 1.

In the embodiment shown in Figures 2 and 3, the electrolysis unit 6 comprises a single electrolysis cell 25. In other embodiments, as exemplified in Figures 6 and 7, the electrolysis unit 6 comprises a plurality of electrolysis cells 25. The provision of multiple cells may allow the electrolysis unit 6 to have a larger output. In some embodiments of this type, at least two of the electrolysis cells 25 share an anode or a cathode. Sharing electrodes in this way reduces the total number of electrodes that are needed, thus reducing device cost and/or improving compactness. Figures 6 and 7 show two different possible ways in which electrodes can be shared.

In one class of embodiments, exemplified in Figure 6, at least one pair of electrolysis cells 25 that share an anode 10 or a cathode 11/12 are connected together electrically in series. The electrical connection in series means that a voltage applied to the pair by the electrolysis unit 6 results in a voltage of the shared anode 10 or cathode 11/12 of the pair being at an intermediate value between voltages of the two other electrodes of the pair. In the example of Figure 6, the shared electrode is the cathode 11 in the middle and the other electrodes of the pair are the anode 10 on the left and the cathode 12 on the right. In this example, the cathode 11 will therefore be held at an intermediate value (e.g. halfway) between the voltages of the anode 10 and the cathode 12.

In another class of embodiments, exemplified in Figure 7, at least one pair of the electrolysis cells 25 that share an anode 10 or a cathode 11 are connected together electrically in parallel. The connection in parallel may result in a voltage applied to the pair by the electrolysis unit 6 causing a voltage of the shared anode 10 or cathode 11 of the pair to have opposite polarity to both of the other electrodes of the pair. In the example of Figure 7, two pairs of electrolysis cells 25 are provided. The shared electrode of the pair on the left is the leftmost cathode 11 and the shared electrode of the pair on the right is the rightmost anode 10. In this example, the middle electrolysis cell 25 thus shares each of its electrodes with a respective electrolysis cell 25 on each side.

Claims

1. A waste water treatment system, comprising: an electrolysis unit comprising at least one electrolysis cell, the electrolysis unit being configured to apply a voltage between an anode and a cathode of each electrolysis cell to electrolyse a flow of an aqueous solution comprising a chloride salt through the electrolysis cell, wherein the flow of the aqueous solution is separated from the anode in each electrolysis cell by a first ion-exchange structure in the electrolysis cell and is separated from the cathode in each electrolysis cell by a second ion-exchange structure in the electrolysis cell; and a flow management system configured, for each electrolysis cell, to: drive the flow of aqueous solution through a primary region of the electrolysis cell; drive a first auxiliary flow of liquid through a first auxiliary region of the electrolysis cell between the anode and the first ion-exchange structure during the electrolysis; drive a second auxiliary flow of liquid through a second auxiliary region of the electrolysis cell between the cathode and the second ion-exchange structure during the electrolysis; and use the first auxiliary flow, or liquid from the first auxiliary flow, to treat waste water received by the system.

2. The system of claim 1, wherein the using of the first auxiliary flow to treat the waste water comprises incorporating at least a portion of the waste water into the first auxiliary flow through the first auxiliary region of the electrolysis cell.

3. The system of claim 1, wherein the using of the liquid from the first auxiliary flow to treat the waste water comprises mixing liquid extracted from the first auxiliary flow with the waste water.

4. The system of claim 3, wherein the liquid extracted from the first auxiliary flow is mixed with the waste water without allowing the waste water to flow through the first auxiliary region of the electrolysis cell.

5. The system of any preceding claim, wherein the first ion-exchange structure is configured to allow anions to pass through the first ion-exchange structure during the electrolysis and thereby produce HCIO and O2 in the first auxiliary flow.

