Wastewater purification and recycling

Abstract

The present disclosure provides a method for processing a wastewater stream The method comprises providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream to an electrochemical cell; and oxidising at least some organic compounds in the wastewater stream at an anode of the electrochemical cell to thereby lower the concentration of the organic compounds in the wastewater stream. Also provided is a system for carrying out the method.

Description

[0001] WASTEWATER PURIFICATION AND RECYCLING

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method and system for purifying wastewater issued from an industrial process plant. Also disclosed are an integrated method and system capable of recycling outputs of the wastewater purification.

[0004] BACKGROUND

[0005] Industrial process plants are designed to output one or more desired products, commonly through processing one or more input materials through chemical (including biochemical), or mechanical (including biomechanical) means. Many industrial process plants generate, alongside their desired or target product(s), one or more byproducts. By-products are typically not a useful output of the industrial process, or they may require substantial further processing before they can be used. One common byproduct of many industrial process plants is water which is contaminated with organic components.

[0006] For example, the decades-old Fischer-Tropsch process can convert synthesis gas (i.e. a mixture of carbon monoxide and hydrogen, also known as syngas) into hydrocarbons having the formula CnH2n+2 according to the following, simplified, overall scheme:

[0007] (2n + 1 ) H2 + nCO -> CnH2n+2 + nH2O

[0008] This scheme shows that the process typically results in not only the desired hydrocarbon product, but also significant quantities of water as a by-product. Other industrial process plant reactors can also produce large quantities of water as a byproduct of their processes.

[0009] The by-product water usually contains contaminants deriving from the reaction process or other source. Several studies have been conducted to analyse the water by-product of Fischer-Tropsch synthesis for example, such as Rahman et al., “Fischer Tropsch water composition study from distillation process in gas to liquid technology with ASPEN simulation”, Case Studies in Chemical and Environmental Engineering 3 (2021) 100106; and Partington et al., “Quantitative carbon distribution analysis of hydrocarbons, alcohols and carboxylic acids in a Fischer-Tropsch product from a Co / TiO2 catalyst during gas phase pilot plant operation”, Journal of Analytical Science and Technology (2020). The water by-product produced from processes such as Fischer-Tropsch are found to contain organic compounds in an amount of around 2-5 wt%.

[0010] Therefore, water by-product of industrial process plants is typically considered to be wastewater, and it typically requires significant further processing to reach legal environmental standards before it can be disposed of. Thus, there are several benefits to improving the efficiency and utilization of such wastewater streams. For example, effective utilization could contribute to the UN sustainability goal of efficient water usage. Additionally, if valuable products could be produced from the wastewater, it could be used elsewhere, or recycled to improve efficiency, especially economic efficiency, of the industrial process plant.

[0011] Ahad and de Klerk, “Fischer-Tropsch acid water processing by Kolbe electrolysis”, Fuel (2018) 415-419 carried out proof-of-concept experiments using a mimic Fischer- Tropsch acid water, which was an aqueous solution of 1 % acetic acid, to investigate use of Kolbe electrolysis to treat by-products in small-scale facilities. Reported current efficiencies were low, and the authors suggest Kolbe electrolysis compares poorly to electrodialysis.

[0012] Given the large amount of wastewater issued by industrial process plants such as Fischer-Tropsch reactors, there is a need to develop methods to clean the wastewater. It would also be desirable to clean the wastewater into useful e.g. recyclable products.

[0013] The present invention has been devised in light of the above considerations.

[0014] SUMMARY OF THE INVENTION

[0015] The invention includes combinations of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0016] Various industrial process plants produce water as a by-product. In some cases, the amount of by-product water produced exceeds e.g. in volume or mass, the amount of target product. The by-product water typically contains components (contaminants) that are undesirable as part of a water stream, so that the by-product water cannot be immediately re-used or re-introduced into the water network. It is desirable to identify processes that can not only remove the contaminants and thereby reduce the burden on other cleaning processes, but also transform the extracted contaminants into useful components that can themselves be recycled in some way. The inventors have found that by-product water streams that are contaminated with organic compounds (also called wastewater streams herein) can be at least partially cleaned by incorporating an appropriate downstream electrochemical cell.

[0017] Accordingly, in a general aspect, the present disclosure describes the use of an electrochemical cell for cleaning a wastewater stream, particularly a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds, the electrochemical cell being capable of oxidizing at least some of the organic compounds in the wastewater stream at an anode thereof. Accordingly, the present disclosure generally provides a system and process for cleaning an industrial process plant wastewater stream contaminated with organic compounds using an electrochemical cell capable of oxidizing at least some of the organic compounds in the wastewater stream at an anode thereof. The oxidation can transform at least some of the organic compounds into gaseous products such as CO2 thereby reducing the concentration of the organic compounds in the wastewater stream to produce a cleaner wastewater stream.

[0018] Peters et al., “A Techno-Economic Assessment of Fischer-Tropsch Fuels Based on Syngas from Co-Electrolysis”, Processes (2022), 10, 699 disclose power-to-fuel concepts in which co-electrolytic processes are used to generate inputs (hydrogen and CO, for example) for process plants such as Fischer-Tropsch in the production of synthetic fuels such as diesel and kerosene. However, the authors do not consider use of an electrochemical cell to clean or make use of a wastewater stream output from an industrial process plant.

[0019] In a first aspect, provided herein is a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream to an electrochemical cell; and oxidising at least some organic compounds in the wastewater stream at an anode of the electrochemical cell to thereby lower the concentration of the organic compounds in the wastewater stream.

[0020] Thus, the wastewater stream output from the industrial process plant herein contains organic compounds (i.e. more than 0 wt% organic compounds, based on the total weight (100 wt%) of the wastewater stream). The method is expected to work with any measurable minimum quantity of organic compounds above 0 wt%. The wastewater stream referred to herein is typically water comprising organic compounds, and so the amount of the organic compounds in the water by-product produced in the industrial process plant is typically around 25 wt% at most. Thus, the wastewater stream may comprise the organic compounds at a first concentration of more than 0 wt% and at most 25 wt%.

[0021] A concentrating unit or a diluting unit may or may not be desirable in the present method. For example, if the industrial process plant is configured to output the byproduct wastewater stream at a concentration - referred to as the first concentration herein - where the first concentration is suitable to input to the particular electrochemical cell, then there is no need to adjust the concentration of the organic compounds in the wastewater stream. Therefore, the concentrating unit or the diluting unit may not be required.

[0022] On the other hand, in a (more typically-expected) situation in which the wastewater stream output by the industrial process plant comprises organic compounds at a first concentration where the first concentration is too high or too low to input directly to the electrochemical cell, then adjustment of the organic compound concentration may be desirable before it reaches the electrochemical cell. Such adjustment can result in an adjusted first concentration suitable as an input for the electrochemical cell. In such cases, a concentration-adjustment unit, taking the form of a concentrating unit and / or a diluting unit, may be used.

[0023] In this way, the concentration of the organic compounds that issue from the industrial process plant (first concentration) may be adjusted to a desired concentration (adjusted first concentration).

[0024] If the wastewater stream output by the industrial process plant comprises the organic compounds at a first concentration where the first concentration is too high for use as input for the electrochemical cell, then a diluting unit may suitably be used. The adjusted concentration may be, in this case, lower than the first concentration.

[0025] If the wastewater stream output by the industrial process plant comprises the organic compounds at a first concentration where the first concentration is too low for use as input for the electrochemical cell, then a concentrating unit may suitably be used. The adjusted concentration may be, in this case, higher than the first concentration.

[0026] If the first concentration of organic compounds can vary, e.g. between runs of the industrial process plant, then it may be desirable to include both a concentrating and a diluting unit in the relevant system, so that the wastewater stream can be directed appropriately according to the adjustment required.

[0027] In a method and system in which one or both of a concentrating unit and a diluting unit is present, it should be noted that, in the present method, the wastewater stream output by the industrial process plant may be directed to the electrochemical cell without being routed to either of the concentrating unit or diluting unit, or the wastewater stream may be directed via one of the concentrating unit and diluting unit as appropriate. It may also be possible to direct the wastewater stream via both of the concentrating unit and diluting unit, though this may be less efficient.

[0028] In the method, if wanted, the wastewater stream may be sent to the electrochemical cell via other units in addition to or instead of the concentrating unit or diluting unit, as discussed further elsewhere herein. The other units may, or generally may not significantly, cause the concentration of the organic compounds in the wastewater stream to change.

[0029] Once the wastewater stream having the desired input concentration of organic compounds arrives at the electrochemical cell, the electrochemical cell oxidizes at least some of the organic compounds at an anode thereof. The oxidation of the organic compounds causes the formation of at least some gaseous product, such as CO2. In this way, the concentration of the organic compounds in the wastewater stream output from the electrochemical cell is decreased compared to the concentration that is input to the electrochemical cell.

[0030] Therefore, in general, the electrochemical cell takes the wastewater stream having organic compounds at an input concentration, oxidises at least some of the organic compounds at an anode thereof to form at least some gaseous product, such as CO2, and outputs the wastewater stream having organic compounds at an output concentration wherein the output concentration is lower than the input concentration.

[0031] In some embodiments, the input concentration is the first concentration (the concentration output by the industrial process plant). In such embodiments, the wastewater stream is not sent to a concentrating unit or a diluting unit. Accordingly, the output concentration may be lower than the first concentration.

[0032] In some embodiments, the input concentration is the adjusted first concentration. In such embodiments, the wastewater stream is directed to a concentration unit or to a diluting unit, to thereby adjust the concentration of organic compounds in the wastewater stream. Accordingly, the output concentration may be lower than the first adjusted concentration. The relationship between the first concentration and the second concentration may depend on whether the wastewater stream was directed to a concentrating unit or to a diluting unit.

[0033] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and / or a diluting unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit and / or diluting unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to an electrochemical cell; and oxidising at least some of the organic compounds in the wastewater stream at an anode of the electrochemical cell to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration.

[0034] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to an electrochemical cell; and oxidising at least some organic compounds in the wastewater stream at an anode of the electrochemical cell to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration.

[0035] Preferably, the electrochemical cell is not a Kolbe electrolyser.

[0036] Preferably, the electrochemical cell comprises or is one of: (i) a direct alcohol fuel cell; (ii) an alcohol electrolyser; or (ill) a CO2 electrolyser.

[0037] The inventors consider these electrochemical cells to be particularly suitable for use in a method in which the industrial process plant includes a reactor, particularly a chemical reactor (i.e. a reactor in which a chemical reaction occurs), and the wastewater stream issues from the reactor. Particularly suitable are industrial process plants comprising a Fischer-Tropsch reactor, or a reactor having a similar wastewater by-product stream. In addition, the inventors consider that these electrochemical cells can output products that can be used within a system suitable for use in the present method, thereby promoting recycling.

[0038] Accordingly, preferably, the industrial process plant comprises a reactor, such as a chemical reactor, and the wastewater stream issues from the reactor. Particularly preferably, the reactor is or comprises a Fischer-Tropsch reactor.

[0039] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream to a direct alcohol fuel cell; and oxidising at least some organic compounds in the wastewater stream at an anode of the direct alcohol fuel cell to thereby lower the concentration of the organic compounds in the wastewater stream.

[0040] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and / or a diluting unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit and / or diluting unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to a direct alcohol fuel cell; and oxidising at least some of the organic compounds in the wastewater stream at an anode of the direct alcohol fuel cell to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration. In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to a direct alcohol fuel cell; and oxidising at least some organic compounds in the wastewater stream at an anode of the direct alcohol fuel cell to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration.

[0041] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream to an alcohol electrolyser; and oxidising at least some organic compounds in the wastewater stream at an anode of the alcohol electrolyser to thereby lower the concentration of the organic compounds in the wastewater stream.

[0042] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and / or a diluting unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit and / or diluting unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to an alcohol electrolyser; and oxidising at least some of the organic compounds in the wastewater stream at an anode of the alcohol electrolyser to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration. In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to an alcohol electrolyser; and oxidising at least some organic compounds in the wastewater stream at an anode of the alcohol electrolyser to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration.

[0043] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream to a CO2 electrolyser; and oxidising at least some organic compounds in the wastewater stream at an anode of the CO2 electrolyser to thereby lower the concentration of the organic compounds in the wastewater stream.

