HK1211565B - Efficient treatment of wastewater using electrochemical cell - Google Patents

Abstract

An efficient method and system for the electrochemical treatment of waste water comprising organic and/or inorganic pollutants is disclosed. The system comprises at least first and second solid polymer electrolyte electrolytic cell stacks in which each cell comprises a solid polymer, proton exchange membrane electrolyte operating without catholyte or other supporting electrolyte. The first and second stacks differ either in construction or operating condition. The cell stack design and operating conditions chosen provide for significantly greater operating efficiency.

Description

Efficient treatment of wastewater using electrochemical cells

Technical Field

The present invention relates to a method and system for electrochemically treating wastewater. In particular, the present invention relates to methods and systems for removing organic contaminants and oxidizing inorganic compounds using solid polymer membrane electrolyte electrochemical cells.

Background

The demand for new wastewater treatment technologies has increased substantially, driven by population growth and increased volumes of wastewater produced, stricter wastewater quality regulations, increased clean water costs and water shortages, awareness of conserving clean water sources, and replacement of aged wastewater systems. The industry is particularly forced by stricter discharge standards and cost pressures to eliminate its recalcitrant wastewater pollutants prior to discharge and to avoid increased water supply and effluent discharge costs by resorting to on-site water reuse and recirculation systems. There is a need for a cost effective, sustainable water treatment technology that does not require the addition of chemicals and does not produce secondary pollution, meets stringent water quality standards, and has minimal operational and maintenance requirements.

Industrial wastewater may contain organic compounds, many of which are toxic, persistent, and resistant to conventional biological and chemical wastewater treatment. The best way to treat refractory wastewater is by non-chemical oxidation techniques, such as electrochemical oxidation, which can mineralize the contaminants and reduce the organic load and toxicity of the waste. Electrochemical oxidation is sustainable, safe, and highly process efficient, eliminating a wide variety of contaminants such as persistent organic contaminants, dioxins, nitrogen-containing species (e.g., ammonia), drugs, pathogens, microorganisms, most preferential contaminants, and pesticides. There are two main ways of electro-oxidizing pollutants in wastewater. The first way is to oxidize the contaminant by indirect electrolysis, thereby generating a redox reagent in situ as a chemical reactant. The mediator may be a metal redox couple or a chemical agent (e.g., chlorine, ozone, peroxide). These processes require the addition of large amounts of chemicals and/or the supply of oxygen and produce secondary pollution, resulting in additional costs for disposing of the treated wastewater and operating and maintaining the process. The second way is to use direct electrochemical oxidation, where organic contaminants are oxidized on the anode surface.

A wide variety of cell configurations have been developed for direct electrochemical wastewater treatment including flow-through parallel plates, compartments, packed bed electrodes, stacked disks, concentric cylinders, moving bed electrodes, and pressure filters. However, common to all of these electrochemical cell configurations is poor operating efficiency, which results in high energy consumption. The waste water is used as an electrolyte and, in the case of a separate cell, as an anolyte and a catholyte. However, due to the extremely low ionic conductivity of the wastewater, a supporting electrolyte needs to be added to improve the cell efficiency and to obtain a reasonable cell voltage. This typically results in salt, base and/or acid concentrations that exceed the permitted pollutant discharge limits, thereby increasing the cost of disposing of the treated wastewater and balancing the cost of the plant for liquid electrolyte treatment. Large electrode spacing and low surface area electrodes are also major contributors to efficiency losses and increased energy consumption. Slow mass transport in the pores of the porous bed, un-optimized catalytic materials with poor reaction kinetics, high electrode overpotentials, and catalysts with low overpotentials for side reactions (e.g., oxygen evolution) also result in lower performance and efficiency losses. The use of cell component materials that passivate rapidly and increase cell resistivity and instability results in a loss of efficiency. Operating conditions also result in efficiency losses. At high mass and ion transport losses, at nominal operating current densities, the voltage is too low, so that incomplete destruction of organic contaminants occurs and an organic film blocks the catalyst sites, reducing performance and requiring cleaning of the electrode surface using cell reversal techniques.

For example, published PCT application WO9901382 discloses an electrolytic cell method and apparatus for purifying a fluid. The system advantageously includes means for adding one or more chemicals (e.g., acid, carbon dioxide, base, hydrogen peroxide, or salt) to the fluid to be treated. In another example, Andreward et al, in hazardous materials journal (J.Haz.Mats.)153,252-260(2008), disclose the use of a divided electrolytic cell to treat simulated phenol wastewater. A sulfuric acid supporting electrolyte is required.

To eliminate the need for supporting electrolyte addition, different approaches have been developed that reduce the electrode spacing in single compartment electrochemical cell configurations. For example, US6328875 discloses the use of a porous anode allowing wastewater to flow through the capillary inter-electrode spacing penetrating the anode. However, the energy consumption is still high when operating without supporting electrolyte. As with all single-cell electrochemical systems, hydrogen is produced simultaneously and the wastewater constituents are reduced at the cathode, which consumes a large amount of energy. Cathode fouling typically occurs from these reaction products, reducing cell efficiency and resulting in increased energy consumption. Another problem encountered in single chamber systems during oxidation is the generation of intermediate compounds. These compounds are reduced at the cathode and then re-oxidized at the anode, thereby reducing cell efficiency and increasing energy consumption.

One way to eliminate the need for the addition of a supporting electrolyte is to use a Solid Polymer Electrolyte (SPE) in the electrolytic cell. SPE technology has been developed for other purposes including the production of hydrogen by water electrolysis and the production of energy using polymer electrolyte membrane fuel cells. For example, in the system disclosed in WO03093535, dehalogenation of halogenated organic compounds and destruction of nitrates are carried out at the cathode by electrochemical reduction. In this configuration, the anodic and cathodic compartments are separated by an ion exchange membrane and the anolyte and the halogen-containing catholyte are passed through their respective compartments. Although the system operates without a supporting electrolyte, a supporting electrolyte is required in the anolyte and/or catholyte in order to operate at low current densities (high cell efficiencies). Murphy et al, in Water research (Watt.Res.) 26(4) 1992443-. The wastewater is recycled through both the anode and the cathode. However, the energy consumption is very high and is due to the low rate of phenol oxidation and side reactions, mainly oxygen evolution from water. J.H. Grim (J.H.Grimm) et al used an SPE cell to treat simulated phenol-containing wastewater in J.appl.electric 30,293-302 (2000). Wastewater is pumped through an anode chamber and a cathode chamber in series. However, the energy consumption for phenol removal is also high, which was attributed by the authors to the loss of current efficiency due to side reactions such as oxygen evolution. In addition, A.Heyl et al studied a series of SPE cell configurations for dechlorinating 2-chlorophenol simulated wastewater at higher temperatures in journal of applied electrochemistry (2006)36: 1281-1290. In all cases, wastewater is pumped from the cathode or anode to the opposite chamber through the membrane via perforations in the membrane or by an auxiliary electro-osmotic drag of the treated membrane. Energy consumption was found to be impractically high for untreated membranes, lower for chemically treated membranes, and lowest for porous membranes. However, the best mineralization is obtained using anodic oxidation first followed by cathodic reduction with higher energy consumption. Furthermore, another way for treating low conductivity wastewater without using supporting electrolytes is disclosed in WO 2005095282. The system uses a solid polymer electrolyte sandwiched between anode and cathode electrodes placed in a low conductivity wastewater single chamber. The energy consumption for the mineralization of pollutants for this setup is high due to the high voltages required.

Systems have also been developed in the art to reduce the cost of hydrogen production from electrolysis by combining with the electrolytic treatment of wastewater. The electrolytic cell concerned can use an anolyte containing organic contaminants. For example, Park (Park) et al, in journal of physico-chemical C (j.phys.chem.c.)112(4)885-889(2008), use a single-chamber cell to treat aqueous contaminants and generate hydrogen. As with all single chamber systems, a supporting electrolyte is required. The hydrogen produced is contained in a mixed product gas that requires further processing to recover useful hydrogen. Similar single-chamber configurations are disclosed in WEFTEC 2008 Conference Proceedings (Conference Proceedings) and j. jiang (j.jiang et al in environs.sc. & Tech.) -42 (8),3059 (2008). The split cell configuration is disclosed, for example, in WO2009045567 and in the International journal of Hydrogen Energy (I JHydrogen Energy)35(2010)10833-10841 by Navarlo-Solis et al. All of the above systems involve the use of an additional supporting electrolyte. Systems without supporting electrolytes are also disclosed, for example, in the journal of hydrogen energy 36(2011) 3450-.

Systems using a solid polymer electrolyte based electrolytic cell to generate hydrogen and treat wastewater have also been disclosed in the art. For example, US65333919 discloses a method for electrolyzing an aqueous organic fuel solution. In this system, permeation of unreacted methanol to the cathode (fuel permeation) occurs and causes high cathode overpotential and requires an additional hydrogen cleaning operation. In addition, e.o. kilic et al disclose a system for processing formic acid and oxalic acid and generating hydrogen in Fuel processing technology (Fuel proc. tech.)90(2009) 158-. However, specific energy consumption is high due to the required higher current density.

While substantial developments have been made in the art, there is a continuing need for more efficient and cost-effective methods for wastewater treatment. The present invention addresses this need while additionally providing other benefits as disclosed herein.

Summary of The Invention

Various methods and systems have been found for energy efficient treatment of contaminated wastewater using certain cell designs and a combination of voltage and current density limitations. Lower current densities lead to better efficiencies, and lower voltages lead to reduced undesirable side reactions (e.g., oxygen evolution). Higher flow rates result in lower energy consumption. Improved energy efficiency can be achieved while removing substantially all contaminants.

The electrolytic cell used comprises a solid polymer electrolyte electrolytic cell comprising an anode, a cathode and a solid polymer membrane electrolyte separating the anode and the cathode. The anode includes an anode catalyst layer, and the anode catalyst layer contains an anode catalyst. In a similar manner, the cathode includes a cathode catalyst layer and the cathode catalyst layer contains a cathode catalyst. The cathode in the electrolytic cell is free of liquid electrolyte. That is, the cathode contains neither a liquid catholyte nor a liquid supporting electrolyte.