6. The system of claim 5, wherein the anions comprise Cl and OH ions.

7. The system of any preceding claim, wherein the second ion-exchange structure is configured to allow H⁺ ions and one or more metal cations, selected from alkali metal cations and alkaline earth metal cations, to pass through the second ion- exchange structure during the electrolysis and thereby produce ¾ and one or more compounds of the form XOH in the second auxiliary flow, where X is a metal.

8. The system of claim 7, wherein the one or more metal cations comprises Na⁺ cations, such that at least ¾ and NaOH are produced in the second auxiliary flow.

9. The system of any preceding claim, wherein the aqueous solution comprises at least NaCl.

10. The system of any preceding claim, wherein each of the first ion-exchange structure and the second ion-exchange structure comprises an ion-exchange membrane or an ion-exchange separator.

11. The system of any preceding claim, wherein O2 liberated in the first auxiliary flow is prevented from mixing with ¾ liberated in the second auxiliary flow.

12. The system of any preceding claim, wherein the system is further configured to use liquid from the second auxiliary flow to treat the waste water.

13. The system of claim 12, wherein each volume of waste water treated by liquid from the first auxiliary flow is treated at a different time by the liquid from the second auxiliary flow.

14. The system of claim 13, wherein each volume of waste water treated using the first auxiliary flow, or using liquid from the first auxiliary flow, is treated using the first auxiliary flow, or using liquid from the first auxiliary flow, before being treated by liquid from the second auxiliary flow.

15. The system of any preceding claim, wherein the system is configured to use liquid from the second auxiliary flow to adjust a pH of waste water treated using the first auxiliary flow, or using liquid from the first auxiliary flow, to be in the range of 6.5 < pH < 8.5.

16. The system of any preceding claim, further comprising a bioreactor unit configured to use bacteria to treat waste water received by the system.

17. The system of claim 16, configured to direct O2 produced in the first auxiliary flow by the electrolysis to the bioreactor unit.

18. The system of claim 16 or 17, wherein waste water treated by the bioreactor unit is provided as input to the electrolysis unit.

19. The system of any preceding claim, configured to direct ¾ produced in the second auxiliary flow by the electrolysis to an energy storage system.

20. The system of claim 19, wherein the energy storage system comprises a fuel cell.

21. The system of any preceding claim, wherein: the electrolysis unit comprises a plurality of the electrolysis cells; and at least two of the electrolysis cells share an anode or a cathode.

22. The system of claim 21, wherein at least one pair of electrolysis cells that share an anode or a cathode are connected together electrically in series.

23. The system of claim 21 or 22, wherein at least one pair of the electrolysis cells that share an anode or a cathode are connected together electrically in parallel.

24. The system of any preceding claim, wherein the waste water received by the system comprises polluted water from a toilet, bathroom or kitchen facility.

25. The system of any preceding claim, wherein each of one or more of the electrolysis cells comprises: liquid from the flow of aqueous solution in the primary region of the electrolysis cell; liquid from the first auxiliary flow of liquid in the first auxiliary region; and liquid from the secondary auxiliary flow of liquid in the second auxiliary region.

26. A method of treating waste water, comprising: electrolysing a flow of an aqueous solution comprising a chloride salt between an anode and a cathode of an electrolysis cell, wherein the flow of aqueous solution is separated from the anode by a first ion-exchange structure and is separated from the cathode by a second ion-exchange structure; driving a first auxiliary flow of liquid through a first auxiliary region between the anode and the first ion-exchange structure during the electrolysis; driving a second auxiliary flow of liquid through a second auxiliary region between the cathode and the second ion-exchange structure during the electrolysis; and using the first auxiliary flow, or liquid from the first auxiliary flow, to treat waste water.

27. The method of claim 26, further comprising using liquid from the second auxiliary flow of liquid to treat the waste water.

28. The method of claim 26 or 27, further comprising: using a bioreactor to pretreat waste water before the waste water is treated using the first auxiliary flow, or using liquid from the first auxiliary flow; and using O2 produced in the first auxiliary flow by the electrolysis to increase bacterial activity in the bioreactor.