[0044] In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and / or a diluting unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit and / or diluting unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to a CO2 electrolyser; and oxidising at least some of the organic compounds in the wastewater stream at an anode of the CO2 electrolyser to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration. In some embodiments, the method of the first aspect includes a method of processing a wastewater stream, the method comprising: providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and adjusting the concentration of the organic compounds in the wastewater stream at the concentrating unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to a CO2 electrolyser; and oxidising at least some organic compounds in the wastewater stream at an anode of the CO2 electrolyser to thereby lower the concentration of the organic compounds in the wastewater stream. The concentration of the organic compounds here is lowered relative to the adjusted first concentration.

[0045] Oxygenated organic compounds are polar, and therefore it is considered that this kind of organic compound is generally more difficult to remove from wastewater streams than other kinds of organic compounds. This is further true for short chain organic compounds, such as those having a carbon chain length of C1-C5. Such compounds can be processed at an electrochemical cell, particularly the kinds of electrochemical cell preferred herein. Accordingly, in preferred embodiments the organic compounds comprise or are oxygenated organic compounds, particularly the organic compounds may comprise or be oxygenated hydrocarbons.

[0046] In preferred embodiments, the organic compounds comprise or are C1-C5 organic compounds i.e. having a carbon chain length of up to 5. Preferably, the organic compounds comprise C1-C5 oxygenated organic compounds, particularly C1-C5 oxygenated hydrocarbons. Preferably, the organic compounds comprise C1-C5 alcohols and / or C1-C5 carboxylic acids as the majority organic compound component, particularly preferably C1-C5 alcohols. These are expected to be the main kind of organic compound components of the wastewater stream from a Fischer-Tropsch reactor.

[0047] By “majority organic compound component”, we mean that there are more of that kind of organic compound in the wastewater stream (by wt%) than the other individual kinds of organic compounds. So, for example, in some embodiments the wastewater stream comprises more C1-C5 alcohols than, for example, higher chain alcohols, than carboxylic acids, than aldehydes, etc. In general, it is not envisioned that the concentration of any particular organic compound will be increased by the methods and systems herein.

[0048] Preferably, at least one upstream electrolyser is provided upstream of the electrochemical cell, and in the method an output from the at least one upstream electrolyser is fed to a cathode of the electrochemical cell. Advantageously, the at least one upstream electrolyser may comprise or be a water electrolyser.

[0049] Preferably, a wastewater stream output from the anode of the electrochemical cell is sent to at least one downstream electrolyser located downstream of the electrochemical cell. Advantageously, the at least one downstream electrolyser may comprise or be a Kolbe electrolyser.

[0050] Preferably, an output from the at least one downstream electrolyser is used as a fuel for the industrial process plant, such as a reactor. Recycling in this manner may beneficially e.g. reduce the amount of fuel for the reactor that needs to be provided by external sources.

[0051] The inventors consider the upstream and downstream electrolysers to be particularly suitable for use in a method having the above-preferred electrochemical cells.

[0052] Thus, the present disclosure particularly envisages a method using the upstream electrolyser and / or the downstream electrolyser in combination with the preferred electrochemical cells disclosed herein.

[0053] Furthermore, the upstream and / or downstream electrolysers are considered particularly suitable for use in a method in which the wastewater is output from a Fischer-Tropsch reactor, or in a system whose reactors having similar wastewater byproduct stream profiles to those of Fischer-Tropsch reactors, i.e. reactors having wastewater stream outputs with a significant proportion of oxygenated hydrocarbon contaminants. In addition, the inventors consider that such electrolysers can output products that can be re-used in the present method, thereby promoting recycling.

[0054] Thus, the present disclosure particularly envisages a method using both the upstream electrolyser and the downstream electrolyser.

[0055] Particularly advantageously, the present disclosure envisages a method using each of the upstream electrolyser to provide input for the electrochemical cell cathode; the electrochemical cell to use input wastewater stream and oxidize the organic compounds at an anode thereof, and output products suitable for re-use in the method; and the downstream electrolyser to produce products from the output of the electrochemical cell that can be re-used.

[0056] Further advantageously, the present disclosure envisages a method using a concentrating unit upstream of the electrochemical cell, and the downstream electrolyser.

[0057] Preferably, a wastewater stream output from the electrochemical cell is recycled. This may provide both economic and environmental benefits.

[0058] Preferably, a wastewater stream output from the anode of the electrochemical cell comprises CO2. The CO2 may be captured using a CO2 capture unit. Such capture units may be of a conventional kind.

[0059] Preferably, a wastewater stream output from the anode of the electrochemical cell is further purified.

[0060] Such separation may be carried out at a purification unit downstream of the electrochemical cell. The purification unit may be a liquid-liquid separation unit, a unit comprising an osmotic membrane, or similar. In one example, inorganic components may be removed from the wastewater stream using e.g. reverse osmotic processes. In another example, non-oxygenated organic compounds such as hydrocarbons (alkanes and alkenes and the like) may be separated from the water component of the wastewater stream output from a downstream electrolyser such as a Kolbe electrolyser. Such separation may be carried out at a purification unit downstream of the electrochemical cell.

[0061] The purification unit may be of a conventional kind.

[0062] There may be one or more than one kind of purification unit, and therefore more than one purification as described herein may be carried out in the present method.

[0063] Preferably, the system comprises a separator unit.

[0064] In the method, organic compounds of the wastewater stream are oxidized in the electrochemical cell to form at least some CO2. This lowers the concentration of the organic compounds in the wastewater stream output from the electrochemical cell compared to the input concentration. Accordingly, one or more gas / liquid separation processes can be carried out at the electrochemical cell or downstream of the electrochemical cell at a downstream separation unit. The separation processes separate the gaseous product of the oxidation at the electrochemical cell, from the liquid and in particular the water component of the wastewater stream resulting from the oxidation at the electrochemical cell. The separation unit may be of a conventional kind. There may be one, or more than one, separation unit and thus separation steps in the present disclosure.

[0065] In some preferred embodiments, the electrochemical cell comprises a direct alcohol fuel cell (DAFC) and, in the method, O2 is fed to a cathode thereof and the direct alcohol fuel cell outputs electricity. Electricity as an output of the electrochemical cell can be used in several advantageous ways.

[0066] In some embodiments, the output electricity is used to at least partially power another part of the industrial process plant, such as a reactor thereof, or the electrochemical cell. In this way, the electricity can reduce the reliance of the system on external sources, which can have economic and environmental advantages. In some embodiments, the electricity produced is stored e.g. for future use in the present method. In some embodiments, the electricity is returned to the power grid.

[0067] In some embodiments, the O2 is fed from a water electrolyser located upstream of the direct alcohol fuel cell. Advantageously, integration of an upstream water electrolyser with a DAFC means that there may be reduced reliance of the system on external sources of O2 for the DAFC. This can have economic and environmental advantages.

[0068] In some preferred embodiments, the electrochemical cell comprises an alcohol electrolyser and, in the method, the alcohol electrolyser outputs hydrogen at a cathode thereof. Hydrogen can be a valuable output, for example, in some embodiments the output hydrogen is used as an input for the industrial process plant where such plant utilises hydrogen as an input material or otherwise. In this way, there may be reduced reliance of the system on external sources of hydrogen for the industrial process plant. In embodiments where the industrial process plant comprises a reactor such as a Fischer-Tropsch reactor, this means valuable fuel products may be produced particularly economically.

[0069] In some preferred embodiments, the electrochemical cell comprises a CO2 electrolyser and, in the method, CO2 is fed to a cathode thereof and the CO2 electrolyser outputs at least one of syngas, C2H4 (also called ethylene or ethene herein), formic acid, ethanol and methanol at the cathode. Such outputs can be valuable, for example in some embodiments the output at least one of syngas, ethylene, formic acid, ethanol and methanol may be used as input for the industrial process plant where such plant utilises one or more of syngas, ethylene, formic acid, ethanol and methanol as an input material or otherwise. In this way, there may be reduced reliance of the system on external sources of these materials for the industrial process plant. In some embodiments, the output of the CO2 electrolyser cathode is at least one of syngas, C2H4 and formic acid. In embodiments where the reactor is a Fischer-Tropsch reactor, the production of syngas by the CO2 electrolyser can mean valuable fuel products may be produced particularly economically. Alternatively or additionally, the CO2 may be fed from a reactor of the industrial process plant. That is, where a reactor of the industrial process plant also outputs CO2 as a by-product (or as a product) alongside the wastewater stream, there may be reduced reliance of the system on external sources of CO2 for the electrochemical cell. Furthermore, where the CO2 is a by-product, it may provide an economical and environmentally valuable use for the by-product which would ordinarily not be used.

[0070] Preferably, the method of the first aspect is carried out in or using a system according to the second aspect described now.

[0071] In a second aspect, provided herein is a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; an electrochemical cell downstream of the wastewater stream output unit, wherein the electrochemical cell is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the electrochemical cell.

[0072] The explanations, preferences and options set out herein for the method of the first aspect apply to the system of the second aspect as appropriate.

[0073] The industrial process plant of the present system is configured to output a wastewater stream comprising organic compounds at a concentration - referred to as a first concentration herein - of more than 0 wt% and typically up to 25 wt%. Thus, the wastewater stream may comprise the organic compounds at a first concentration of more than 0 wt% and at most 25 wt%. The nature of the industrial process plant, any input material or materials, the processing, such as reaction, that occurs in the industrial process plant, are not otherwise limited. The industrial process plant may be configured to output one or more products and / or one or more other by-products alongside the wastewater stream.

[0074] The system comprises an electrochemical cell downstream of the wastewater stream output unit. Preferably, the industrial process plant wastewater stream output unit is or comprises a reactor, such as a chemical reactor. An example of a suitable industrial process plant wastewater stream output unit is a Fischer-Tropsch reactor. As explained for the first aspect, in general, the electrochemical cell takes the wastewater stream having organic compounds at the input concentration, oxidises at least some of the organic compounds at an anode thereof to form at least some CO2, and outputs the wastewater stream having organic compounds at the output concentration wherein the output concentration is lower than the input concentration.

[0075] Preferably, the system comprises a concentrating unit and / or a diluting unit, located downstream of the industrial process plant wastewater stream output unit and upstream of the electrochemical cell, wherein the concentrating unit and / or the diluting unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream to the electrochemical cell via the concentrating unit and / or the diluting unit.

[0076] In this way, a concentration adjustment unit in the form of a concentrating unit and / or a diluting unit may or may not be present in the system of the second aspect for at least corresponding reasons as for the method of the first aspect. If a concentration adjustment unit is not present, then in some embodiments the input concentration of organic compounds is the first concentration. If a concentration adjustment unit is present, then the concentration adjustment unit outputs the wastewater stream comprising the organic compounds at an adjusted first concentration. Thus, in some embodiments, the input concentration of organic compounds is the adjusted first concentration. The relationships between the first concentration and the output concentration are as discussed in relation to the first aspect.

[0077] Thus, the present disclosure envisages a system having any of (i) none of a concentrating unit or a diluting unit; (ii) one concentrating unit or one diluting unit; or (iii) each of a concentrating unit and a diluting unit. In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; an electrochemical cell downstream of the wastewater stream output unit, wherein the electrochemical cell is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit and / or diluting unit, located downstream of the wastewater stream output unit and upstream of the electrochemical cell, wherein the concentrating unit and / or diluting unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the electrochemical cell via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration.

[0078] In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; an electrochemical cell downstream of the wastewater stream output unit, wherein the electrochemical cell is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit, located downstream of the wastewater stream output unit and upstream of the electrochemical cell, wherein the concentrating unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the electrochemical cell via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration. Other units may be present between the wastewater stream output unit and the concentrating unit and / or diluting unit or between the wastewater stream output unit and the electrochemical cell, or between the concentrating unit and / or diluting unit and the electrochemical cell. Accordingly, in some embodiments, the input concentration of organic compounds is different from the first concentration and from a first adjusted concentration, depending on the nature of any further units. In some embodiments, the further units are not present.

[0079] Preferably, the electrochemical cell is not a Kolbe electrolyser.

[0080] Preferably, the electrochemical cell comprises or is one of:

[0081] (i) a direct alcohol fuel cell;

[0082] (ii) an alcohol electrolyser; or

[0083] (iii) a CO2 electrolyser.