The method of the invention comprises providing at least a first solid polymer electrolyte cell stack and a second solid polymer electrolyte cell stack, supplying a wastewater stream containing a contaminant to the anode of each of the first and second cell stacks at a flow rate and flow pressure, providing a pressure of less than about 3 volts across each cell of the first and second cell stacks (where the anode is positive with respect to the cathode), at an operating temperature and less than about 20mA/cm²And specifically less than about 10mA/cm 2. This causes the contaminants to degrade and hydrogen gas to be generated at the cathode. The generated hydrogen gas is discharged from the cathode. The wastewater stream can be supplied to the anode without supporting electrolyte, and the cell can be operated over a wide range of wastewater temperatures. In this case, in particular, the stack components in each of the two stacks are different or the operating conditions of the two stacks are different. In other words, in the first placeAt least one of operating conditions of a stack component of a solid polymer electrolyte cell stack and the first solid polymer electrolyte cell stack is different from operating conditions of a stack component of the second solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack.

In embodiments where a stack component between the first and second solid polymer electrolyte cell stacks is different, the different cell component may be selected from the group consisting of: an anode fluid delivery layer, the anode catalyst layer, an anode flow field plate, an anode filter layer, the solid polymer electrolyte membrane, and a plurality of cells in the stack.

In embodiments where the different stack component is an anode catalyst layer, it may be at least one of a catalyst loading and a catalyst active area in the anode catalyst layer of the first solid polymer electrolyte cell stack that differs by more than about 5% from at least one of a catalyst loading and a catalyst active area in the anode catalyst layer of the second solid polymer electrolyte cell stack. In certain embodiments, it may be that the catalyst loading or catalyst active area in the anode catalyst layer of the first solid polymer electrolyte cell stack differs by more than about 10% from the catalyst loading and catalyst active area in the anode catalyst layer of the second solid polymer electrolyte cell stack.

In an embodiment in which an operating condition is different between the first and second solid polymer electrolyte cell stacks, the different operating condition may be selected from the group consisting of: flow rate of wastewater, flow pressure of wastewater, voltage, operating temperature, and current density. The difference in the operating conditions of the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack may be more than about 5%, and in certain embodiments the difference in the operating conditions may be more than about 10%.

In the method and system of the present invention, the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack may each include a single electrolytic cell. Alternatively, one or both of the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack may include more than one electrolytic cell. In addition, additional solid polymer electrolyte cell stacks may be used.

In one configuration of the invention, the first solid polymer electrolyte cell stack is connected upstream of and in series flow connection with the second solid polymer electrolyte cell, and the anode outlet of the first solid polymer electrolyte cell stack is connected to the anode inlet of the second solid polymer electrolyte cell stack. In certain such embodiments, the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack may share a common end plate.

In another embodiment of the invention, the first and second solid polymer electrolyte cell stacks are connected in parallel with the second solid polymer electrolyte cell and the supplied waste water is divided between the anode inlets of the first and second solid polymer electrolyte cell stacks.

In the methods and systems of the present invention, one or more treatment units may be incorporated into the wastewater stream. The treatment unit or units may be a filter, a degassing unit, and a pH controller. Such treatment units may be incorporated at different locations throughout the system, including upstream or downstream of the first or second solid polymer electrolyte cell stack.

The process is suitable for removing a variety of contaminants from wastewater, for example, an organic substance or a mixture of organic substances, an inorganic substance such as ammonia or hydrogen sulfide, or a mixture of organic and inorganic substances. As demonstrated in the examples, theThe method is suitable for removing an organic contaminant such as acid blue dye, phenol, acetaminophen, formic acid, ibuprofen, or a mixture of organic contaminants from kraft pulp and papermaking waste water. Contaminants oxidized using the method include dissolved organic matter, Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), refractory organic matter remaining after the biological treatment process, ammonia, dissolved gases (VOC light hydrocarbons and H)₂S hydrogen sulfide), microorganisms, pathogens, and metal ions.

In a wastewater mixture of contaminants, the energy requirements and cell operating conditions for optimizing decomposition and/or oxidation are not equal for all components. Moreover, different catalysts can accelerate the oxidation and/or decomposition of a particular component. Thus, by combining stacks operating at a combination of lower and higher voltages, current densities, temperatures, pressures, and flow rates in series and parallel, the decomposition and oxidation of wastewater contaminants can be optimized to reduce treatment costs.

Additionally or alternatively, each cell stack may include different component designs and materials, such as anode fluid delivery layers, anode filter layers, catalyst compositions and loadings, flow field plate types and designs, polymer electrolyte membranes, electrode active areas, and cell counts. Furthermore, each cell stack may be optimized for different types of contaminants that may be in the wastewater stream. For example, as shown in the examples below, certain anode catalysts have a higher affinity for oxidizing different contaminants. Thus, in a wastewater stream having several different contaminants, one skilled in the art would be able to determine the best anode catalyst (or membrane electrode assembly design) for a particular type of contaminant and use them in a separate segmented cell stack or stack to improve contaminant removal from the wastewater stream.

Embodiments of the system may include a plurality of electrolysis cells in a stack in a series and/or parallel flow arrangement. For example, the wastewater may be split and fed to multiple cell stacks and the streams combined thereafter at the cell or stack outlet. Each of the cell stacks may be different, e.g., operate under different operating conditions and/or include different components. This applies in particular to waste waters containing appreciable concentrations of oxidizable components such as ammonia, hydrogen sulfide, metals and inorganics or components which decompose at low electrolytic potentials, decompose with heat and decompose with different catalysts. By optimizing the design of each stack for a particular type of contaminant that may be in the wastewater stream, improved contaminant removal, energy efficiency, operating costs, and battery life may be achieved. As shown in the examples below, cell (and membrane electrode assembly) design and operating conditions have a great effect on the removal of various contaminants.

The contaminant-specific decomposition and oxidation catalyst may desirably be incorporated into the anode flow field plate, anode filter layer, anode fluid diffusion layer or anode catalyst layer. These enable decomposition and/or oxidation of contaminants at lower voltages, higher flow rates, and lower energy consumption. Contaminant-specific decomposition catalysts may be desirably incorporated into the catalyst layer to provide a faster contaminant removal rate. This can achieve higher flow rates and lower cell active area required for reduced power consumption. The anode catalyst layer may alternatively contain only the component(s) that accelerate the decomposition of a particular contaminant (e.g., MnO)₂Decomposition of H₂O₂) But do not react with other contaminants in the wastewater. It may be advantageous to rapidly remove the resulting product in this manner prior to oxidizing the remaining organic and inorganic species. For example, if these products are gases and/or solids, the waste water may advantageously be degassed or filtered in an intermediate step to prevent them from interfering with downstream processes.

The total energy required to remove contaminants from mixed wastewater can be reduced by configuring the system to first remove easily decomposed or oxidized contaminants at a lower energy. The wastewater may pass through a series of stacks, each having a catalyst layer that targets one or more contaminants to decompose and/or oxidize them at low energy. For wastewater with rapidly oxidizing and decomposing contaminants, the flow rate can be increased and the total cell area or number of cells can be reduced to reduce cost and system footprint (system footprint).

For contaminants that oxidize and/or decompose into gases, one or more degassing units or methods can be used in the system to remove the resulting product gas. Dissolved gases (e.g. CO)₂、O₂) May need to be removed due to corrosion and/or unwanted reactions in downstream equipment and processes. For example, in water with low concentrations of minerals, carbon dioxide forms corrosive carbonic acid. Degassing methods include heating (e.g., an oxygen removal heater), reducing pressure (e.g., a vacuum deoxygenator), membrane processing (e.g., a membrane contactor), air purging, substitution with an inert gas (e.g., bubbling argon), vigorous stirring, contact with a catalytic resin, and freeze-thaw cycles for dissolved oxygen, chemical oxygen scavengers (e.g., ammonium sulfite) may also be added. For dissolved carbon dioxide, additional removal methods include contact with limestone and/or magnesium oxide (to form carbonates and bicarbonates), chemical reaction with sodium carbonate solution to form sodium bicarbonate, and carbonation by controlling the pH between 7.5 and 8.5.

The following are operating conditions that may be adjusted in a system, either individually or in combination, stack by stack to provide lower energy consumption:

for species that are prone to decomposition or oxidation, the voltage may be reduced in one or more stacks to reduce the energy required in one or more stacks;

pressure may be increased in one or more stacks to keep the gas dissolved;

the flow rate can be increased in one or more stacks;

the temperature may be increased in one or more stacks to increase the reaction kinetics;

the current density may be reduced in one or more stacks.

For contaminants that oxidize and/or decompose into gases, one or more degassing units or methods can be used in the system to remove the resulting product gas. The method may comprise a degassing step and/or an intermediate step, and/or a post-degassing step, performed between the stacks.

The method may comprise a pre-filtration step and/or an intermediate step, and/or a post-filtration step, performed between the stacks.

The method may include combining a plurality of stacks, wherein some cells include an anode filter layer and other cells do not. The anode filter layer may be conductive or non-conductive. The anode and cathode flow field plates can also be conductive or non-conductive or a combination of both. The anode catalyst layer may have different compositions of catalyst and different concentrations of ionomer.

The process may include a pre-pH adjustment step and/or an intermediate step, and/or a post-degassing step, performed between the stacks. This is advantageous for removing contaminants such as increasing the pH to precipitate metals or decreasing the pH to precipitate silica and for reducing the corrosivity of wastewater with acids to allow the use of less corrosion resistant cell components and thus reduce stack costs.

The method may additionally comprise a post-treatment step for removing free chlorine selected from the group consisting of: electrochemical reduction, adsorption, decomposition by contact with a transition metal, reaction with a salt, reaction with a chemical reductant, reaction with organic matter, decomposition by contact with a redox filter, decomposition by light exposure, and decomposition by heating.

In addition, the method may comprise a step for preventing the formation of chlorine selected from the group consisting of: controlling the pH of the wastewater to greater than about 2, increasing the ionomer concentration at the anode fluid delivery layer, increasing the ionomer concentration at the anode catalyst layer, and incorporating materials known to catalyze the decomposition of free chlorine into the anode. The latter materials may include transition elements such as iron, copper, manganese, cobalt and nickel, raney metals of copper, nickel and cobalt, oxides thereof and spinels; and may be mixed into the anode catalyst layer. Alternatively, such materials may be used as coatings for the anode fluid delivery layer and/or the anode plate to effect decomposition of free chlorine.

In addition, the method may additionally comprise a cleaning step selected from the group consisting of: purging the anode and cathode with a cleaning solution, flowing solid particles through the anode flow field, in situ backwashing, oxygen scrubbing, chemical cleaning, ultrasonic cleaning, gas purging, liquid purging, potentiostatic cleaning, flowing water, and generating chlorine and oxygen intermediates at higher anode voltages.

Brief description of the drawings

FIG. 1 shows a schematic diagram of one embodiment of the system of the present invention and is used to perform laboratory scale wastewater treatment in an example.

Fig. 2 shows a schematic diagram of a solid polymer electrolyte battery used in the system of fig. 1.