[0084] The inventors consider these electrochemical cells to be particularly suitable for use in a system in which the industrial process plant includes a reactor, particularly a chemical reactor (i.e. a reactor in which a chemical reaction occurs), and the wastewater stream issues from the reactor. Put differently, the wastewater stream output unit may preferably be a reactor, particularly a chemical reactor. Particularly suitable are industrial process plants comprising a Fischer-Tropsch reactor. They are also considered particularly suitable for use in a system whose reactors having similar wastewater by-product stream profiles to those of Fischer-Tropsch reactors, e.g. reactors having wastewater stream outputs with a significant proportion of oxygenated hydrocarbon contaminants. Thus, the organic compounds are preferably oxygenated organic compounds, particularly oxygenated hydrocarbons. In addition, the inventors consider that these electrochemical cells can output products that can be used within the present system, thereby promoting recycling.

[0085] In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; a direct alcohol fuel cell downstream of the wastewater stream output unit, wherein the direct alcohol fuel cell is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit and / or diluting unit, located downstream of the wastewater stream output unit and upstream of the direct alcohol fuel cell, wherein the concentrating unit and / or diluting unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the direct alcohol fuel cell via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration.

[0086] In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; a direct alcohol fuel cell downstream of the wastewater stream output unit, wherein the direct alcohol fuel cell is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit, located downstream of the wastewater stream output unit and upstream of the direct alcohol fuel cell, wherein the concentrating unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the direct alcohol fuel cell via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration.

[0087] In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; an alcohol electrolyser downstream of the wastewater stream output unit, wherein the alcohol electrolyser is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit and / or diluting unit, located downstream of the wastewater stream output unit and upstream of the alcohol electrolyser, wherein the concentrating unit and / or diluting unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the alcohol electrolyser via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration.

[0088] In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; an alcohol electrolyser downstream of the wastewater stream output unit, wherein the alcohol electrolyser is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit, located downstream of the wastewater stream output unit and upstream of the alcohol electrolyser, wherein the concentrating unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the alcohol electrolyser via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration.

[0089] In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; a CO2 electrolyser downstream of the wastewater stream output unit, wherein the CO2 electrolyser is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit and / or diluting unit, located downstream of the wastewater stream output unit and upstream of the CO2 electrolyser, wherein the concentrating unit and / or diluting unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the CO2 electrolyser via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration.

[0090] In some embodiments, the system of the second aspect includes a system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; a CO2 electrolyser downstream of the wastewater stream output unit, wherein the CO2 electrolyser is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit, located downstream of the wastewater stream output unit and upstream of the CO2 electrolyser, wherein the concentrating unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the CO2 electrolyser via the concentrating unit. The configuration here leads to a lower output concentration relative to the adjusted first concentration.

[0091] Accordingly, preferably, the industrial process plant comprises a reactor, such as a chemical reactor, and the wastewater stream output unit is or comprises the reactor. Particularly preferably, the reactor is or comprises a Fischer-Tropsch reactor.

[0092] Preferably, the system comprises an upstream electrolyser located upstream of the electrochemical cell. Advantageously, the at least one upstream electrolyser may comprise or be a water electrolyser. In some embodiments, the system is configured so that an output from the at least one downstream electrolyser is directed to the industrial process plant, and such may be used as a fuel for at least part of the industrial process plant, such as a reactor thereof. Recycling in this manner may beneficially e.g. reduce the amount of fuel for the industrial process plant that needs to be provided by external sources.

[0093] Preferably, the system comprises a downstream electrolyser located downstream of the electrochemical cell. Advantageously, the at least one downstream electrolyser may comprise or be a Kolbe electrolyser.

[0094] The advantages and preferences of each of these are discussed in relation to the method of the first aspect, and corresponding remarks apply to the second aspect.

[0095] The inventors consider the upstream and downstream electrolysers to be particularly suitable for a system having the above-preferred electrochemical cells.

[0096] The present disclosure particularly envisages a system comprising the upstream electrolyser and / or the downstream electrolyser in combination with the preferred electrochemical cells disclosed herein.

[0097] The upstream and / or downstream electrolysers are considered particularly suitable for a system in which the wastewater is output from a Fischer-Tropsch reactor, or in a system whose reactors have a similar wastewater by-product stream profiles to those of Fischer-Tropsch reactors.

[0098] The present disclosure particularly envisages a system comprising both the upstream electrolyser and the downstream electrolyser.

[0099] Particularly advantageously, the present disclosure envisages a system comprising the upstream electrolyser arranged to provide input for the electrochemical cell cathode; and the downstream electrolyser configured to produce products from the output of the electrochemical cell that can be re-used.

[0100] Further advantageously, the present disclosure envisages a system comprising the concentrating unit upstream of the electrochemical cell, and the downstream electrolyser.

[0101] Preferably, the system is configured to recycle the output from the cathode of the electrochemical cell. This may provide both economic and environmental benefits. Preferably, the system comprises a separator unit capable of separating gases from liquids and / or an oxidation treatment unit, wherein the separator unit and / or the oxidation treatment unit are located downstream of the electrochemical cell.

[0102] Thus, the present disclosure envisages a system comprising no separator unit and an oxidation treatment unit, a system comprising a separator unit and no oxidation treatment unit, and a system comprising a separator unit and an oxidation treatment unit.

[0103] As described for the first aspect, since the electrochemical cell is configured to oxidise organic compounds to form gaseous product including CO2, the separator unit can be configured to separate the gaseous product from the liquid wastewater stream comprising the organic compounds at the lowered concentration.

[0104] Advantageously, the separator unit permits separation of gaseous from liquid components output from the electrochemical cell, before the liquid component is directed to a downstream electrolyser or otherwise used. Useful gases can subsequently be stored and / or captured and / or re-used in the system as described later herein. For example, where the electrochemical cell outputs CO2, a CO2 capture unit may advantageously be provided.

[0105] The separator unit may be located downstream of the electrochemical cell. The separation unit may be of a conventional kind. There may be one, or more than one, separation unit in the present disclosure. Where there is more than one separation unit, they may be of the same kind or different kinds.

[0106] The oxidation treatment unit may be a chemical oxidation unit. It may be capable of oxidizing oxygenated hydrocarbons such as aldehydes to acids and the like. The method and system may alternatively or additionally comprise an alkali treatment unit comprising any suitable alkali. The oxidation treatment unit and alkali treatment unit may be located downstream of the electrochemical cell.

[0107] The alkali treatment unit may have particular utility in embodiments having a downstream electrolyser, particularly a Kolbe electrolyser in view of the mode of action of a Kolbe electrolyser. That is, an alkali treatment unit may be particularly beneficial in embodiments where a higher concentration of organic compound anions is wanted as input for a Kolbe electrolyser. Such alkali treatment unit can be of a conventional kind. Preferably, the system comprises a water purification unit.

[0108] In some embodiments, the water purification unit is located upstream of the electrochemical cell. In some such embodiments, the water purification unit is located downstream of any concentration adjustment unit i.e. concentrating unit and / or diluting unit.

[0109] Such water purification unit may for example be used to remove contaminants that may influence the operation of the electrochemical cell. For example, inorganic components may be removed from the wastewater stream to be input to the electrochemical cell using e.g. reverse osmotic processes.

[0110] In some embodiments, the water purification unit is located downstream of the electrochemical cell.

[0111] For example, non-oxygenated organic compounds such as hydrocarbons (alkanes and alkenes and the like) may be separated from the water component of the wastewater stream output from a downstream electrolyser such as a Kolbe electrolyser. Such separation may be carried out at a purification unit downstream of the electrochemical cell. The purification unit may be a liquid-liquid separation unit.

[0112] Alternatively or additionally, the water purification unit may remove inorganic components from the wastewater stream that is output from the electrochemical cell using e.g. osmotic processes.

[0113] The purification unit may be of a conventional kind.

[0114] There may be one or more than one kind of purification unit in the present system.

[0115] Preferably, the system comprises a CO2 capture unit downstream of the electrochemical cell. This may suitably be used to capture CO2 produced by the electrochemical cell.

[0116] Preferably, the system is configured to direct at least one output of the electrochemical cell and / or of the downstream electrolyser as fuel for at least part of the industrial process plant, such as a reactor thereof. For example, in a system not comprising the downstream electrolyser, a product of the electrochemical cell may be directly used to fuel at least a part of the industrial process plant, such as a reactor thereof. In a system comprising the downstream electrolyser, the fuel may be a product of the electrochemical cell and / or the downstream electrolyser.

[0117] Preferably, where the electrochemical cell of the system comprises or is a direct alcohol fuel cell (DAFC), the system is configured to feed O2 to a cathode thereof, so that the direct alcohol fuel cell outputs electricity. The electricity produced can be used or stored as described for the first aspect.

[0118] In particular, preferably the system is configured to use the output electricity to at least partially power the system. Alternatively or additionally, the system is preferably configured to feed the O2 from a water electrolyser. That is, the O2 which is fed to the cathode of the alcohol fuel cell can be provided at least partially by an upstream electrolyser, particularly an upstream water electrolyser.

[0119] Preferably, the electrochemical cell comprises or is an alcohol electrolyser capable of outputting hydrogen at a cathode thereof. Further preferably, the system is configured to use the output hydrogen as an input elsewhere in the system, such as a reactor of the industrial process plant. Advantages of output hydrogen are as discussed for the first aspect.

[0120] Preferably, the electrochemical cell comprises a CO2 electrolyser and the system is configured to feed CO2 to a cathode thereof, so that the CO2 electrolyser outputs at least one of syngas, ethylene, formic acid, ethanol and methanol at the cathode. Advantages of output at least one of syngas, ethylene, formic acid, ethanol and methanol are as discussed for the first aspect.

[0121] In particular, further preferably, the system is configured to use at least one of the output syngas, ethylene, formic acid, ethanol and / or methanol as input elsewhere in the system. Alternatively or additionally, the system is preferably configured to feed the CO2 to the cathode of the CO2 electrolyser from the reactor. That is, the CO2 which is fed to the cathode of the CO2 electrolyser can be provided at least partially by a reactor of the industrial process plant, located upstream. Advantageously, this allows a further by-product of a reactor of the industrial process plant to be used within the system.

[0122] BRIEF DECRIPTION OF THE FIGURES

[0123] The accompanying drawings are included to provide a further understanding of the method and system of the disclosure. The drawings are not intended to be drawn to scale. Fig. 1 is a schematic flow diagram of a gas phase pilot plant.

[0124] Fig. 2 is a schematic flow diagram of an exemplary system integrating an alcohol fuel cell as electrochemical cell.

[0125] Fig. 3 is a schematic flow diagram of an exemplary system integrating an alcohol electrolyser as electrochemical cell.

[0126] Figs. 4-8 are schematic flow diagrams of exemplary systems integrating a CO2 electrolyser as electrochemical cell.

[0127] Fig. 9 is a schematic diagram of an exemplary system integrating a CO2 electrolyser as electrochemical cell and recycling all products formed by the electrolysers within the system.

[0128] DETAILED DESCRIPTION OF THE INVENTION

[0129] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0130] General

[0131] The present disclosure generally concerns a method and system for cleaning of industrial process plant wastewater streams by removing contaminant organic compounds by oxidation using an electrochemical cell. The oxidation process thereby reduces the concentration of the contaminant organic compounds in the wastewater stream, typically by generating at least some gaseous product, particularly CO2, which may then be separated readily from the wastewater stream.

[0132] Accordingly, in general, the method and system of the present disclosure include an industrial process plant which has as part of its output an aqueous (water-based) stream comprising organic compounds. This stream comprising organic compounds is typically a by-product of a reaction carried out by the industrial process plant. The stream comprising organic compounds is therefore referred to herein as a wastewater stream.

[0133] The wastewater stream output by the industrial process plant wastewater stream output unit is directed - either directly or via intervening units such as those as described herein - to an electrochemical cell capable of oxidizing organic compounds of the input wastewater stream at an anode thereof to form, for example, at least some gaseous product such as CO2. In this way, the electrochemical cell lowers or decreases the amount of the organic compounds in the wastewater stream. Thus, the system of the present disclosure comprises an electrochemical cell located downstream of the industrial process plant wastewater stream output unit.

[0134] As used herein, upstream and downstream refer in the conventional way to the direction of flow through the system. For example, by “y is located upstream of x” we refer to a component y through which material flows earlier in the system than component x. Similarly, “z is located downstream of x”, we refer to a component z through which material flows later in the system than component x. In this way, an electrochemical cell located downstream of the industrial process plant wastewater stream output unit indicates that material flows from the industrial process plant wastewater stream output unit to the electrochemical cell (and not in the reverse direction).