Fig. 3 shows a schematic view of an alternative embodiment of an electrochemical cell suitable for use in the system of the present invention.

Figure 4 shows a schematic of an embodiment of the system of the present invention having more than one electrochemical stack.

Figure 5 shows a schematic cross-sectional view of one embodiment of an electrochemical cell stack suitable for use in the system of the present invention, wherein the stack comprises a segmented battery.

Figure 6 shows a schematic view of another embodiment of the system of the present invention having more than one electrochemical stack.

Figure 7 shows a schematic view of yet another embodiment of the system of the present invention having more than one electrochemical stack.

Fig. 8 is a qualitative prior art illustration showing how the initial compound concentration change can be distinguished from the COD change during oxidation of a refractory organic compound such as phenol.

Figure 9 compares the average actual hydrogen generated from various tests performed on phenol-contaminated wastewater at several different currents with ideal or perfect hydrogen generation.

Detailed Description

Certain terms are used in this description and are intended to be interpreted according to the definitions provided below. Furthermore, terms such as "a" and "comprising" are to be understood as open-ended. Additionally, all US patent publications and other references cited herein are intended to be incorporated by reference in their entirety.

Here, SPE represents a solid polymer electrolyte and may be any suitable ion-conducting ionomer, such asAn SPE electrolytic cell is thus a cell containing SPE as the electrolyte, to which electrical energy is supplied to achieve the desired electrochemical reaction (with a positive voltage applied to the anode of the cell).

Herein, unless otherwise indicated, the term "about" when referring to a numerical value is intended to be interpreted to include a range of values within plus or minus 10% of the referenced value.

One electrode in the cell is "liquid electrolyte free", which means that the electrode is not intentionally supplied with a liquid containing a large amount of ions, as is provided in some systems of the prior art. However, it is not intended to exclude, for example, the minimum amount of waste water that can pass through a solid polymer electrolyte at the cathode.

By "cell stack" is meant a series of cell stacks comprising one or more electrolytic cells.

The "stack component" means any component constituting the solid polymer electrolyte electrolytic cell stack of the present invention. It includes, but is not limited to, an anode fluid delivery layer, the anode catalyst, an anode filter layer, the anode catalyst layer, an anode flow field plate, the solid polymer electrolyte membrane, and a plurality of cells. In addition, it includes any particular sub-layer used, the cathode catalyst layer, a cathode gas diffusion layer, and a cathode flow field plate.

"operating conditions" means any of the variable operating conditions used in the operation of a solid polymer electrolyte cell stack of the present invention. It includes, but is not limited to, the flow rate of the wastewater, the flow pressure of the wastewater, the voltage, the operating temperature, and the current density.

The energy efficient system of the present invention uses a simple compact electrolytic cell structure to minimize ionic, ohmic, and mass transfer resistances and is characterized by reduced operating voltage and current density, low cost components, a chemically stable non-liquid electrolyte membrane, and low cost, durable, high performance electrode and catalyst designs. Recovery of high purity by-product hydrogen is possible for improved efficiency.

One exemplary system is shown in the schematic diagram of fig. 1. The system 100 includes an SPE electrolytic cell 101 for direct electrochemical treatment of organically-polluted wastewater. A controlled waste water stream 102 is supplied to the anode inlet 11 of the cell 101 by some suitable delivery means, such as a peristaltic pump 103. After sufficient treatment/transit time in the cell 101, the treated wastewater is discharged at the anode outlet 12 and delivered as shown here into the treated waste tank 104, where entrained or by-product gases (e.g., carbon dioxide, nitrogen, oxygen) generated during treatment are allowed to vent to the atmosphere. A pressure gauge 105, a valve 106, and a flow meter 107 are provided in the anode outlet line for monitoring and flow control purposes.

The battery 101 is supplied with electric power through the DC power supply 108 and the temperature of the battery 101 is monitored and controlled through the temperature controller 109. Hydrogen is generated at the cathode of cell 101 as a result of the electrochemical process and is discharged at cathode outlet 13. As shown in fig. 1, relatively pure hydrogen gas may be collected and stored in storage vessel 110 for subsequent use in generating electricity or as a fuel or chemical reactant.

Fig. 2 shows a detailed schematic of the solid polymer electrolyte electrolytic cell 101. The battery 101 comprises an SPE membrane electrolyte 6. The cell anode comprises an anode catalyst layer 8 and an anode fluid delivery layer 9. The cell cathode includes a cathode catalyst layer 5 and a cathode gas diffusion layer 4. An anode flow field plate 10 is disposed adjacent the anode fluid delivery layer 9. The anode flow field plate 10 includes one or more flow field channels 10a fluidly connected to an anode inlet 11 and an anode outlet 12. The wastewater 101 is delivered evenly back and forth to the anode fluid delivery layer 9 by directing it through the flow field channels 10 a. The cathode flow field plate 3 is disposed adjacent to the cathode gas diffusion layer 4. The cathode flow field plate 3 includes one or more flow field channels 3a fluidly connected to the cathode inlet 13. Since no catholyte or other liquid or fluid is supplied to the cathode, a cathode inlet is not required. However, the hydrogen generated during the electrochemical treatment of the waste water 101 is collected from the cathode and is conducted out of the cell by means of the flow field channels 3 a. A lead 2 is provided at the battery electrode to make an electrical connection with the power source 108. Mechanical support for the components in the cell 101 is provided by means of the end plates 1 which clamp the cell together. The seal is provided to the cell by seal 7. A drain port (not shown in fig. 2) may be incorporated into the cathode for the purpose of cleaning and/or purging any water crossover build-up. Finally, fig. 2 shows a heating element 14 that can be used to control the battery temperature during operation.

The cell 101 may optionally include an anode filter layer (not shown) bonded between the anode flow field plate 10 and the anode fluid delivery layer 9. This filter layer may be applied to the anode fluid delivery layer 9 or to the anode flow field plate 10 during assembly, or as a separate component held in place by the end plate 1. Such a filter layer may be provided to prevent particulates and suspended solid contaminants from entering the anode fluid delivery layer 9. The average pore size of this filter layer is selected to remove particles expected to be present in the wastewater. For example, to filter particles of 50 microns in size or larger, the average pore size should be less than 50 um. In addition, the average pore size of one filter layer is preferably smaller than the average pore size of the adjacent anode fluid delivery layer 9. In the case where the pore size is not uniform throughout the anode fluid delivery layer 9, the average pore size of one filter layer is preferably smaller than the pore size on the flow field side of the anode fluid delivery layer 9. This configuration achieves removal of contaminants while still allowing filtered wastewater to be treated proximate the anode catalyst layer. Filter cake formation on the surface of one filter layer is promoted and this prevents clogging of both the filter layer and the anode fluid delivery layer 9. The oxidation products are also easily removed from the catalyst layer.

Surprisingly, high energy efficiency can be obtained from the system 100 and can be facilitated by appropriate limitations on the voltage and current density applied to the cell and by employing some of the designs and components used in advanced SPE fuel cells for generating electricity. Specifically, the voltage applied to the electrolytic cell 101 (or to a single cell if more than one cell is used in a system) should be less than about 3 volts. The current density is limited to less than per cm²The electrode area was about 20 mA. And as discussed further below, certain catalyst options, catalyst layer configurations, fluid delivery layers, and gas diffusion layer configurations may facilitate operating efficiency.

The reasons for improving the efficiency of the present invention are not fully understood. However, without being bound by theory, several mechanisms for mineralizing organic contaminants may be involved at the anode. Oxygen for "electrochemical incineration" of organic pollutants in wastewater is obtained from water via an oxygen evolution reaction. Adsorbed hydroxyl and oxygen radical species generated on the anode catalyst surface can mineralize the organic contaminants present. Additionally, for certain n-type semiconductor oxide catalysts, the anion (oxygen) vacancies may preferably react with water and form OH^*A free radical. The oxidation of organic pollutants via intermediates/hydroxyl radicals that evolve oxygen at anodic potentials in the drainage areas can mineralize or partially oxidize the organic pollutants. Direct oxidation of ammonia to nitrogen may occur. Alternatively, the treatment may be carried out by passing through sulfate, carbonate, or phosphoric acid in the wastewaterThe inorganic oxidizing agent generated by anodic oxidation of the radical ions undergoes indirect electrochemical oxidation. Decomposition of the contaminants may occur. Direct electrolysis of the contaminants may occur. And, in addition, indirect electrochemical oxidation can occur by a redox reagent electrochemically generated from a mediator present in the wastewater.

The chemical reactions involved at the anode may include:

direct electrolysis of organic compounds R by electron transfer:

R→P+e^-

for the mineralization of organic compounds R by oxygen transfer from water and oxygen evolution:

2H₂O→O₂+4H⁺+4e^-

hydroxyl and oxygen radicals and O evolution on a catalyst surface₂The intermediate (2) of (a):

H₂O→OH*_adsorbed+H⁺+e^-

(h⁺)_Vacancy+H₂O→(OH*)_Adsorbed+H⁺+e^-

R + [ OH radical/O substance/intermediate]_Adsorbed

→ mineralized product [ CO >₂ ^-+ salts and the like]+nH⁺+ne^-

For the oxidation of ammonia

4HN₃+3O₂→2N₂+6H₂O

NH₃/NH₄+OH*→N₂+H₂O+H⁺+e^-

And if the waste water is alkaline, is removed by free chlorine

HOCl+2/3NH₃→1/3N₂+H₂O+H⁺+Cl^-

NH₃/NH₄+HOCl/OCl^-→N₂+H₂O+H⁺+Cl^-

For the formation of inorganic oxidants, for example:

2HSO₄ ^-→S₂O₈ ^2-+2H⁺+2e^-

for in situ generation of oxidants, such as NaCl in wastewater:

2Cl^-→Cl₂+2e^-

HOCl→H⁺+OCl^-

for H₂S：

H₂S→S^o+2H⁺+2e^-

And if the wastewater is Alkaline, a pH control device can be used to facilitate Alkaline decomposition by Electrochemical decomposition (see "Modified Electrochemical Process for the decomposition of Hydrogen Sulfide in Alkaline Aqueous Solution", Z. Hair (Z. Mao), A. Anani (A. Anani), Lalf E. white (Ralph E. white), S. Srinivasan (A.J. Appleby) Electrochemical Society note (Journal of the Electrochemical Society), 1991, page 1299-1303.) A pH control device can be used to facilitate Alkaline decomposition

And for metal ions [ e.g., transition metal ions such as iron, manganese ]:

oxidation by hydroxyl radicals and oxygen

By oxidation by hydroxy radicals, e.g. Mn + OH → Mn^-1+OH^-

Or by oxidation with oxygen, e.g.