[0135] Herein, the manner of connection of the various components of the system, and the manner in which the wastewater stream is directed in the method, is not particularly limited, though pipes as known in the art may be mentioned.

[0136] A particular advantage of the present method and system is high flexibility. Different electrochemical cells can be used in the present method and system, according to for example commercial considerations and desired output products. In some embodiments known methods and systems can be adapted to arrive at a method and system in accordance with the present disclosure, e.g. by integrating an electrochemical cell as described herein.

[0137] In addition to the herein-described cleaning advantages, the present method and system also have the capacity to lead, in certain configurations, to increased recycling capabilities. A general object of many industries is to increase their “green” capacity, for example reduce carbon footprint. The present method and system can increase the overall “green” capacity of industrial process plants, not only by effective and efficient cleaning of wastewater streams but also by making use of the products of the electrochemical cell as inputs elsewhere in the industrial process plant. In this way, the system may re-use its waste products to a greater extent than previously. Thus, the present disclosure encompasses, but is not limited to, the effective utilization of wastewater streams contaminated with organic compounds to provide valuable feedstock and thus reduce waste.

[0138] Fig. 1 is a schematic diagram of an example gas phase pilot plant according to the present disclosure. In the system 1 of Fig. 1 , a feed gas 9 is fed in and sent to a compressor 5. The gas proceeds to a reactor 3, which is part of an industrial process plant. The contents of the compressed feed gas may be monitored using an on-line gas chromatograph (GC) 7a or similar. The monitoring is optional, but generally useful.

[0139] A Fischer-Tropsch reactor is an exemplary reactor 3, but the present method and system are not limited thereto. Other industrial process plants and reactor types producing wastewater streams contaminated with organic compounds can also make use of the present method and system, as described elsewhere herein.

[0140] In some embodiments, the reactor 3 is configured to process one or more input materials and output one or more products and at least one by-product. The nature of the input material(s) and the output product(s) and any by-product(s) may depend on the reaction being carried out and is not particularly limited herein except insofar as the output should include a by-product wastewater stream comprising organic compounds as defined herein. The output(s) of the reactor may be processed through one or more processing units 11 a, 11b, 11c - there are three such processing units in the embodiment of Fig. 1 , labelled V1 , V2 and V3. As shown in Fig. 1 , using a Fischer- Tropsch reactor as an example, at unit V1 wax is separated from the product stream. At units V2 and V3, the liquid products are separated from the gaseous products, and the liquids sent to a decanter 13. Some of the organic compound liquid can be separated from the water phase e.g. by distillation. The gaseous products 15 exit unit V3, optionally monitored by a second on-line GC 7b, and are collected.

[0141] The wax, organic compound liquids, and gaseous products shown in the example of Fig. 1 can be used later in various applications. More generally, any output(s) of the industrial process plant described herein other than the wastewater stream can be separated from the wastewater stream, and / or processed in any suitable and conventional manner. This may involve multiple separation / processing steps / units as appropriate.

[0142] The water phase of a Fischer-Tropsch wastewater stream typically contains around 2- 5 wt% organic compounds, including organic acids and C1-C5 alcohols. These oxygenated organic compounds are difficult to separate from the water, as they are polar and therefore, they mix easily with the polar water component. The wastewater stream has a flow rate similar to water. It is therefore considered difficult to separate the organic compounds by e.g. a distillation-based method. A variety of technologies are currently used to sufficiently clean the wastewater to environmental standards suitable for disposal, including biological treatments, distillation, reverse osmosis, filtration methods such as ultrafiltration, membrane-based procedures including ion exchange, chemical processes such as destabilization, flocculation, adsorption methods, coagulation processes, anaerobic treatments, and dissolved air flotation to name a few. Further details may be found in e.g. Environmental Science and Pollution Research (2020) 27:27172-27180).

[0143] The present invention aims to provide a useful way of cleaning the wastewater stream, and optionally but advantageously also to generate valuable additional products through integration of an electrochemical cell. The present method and system can be integrated alongside, or alternative to, current methods and systems.

[0144] Industrial process plant

[0145] As described above, the present method and system make use of wastewater issued from an industrial process plant, which wastewater stream forms during the processing carried out in the industrial process plant. The nature of the industrial process plant is not particularly limited. The process plants described herein are designed to output, on an industrial scale, one or more desired products, optionally through processing one or more input materials through chemical (including biochemical) or mechanical (including biomechanical) means, alongside at least one by-product wherein the at least one by-product comprises a wastewater stream contaminated with organic compounds as described herein.

[0146] The industrial process plants described herein may include, but are not limited to, process plants associated with: refinery processing (including bio-refinery processing); fracking such as shale gas fracturing; fuel production; fermentation processing; pulp manufacture; paper manufacture; food and drink processing such as meat or poultry processing, alcohol production such as beer production and starch production; power generation; thermal management water; cooling water including heat exchangers. The industrial process plant may comprise a reactor, such as a chemical reactor. Typically, the reactor is or comprises a vessel in which a chemical reaction occurs to transform one or more input materials into one or more product materials and one or more byproduct materials. A suitable reactor is capable of processing one or more input materials. Suitable examples of chemical reactors that may issue wastewater streams suitable for use in the present method and system include but are not limited to: Fischer-Tropsch reactors, CO2 conversion reactors including methanol synthesis or modified Fischer-Tropsch reactors; methanol to olefin (MtO) reactors (reactors associated with MtO type processes); alcohol to jet reactors; and reactors producing organic chemicals via oxidative treatments. Particularly discussed herein are Fischer- Tropsch reactors as preferred, but the present disclosure is not limited thereto. Such reactors may take any suitable form and are not particularly limited. Examples may include one or more of a fixed bed reactor, slurry bed reactor, trickle bed reactor, fluidised bed, continuous stirred tank reactor (CSTR), for example.

[0147] The present disclosure is not particularly limited by the nature of any input material(s) to the industrial process plant or reactor, and they may be in the form of a gas, a liquid or a solid according to the processing or reaction which is being carried out. There may be one or more than one input material. Any reaction conditions (e.g. temperature, pressure, presence of catalyst, etc.) will be dictated by the nature of the industrial process plant and are not particularly limited herein.

[0148] Similarly, the nature of any output from the industrial process plant is not particularly limited - and each may be in the form of a gas, a liquid or a solid according to the nature of the process - except that at least one output must be or include the water stream referred to herein as the wastewater stream. Accordingly, the industrial process plants herein comprise a wastewater stream output unit. The wastewater stream output unit may be or comprise a reactor as described elsewhere herein. There may be one or more than one output from the industrial process plant, including one or more products and optionally one or more by-product (i.e. one or more target output of the reaction carried out by the reactor, and optionally one or more outputs which are not a target output).

[0149] In some embodiments, the industrial process plant or a component reactor thereof operates in a continuous process. In some embodiments, the industrial process plant or a component reactor thereof operates in a discontinuous process.

[0150] It is described herein that the electrochemical cell (and other unit(s)) is located downstream (or upstream, in the case of other units such as the upstream electrolyser) of the industrial process plant. By this it is intended to refer to the part of the industrial process plant that issues the wastewater stream, i.e. the wastewater stream output unit, which unit may be or include a reactor. It is not intended that there is any particular limitation to the configuration of the system.

[0151] Wastewater stream

[0152] The wastewater stream described in the present method and system is a water-based stream comprising organic compounds. Thus, the primary constituent of the wastewater stream is water. The organic compounds are present to a significantly lesser extent than the water. The term “water” herein is intended to refer to the molecule “H2O” and not to limit the state of matter. The wastewater stream may be provided by the industrial process plant in a liquid phase or in a vapour phase. If desired, a cooling or heating unit may be used to change the phase of the wastewater stream provided by the industrial process plant. This may be suitable, for example, if the electrochemical cell works more efficiently with the wastewater stream in a different phase to the phase provided by the industrial process plant. Further, a cooling or heating unit may be used to change the temperature of the wastewater stream provided by the industrial process plant. This may be suitable, for example, if the electrochemical cell works more efficiently with the wastewater stream at a different temperature to the temperature provided by the industrial process plant.

[0153] The wastewater stream comprises organic compounds. Typically, the wastewater stream is expected to have a number of different kinds of organic compounds i.e. a mixture of organic compounds having different functional groups. For example, the mixture may include organic compounds that are alcohols, aldehydes and / or carboxylic acids. However, the present disclosure encompasses wastewater streams having only one kind of organic compound e.g. only alcohols, such situation may dictate the nature of the electrochemical cell used.

[0154] Herein, an organic compound is a compound including one or more C-H bonds. The organic compound may be a hydrocarbon, i.e. containing only C and H. The organic compound may contain heteroatoms such as oxygen, sulfur or nitrogen. Organic compounds containing heteroatoms are particularly advantageously present in the wastewater stream of the present disclosure, because these are typically considered to be difficult to remove for the reasons explained elsewhere herein.

[0155] The present disclosure particularly envisages embodiments in which the organic compounds include or consist of hydrocarbons and oxygenated hydrocarbons (oxygenated hydrocarbons referring to hydrocarbons having one or more oxygencontaining functional groups), and particularly oxygenated hydrocarbons.

[0156] As used herein, “oxygenated” refers to compounds containing one or more oxygen (O) atoms, e.g. an oxygen-containing functional group.

[0157] Accordingly, the wastewater stream may comprise organic compounds including one or more kinds selected from hydrocarbons such as alkanes, alkenes, alkynes, and aromatic organic compounds, and oxygenated hydrocarbons such as oxygenated alkanes, oxygenated alkenes, oxygenated alkynes and oxygenated aromatic compounds, and particularly oxygenated hydrocarbons. In particular, the wastewater stream may advantageously contain organic compounds including or consisting of one or more of alcohols, carboxylic acids, aldehydes, ketones, esters, and ethers. In some embodiments, the wastewater stream may advantageously contain organic compounds including or consisting of one or more of alcohols, carboxylic acids, aldehydes and ketones. In some embodiments, the wastewater stream may advantageously contain organic compounds including or consisting of one or more of alcohols and carboxylic acids. In each of these, the oxygenated organic compounds are preferably oxygenated hydrocarbons containing only C, H and O atoms.

[0158] Preferably, the carbon chain length (Cx) of the organic compounds is short, such as up to C10, up to Cs or up to Cs.

[0159] Preferably, the organic compounds include short-chain oxygenated hydrocarbons, particularly C1-C5 alcohols, C1-C5 carboxylic acids, C1-C5 aldehydes and / or C1-C5 ketones. Further preferably, the organic compounds include these short-chain oxygenated hydrocarbons as the majority component of the organic compounds. Further preferably, the organic compounds include C1-C5 alcohols as the majority component of the organic compounds.

[0160] As explained above, the proportion of organic compounds is lower than the proportion of aqueous component by weight. The wastewater stream which is produced by or issued from the industrial process plant typically comprises the organic compounds in a first concentration of at most 25 wt%. That is, the first concentration, which is the total concentration of all organic compounds in the wastewater stream, is more than 0 wt% and may be up to 25wt%, based on the total weight (100 wt%) of the wastewater stream.

[0161] The first concentration may be at most 20 wt%, at most 15 wt% or at most 10 wt%. The first concentration may be at least 0.5 wt%, at least 0.75 wt%, at least 1 .0 wt% or at least 1 .5 wt%. Any of the foregoing may be combined to form a suitable range, such as between 0.5 and 25 wt%, between 0.5 and 20 wt%, between 0.75 and 15 wt% or between 1 .5 and 10 wt%.

[0162] The concentration of the organic compounds may be measured using any method known in the art. Particularly mentioned is the total organic carbon (TOC) measurement method. TOC measurement involves oxidizing the organic compounds to forms which can be quantified, using for example high-temperature combustion (e.g. at around 1200°C) or catalytic oxidation (at e.g. around 680°C) in oxygen to produce CO2, among others, and measuring TOC using non-dispersive infrared absorption (NDIR). Suitable TOC analyzers are available from e.g. ELGA® LabWater.

[0163] Other methods of measuring the amounts of organic compounds in a wastewater stream may include gas chromatography including 2D gas chromatography, NMR, combustion-based methods such as TOC or elemental analysis such as x-ray fluorescence or inductively coupled plasma spectroscopy. TOC may be particularly suitable for in-line measurements.

[0164] The wastewater stream output from the industrial process plant wastewater stream output unit is directed to an electrochemical cell in the present method. The manner in which the system of the present disclosure is configured to direct the wastewater is not particularly limited.