2Fe²⁺+1/2O₂+5H₂O→2Fe(OH)₃↓+4H⁺

Mn²⁺+1/2O₂+H₂O→MnO₂↓+2H⁺

For such purposes, the oxygen-generating electrochemical catalyst may be desirably incorporated into a catalyst layer deposited on a fluid diffusion layer. In addition, the residence time of the wastewater in contact with the catalyst layer may be increased to complete the oxidation, and a microfilter may be used in the system to remove the resulting metal precipitates.

And catalytic decomposition:

H₂O₂→H₂O+1/2O₂

contaminant-specific decomposition and oxidation catalysts may desirably be incorporated into the anode flow field plate, an anode filter layer, the anode fluid diffusion layer, and anode catalyst layer. These may enable decomposition and/or oxidation of contaminants at lower voltages, higher flow rates, and lower energy consumption.

The contaminant-specific decomposition catalyst may be desirably incorporated into the anode catalyst layer to provide a faster contaminant removal rate at higher voltages. This can enable higher flow rates and lower required cell active area, which allows the use of smaller stacks at lower cost.

For contaminants that oxidize and/or decompose into gases, one or more degassing units or methods can be used in the system to remove the resulting product gas.

At the same time, on the cathode, hydrogen evolution takes place, such as:

the kinetic effects are generally considered to be dominant in the low current densities involved in the process of the invention and therefore the catalysts used may have a large effect. The high active surface area may allow more OH radicals to be available, the presence of electron and proton transfer media (e.g., conductive particles and ionomers) enhance charge transfer, and additional particles may also contribute to the local generation of oxygen (e.g., high surface area graphite particles). The use of advanced fuel cell components may also help improve mass transfer and current collection and help local mixing of fluids at the catalyst surface if no excess oxygen is generated at the anode.

In the present invention, a preferred amount of oxygen can be generated, where too little means that there is not enough oxygen present for the contaminant removal related reaction to proceed at a suitable rate, while too much oxygen generation is parasitic and the current density is ramped up while the contaminant removal rate remains the same. In the above list of anodic reactions, organic compound mineralization reactions are frequently cited in the literature. However, hydroxyl and oxygen radicals and O evolution on one catalyst surface₂The reaction of the intermediates of (a) may be important. Small amounts of locally generated oxygen can be generated on the substitute particles without damaging the catalytic sites for OH radicals. In practice, this may lead to increased reaction kinetics and the same organic contaminant removal rate may be achieved at lower applied voltages and current densities. For electrodes of the prior art, in order to obtainThe appropriate level of OH radicals requires an increased applied voltage to drive the cell to a larger range of oxygen production, which can then compete with the radical generation sites. That is, higher voltage and current densities may be required in the prior art to obtain an equivalent amount of OH radicals.

In any event, unexpectedly improved energy efficiency is obtained when the applied voltage and current density are appropriately limited as previously mentioned and also by using certain cell designs and components. Energy efficiency can be further improved by using a combination of the cell stack at a limited applied voltage and current, along with a faster wastewater flow rate. The SPE membrane electrolyte 6 is a suitable proton conducting solid polymer electrolyte and is preferably a thin, extended lifetime material of choice for increased efficiency (e.g., sulfonated tetrafluoroethylene based fluoropolymer-copolymers such as sulfonated tetrafluoroethyleneLess than about 30 microns thick). However, for durability and/or high temperature operation, the membrane electrolyte thickness may desirably be increased to between 50 and 100 microns (e.g., by laminating thinner films together or using thicker films).

As for the anode catalyst, platinum, tin oxide, antimony tin oxide, manganese oxide and mixtures thereof have been successfully used in examples. In the case of antimony tin oxide, heat treatment to improve its conductivity or doping with, for example, Nb, may be considered to improve durability. The manganese oxide may be considered for the purpose of decomposing any hydrogen peroxide that may form at the anode. Other n-type and p-type semiconductor oxides, perovskite-type oxides, and amorphous or nanocrystalline transition metal oxides (e.g., MoO)₂) May also be considered an anode catalyst. In addition, cobalt and nickel spinels and high surface area nickel oxides are also contemplated. As is known in the art, the use of supported catalysts (e.g., Pt dispersed on carbon or antimony tin oxide on high surface area graphite or Nb particles) can improve the dispersion and thus utilization of catalytic materials, and the interaction between certain catalysts and supportsThe effect may also enhance catalytic activity and durability. Dopants can generally be used to enhance conductivity (e.g., antimony doped SnO₂SnO doped with chlorine and fluorine₂) Or increased durability and stability at elevated voltages (e.g., cobalt, nickel, palladium, niobium, tantalum, platinum, palladium, iridium, ruthenium, vanadium, rhenium), and mixtures of dopants may be used to increase conductivity and stability/durability (e.g., Nb-doped SnO)₂And a dopant selected from the group consisting of: sb, Fe, F, Pt, and Ni). Other possible dopants include Mo, Cr, Bi, and W.

Contaminant-specific decomposition and oxidation catalysts may desirably be incorporated into the anode flow field plate, an anode filter layer, the fluid diffusion layer and/or anode catalyst layer. These enable decomposition and/or oxidation of contaminants at lower voltages, higher flow rates, and lower energy consumption. Contaminant-specific decomposition catalysts may be desirably incorporated into the catalyst layer to provide a faster contaminant removal rate at higher voltages. This can enable higher flow rates and lower required cell active area, thus enabling smaller stacks and lower capital costs.

Depending on the composition of the wastewater, the decomposition and contaminant specific catalyst may be MnO₂、PbO₂、Fe₂O₃Metal oxides, mixed metal oxides, doped metal oxides, metal oxides supported on zeolites, alumina, calcium oxide and potassium oxide and mixed metal oxides and doped metal oxides; metal sulfides, bimetallic catalysts such as Ni-Pt and Pt-Sn, cobalt compounds, transition metals and alloys, Pt, Au, Ru, Ir, Pd, Au and compounds thereof, noble metals supported on metal oxides such as alumina, silica and ceria, transition metal exchanged zeolites, perovskites, metalloporphyrins, silver compounds, activated carbon, Cu, CeO₂Promoted cobalt spinel catalysts, carbides, nitrides, and functionalized silica catalysts.

The composition of the catalyst layer may also include a higher concentration of ionomer because it acts as an acid catalyst.

The catalyst material is selected to catalyze organic contaminants at lower voltages (e.g., have a lower overpotential), so the applied voltage required is lower and thus the current density is lower. Such catalyst materials have a high overpotential for water electrolysis so that the generation of oxygen can be controlled at the operating voltage, thereby reducing the current density associated with this reaction.

Other considerations in anode catalyst selection include the use of nanoparticles, nanostructures, and/or mesoporous materials to achieve high surface areas. The supported catalyst may be used using a graphite carrier. If graphite stability is an issue at high anode voltages, stable conductive particles including carbides, nitrides, borides, corrosion resistant metals, alloys, and metal oxides (e.g., Nb) may be used₂O₅ZnO, NbC and/or mixtures thereof). The additive may include a perovskite-based metal oxide that exhibits mixed electronic and ionic conductivity.

The anode catalyst layer 8 typically includes particles that enhance electronic conduction, an ionomer that serves for ionic conduction and as a binder (e.g., similar to the ionomer used in membrane electrolytes), and a material that controls wetting characteristics (e.g., dispersed PTFE). The pore size and total porosity can be engineered to a certain extent by selecting the particle size and agglomerate size (this can be improved, for example, by controlling the high shear mixing rate during the preparation of the catalyst ink or slurry used to prepare the catalyst layer). The pore characteristics, surface chemistry, and surface area of the anode catalyst layer can be important for mass transport of wastewater to the catalyst and removal of product gases such as carbon dioxide. Preferably, the pore structure and hydrophobic surface of the anode catalyst layer promote bubble jump so that gas filling and/or pore blocking do not occur. A graded particle size and pore size distribution may be used in catalyst layer 8 to allow deeper penetration of wastewater and greater utilization of catalyst surface area.

The anode fluid delivery layer 9 is provided to facilitate delivery of fluid to and from the anode catalyst layer 8 in a uniform manner. In addition, it provides electrical contact and mechanical support to the anode catalyst layer. Carbon fiber paper, foam, and other materials commonly used in SPE fuel cell embodiments are contemplated herein as substrates. And materials for conductivity and wettability may be added. As with the anode catalyst layer 8, the pore size distribution and the volumetric porosity of the anode fluid delivery layer 9 are carefully controlled, as it may be important for the carbon dioxide bubbles formed (affecting size and mixing) and their effect on mass transport. Sublayers (not shown in fig. 2) typically used in fuel cell embodiments may be incorporated in the anode fluid delivery layer 9 and located near the anode catalyst layer 8 to improve contact with the latter and to provide an asymmetric pore size distribution on the layer 9 (e.g., to provide larger pores on the side adjacent the anode flow field plate 10 that may serve as a pre-filter to prevent suspended solids from plugging catalyst sites).

If an increased anodic potential is involved, decomposition of materials such as carbon fibre paper may occur. In such cases, more stable media may be used, including metal-coated (e.g., nickel-coated) carbon fiber paper or woven cloth, metal screen/wire mesh/cloth (particularly using 2 or more ply screens, which have different mesh sizes and smaller meshes closest to the membrane, have a woven pattern to improve in-plane water permeability, are flattened and diffusion bonded or spot welded together), sintered metal screen/wire mesh/cloth (again using 2 or more ply screens to improve current distribution and are flattened), expanded metal foil/film/membrane (using 1 or more plies and are flattened), sintered metal fiber and powdered media (again using 1 or more plies and are flattened, have asymmetric pore sizes and have smaller pore diameters closest to the membrane, and has high in-plane water permeability), flat photo-etching media, chemical etching media, micro-porous plates, or combinations thereof. The above materials are electrically conductive and may be of the corrosion resistant type [ stainless steel, inconel, monel, titanium, alloys, valve metals ] or have a corrosion resistant coating applied thereto [ e.g., carbides, nitrides, borides, noble and valve metals and metal alloys, metal oxides ]. If the corrosion resistant material used forms a passivation layer, a conductive coating can be applied to those surfaces that contact the catalyst coated membrane. Sublayers incorporating corrosion-resistant conductive particles [ e.g., carbides, nitrides, borides, noble and valve metals and metal alloys, metal oxides ] may be employed. For monopolar designs, high in-plane conductivity is desirable, which recommends the use of corrosion-resistant conductive materials and coatings.

The cathode catalyst may be selected from the group consisting of: conventional catalysts commonly used for hydrogen evolution include platinum or supported platinum (e.g., platinum on carbon), palladium alloys, supported Pd/C, nickel and its oxides, rhodium (e.g., metal, wherein H is passed through)₂Significant coverage of species is possible), molybdenum disulfide, perovskite-based metal oxides exhibiting mixed electronic and ionic conductivities, amorphous or nanocrystalline transition metal oxides, and high surface area raney metals and metal blacks. Manganese oxide, graphite, and carbon may also be used for the cathode. Furthermore, the manganese oxide may facilitate the decomposition of any hydrogen peroxide present. Along with the cathode catalyst, the cathode catalyst layer 5 may also generally include particles to enhance electron conduction, ionomers for ion conduction and to act as a binder, and materials to control wetting characteristics. The cathode catalyst layer 5 may be prepared by coating on the cathode gas diffusion layer and sintering at an appropriate temperature (e.g., 150 ℃ or 370 ℃ depending on whether ionomer or PTFE is used, respectively). The conductive particles in layer 5 may be desirably mixed to provide a size distribution that optimizes current distribution and porosity for hydrogen recovery. If corrosion is an issue, the PTFE and/or other stabilizing binder in the catalyst layer 5 may be used to improve corrosion/abrasion resistance.

The cathode gas diffusion layer 4 is provided to facilitate the delivery of gas to and from the cathode catalyst layer 5 in a uniform manner. Layer 4 is ideally designed to dissipate waste water that may cross from the anode side through the membrane electrolyte, while still allowing for rapid removal of the generated hydrogen. Thus, a hydrophobic construction, such as a teflon @ -stainless steel mesh substrate, may be used. In addition, the use of a hydrophobic sublayer with a small pore structure near the cathode catalyst layer 5 can also be used to prevent wastewater cross-over into the rest of the cathode. This, in turn, may reduce or eliminate parasitic reactions and contamination at the cathode and thus help keep the current density low. In general, materials similar to those used in the anode fluid delivery layer 9 may be considered. For unipolar designs, high in-plane conductivity is desirable, which recommends the use of conductive materials and coatings (e.g., nickel, palladium alloys, titanium nitride, etc.) that are corrosion resistant and resistant to hydrogen.

The flow field channels 3a, 10a in the cathode flow field plate 3 and the anode flow field plate 10 can have a variety of configurations, including a single serpentine, interdigitated and/or a variety of linear designs, and can have different shapes in cross-section. A gravity assist design may be used. The regulation of the hydrogen generated at the cathode is relatively simple and one end of the cathode flow field may be dead-ended. At the anode, the channel design preferably maximizes residence and promotes uniform mixing of the liquid and the generated gas. It may be adapted to provide turbulence to promote mixing of the gas and liquid and to prevent coalescence of bubbles and formation of large plug flows. This can be achieved by providing static means for coaxial mixing within the flow field channel 10a in different locations of the channel, such as helical bands, twisted bands or helical static mixing elements. Such mixing can serve different purposes, including reducing concentration overvoltage at the anode, eliminating radial gradients in temperature, velocity and material composition, and improving mass transport of the wastewater, allowing the use of larger channels and higher wastewater flow rates without any performance loss. Suitable mixing elements can continuously mix and direct the wastewater past the outer perimeter such that the contaminants are efficiently delivered to the catalyst layer and such that the gas bubbles are in contact with the perforated plate surface for removal.

Fig. 1 and 2 depict one possible embodiment of the system and electrolytic cell and a version of this embodiment is used in the following examples. However, many other variations are possible and include a monopolar cell design comprising a non-conductive plastic plate with a conductive film for current collection on a platform or with a metal substrate for current collector used in the anode fluid delivery layer. Other unipolar and bipolar variations are contemplated, including bipolar pairs in a unipolar stack. In such cases the plate material may be different. In a monopolar design, the plates may be electrically insulating and made of plastic, composite (e.g., fiberglass reinforced plastic), ceramic, or insulation coated metal, corrosion resistant coating. In a bipolar design, the plates are electrically conductive and may be made of composite materials (carbon plastic, reinforced fibers (where the fibers are an electrically conductive metal), carbides, nitrides, etc.), metals, alloys, and substrates containing appropriate coatings (similar to those of the anode delivery layer 9 on the anode side and the gas diffusion layer 4 on the cathode side). In a monopolar stack comprising a bipolar pair, an electrically conductive cathode plate may be used between two electrically insulating anode plates.

Dissolved gases (e.g. CO)₂、O₂) May need to be removed due to corrosion and/or unwanted reactions in downstream equipment and processes. For example, in water with low concentrations of minerals, carbon dioxide forms corrosive carbonic acid. Degassing methods include heating (e.g., an oxygen removal heater), reducing pressure (e.g., a vacuum deoxygenator), membrane processing (e.g., a membrane contactor), air purging, substitution with an inert gas (e.g., bubbling argon), vigorous stirring, contact with a catalytic resin, and freeze-thaw cycles for dissolved oxygen, chemical oxygen scavengers (e.g., ammonium sulfite) may also be added. For dissolved carbon dioxide, additional removal methods include contact with limestone and/or magnesium oxide (to form carbonates and bicarbonates), chemical reaction with sodium carbonate solution to form sodium bicarbonate, and carbonation by controlling the pH between 7.5 and 8.5.

It is also possible to use a porous anode plate such as porous graphite or a porous metal plate with small pores for degassing the wastewater. In this design, the channel surfaces may be made hydrophobic to prevent water ingress, with the maximum pore size depending on the contact angle of the plate surface and the operating pressure of the wastewater stream. Fig. 3 shows a schematic diagram of this alternative embodiment 111 based on a porous anode plate option. (in figure 3, similar numerical values are used to indicate components similar to those shown in figures 1 and 2.) here, the cell includes a porous anode plate 15 and a gas collection manifold 16. Vacuum assistance is also provided at the anode outlet by a vacuum pump 17 to assist in gas removal. Other options include using a 2-stage system instead of a single-stage system, where two electrolytic cells are used in series, where the anode outlet of one electrolytic cell is connected to the anode inlet of the other electrolytic cell, and where the generated hydrogen is collected from both cathodes.

The energy efficient benefits of the present invention are obtained by limiting the current density and voltage applied to each cell in the system. Other operating conditions are quite flexible. Any operating temperature between the freezing and boiling points of the wastewater (e.g., from about 3 ℃ to 95 ℃) is contemplated, although a suitable increase above ambient temperature may be used to increase the reaction rate (e.g., from about 25 ℃ to 50 ℃). The wastewater is typically supplied at a pressure of from about 0 to 30 psi. The transit time or residence time of the wastewater is selected to ensure adequate removal of contaminants from the wastewater.

Depending on the particular substances in the wastewater, certain modifications may be considered. For example, if the wastewater contains acids, bases, base salts, and/or other ionic species that make it electrically conductive, an ionomer may not be needed in the catalyst layer and an alternative binder (e.g., PTFE) may be used. If high chloride ion levels are present in the wastewater, it can react at the anodic electrocatalytic site to produce free chlorine (defined as dissolved Cl that is in equilibrium together)₂Gas, HOCl hypochlorite and/or OCl hypochlorite ions^-And its concentration is a function of pH). Here, the pH may be controlled to prevent dissolved Cl₂Gas (pH)>2). And can be used forDivalent ions added to the wastewater to increase the concentration thereof (e.g. sulfate SO)₄ ^2-And/or sulfates such as NaSO₄). These divalent ions preferably adsorb onto the electrode, catalyze oxygen formation, and inhibit chloride oxidation. In addition, raney metals of transition elements such as iron, copper, manganese, cobalt and nickel, copper, nickel and cobalt, oxides thereof, and spinels may be mixed into a catalyst layer known to catalyze the decomposition of free chlorine. Such materials may be used as coatings for the anode fluid delivery layer and/or the anode plate to effect decomposition of free chlorine. In addition, a post-treatment step may be used to remove free chlorine, including: electrochemical reduction, adsorption by granular activated carbon or kaolin, by contact with transition metals (especially copper, iron, nickel and cobalt and/or their oxides and spinels such as substituted cobalt oxide spinels), reaction with salts such as ammonium acetate, ammonium carbonate, ammonium nitrate, ammonium oxalate and ammonium phosphate, reaction with chemical reducing agents such as sodium metabisulphite, reaction with organic substances such as glycerol, decomposition by contact with redox filters such as copper/zinc alloys, decomposition by light exposure (especially UV), and decomposition by heating of the solution. In addition, the ionomer concentration at the anode fluid delivery layer or catalyst layer may be increased to block chloride ions from reaching the catalytic reaction sites.

In some cases during operation, substances may undesirably migrate into the area of the electrolytic cell. For example, if the wastewater contains high levels of metal ions that are not fully oxidized, a portion may diffuse into the membrane. This problem may be solved by performing an in situ ion exchange cleaning procedure, or alternatively a pre-treatment step may be used to pass through chemical coagulation flotation/filter/clarifier, electrocoagulation&Flotation/filters/clarifiers, lime softening, chemical precipitation, etc. remove or reduce these metal ions. Additionally, one or more of the following steps may be performed to reduce contamination and cleaning requirements: removal of suspended solids, particulate matter, and colloidal particles (e.g., filtration, gravity separation by agglomeration, flotation)&Purify), remove or reduce scale-forming minerals (e.g., lime softening, deionization, and ion exchange), toAnd removal of free lipids, oils and greases (e.g., coagulation, flotation, and filtration). When leakage of metal ions to the cathode undesirably occurs, the following procedure or modification may be considered: a step of purging or rinsing the cathode with deionized water, acid, base, chelating agent, or other cleaning solution, a potentiostatic cleaning procedure, modifying the ion-exchange membrane to make it more selective for protons versus metal cations, and/or modifying the cathode catalyst layer and gas diffusion layer to make them more hydrophobic to facilitate cleaning. When sodium ion (Na) undesirably occurs⁺) In the event of ion leakage into the membrane, an in situ ion exchange cleaning procedure may be performed. Also, when leakage of sodium ions to the cathode undesirably occurs, one of the above steps of purging or flushing the cathode with deionized water, acid, base, or other cleaning solution may be used. In particular, a deionized water purge that causes sodium hydroxide formation can provide a valuable by-product that can be recovered. And when leakage of oxygen to the cathode undesirably occurs, MnO₂Or other catalysts may be incorporated into the cathode gas diffusion layer and/or the catalyst layer to decompose the hydrogen peroxide. To provide some of the above cleaning methods, the cell and/or system can include a drain for the cleaning solution on the cathode side and a valve at the hydrogen gas outlet to prevent solution from entering the gas line during cleaning. Typically may incorporate a drain that drains into a waste outlet or other general disposal. For clean-in-place capability, the battery or batteries can be powered down and a valve at the waste inlet can be used to bypass the waste and connect a cleaning solution line. A valve at the outlet may be used to collect the cleaning solution. A similar method can be used on the hydrogen line.