[0165] In some embodiments, the wastewater stream is sent directly to the electrochemical cell. In some such embodiments, the concentration of organic compounds input to the electrochemical cell corresponds with the first concentration.

[0166] In other embodiments, the wastewater stream is sent indirectly to the electrochemical cell, i.e. there are other units in the system of the disclosure between the wastewater stream output unit and the electrochemical cell through which the wastewater stream passes. Such other unit(s) may affect the concentration of the organic compounds in the wastewater stream. In some such embodiments, the concentration of organic compounds input to the electrochemical cell does not correspond with the first concentration.

[0167] In some embodiments, the wastewater stream is sent to the electrochemical cell via a concentration adjustment unit i.e. a concentrating unit and / or a diluting unit is included in the system of the disclosure. Such unit is intended to adjust the concentration of the organic compounds in the wastewater stream. The resulting concentration output from a concentration adjustment unit is labelled herein as an adjusted first concentration.

[0168] In some embodiments, the wastewater stream is sent to the electrochemical cell via one or more other kinds of unit i.e. a different unit is included in the system of the disclosure. Such unit(s) may change the concentration of the organic compounds in the wastewater stream from the first concentration or from the first adjusted concentration, depending on the location and nature of such unit(s). This change may be to a lesser extent than from the first concentration to the adjusted first concentration. For example, the wastewater stream may have a high temperature (such as more than 100°C, more than 150°C, or more than 200°C) when issued from the industrial process plant. This may be particularly true when the industrial process plant wastewater stream output unit includes a reactor, and the reactor is at high temperature to create effective reaction conditions, so that the issuing wastewater stream is also at a high temperature and may therefore be gaseous. In some embodiments, the wastewater stream is passed through one or more cooling units before it arrives at the electrochemical cell. The system of the disclosure may comprise one or more cooling unit upstream of the electrochemical cell. This may be useful in embodiments where the optimal operating temperature of the electrochemical cell is lower than the temperature of the wastewater stream output from the industrial process plant wastewater stream output unit. For example, some CO2 electrolysers optimally function at room temperature.

[0169] In another example, the wastewater stream may pass through one or more water purification units as described herein. The system of the disclosure may comprise one or more water purification unit upstream of the electrochemical cell. A water purification unit may be used e.g. to remove inorganic contaminants as discussed elsewhere herein. This may cause a change to the concentration of the organic compounds in the wastewater stream.

[0170] A water purification unit might be useful if the wastewater stream output from the industrial process plant wastewater stream output unit contains other contaminants that might affect the operation of the electrochemical cell. The amount or proportion of other contaminants is not considered relevant to the present method and system in principle. It may be preferable to reduce, minimise or remove such contaminants before sending the wastewater stream to the electrochemical cell in some embodiments. Examples of such contaminants include metallic or metallic ion contaminants, for example those containing Fe, Ni, Cr, their ions, or inorganic contaminants. Metal and metal ion contaminants may originate from sources such as reactor walls, any piping through which the wastewater stream passes, any catalyst used in a reactor or elsewhere. Inorganic contaminants may originate from, for example, components present in a reactor. A water purification unit may be included upstream of the electrochemical cell and downstream of the industrial process plant wastewater stream output unit. The water purification unit may be upstream or downstream of any concentrating or diluting unit. The present disclosure refers to an input concentration of organic compounds in the wastewater stream, which is the concentration input to the electrochemical cell. The input concentration may be the first concentration. The input concentration may be the adjusted first concentration.

[0171] In some embodiments, the concentration of the organic compounds in the wastewater stream is lowered or decreased by the electrochemical cell from the input concentration by at least 10 wt%, at least 20 wt%, at least 30 wt% or at least 40 wt%, where 100 wt% is the total amount of organic compounds input to the electrochemical cell. In some embodiments, the concentration of the organic compounds in the wastewater stream is lowered or decreased by the electrochemical cell by up to 100 wt% (i.e. 100% purification), up to 90 wt%, up to 80 wt% or up to 75 wt%. Any of the foregoing may be combined to form a suitable range, such as between 10 and 100 wt%, between 20 and 80 wt%, between 30 and 90 wt%, or between 40 and 75 wt%.

[0172] It will be appreciated that the electrochemical cell may lower the concentration of one organic compound by a different amount than it lowers another organic compound. The relative reduction across different organic compounds is not particularly limited herein.

[0173] It will also be appreciated that the first concentration and the amount by which the input concentration is decreased, may vary between runs or cycles, or within a single run or cycle, of the industrial process plant e.g. reactor thereof. This can be monitored as discussed elsewhere herein, and / or adjusted using any of the proposals herein.

[0174] Electrochemical cell

[0175] The method of the disclosure includes sending the wastewater stream issued by the industrial process plant wastewater stream output unit to an electrochemical cell. The system of the disclosure thus comprises an electrochemical cell downstream of the industrial process plant wastewater stream output unit, for example a reactor which issues the wastewater stream.

[0176] The electrochemical cell is capable of oxidizing at least some of the organic compounds of the wastewater stream at an anode thereof. The electrochemical cell may be capable of introducing oxygen into the organic compounds of the wastewater stream. Accordingly, at least some of the organic compounds present in the wastewater stream may form one or more gaseous compounds such as CO or CO2 in the electrochemical cell. In this way, the concentration of the organic compounds in the wastewater stream output from the electrochemical cell is lower than that input into the electrochemical cell.

[0177] Appropriate input concentrations for use in the present method and system may depend on the choice of electrochemical cell, but may be for example up to 20 wt%, up to 15 wt% or up to 10 wt%. Appropriate minimum input concentrations may be for example at least 1 wt%, at least 2 wt%, at least 3 wt%, or at least 4 wt%. Any of the foregoing may be combined to form an appropriate range, such as between 1 -20 wt%, between 2-15 wt%, between 3-20 wt% or between 4-10 wt%.

[0178] The method described herein may operate continuously or discontinuously. Accordingly, wastewater may be sent to the electrochemical cell continuously or discontinuously. The extent of discontinuity is not particularly limited.

[0179] As used herein, electrochemical cell includes a device capable of using electrical energy in carrying out a chemical reaction. The electrochemical cell used in the present disclosure may be any suitable, as long as it is capable of carrying out the oxidation reaction at the anode thereof, and examples include a fuel cell and an electrolyser.

[0180] Preferably, the electrochemical cell is capable of operating at temperatures up to around 100°C, such as up to around 90°C, up to around 80°C, up to 70°C or up to 60°C. Such operating temperatures may advantageously reduce, minimise or eliminate the need to cool the wastewater stream output from the industrial process plant wastewater stream output unit before it is processed in the electrochemical cell. In some embodiments, a cooling unit is provided downstream of the industrial process plant and upstream of the electrochemical cell as explained elsewhere herein.

[0181] Preferably, the electrochemical cell operates at ambient (atmospheric) pressure.

[0182] Preferably, the electrochemical cell is capable of oxidizing a variety of different kinds of organic compounds. Preferably, the electrochemical cell is capable of oxidizing one or more hydrocarbons, particularly one or more oxygenated hydrocarbons such as alcohols, carboxylic acids, aldehydes, and ketones, particularly all of these. Preferably, the electrochemical cell is capable of oxidizing organic alcohols, particularly preferably C1-C5 organic alcohols.

[0183] Particularly preferred electrochemical cells include direct alcohol fuel cells (DAFCs), alcohol electrolysers and CO2 electrolysers. These kinds of electrochemical cells are known in themselves. See, for example, Berretti et al., “Direct Alcohol Fuel Cells: A Comparative Review of Acidic and Alkaline Systems”, Electrochemical Energy Reviews (2023) 6:30; Zakaria et al., “Membranes for direct ethanol fuel cells: An overview”, Applied Energy 163 (2016) 334-342; Cloutier and Wilkinson, “Electrolytic production of hydrogen from aqueous acidic methanol solutions”, International Journal of Hydrogen Energy 35 (2010) 3967-3984; and Lamy et al., “Clean hydrogen generation through the electrocatalytic oxidation of ethanol in a Proton Exchange Membrane Electrolysis Cell (PEMED): Effect of the nature and structure of the catalytic anode”, Journal of Power Sources 245 (2014) 927-936. Accordingly, the form of the electrochemical cells in terms of e.g. the nature of the electrode catalysts, any separator etc. may be of the conventional or known type.

[0184] The system of the present disclosure may comprise more than one of these kinds of electrochemical cell, though in general it is envisaged that the system will typically have only one of these for economic reasons.

[0185] In general, the oxidation reaction described herein occurs at the anode of the electrochemical cell.

[0186] The reaction(s) that occur(s) at the cathode of the electrochemical cell may vary according to the type of electrochemical cell that is used.

[0187] Some of the organic molecules of the wastewater stream may be only partially oxidised by the electrochemical cell. For example, hydrocarbons may be partially oxidized to form organic acids or aldehydes / ketones etc., or oxygenated hydrocarbons such as alcohols may be partially oxidised to form an aldehyde or ketone, or to form a carboxylic acid. For these organic compounds, further oxidation may be desirable to remove them from the wastewater stream. This can be carried out by, for example, any suitable oxidation process such as a chemical oxidation process.

[0188] Concentratinq / Dilutinq Units

[0189] In some embodiments, the first concentration of organic compounds in the wastewater stream as output from the industrial process plant wastewater stream output unit is not suitable for use directly in the electrochemical cell. For example, the first concentration may be too high or too low for the electrochemical cell to function, or the first concentration may not be optimal e.g. for efficiency reasons. Accordingly, it may be desirable to include a concentration adjustment unit between the industrial process plant wastewater stream output unit and the electrochemical cell, that is capable of adjusting the concentration of organic compounds to a desired adjusted first concentration, which adjusted first concentration corresponds with the input concentration. In some such embodiments, the concentration of organic compounds in the wastewater stream output from the electrochemical cell is lower than the adjusted first concentration.

[0190] In a method and system where the first concentration of organic compounds in the wastewater stream as output from the industrial process plant wastewater stream output unit is higher than desirable for use in the electrochemical cell, then a diluting unit may preferably be included in the system, upstream of the electrochemical cell and downstream of the industrial process plant wastewater stream output unit. In this way, the wastewater stream having a first concentration of organic molecules can flow from the industrial process plant wastewater stream output unit to the diluting unit, become diluted to a desired adjusted first concentration, and then flow to the electrochemical cell for oxidation.

[0191] In a method and system where the first concentration of organic compounds in the wastewater stream as output from the industrial process plant wastewater stream output unit is lower than desirable for use in the electrochemical cell, then a concentrating unit may preferably be included in the system, upstream of the electrochemical cell and downstream of the industrial process plant wastewater stream output unit. In this way, the wastewater stream having a first concentration of organic molecules can flow from the industrial process plant wastewater stream output unit to the concentrating unit, become concentrated to a desired adjusted first concentration, and then flow to the electrochemical cell for oxidation.

[0192] Suitable concentrating units and diluting units are known in the art. For example, a concentrating unit may contain or comprise a molecular sieve capable of removing water to thereby increase the concentration of the organic compounds in the wastewater stream.

[0193] The present method and system may employ a concentrating unit, or a diluting unit, or both a concentrating unit and a diluting unit as desired. The present method and system may employ more than one concentrating unit or diluting unit or more than one of each of the concentrating unit and diluting unit. Typically, the presence of only one is expected to be most economically useful.

[0194] Other options Once the wastewater stream comprising the organic compounds at a lowered concentration (e.g. down to 0 wt%) is output from the electrochemical cell, one or more other units may be included.

[0195] In some embodiments, the method and system include one or more separation units e.g. to separate gases from liquids, or to separate liquids from liquids.

[0196] In some embodiments, the method and system include one or more purification units downstream of the electrochemical cell. Such purification unit may remove inorganic contaminants or metal contaminants, for example, as discussed elsewhere herein.

[0197] In some embodiments, the method and system include one or more oxidation treatment units. The oxidation treatment unit may be capable of further oxidising organic compounds in the wastewater stream which are not oxidized, or only partially oxidized, by the electrochemical cell. The presence of the oxidation treatment unit may depend on the extent to which the electrochemical cell is capable of oxidizing the organic compounds. Typically, the oxidation treatment unit is downstream of the electrochemical cell, and preferably downstream of any gas / liquid separator unit.

[0198] The method and system herein preferably include one or more downstream electrolyser, located downstream of the electrochemical cell. In some embodiments, the downstream electrolyser is preferably a Kolbe electrolyser. The system may be configured so that the downstream electrolyser receives the wastewater stream output from the electrochemical cell at the anode of the downstream electrolyser. The wastewater stream may have passed through a separator unit and / or an oxidation treatment unit located upstream of the downstream electrolyser and downstream of the electrochemical cell.

[0199] The downstream electrolyser may be capable of oxidizing at an anode thereof any remaining organic acids, or anions of such acids. Accordingly, the system and method herein comprising the downstream electrolyser also comprises at least one alkali treatment unit.

[0200] In some embodiments, the method and system include one or more alkali treatment units. The alkali treatment unit may be capable of generating anions suitable as input for the downstream electrolyser, particularly a Kolbe electrolyser. The alkali treatment unit may be suitably located upstream of a downstream electrolyser. The downstream electrolyser, particularly a Kolbe electrolyser, may output hydrocarbons, CO2 and / or hydrogen. Optionally, the method and system may advantageously be configured to combust output hydrocarbons to generate heat for the industrial process plant. Following combustion, the combustion gas(es) may advantageously be captured and returned to the electrochemical cells.

[0201] The method and system herein preferably include an upstream electrolyser, preferably a water electrolyser, located upstream of the electrochemical cell. The system may be configured so that the upstream electrolyser receives any water which is removed at a concentrating unit or at a water purification unit downstream of the industrial process plant wastewater stream output unit and upstream of the electrochemical cell, at an anode thereof.

[0202] In some embodiments, a purifier, such as a reverse osmosis (RO) purifier, is present upstream of the upstream electrolyser, for purifying the water sent thereto. The upstream electrolyser, particularly a water electrolyser, may output oxygen at an anode thereof and hydrogen at a cathode thereof.

[0203] In the method and system herein, any like products produced by any of the various units may optionally be combined. For example, CO2 output from the electrochemical cell (optionally via a gas / liq u id separator unit) may be combined with CO2 produced by the anode of the downstream electrolyser. Similarly, hydrogen produced at the cathode of a downstream electrolyser may be combined with hydrogen produced at the cathode of an upstream electrolyser.

[0204] Any method and system herein may include a CO2 capture unit. Such unit is configured to capture CO2 produced, which may be produced at any of the electrochemical cell and / or downstream electrolyser units.

[0205] Alternatively or additionally, any product output from the electrochemical cell or other optional units described herein may be used elsewhere in the present method and system. In such cases, the system may be configured to allow such use.

[0206] For example, where the electrochemical cell is a DAFC, oxygen produced at the anode of an upstream electrolyser may be used as input fuel for the cathode of the DAFC. Thus, the system may preferably be configured to direct the oxygen so produced to the cathode of the DAFC. For example, hydrocarbons and / or hydrogen produced by a downstream and / or upstream electrolyser may be converted into fuel for use in the industrial process plant, such as at a reactor thereof (e.g. the reactor from which the wastewater stream issues). Similarly, where the electrochemical cell is an alcohol electrolyser, the hydrogen produced at the cathode thereof may also or alternatively be converted into fuel for use in the industrial process plant, such as at a reactor thereof (e.g. the reactor from which the wastewater stream issues). Thus, the system may preferably be configured to produce such fuel and direct the fuel so produced.

[0207] For example, where the electrochemical cell is a CO2 electrolyser, any syngas (CO and hydrogen) produced at a cathode thereof may be used as input for the industrial process plant, such as a reactor thereof e.g. where the reactor is a Fischer-Tropsch reactor, this may be the same reactor as the reactor from which the wastewater stream issues. In some such embodiments, the system is configured to direct at least a portion of the hydrogen produced at the upstream electrolyser to the reactor, to adjust the ratio of CO:hydrogen.

[0208] Any of the method and system herein may include assessment of the wastewater stream at any stage. For example, the wastewater stream content may be assessed as it exits the industrial process plant wastewater stream output unit (e.g. to determine whether concentration or dilution may be valuable before input to the electrochemical cell), as it exits the electrochemical cell, and / or at any other desired point. The system may include suitable analyzers at the desired location.

[0209] DIRECT ALCOHOL FUEL CELL

[0210] In embodiments where the electrochemical cell is a DAFC and the system comprises an upstream water electrolyser, advantageously oxygen produced at the water electrolyser anode can be used as fuel for the cathode of the DAFC.

[0211] Where the electrochemical cell is a DAFC, advantageously electricity is produced at the cathode. The system herein may be configured to capture such electricity, and / or store the electricity and / or to use the electricity to power one or more of the electrochemical cell, upstream electrolyser and downstream electrolyser.

[0212] In some embodiments, the wastewater stream that is input to the DAFC has organic compounds at a concentration of at least 1 wt%, at least 2 wt%, at least 3 wt% or at least 4 wt%. In some embodiments, the wastewater stream that is input to the DAFC has organic compounds at a concentration of up to 15 wt%, up to 12 wt%, up to 10 wt% or up to 8 wt%. Any of the foregoing can be combined to form a suitable range, such as between 1 -15 wt%, 2-12 wt%, 2-8 wt% or 4-8 wt%, particularly 2-10 wt% (0.5- 2M).

[0213] Suitable set-ups for a DAFC are known in the art and conventional or commercially available DAFCs may be used. The particular form, catalyst (typically containing Pt) etc. is not particularly limited herein.

[0214] As shown in the exemplary system of Fig. 2, a system 21 comprising a DAFC 24 as electrochemical cell, are configured to direct the wastewater stream from the industrial process plant wastewater stream output unit 22 (a reactor in the present embodiment), optionally via a concentration or diluting unit and / or a purification unit 23, to the anode 24a of the DAFC 24. The organic compounds of the wastewater stream are oxidised at the anode 24a to form oxidized organic compounds that may include for example aldehydes, acids and CO2. Since the CO2 is a gaseous product, the wastewater stream that is output from the anode 24a has organic compounds at a lower concentration than the wastewater stream that is input at the anode of the DAFC 24.

[0215] The system 21 may comprise a separator unit 25 downstream of the DAFC 24. The separator unit 25 may be capable of separating gaseous component(s) output by the DAFC anode 24a from liquid component(s). As shown in Fig. 2, at the separator unit 25, the gaseous products, such as CO2, are separated from liquid.

[0216] The system 21 may comprise a CO2 capture unit 26, and the separated CO2 can be captured by the CO2 capture unit 26.

[0217] The system 21 may comprise a further oxidation treatment unit 25b, for oxidation of any organic compounds not oxidized by the electrochemical cell 24. In the example of Fig. 2, the further oxidation treatment unit 25b is included in the system 21 alongside the separator unit 25. It could be possible to include the further oxidation treatment unit 25b upstream of the separator unit 25, and downstream of the DAFC 24, if wanted.

[0218] The system 21 may comprise an alkali treatment unit 27, for generating organic acid anion for the Kolbe electrolysis. In the example of Fig. 2, the alkali treatment unit 27 is included in the system 21 downstream of the separator unit 25.

[0219] The system 21 may comprise an electrolyser unit 28 downstream of the electrochemical cell 24 (DAFC in the embodiment of Fig. 2). As shown in Fig. 2, the wastewater which has a lowered concentration of organic compounds and which has had the gaseous component(s) separated therefrom (and optionally which has undergone further oxidation or alkali treatment) may be directed to the anode 28a of the electrolyser. In some embodiments, the electrolyser 28 is a Kolbe electrolyser. The anode 28a of a Kolbe electrolyser may output CO2 and other hydrocarbons such as methane and ethane.

[0220] In some configurations, the CO2 output from the Kolbe electrolyser anode 28a may be captured, separately to or along with the separated CO2 output from the DAFC anode 24a, at the CO2 capture unit 26.

[0221] The hydrocarbons output from the Kolbe electrolyser anode 28a may be used for any desired purpose such as fuels.

[0222] The Kolbe electrolyser cathode 28c may output hydrogen, which can similarly be used for any desired purpose such as fuel.

[0223] The system 21 may be configured to supply the DAFC cathode 24c with oxygen as input. This may permit the DAFC cathode 24c to output electricity. The system 21 may be configured to capture the electricity, and store and / or use the electricity to provide power elsewhere in the system.

[0224] The system 21 may comprise an electrolyser 29 upstream of the electrochemical cell 24. The electrolyser 29 may be a water electrolyser. As shown in Fig. 2, the water electrolyser anode 29a may output O2 which can be advantageously used to supply the DAFC cathode 24c.

[0225] In embodiments where the system 21 includes a concentrating unit or purifying unit 23, for example, water of a higher purity than the wastewater stream may be generated during the concentrating process. In some embodiments, the system 21 is configured to direct this water to the water electrolyser anode 29a. Optionally, a water purifier, such as a reverse osmosis (RO) purifier 25d, may be included in the system 21 between the concentrating unit or purifying unit 23 and the water electrolyser anode 29a. In other embodiments, the water is provided by any other suitable route.

[0226] The water electrolyser cathode 29c may output hydrogen, which can be used for any desired purpose such as fuel.

[0227] ALCOHOL ELECTROLYSER

[0228] In embodiments in which the electrochemical cell is an alcohol electrolyser, it is preferred that the concentration of organic compounds in the wastewater stream input into the alcohol electrolyser is 25 wt% or lower. Thus, in some embodiments, the system is configured so that the wastewater stream that is output from the industrial process plant wastewater stream output unit is present at, or concentrated in a concentrating unit to achieve, an input concentration of 25 wt% or lower.

[0229] Accordingly, in some embodiments, the wastewater stream that is input to the alcohol electrolyser has organic compounds at a concentration of at least 10 wt%, at least 12 wt%, or at least 15 wt%. In some embodiments, the wastewater stream that is input to the alcohol electrolyser has organic compounds at a concentration of up to 25 wt%, up to 22 wt%, or up to 20 wt%. Any of the foregoing can be combined to form a suitable range, such as between 10-25 wt%, 12-25 wt%, 22-25 wt% or 15-25 wt%.

[0230] Embodiments including a concentrating unit may particularly benefit from the presence of a water electrolyser upstream of the electrochemical cell and upstream of the concentrating unit. For example, the water which is removed from the wastewater stream by the concentrating unit can be used as input for the upstream electrolyser. Accordingly, in preferred embodiments, the system is configured to have a concentrating unit and so that water from the wastewater stream which is not sent to the electrochemical cell for oxidation of the organic compounds is sent to the upstream electrolyser. Optionally, a purifier such as a reverse osmosis purification unit is included in such a system, depending on the purity of this water.

[0231] In an alcohol electrolyser, alcohol oxidation occurs at a thermodynamically lower potential than the oxygen evolution reaction. This can mean that the alcohol oxidizes more easily (i.e. oxidizes at a lower electrical energy input) than water. Following the electrochemical oxidation at the anode, the generated proton passes through a membrane of the alcohol electrolyser to the cathode and forms hydrogen when it combines with electrons from the power supplying the electrolyser cathode.

[0232] Suitable catalysts for use in the alcohol electrolyser are known to the skilled person. For example, bimetallic catalyst materials such as those comprising Pt, for example PtRu and PtSn, are considered suitable.

[0233] The alcohol electrolyser may preferably be a methanol electrolyser or an ethanol electrolyser. Preferably, the cathode is left open to the atmosphere (atmospheric pressure) and can be exposed to a temperature of from room temperature - around 20°C - to around 80°C. Accordingly, when a potential is applied across the anode and cathode, alcohol in the wastewater stream becomes oxidized on the anode generating CO2and protons. The CO2 may be captured using a CO2 capture unit or may be fed to a CO2 electrolyser discussed elsewhere herein.

[0234] The protons move through a membrane of the electrolyser to the cathode and combine e.g. with electrons from the power supply to the electrolyser, to form hydrogen.

[0235] Thus, advantageously, an alcohol electrolyser may produce hydrogen at the cathode. The hydrogen may be used, for example, as part of an input gas for the industrial process plant e.g. a reactor thereof, or as a fuel.

[0236] As shown in the exemplary system of Fig. 3, a system 31 comprising an alcohol electrolyser 34 as electrochemical cell, are configured to direct the wastewater stream from the industrial process plant wastewater stream output unit 32 (a reactor in the present embodiment), optionally via a concentration or diluting unit and / or a purification unit 33, to the anode 34a of the alcohol electrolyser 34. The organic compounds of the wastewater stream are oxidised at the anode 34a to form oxidized organic compounds that may include for example aldehydes, acids and CO2. Since the CO2 is a gaseous product, the wastewater stream that is output from the anode 34a has organic compounds at a lower concentration than the wastewater stream that is input at the anode of the alcohol electrolyser 34.