One of ordinary skill in the art would expect to know the factors involved and thus be able to determine what is sufficient and how to adjust parameters such as flow rate, etc. As shown in the examples, simulated wastewater can be treated without contaminating the cell electrodes. The oxygen evolution that occurs on the anode side due to the electrolysis of water as a side reaction can help prevent the electrodes from forming any organic film. However, in other cases, occasional cleaning of the electrodes may be required and may be accomplished by temporary cell reversal or other techniques known to those skilled in the art.

The method and system of the present invention have several advantages. First, they provide improved energy efficiency in the treatment of contaminated wastewater. No solid waste or sludge is produced, nor toxic by-product gases that may subsequently require additional disposal. No catholyte is used at the cathode, no fresh water is required to generate hydrogen, and no waste is generated here. Thus, no additional chemicals need to be added and subsequently removed to complete the process. The system is versatile and can efficiently treat sewage from industrial and municipal wastewater and can mineralize many contaminants and microorganisms under the same operating conditions, thereby combining organic contaminant removal and disinfection in one single step. Fundamentally, a wide operating range of temperatures, pressures, and variable wastewater flow rates may be used. The system is scalable and can be considered for treating wastewater in quantities ranging from a few milliliters to millions of liters. The cell components are suitable for low cost, high volume manufacturing processes and/or are already mass produced. In connection with low cost construction, the operating costs and energy consumption are low, especially in view of the possible capture of high purity by-product hydrogen for energy recovery or for other industrial operations.

Embodiments of the system may include a plurality of electrolysis cells in a stack in a series and/or parallel flow arrangement, as shown in fig. 4-7. For example, the wastewater may be split and fed to multiple cell stacks and the streams thereafter combined at the cell or stack outlet, as shown in fig. 6 and 7. Each of the cell stacks may be different, e.g., operate under different operating conditions and/or include different components. This applies in particular to waste waters which contain appreciable concentrations of oxidizable constituents, such as ammonia, hydrogen sulfide, metals and also inorganic and/or constituents which decompose at low electrolytic potentials, decompose with heat or decompose with different catalysts. By optimizing the design of each stack for a particular type of contaminant that may be in the wastewater stream, improved contaminant removal, energy efficiency, operating costs, and battery life may be achieved. As shown in the examples below, cell (and membrane electrode assembly) design and operating conditions have a great effect on the removal of various contaminants.

In fig. 4, a first cell stack 201 is connected upstream of a second cell stack 202 and in series with the second cell stack 202, wherein the anode outlet of the first cell stack 201 is connected to the anode inlet of the second cell stack 202, wherein the generated hydrogen is collected from all cathodes by stream 203. At least one of the first cell stack 201 and the second cell stack 202 operates at different operating conditions than the other cell stacks, such as anolyte flow rate, current, voltage, temperature, and/or pressure.

In fig. 5, the end plates common to the three stacks are series-connected so that the reactants flow from the first stack 204, then to the second stack 205 and then to the third stack 206. Each of the stacks 204, 205, 206 may be of a monopolar design or a bipolar design, as described above, and may be comprised of one or more cells. Each stack is sandwiched between common end plates 207, 208 which may contain pockets (not shown) for holding each stack in place. The end plates may be electrically insulating or electrically conductive. If the end plates are electrically insulated, current or voltage control can be performed at each anode and cathode electrode to provide different operating conditions for each cell. Alternatively, each stack may have electrically conductive end plates (placed in pockets of insulating end plates), and current or voltage control may be performed at these end plates so that the operation of each cell in the stack will be the same, but may be different from the other stacks. In another alternative, electrically conductive end plates may be used, and current or voltage control may be performed at these electrically conductive end plates so that each stack will operate under the same conditions. Additionally, there may be a collection device between each stack for collecting wastewater for sampling and determining contaminant levels, which may optionally be used to control the current or voltage to a downstream section (not shown). Those skilled in the art will appreciate the advantages of this design, such as requiring less hardware and accompanying facilities, while providing a smaller footprint. Furthermore, in a single pole design, each cell can be operated at a different current or voltage, and thus the performance of each cell can be controlled to be the same without affecting the other cells. (electrical connections have been omitted from fig. 5 for ease of understanding.) while those stacks are shown as being series-flow connected, it will be understood that the stacks may also be connected in different ways, such as those described with respect to fig. 6 and 7.

In another embodiment, as shown in fig. 6, the first stack 210 is connected upstream of and in series with the second stack 211 and the third stack 212, wherein the generated hydrogen is collected from all cathodes by stream 213. In this embodiment, at least one of the first stack 210, the second stack 211, and the third stack 212 operates at different operating conditions than the other stacks, such as anolyte flow rate, current, voltage, temperature, and/or pressure. The flow of anolyte from the first stack 210 is split into the second stack 211 and the third stack 212 by a valve 214. Those skilled in the art will appreciate that the first stack may be in a position that is reversed from that shown in fig. 5, i.e., the second and third stacks are in a parallel configuration, with the first stack being downstream of the second and third stacks in series, such that the two anolyte streams discharged from the second and third stacks merge into a single anolyte stream that is then supplied to the first stack.

In another embodiment, as shown in fig. 7, the first stack 210, the second stack 211, and the third stack 212 are connected in a parallel arrangement, e.g., the anolyte flow is split into stacks 210, 211, and 212 by valve 215. In this embodiment, at least one of the first cell stack 210, the second cell stack 211, and the third cell stack 212 operates under an operating condition different from the other cell stacks. This arrangement can be applied to situations where a portion of the wastewater is reused for other applications that can tolerate a higher level of contaminants while another portion of the wastewater is recycled and requires a lower level of contaminants. For example, a portion of the wastewater may be treated to reduce Chemical Oxygen Demand (COD) or ammonia or hydrogen sulfide to about 99% removal levels, such that the treated wastewater may be reused in a reverse osmosis unit or other industrial process requiring very low COD or other contaminants, while the remaining portion of the wastewater only needs to be treated to 50% COD levels for discharge and/or for disinfection.

In another embodiment, the processing unit 218 may be a filter, a degassing unit, a pH controller, etc., which may be disposed upstream of the stacks, between the stacks and/or downstream of the ends of the stacks (as shown in fig. 5 and 6), or between the stacks of fig. 4 (processing unit 218 not shown). As a filter, the processing unit 218 captures oxidation and decomposition products between stacks to prevent such products from entering downstream stacks. As a filter, the treatment unit 218 may be cleaned by any method known in the art, such as backwashing, air or gas scrubbing, and cartridge replacement. As a degassing unit, processing unit 218 removes product gases to prevent such products from entering the downstream stack. As a pH controller, the treatment unit 218 adjusts the pH of the wastewater to prevent corrosion of downstream components, precipitate contaminants, and/or impart a desired pH to the wastewater.

For example, for wastewater with organic contaminants, ammonia, and hydrogen sulfide, two stacks of electrolysis cells may be connected in series. The first stack may be set at a lower voltage and current and a higher anolyte flow rate to oxidize ammonia, hydrogen sulfide, and other readily oxidizable organics. The second stack may be set at a higher voltage and current and at the same or a lower anolyte flow rate to oxidize the remaining organics. A filter between the first stack and the second stack may be used to remove oxidation products, such as sulfur-containing oxidation products. Furthermore, a degassing unit may be placed before the first stack, between the first stack and the second stack and/or at the end of the second stack. The pH may also be adjusted after the first pile and/or after the second pile.

In another example, for wastewater containing organic contaminants of different molecular weights, such as volatiles and petroleum hydrocarbons, a first stack may be operated at a lower voltage and/or current to oxidize a large number of readily oxidizable organic components and partially oxidize large molecular weight organics, and a second stack connected in series and operated at a higher voltage and/or current to oxidize the remaining species.

Additionally or alternatively, each cell stack may include different components, such as an anode fluid delivery layer, an anode filter layer, catalyst composition and loading, flow field plate type and design, polymer electrolyte membrane, electrode active area, and cell count. Furthermore, each cell stack may be optimized for different types of contaminants that may be in the wastewater stream. For example, as shown in the examples below (see tables 1-9), certain anode catalysts have a higher affinity for oxidizing different contaminants. Thus, in a wastewater stream having several different contaminants, one skilled in the art would be able to determine the best anode catalyst (or membrane electrode assembly design) for a particular type of contaminant and use them in a separate segmented cell stack or stack to improve contaminant removal from the wastewater stream.

The method may include combining a stack with a filter layer with a stack without a filter layer. The filter layer may be electrically conductive or non-conductive. The anode and cathode flow field plates can also be conductive or non-conductive or a combination of both.

For wastewater containing solid particles, the method may include a stack having one anode filter layer adjacent to the anode fluid diffusion layer and a stack without one filter layer. For example, if the particles are in incoming wastewater, the first set of piles may desirably have such a filter layer. An intermediate filtration step may then be performed and the remaining stack may not require such a filtration layer. For wastewater effluent without any particles, the first set of piles may not have such a filter layer, but if solid particles are produced during oxidation and/or decomposition, then the subsequent piles may ideally have such a filter layer. Furthermore, intermediate and post-filtration steps and/or a pH adjustment step and/or a degassing step may also be used.

The anode flow field plate may be electrically conductive with the electrically conductive anode filter layer and the fluid diffusion layer. Alternatively, the flow field plate may be made of plastic, the anode filter layer may be a non-conductive filter layer and the fluid diffusion layer will be electrically conductive, for example if the waste water is very corrosive.

In one example, for landfill leachate, which typically contains ammonia nitrogen, organics, and chloride ions, the wastewater treatment system may include three separate stacks of electrolytic cells in series. The first stack is designed to oxidize ammonia at a lower voltage, such as from about 1.4 to about 2.0V, while carrying the anolyte at a relatively faster flow rate than the second stack due to a faster reaction rate and/or lower contaminant concentration. The stack may also include fewer cells than the second cell stack due to the faster reaction rate. The reaction in the first cell stack may comprise the following:

2NH₃+6OH^-→N₂+6H₂O+6e^-(1)

2Cl^-→Cl₂+2e^-(2)

Cl₂+H₂O→HOCl+H⁺+Cl^-(3)

2/3NH₃+HOCl→1/3N₂+H₂O+H⁺+Cl^-(4)

the second cell stack is designed to oxidize organics and may be operated at a higher voltage than the first cell stack, such as greater than about 2.5V, while carrying the anode electrolyte at a relatively slower flow rate than the other cell stacks due to slower reaction rates and/or higher contaminant concentrations. Additionally or alternatively, the stack may also include more cells than other stacks due to slower reaction rates and/or higher contaminant concentrations.

The third cell stack is designed to remove remaining microbial contaminants from the wastewater stream by disinfection. Thus, the third stack may comprise means for generating free chlorine from chloride ions in the chlorine-containing waste water. The third stack may be operated at a lower voltage than the second stack because the voltage for generating free chlorine is generally lower than the voltage required to generate hydroxyl radicals and may include fewer cells than the second stack because the wastewater requires less residence time because the free chlorine will disinfect the wastewater and have a residual disinfection effect once the free chlorine is generated.

Those skilled in the art will recognize that the above described embodiments may be further combined in a number of different ways to optimize contaminant removal from a wastewater stream and to improve the energy efficiency and life of an electrolytic cell. The embodiments described above are merely illustrative of several aspects of the invention and should not be construed as limiting in any way.

In the construction of a multiple cell system, an electrically conductive layer may be used between the fluid diffusion layer and the plate or between the gas diffusion layer and the plate. Alternatively, the conductive foil or membrane may be welded to the fluid diffusion layer or gas diffusion layer.

The following examples are provided to illustrate certain aspects of the invention and in particular the different results obtained when using the electrolytic cells of the invention having different cell components and/or operating under different conditions. These examples should not be construed as limiting in any way.

Examples of the invention

A number of laboratory scale solid polymer electrolyte electrolytic cells were constructed as generally shown in fig. 2 and used to remove contaminants from wastewater samples by the method of the present invention. The contaminants removed were acid blue 29, phenol, acetaminophen, ibuprofen, kraft mill sewage, or formic acid and these were present in different concentrations as indicated below.

Testing the use of one cell for allA single Membrane Electrode Assembly (MEA) comprising fluid and gas distribution layers adjacent each of the anode and cathode electrodes. The fluid dispersion layer was made of different porous carbon papers (as indicated below) onto which different microporous sublayers had been applied and a niobium mesh with one tungsten mesh sublayer. In some cases, commercially available MEAs are used and in other cases, catalyst layers comprising specific catalyst compositions are prepared and applied to the fluid distribution layers (again as indicated below). The MEA with fluid diffusion layers was sandwiched between graphite resin composite plates in which serpentine flow field channels had been mechanically formed. The size of the MEA varies somewhat from cell to cell, as indicated below, but is about 50cm in size²。

In these laboratory scale tests, several thicknesses of porous graphite paper from Toray corporation (Toray) were used as substrates for fluid diffusion layers (i.e., Toray)^TMTGP-H-030 ═ 110 μm, TGP-H-60 ═ 190 μm, TGP-H-90 ═ 280 μm, and TGP-H-120 ═ 370 μm). These papers are impregnated with PTFE using a variety of sequential conventional impregnation or flow techniques to slowly increase the thickness of the PTFE coating without forming cracks. Each coating layer was dried to remove water at 80 ℃. The PTFE impregnated substrate was sintered at 400 ℃ for 10 minutes to increase the surface hydrophobicity prior to application of the microporous sublayer coating, or left unsintered to allow control of the permeation of the microporous coating solution.

The microporous sublayer coating is then applied to the fluid diffusion layer substrate. A suspension of conductive particles and hydrophobic PTFE was prepared in a solution containing water, a wetting agent, and a pore-forming agent, as indicated in table 1 below. First, the conductive particles were suspended in water and wetting agent by dispersing/mixing at 1500rpm for 5 minutes. Then, PTFE and pore former in water were added and mixed using a high shear mixer at 2500rpm for 30 minutes or more until no agglomeration was present (as determined by grindometer fineness). The sub-layer suspension is then applied to the substrate by bar coating or knife coating. The coated substrate was heated to remove water and then calendered. Finally, both the wetting agent and pore former were removed and the applied PTFE was sintered by heating the coated substrate at 400 ℃ for 10 minutes. Table 1 below summarizes the different sub-layer compositions of the 8 different sub-layers present in these examples. Sublayers #4, 5 and 6 have the same composition and are prepared in the same manner but applied in different amounts to the substrates involved.

Table 1.

Note that:

Timrex HSAG300^TMthe content of graphite is 90 percent<A particle size distribution of 32 μm and 280m²One surface area of/g

Super P-Li^TMThe conductive carbon black has a particle size of 40nm and 62m²Surface area per gram

The Timrex KS150 synthetic graphite had a particle size distribution wherein 95% <180 μm

The Timrex KS25 synthetic graphite had 90% of it<A particle size distribution of 27.2 μm and 12m²One surface area of/g

MnO₂The powder has<Particle size distribution of 5 μm

HPMC stands for hydroxypropylmethylcellulose

> 95% niobium is-325 mesh powder

Nine different anode catalyst layers (indicated as a 1-a 9) and five different cathode catalyst layers (indicated as C1-C5) are present in these examples. The different catalyst layer and preparation suspension compositions are summarized in table 2 below. A1 and C1 are commercially available platinum catalyst layers coated on a membrane electrode provided as a fully Catalyst Coated Membrane (CCM) product from ion power, Inc. The catalyst layers presented in table 2 were applied in suspension to the sublayer coated fluid diffusion layer or membrane electrode as indicated in tables 4-7 below. The suspension was prepared by adding the indicated catalyst and electrical conductor powders to a liquid carrier. The suspension was mixed at 2500-. Multiple passes are then used to spray the catalyst coating suspension in small amounts onto each membrane (CCM) surface or into the fluid diffusion layers and cathode gas diffusion layers (electrodes) using pneumatic gravity feed spray guns. The coating is dried between passes until the desired coating weight is reached.

Table 2.

Note that:

ATO (1) represents antimony tin oxide nanoparticles; sb₂O₅:SnO₂The ratio of (a) is 10:90 wt%; 22-44nm particle size; and 20-40m²Per g surface area

ATO (2) is ATO (1) which has been treated in air at 550 ℃ for 4 hours

ATO (3) is antimony tin oxide modified Timrex HSAG300^TMGraphite (II)

ATO (4) is Nb and Sb doped antimony tin oxide particles; nb₂O₅:Sb₂O₅:SnO₂Nominal ratio 5:10: 85% by weight

The platinum used is HiSPEC 4100^TM(ii) a Nominally 40% by weight of the carbon support

Timrex HSAG300^TMThe graphite is 90 percent of the total weight<A particle size distribution of 32 μm; and 280m²A conductive high surface area graphite per surface area of g

Super P-Li^TMIs a conductive carbon black; having a particle size of 40 nm; and 62m²One surface area of/g

The silver used is a spherical powder, 99.9% (purity of powder), having a particle size distribution of 1.3-3.2 μm; and 0.3-0.7m²One surface area of/g

MnO₂The powder has<Particle size distribution of 5 μm

Sn-Ag is an alloy nanopowder with a particle size of <150nm, 3.5% Ag

SnO₂Is-325 mesh powder

Nafion^TMEW1100 is a dispersion comprising colloidal particles in a 10 wt% solution

Ta is-325 mesh powder

Nb is-325 mesh powder

TiC powder has a particle size distribution of not more than 4 mu m

In addition, in the above, 9.5gm of SnCl was dissolved in 10ml of concentrated hydrochloric acid₂-2H₂O and 0.5gm SbCl₃To prepare ATO (3). The mixture was stirred until the solution was clear. Then 10gm of pretreated Timrex HSAG300^TMGraphite was dispersed in 100ml ethanol. This graphite suspension was heated to 80-90 ℃ and the acid solution was slowly added while stirring was continued. Heating and stirring were continued until the ethanol evaporated. The powdered product was filtered and washed with deionized water, and then dried in a 100 ℃ oven. In this procedure, Timrex HSAG300^TMThe pretreatment has been carried out by: first, 0.25gm of PdCl was combined₂、12.5gm SnCl₂-2H₂O, 150ml deionized water, and 75ml concentrated hydrochloric acid, stirred at room temperature until the color turns green (≧ 1h), then 20gm of graphite powder was added to this suspension, stirred for 1-3 minutes, and finally filtered, rinsed, and dried.

The test MEAs including the fluid diffusion layers were incorporated together into a unitary assembly prior to testing. When using commercially available and room-fabricated catalyst coated membrane electrolytes, these can be placed between an appropriate anode and cathode fluid distribution layer (hereinafter referred to as the cathode gas diffusion layer since the fluid on the cathode side is always gaseous) and hot pressed at 140 ℃ for 5 minutes or left unbound for testing. When using the catalyst coated fluid diffusion layers described herein, the electrodes were placed on either side of a commercially available membrane electrolyte and hot pressed at 140 ℃ for 5 minutes to bond them together. PTFE tape was used to mask the edges of the unbonded CCM to provide a dimensionally stable perimeter for the cell assembly.

The composition and loading of the different catalyst layers and fluid distribution layers in the MEAs used in these examples are summarized in table 3 below.

Electrochemical cell assembly was completed by sandwiching the test MEA between an anode flow field plate and a cathode flow field plate made of a polymer-graphite composite. Machining a 4-pass serpentine channel on a cathode flow field plate, the channel having a channel width of 1mm, a channel height of 1mm, a junction width of 1mm, and 50cm²Geometric area. Using two different anode flow field plates; a first anode flow field plate has a channel serpentine channel machined in the flow field plate with a channel width of 1mm, a channel height of 1mm, and a channel height of 1mmmm bonding width, and 50cm²Geometric area, and a second anode flow field plate having a single channel machined therein having a 5mm channel width, 8mm channel height, 2mm junction width, and 50cm²Geometric area. A spiral coaxial hybrid fabricated from 2mm width twisted PTFE tape was used for the single channel anode flow field plate and the channel interior was coated with PTFE. The sealing gasket used is made ofAndmade, the current collector is gold coated copper and the end compression plate is made of steel and contains internal resistance heating elements. In all of the following experimental tests, the 4-pass channel design was used, except that the tests involving MEA K2 in table 5 used single-pass and coaxial mixing elements.