[0237] The system 31 may comprise a separator unit 35 downstream of the alcohol electrolyser 34. The separator unit 35 may be capable of separating gaseous component(s) output by the alcohol electrolyser anode 34a from liquid component(s). As shown in Fig. 3, at the separator unit 35, the gaseous products, especially CO2, are separated from liquid.

[0238] The system 31 may comprise a CO2 capture unit 36, and the separated CO2 can be captured by the CO2 capture unit 36.

[0239] The system 31 may comprise a further oxidation treatment unit 35b, for oxidation of any organic compounds not oxidized by the electrochemical cell 34. In the example of Fig. 3, the further oxidation treatment unit 35b is included in the system 31 alongside the separator unit 35. It could be possible to include the further oxidation treatment unit 35b upstream of the separator unit 35, and downstream of the alcohol electrolyser 34, if wanted. The system 31 may comprise an alkali treatment unit 37 for generating organic acid anion for the Kolbe electrolysis. In the example of Fig. 3, the alkali treatment unit 37 is included in the system 31 downstream of the separator unit 35.

[0240] The system 31 may comprise an electrolyser unit 38 downstream of the electrochemical cell 34 (alcohol electrolyser in the embodiment of Fig. 3). As shown in Fig. 3, the wastewater which has the decreased concentration of organic compounds and which has had the gaseous component separated therefrom (and optionally which has undergone further oxidation treatment) may be directed to the anode 38a of the electrolyser. In some embodiments, the electrolyser 38 is a Kolbe electrolyser. The anode 38a of the Kolbe electrolyser may output CO2 and other hydrocarbons such as methane and ethane.

[0241] In some configurations, the CO2 output from the Kolbe electrolyser anode 38a may be captured, separately to or along with the separated CO2 output from the alcohol electrolyser anode 34a, at the CO2 capture unit 36.

[0242] The hydrocarbons output from the Kolbe electrolyser anode 38a may be used for any desired purpose such as fuels.

[0243] The Kolbe electrolyser cathode 38c may output hydrogen, which can similarly be used for any desired purpose such as fuel.

[0244] The alcohol electrolyser cathode 34c may output hydrogen, which can similarly be used for any desired purpose such as fuel. The system 31 may be configured to capture the hydrogen from both the alcohol electrolyser cathode 34c and the Kolbe electrolyser cathode 34c and combine them, if wanted.

[0245] The system 31 may comprise an electrolyser 39 upstream of the electrochemical cell 34. The electrolyser 39 may be a water electrolyser. As shown in Fig. 3, the water electrolyser anode 39a may output O2 which can be used in any desired way.

[0246] In embodiments where the system 31 includes a concentrating unit or purifying unit 33, for example, water of a higher purity than the wastewater stream may be generated during the concentrating process. In some embodiments, the system 31 is configured to direct this water to the water electrolyser anode 39a. Optionally, a water purifier, such as a reverse osmosis (RO) purifier 35d, may be included in the system 31 between the concentrating unit or purifying unit 33 and the water electrolyser anode 39a. In other embodiments, the water is provided by any other suitable route. The water electrolyser cathode 39c may output hydrogen, which can be used for any desired purpose such as fuel.

[0247] The system may be configured to use the hydrogen output from the alcohol electrolyser cathode 34c and, where present, the Kolbe electrolyser anode 38a and / or the water electrolyser cathode 39c, to use as input for the reactor 32. This may be appropriate where the reactor 32 uses hydrogen as an input gas for reaction, for example. Exemplary such reactors 32 include Fischer-Tropsch reactors 32.

[0248] CO2ELECTROLYSER

[0249] In embodiments in which the electrochemical cell is a CO2 electrolyser, it is preferred that the concentration of organic compounds in the wastewater stream input into the CO2 electrolyser is 25 wt% or lower. Thus, in some embodiments, the system is configured so that the wastewater stream that is output from the industrial process plant wastewater stream output unit is present at, or concentrated in a concentrating unit to achieve, an input concentration of 25 wt% or lower.

[0250] Accordingly, in some embodiments, the wastewater stream that is input to the CO2 electrolyser has organic compounds at a concentration of at least 10 wt%, at least 12 wt%, or at least 15 wt%. In some embodiments, the wastewater stream that is input to the CO2 electrolyser has organic compounds at a concentration of up to 25 wt%, up to 22 wt%, or up to 20 wt%. Any of the foregoing can be combined to form a suitable range, such as between 10-25 wt%, 12-25 wt%, 22-25 wt% or 15-25 wt%.

[0251] Embodiments including a concentrating unit may particularly benefit from the presence of a water electrolyser upstream of the electrochemical cell and upstream of the concentrating unit. For example, the water which is removed from the wastewater stream by the concentrating unit can be used as input for the upstream electrolyser. Accordingly, in preferred embodiments, the system is configured to have a concentrating unit and so that water from the wastewater stream which is not sent to the electrochemical cell for oxidation of the organic compounds is sent to the upstream electrolyser. Optionally, a purifier such as a reverse osmosis purification unit is included in such a system, depending on the purity of this water.

[0252] At the anode of the CO2 electrolyser, the organic compounds are oxidized as discussed elsewhere herein to e.g. aldehydes, organic acids, or CO2. Conventionally, a CO2 electrolyser uses water as feedstock at the anode to counter CO2 reduction on the cathode (generating oxygen at the anode). In the present proposals, the water is provided by the wastewater stream and the oxygen evolution reaction is replaced with a thermodynamically more favourable organic oxidation reaction.

[0253] Preferably, the CO2 electrolyser is Gas Diffusion Electrode (GDE) or Membrane Electrode Assembly (MEA) type.

[0254] The product of the reaction at the anode of the CO2 electrolyser can be influenced by e.g. the potential applied, the chemical composition of the wastewater stream, the catalyst, and temperature.

[0255] The CO2 source for the CO2 electrolyser cathode may be any suitable source. For example, if appropriate, a flue gas preferably from a reactor of the system, or from another reactor, may be used. Alternatively, CO2 may be captured from the air.

[0256] Accordingly, where the electrochemical cell is a CO2 electrolyser, two relatively low- value feedstocks (CO2 and wastewater) may advantageously be used to generate more valuable products (such as syngas, alkenes, organic acids, alcohols etc.). Additionally advantageously, the CO2 produced at the anode can be used to feed the cathode.

[0257] In embodiments where the electrochemical cell is a CO2 electrolyser and the system also comprises a downstream electrolyser e.g. a Kolbe electrolyser, the system can be configured so that the CO2 generated by the downstream electrolyser can feed the CO2 electrolyser cathode.

[0258] In some embodiments, syngas is formed at the CO2 electrolyser cathode, optionally at near 100% faradaic efficiency. The system may be configured to feed the syngas back to a reactor component of the industrial process plant. Optionally, the system comprises a mixing tank and syngas fed from the CO2 electrolyser cathode is mixed with hydrogen from an upstream electrolyser to adjust the ratio of CO:hydrogen mixture.

[0259] In some embodiments, methanoic acid is formed at the CO2 electrolyser cathode, optionally at near 100% faradaic efficiency. The system may be configured to feed the methanoic acid to the downstream (Kolbe) electrolyser, via the further oxidation treatment unit. In some embodiments, ethylene is formed at the CO2 electrolyser cathode, optionally at near 100% faradaic efficiency. The system may be configured to separate the ethylene from other produced products. The separated ethylene may be used in any desired process, such as an intermediate in the manufacture of other products such as fuel.

[0260] In some embodiments, methanol is formed at the CO2 electrolyser cathode, optionally at near 100% faradaic efficiency. The system may be configured to feed the methanol back to the CO2 electrolyser anode inlet for oxidation.

[0261] In some embodiments, ethanol is formed at the CO2 electrolyser cathode, optionally at near 100% faradaic efficiency. The system may be configured to feed the methanol back to the CO2 electrolyser anode inlet for oxidation.

[0262] As shown in the exemplary systems of Figs. 4-8, a system 41 ,51 ,61 ,71 ,81 comprising a CO2 electrolyser 44,54,64,74,84 as electrochemical cell, are configured to direct the wastewater stream from the industrial process plant wastewater stream output unit 42,52,62,72,82 (a reactor in the present embodiments), optionally via a concentration or diluting unit and / or a purification unit 43,53,63,73,83 to the anode 44a, 54a, 64a, 74a, 84a of the CO2 electrolyser 44,54,64,74,84. The organic compounds of the wastewater stream are oxidised at the anode 44a, 54a, 64a, 74a, 84a to form oxidized organic compounds that may include for example aldehydes, acids and CO2. Since the CO2 is a gaseous product, the wastewater stream that is output from the anode 44a, 54a, 64a, 74a, 84a has organic compounds at a lower concentration than the wastewater stream that is input at the anode of the CO2 electrolyser 44,54,64,74,84. The CO2 electrolyser herein is shown as an MEA type for simplification.

[0263] The system 41 ,51 ,61 ,71 ,81 may comprise a separator unit 45,55,65,75,85 downstream of the CO2 electrolyser 44,54,64,74,84. The separator unit 45,55,65,75,85 may be capable of separating gaseous component(s) output by the CO2 electrolyser anode 44a, 54a, 64a, 74a, 84a from liquid component(s). As shown in Figs. 4-8, at the separator unit 45,55,65,75,85 the gaseous products, especially CO2, are separated from liquid.

[0264] The system 41 ,51 ,61 ,71 ,81 may comprise a CO2 capture unit (not shown), and the separated CC can be captured by the CO2 capture unit. The system 41 ,51 ,61 ,71 ,81 may comprise an alkali treatment unit 47,57,67,77,87 for generating organic acid anion for the Kolbe electrolysis. In the examples of Figs. 4-8, the alkali treatment unit 47,57,67,77,87 is included in the system 41 ,51 ,61 ,71 ,81 downstream of the separator unit 45,55,65,75,85.

[0265] The system 41 ,51 ,61 ,71 ,81 may comprise a further oxidation treatment unit 45b, 55b, 65b, 75b, 85b for oxidation of any organic compounds not oxidized by the electrochemical cell 44,54,64,74,84. In the examples of Figs. 4-8, the further oxidation treatment unit 45b, 55b, 65b, 75b, 85b is included in the system 41 ,51 ,61 ,71 ,81 alongside the separator unit 45,55,65,75,85. It could be possible to include the further oxidation treatment unit 45b, 55b, 65b, 75b, 85b upstream of the separator unit 45,55,65,75,85, and downstream of the alcohol electrolyser 44,54,64,74,84, if wanted.

[0266] The system 41 ,51 ,61 ,71 ,81 may comprise an electrolyser unit 48,58,68,78,88 downstream of the electrochemical cell 44,54,64,74,84 (CO2 electrolyser in the embodiment of Figs. 4-8). As shown in Figs. 4-8, the wastewater which has the decreased concentration of organic compounds and which has had the gaseous component separated therefrom (and optionally which has undergone further oxidation treatment) may be directed to the anode 48a, 58a, 68a, 78a, 88a of the electrolyser. In some embodiments, the electrolyser 48,58,68,78,88 is a Kolbe electrolyser, as is seen in the embodiments of Figs. 4-8. The anode 48a, 58a, 68a, 78a, 88a of the Kolbe electrolyser may output CO2 and other hydrocarbons such as methane and ethane.

[0267] In some configurations, the CO2 output from the Kolbe electrolyser anode 48a, 58a, 68a, 78a, 88a may be captured, separately to or along with the separated CO2 output from the alcohol electrolyser anode 44a, 54a, 64a, 74a, 84a at the CO2 capture unit.

[0268] The hydrocarbons output from the Kolbe electrolyser anode 48a, 58a, 68a, 78a, 88a may be used for any desired purpose such as fuels.

[0269] The Kolbe electrolyser cathode 48c, 58c, 68c, 78c, 88c may output hydrogen, which can similarly be used for any desired purpose such as fuel.

[0270] The CO2 electrolyser cathode 44c, 54c, 64c, 74c, 84c may be supplied with CO2 from any suitable source. The system 41 ,51 ,61 ,71 ,81 may comprise an electrolyser 49,59,69,79,89 upstream of the electrochemical cell 44,54,64,74,84. The electrolyser 49,59,69,79,89 may be a water electrolyser. As shown in Figs. 4-8, the water electrolyser anode 49a59a,69a,79a,89a may output O2 which can be used in any desired way.