The test then involved preparing simulated contaminated wastewater (>1L solution) with the specified contaminants in deionized water. The electrochemical cell temperature is kept constant using internal resistive heating elements, a temperature controller, and a thermocouple. Several test temperatures were used as indicated below. The wastewater containing the indicated contaminants was then flowed through the anode of the test cell at 270mL/h using a peristaltic pump while a constant DC voltage was applied to the current collector. A valve downstream of the anode exhaust was used in selected experiments to provide a pressurized stream. The cathode inlet of the test cell was sealed and a valve was also placed downstream of the cathode exhaust to provide a slightly pressurized hydrogen bleed. Most tests were conducted at atmospheric pressure at the anode exhaust pipe and at low pressure (<1psi) at the cathode exhaust pipe to fill the hydrogen storage vessel. No water or purge gas is used or required at the cathode. No supporting electrolyte of any type was used at the cathode in any of the tests. The wastewater effluent is collected in a plastic bottle and the product gas is released to the atmosphere.

Tables 4, 5, 6, 7, 8 and 9 below summarize the results obtained for tests involving acid blue 29 dye, phenol, acetaminophen, formic acid, ibuprofen and kraft paper sewage, respectively.

For acid blue 29 dye contamination, color measurements were used to quantify the efficiency of the treatment. The% color removal was determined by comparing the absorbance against a sample of known concentration using a UV/VIS spectrophotometer.

For the other contaminants tested, Chemical Oxygen Demand (COD) was used to quantify the efficiency of the treatment. COD is used as a measure of pollutants in wastewater and natural water. Both the organic and inorganic components of the sample are subjected to oxidation, but in most cases the organic component dominates and has the greatest benefit (see Standard Methods for the evaluation of Water and Wastewater (Water and Water), 21 st edition, APHA, AWWA, WEF,). In general, the oxidation of a particular compound is characterized by the degree of degradation of the final oxidation product (reference: Industrial Water Quality, 4 th edition, W. Wesley Eckenfelder (W. Wesley Eckenfelder, Jr.), David L. Ford, and Andrew J. England, Jr.), McGraw-Hill Companies (Inc.)). The reason for this is that the degradation of contaminants can be mentioned in several ways. These ways are: (1) primary degradation involving structural changes in the parent compound; (2) to a structural change in the parent compound to the extent of acceptable degradation (lysis) with reduced toxicity; (3) involving organic carbon to inorganic CO₂Final degradation (mineralization) of the transformation of (a); and (4) unacceptable degradation (melting) involving structural changes in the parent compound that result in increased toxicity. Any degradation process that does not lead to overall mineralization of the organic constituents can potentially form end products that may be more toxic than the starting compounds. Drawing (A)4 is a prior art description of how the initial compound concentration change during oxidation of a refractory organic compound such as phenol can be distinguished from the COD change. Although at point a the amount of initial/parent compounds has decreased to zero, the COD of the wastewater has not reached the emission limit for COD concentration.

Therefore, to quantify the contaminant removal efficiency of the system and/or process, the ultimate degradation (mineralization) of organic compounds is preferably measured by Chemical Oxygen Demand (COD). COD will report on almost all organic compounds and is used to monitor and control emissions in industrial applications, emission permits, and to assess process plant performance. COD is a measure of the total amount of oxidizable components (e.g., carbon, hydrogen, nitrogen, sulfur, and phosphorus from hydrocarbons) in a sample, and is measured here by method 5220C (EPA approved-Standard Methods for the evaluation of water and Wastewater, 21 st edition).

The treated wastewater was sampled throughout the test period and the average values of colour and COD were determined from the contaminants present. The current was generally stable throughout the test cell and the average current density was also determined as reported below.

Tables 4 to 9 also list the energy consumption (voltage, average current, and time through all the paths through the cell) per unit volume of wastewater. Where appropriate, specific energy consumption per unit mass of mineralized COD is also listed.

In addition, the volume of hydrogen produced was measured in each case in a storage facility. And from this, H is determined₂The efficiency of the electrolysis is shown in the tables. Ideally, 39.4kWh of electricity is required to produce 1kg of hydrogen under normal conditions (25 ℃ and 1 atm). This represents the High Heat Value (HHV) of the hydrogen, which includes the total amount of energy (thermal and electrical) that dissociates water under normal conditions. System efficiency was calculated by dividing the heating value (HHV) by the actual energy input in kWh/kg. The efficiency of industrial electrolysers typically ranges from 52% to 82% (HHV).

The results using these laboratory test cells show that electrochemical cells with non-liquid polymer electrolytes, containing no other added chemicals, and including low cost catalysts and other electrode components can provide removal efficiencies for refractory acid blue 29 dyes, phenol, acetaminophen, formic acid, ibuprofen, and kraft and paper mill effluents equal to or better than comparable prior art systems. In particular, these results may be at substantially lower energy inputs (i.e., at less than about 10 mA/cm)²At an applied voltage of less than about 3V), in some cases an energy reduction of greater than 60% at 80% COD removal, an energy reduction of greater than 80% at 95% COD removal, and this does not include a recoverable energy contribution from the produced hydrogen gas. A 20% increase in current efficiency was observed for acid blue dye 29 and an increase of over 60% was observed for phenol and acetaminophen. Certain specific in-chamber prepared catalyst selection and electrode design may lead to performance improvements>40％。

In addition, however, the present method is effective to produce hydrogen in a purity equivalent to commercial electrolyzers and in sufficient quantity such that an additional 15% -35% net energy consumption reduction evaluated can be achieved depending on wastewater composition (assuming that a fuel cell stack operating at 50% efficiency is used to convert hydrogen back to electricity and assuming 95% recovery of hydrogen). For illustrative purposes, fig. 5 shows the average actual hydrogen generated from various tests performed on phenol-contaminated wastewater at several different currents compared to ideal or perfect hydrogen generation. As can be seen, there is a high conversion of the phenol contaminant to hydrogen.

Furthermore, recoverable energy in a real-scale industrial system can be assessed based on the above. Assuming that the generated hydrogen is converted back to electricity at 50% efficiency using a prior art fuel cell, table 10 shows the expected recoverable energy in an industrial system operating according to the three data points shown in fig. 5 above. In this table, the scale of the system has been expanded to handle 1m³500mg/l phenol wastewater and the hydrogen generated is converted back to electricity at 95% utilization, assuming a 5kW fuel cell operating at 50% efficiency is used.

Table 10.

All of the above-mentioned U.S. patents and applications, foreign patents and applications, and non-patent publications mentioned in this specification are herein incorporated by reference in their entirety.

While specific embodiments, aspects, and applications of the present invention have been shown and described, it will be understood by those skilled in the art that the present invention is not limited thereto. Many modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the present disclosure. Accordingly, the invention is to be understood in accordance with the following claims.

Claims (18)

1. A method for energy efficient treatment of contaminated wastewater, the method comprising:

providing at least a first solid polymer electrolyte cell stack and a second solid polymer electrolyte cell stack, the cells in the first stack and the second stack each comprising: an anode comprising an anode catalyst layer and the anode catalyst layer comprising an anode catalyst; a cathode comprising a cathode catalyst layer and the cathode catalyst layer comprising a cathode catalyst, wherein the cathode is free of liquid electrolyte; and a solid polymer membrane electrolyte separating the anode and the cathode;

supplying a wastewater stream containing contaminants to the anode of each of the first and second cell stacks at a flow rate and flow pressure;

providing a voltage of less than about 3 volts across each cell in the first and second cell stacks, wherein the anode is positive relative to the cathode;

at one operating temperature and less than about 20mA/cm²Operating each cell in the stack at a current density to degrade the contaminants and generate hydrogen gas at the cathode; and

discharging the generated hydrogen gas from the cathode;

wherein "about" is to be interpreted as including a range of values within plus or minus 10% of the stated value; and

wherein at least one of the stack components in the first solid polymer electrolyte cell stack and the operating conditions of the first solid polymer electrolyte cell stack is different from the stack components of the second solid polymer electrolyte cell stack and the operating conditions of the second solid polymer electrolyte cell stack.

2. The method of claim 1, wherein the different stack component is selected from the group consisting of: an anode fluid delivery layer, the anode catalyst layer, an anode flow field plate, an anode filter layer, the solid polymer electrolyte membrane, and a plurality of cells in the stack.

3. The method of claim 2, wherein the different stack component is the anode catalyst layer and at least one of a catalyst loading and a catalyst active area in the anode catalyst layer of the first solid polymer electrolyte cell stack differs by more than about 5% from at least one of a catalyst loading and a catalyst active area in the anode catalyst layer of the second solid polymer electrolyte cell stack.

4. The method of claim 3, wherein at least one of a catalyst loading and a catalyst active area in the anode catalyst layer of the first solid polymer electrolyte cell stack differs by more than about 10% from at least one of a catalyst loading and a catalyst active area in the anode catalyst layer of the second solid polymer electrolyte cell stack.

5. The method of claim 1, wherein the different operating condition is selected from the group consisting of: a flow rate of the wastewater, a flow pressure of the wastewater, a voltage, an operating temperature, and a current density.

6. The method of claim 5, wherein the different operating conditions of the first solid polymer electrolyte cell stack differ from the operating conditions of the second solid polymer electrolyte cell stack by more than about 5%.

7. The method of claim 6, wherein the different operating conditions of the first solid polymer electrolyte cell stack differ from the operating conditions of the second solid polymer electrolyte cell stack by more than about 10%.

8. The method of claim 1, comprising applying a voltage at less than about 10mA/cm²Each cell in the stack is operated at a current density of (a).

9. The method of claim 1, comprising supplying the wastewater stream to the anode of each cell in the electrolytic cell stacks without added supporting electrolyte.

10. The method of claim 1, wherein the cathode of each cell in the electrolytic cell stacks contains neither a liquid catholyte nor a liquid supporting electrolyte.

11. The method of claim 1, wherein the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack each comprise a single cell.

12. The method of claim 1, wherein the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack comprise more than one cell.

13. The method of claim 1, wherein the first solid polymer electrolyte cell stack is connected upstream of and in series flow with the second solid polymer electrolyte cell, and the anode outlet of the first solid polymer electrolyte cell stack is connected to the anode inlet of the second solid polymer electrolyte cell stack second cell stack.

14. The method of claim 13, wherein the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack comprise a common end plate.

15. The method of claim 1, wherein the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack are connected in co-current flow with the second solid polymer electrolyte cell, and wherein the supplied wastewater is divided between anode inlets of the first solid polymer electrolyte cell stack and the second solid polymer electrolyte cell stack.

16. The method of claim 1, comprising incorporating a treatment unit in the wastewater stream.

17. The method of claim 16, wherein the processing unit is selected from the group consisting of: a filter, a degassing unit, and a pH controller.

18. The method of claim 16, comprising incorporating the processing unit upstream or downstream of the first solid polymer electrolyte cell stack or the second solid polymer electrolyte cell stack.