[0271] In embodiments where the system 41 ,51 ,61 ,71 ,81 includes a concentrating unit or purifying unit 43,53,63,73,83, for example, water of a higher purity than the wastewater stream may be generated during the concentrating process. In some embodiments, the system 41 ,51 ,61 ,71 ,81 is configured to direct this water to the water electrolyser anode 49a, 59a, 69a, 79a, 89a. Optionally, a water purifier, such as a reverse osmosis (RO) purifier, may be included in the system 41 ,51 ,61 ,71 ,81 between the concentrating unit or purifying unit 43,53,63,73,83 and the water electrolyser anode 49a, 59a, 69a, 79a, 89a. In other embodiments, the water is provided by any other suitable route.

[0272] The water electrolyser cathode 49c, 59c, 69c, 79c, 89c may output hydrogen, which can be used for any desired purpose such as fuel.

[0273] As shown in the embodiment of Fig. 4, the CO2 electrolyser cathode 44c may output any one or more of short chain carboxylic acids (e.g. methanoic acid), short chain alkenes (e.g. ethylene), short chain alcohols (e.g. methanol and / or ethanol), CO, CO2, and hydrogen. These outputs can be further processed (for example, CO2 and CO can be separated, or CO can be oxidised to increase CO2 production). In some embodiments, the final output includes oxidized products such as carboxylic acids, alkenes, and CO2. These products can be used as desired. The system 41 may be configured to capture the CO2 from both the CO2 electrolyser cathode 34c and the CO2 electrolyser anode 34a, and, where present, the Kolbe electrolyser anode 34a and combine them, if wanted.

[0274] The system may in some embodiments be configured to use the hydrogen output from, where present, the Kolbe electrolyser anode 48a and / or the water electrolyser cathode 49c, to use as input for the reactor 42. This may be appropriate where the reactor 42 uses hydrogen as an input gas for reaction, for example. Exemplary such reactors 42 include Fischer-Tropsch reactors 42.

[0275] It may be possible to tune the output of the CO2 electrolyser cathode 44c, 54c, 64c, 74c, 84c. In a first example, as shown in the embodiment of Fig. 5, the main output of the CO2 electrolyser cathode 54c may contain gaseous products such as CO, hydrogen, and CO2. These products may be further processed, such as through a CO2 separator, to separate the CO2 from other products such as CO and hydrogen.

[0276] In turn, the recovered CO2 may be captured, optionally combined with the CO2 separated from the gas / liquid separator 55, and, where present, from the Kolbe electrolyser anode 58a, to be used in any desired way.

[0277] Meanwhile, the separated CO and hydrogen may be used as fuel (syngas) for the reactor 52. The particular ratio of CO:hydrogen (H2) may be adjusted, if required, before being fed to the reactor. Accordingly, in some embodiments, the system 51 is configured to adjust the ratio of CO:hydrogen produced by the CO2 electrolyser cathode 54c using the hydrogen produced by the water electrolyser cathode 59c, where present. In particular, the proportion of hydrogen can be increased by such configuration.

[0278] In a second example, as shown in the embodiment of Fig. 6, the main output of the CO2 electrolyser cathode 64c may contain gaseous products such as CO2 and C2H4. These products may be further processed, such as through a CO2 separator, to separate the CC from the C2H4.

[0279] In turn, the recovered CO2 may be captured, optionally combined with the CO2 separated from the gas / liquid separator 55, and, where present, from the Kolbe electrolyser anode 58a, to be used in any desired way.

[0280] Meanwhile, the separated C2H4 may be used in a downstream process such as oligomerization process, and subsequently used as fuel.

[0281] In a third example, as shown in the embodiment of Fig. 7, the main output of the CO2 electrolyser cathode 74c may include methanoic acid and CO2. The CO2 may be separated at a CO2 separator and used as described for the embodiment of Fig. 6. The methanoic acid can be used in the optional oxidation treatment unit 77. That is, the system 71 can be configured to deliver the methanoic acid product of the CO2 electrolyser cathode 74c to the alkali treatment unit 77 so that the CO2 electrolyser cathode 54c product can be used to further oxidise the organic compounds already oxidised at the anode of the CO2 electrolyser 74a. In a fourth example, as shown in the embodiment of Fig. 8, the main output of the CO2 electrolyser cathode 84c may include alcohols such as ethanol and / or methanol. These may be used in any desired downstream process or use. The other features of the system of Fig. 8 are as described for the other embodiments describing use of a CO2 electrolyser.

[0282] In a fifth example, as shown in the embodiment of Fig. 9, a system 91 may comprise a wastewater stream 100 and a CO2 source 90 being fed to the CO2 electrolyser 94 at the anode and cathode thereof, respectively. The anodic product can be sent to a Kolbe electrolyser 98 to thereby produce, at an anode thereof, hydrocarbons 102 and CO2, which CO2 can subsequently be used as the CO2 source for the CO2 electrolyser 94 cathode. The Kolbe electrolyser 98 cathode product hydrogen 140 can be combined with the hydrogen 140 produced at the cathode of a water electrolyser 99. The water electrolyser 99 also produces oxygen at the anode. Renewable electricity 110 can be used to power each of the electrolysers 94,98,99. In this embodiment, the system is configured so that the process uses all the by-products generated in the electrochemical cell 94 and electrolysers 98,99 as valuable feedstocks and recycles them within a closed loop. As a whole, the inlet is CO2, wastewater and renewable energy, and output are syngas, ethene, hydrocarbon fuel and hydrogen fuel. All other products are recycled within the system. The oxygen generated can be used either within the reactor or as a chemical feedstock.

Claims

53CLAIMS1 . A method of processing a wastewater stream, the method comprising providing a wastewater stream from an industrial process plant, the wastewater stream comprising organic compounds; sending the wastewater stream comprising the organic compounds to a concentrating unit and increasing the concentration of organic compounds in the wastewater stream at the concentrating unit to provide a wastewater stream comprising the organic compounds at an adjusted first concentration, and sending the wastewater stream comprising the organic compounds at the adjusted first concentration to an electrochemical cell; and oxidising at least some of the organic compounds in the wastewater stream at an anode of the electrochemical cell to thereby lower the concentration of the organic compounds in the wastewater stream.

2. A method according to claim 1 , wherein the electrochemical cell comprises:(i) a direct alcohol fuel cell;(ii) an alcohol electrolyser; or(iii) a CO2 electrolyser.

3. A method according to any one of the preceding claims, wherein the method comprises sending the wastewater stream comprising the organic compounds to a diluting unit and adjusting the concentration of organic compounds in the wastewater stream at the diluting unit to provide a wastewater stream comprising the organic compounds at an adjusted second concentration, and sending the wastewater stream comprising the organic compounds at the adjusted second concentration to the electrochemical cell.

4. A method according to any one of the preceding claims, wherein the organic compounds comprise C1-C5 alcohols as a majority organic compound component.

5. A method according to any one of the preceding claims, wherein at least one upstream electrolyser is provided upstream of the electrochemical cell, and in the method an output from the at least one upstream electrolyser is fed to a cathode of the electrochemical cell, optionally wherein the at least one upstream electrolyser comprises a water electrolyser.

6. A method according to any one of the preceding claims, wherein a wastewater stream output from the anode of the electrochemical cell is sent to at least one54 downstream electrolyser located downstream of the electrochemical cell, optionally wherein the at least one downstream electrolyser comprises a Kolbe electrolyser.

7. A method according to claim 6, wherein the wastewater stream issues from a reactor and an output from the at least one downstream electrolyser is used as a fuel for the reactor.

8. A method according to any one of the preceding claims, wherein:(i) an output from a cathode of the electrochemical cell is recycled, and / or(ii) wherein a wastewater stream output from the anode of the electrochemical cell comprises CO2 and the CO2 is optionally captured using a CO2 capture unit; and / or(iii) wherein a wastewater stream output from the anode of the electrochemical cell is further purified; and / or(iv) a wastewater stream output from the electrochemical cell is sent to a separator unit and gases are separated from liquids at the separator unit; and / or(v) a wastewater stream output from the electrochemical cell is subjected to chemical oxidation at an oxidation treatment unit.

9. A method according to any one of the preceding claims, wherein:(a) the electrochemical cell comprises a direct alcohol fuel cell and, in the method O2 is fed to a cathode thereof and the direct alcohol fuel cell outputs electricity, and optionally wherein:(i) the output electricity is used to at least partially power the industrial process plant or the electrochemical cell;(ii) the O2 is fed from a water electrolyser located upstream of the direct alcohol fuel cell; or(b) wherein the electrochemical cell comprises an alcohol electrolyser and, in the method the alcohol electrolyser outputs hydrogen at a cathode thereof, and optionally wherein the output hydrogen is used as an input for the industrial process plant; or(c) wherein the electrochemical cell comprises a CO2 electrolyser and, in the method, CO2 is fed to a cathode thereof and the CO2 electrolyser outputs at least one of syngas, C2H4, formic acid, ethanol and methanol at the cathode, and optionally wherein(i) the output at least one of syngas, C2H4, formic acid, ethanol and methanol is used as an input for the industrial process plant; and / or(ii) the wastewater issues from a reactor and the CO2 is fed from the reactor.5510. A system comprising: an industrial process plant configured to provide a wastewater stream at a wastewater stream output unit, the wastewater stream comprising organic compounds; an electrochemical cell downstream of the wastewater stream output unit, wherein the electrochemical cell is configured to receive the wastewater stream comprising the organic compounds at an input concentration, oxidize at least some of the organic compounds at an anode thereof, and output the wastewater stream comprising the organic compounds at an output concentration, wherein the output concentration is lower than the input concentration; a concentrating unit, located downstream of the wastewater stream output unit and upstream of the electrochemical cell, wherein the concentrating unit is configured to output a wastewater stream having an adjusted first concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream from the wastewater stream output unit to the electrochemical cell via the concentrating unit.

11. A system according to claim 10, wherein the electrochemical cell comprises:(i) a direct alcohol fuel cell;(ii) an alcohol electrolyser; or(iii) a CO2 electrolyser.

12. A system according to any one of claims 10 to 11 , comprising at least one of:(i) a a diluting unit, located downstream of the wastewater stream output unit and upstream of the electrochemical cell, wherein the diluting unit is configured to output a wastewater stream having an adjusted second concentration of the organic compounds; and wherein the system is configured to direct the wastewater stream to the electrochemical cell via the diluting unit; and / or(ii) an upstream electrolyser located upstream of the electrochemical cell, which upstream electrolyser optionally comprises a water electrolyser; and / or(iii) a downstream electrolyser located downstream of the electrochemical cell, which downstream electrolyser optionally comprises a Kolbe electrolyser.

13. A system according to any one of claims 10 to 12, which is configured to direct at least one output of the electrochemical cell and / or of at least one downstream electrolyser as fuel for the industrial process plant.5614. A system according to any one of claims 10 to 13, comprising at least one of:(i) a separator unit capable of separating gases from liquids and / or an oxidation treatment unit, wherein the separator unit and / or the oxidation treatment unit are located downstream of the electrochemical cell; and / or(ii) a water purification unit; and / or(iii) a CO2 capture unit downstream of the electrochemical cell.

15. A system according to any one of claims 10 to 14, wherein:(a) the electrochemical cell comprises a direct alcohol fuel cell and the system is configured to feed O2 to a cathode thereof, so that the direct alcohol fuel cell outputs electricity, and optionally wherein(i) the system is configured to use the output electricity to at least partially power the system; and / or(ii) the system is configured to feed the O2 from a water electrolyser; or(b) wherein the electrochemical cell comprises an alcohol electrolyser capable of outputting hydrogen at a cathode thereof, and optionally wherein the system is configured to use the output hydrogen as an input for the industrial process plant; or(c) wherein the electrochemical cell comprises a CO2 electrolyser and the system is configured to feed CO2 to a cathode thereof, so that the CO2 electrolyser outputs at least one of syngas, C2H4, formic acid, ethanol and methanol at the cathode, and optionally wherein(i) the system is configured to use at least one of the output syngas, C2H4, formic acid, ethanol and / or methanol as input elsewhere in the system; and / or(ii) the wastewater stream issues from a reactor and the system is configured to feed the CO2 from the reactor.

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