A microbial electrolytic cell and a method for treating uranium-containing wastewater

Abstract

The present invention provides a microbial electrolysis cell and a method for treating uranium-containing wastewater. The microbial electrolysis cell comprises an electrolysis cell; an electrolyte solution and uranium-containing wastewater are disposed within the electrolysis cell; a bioanode and a biocathode disposed within the electrolysis cell; and an external circuit connecting the bioanode and the biocathode. The microbial electrolysis cell is used to perform microbial electrochemical reduction of the uranium-containing wastewater. Compared with existing technologies, the present invention utilizes a microbial electrolysis cell to treat uranium-containing wastewater. This cell can reduce hexavalent uranium ions to a relatively low concentration by applying a relatively low external voltage, and has a wide pH range of applicability. Furthermore, the establishment of a biocathode accelerates the treatment of uranium-containing wastewater, improves treatment efficiency, and reduces operating costs. Furthermore, the microbial electrolysis cell can produce a large amount of hydrogen while treating the uranium-containing wastewater.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a microbial electrolysis cell and a method for treating uranium-containing wastewater. Background Art

[0002] With rapid economic development, fossil fuels are no longer sufficient to meet the needs of today's society. Consequently, more and more countries are turning to nuclear energy. The development of nuclear energy inevitably generates large quantities of uranium-containing wastewater, which, unlike ordinary industrial wastewater, is radioactive. Dissolved uranium (U(VI)) or uranyl ions in uranium-containing wastewater can undergo degeneration and emit radiation after entering plants and animals through the water, stimulating and affecting their growth. Uranium ions entering the human body can severely harm organs and cause complications, posing a significant threat to both humans and the environment. Therefore, to ensure the safety of both humans and the natural environment, timely and effective treatment of uranium-containing wastewater is essential.

[0003] Since the discovery of microbial electrolysis cell (MEC) technology in 2005 by two independent teams at Pennsylvania State University and Wageningen University, MEC has evolved from its initial focus on hydrogen production to include wastewater treatment, desalination, and chemical product production. As an emerging bioelectrochemical technology, MEC has demonstrated significant advantages and potential in the treatment of heavy metal-containing wastewater. The basic principle of MEC treatment of heavy metal-containing wastewater is that microorganisms in the MEC anode chamber catalytically oxidize organic matter and produce electrons and protons. The generated electrons are transferred to the anode via extracellular electron carriers of the microorganisms. These electrons are then transferred to the cathode surface through an external circuit under the influence of the potential difference provided by an external voltage. Protons then travel from the anode region to the cathode region via a proton exchange membrane or diffusion. In the cathode region, heavy metal ions act as electron acceptors, receiving electrons that are reduced and removed. Simultaneously, protons combine with electrons to produce products such as hydrogen and methane, thereby achieving the goal of pollutant reduction.

[0004] At present, many experts and scholars have applied MEC to treat wastewater containing heavy metals. For example, using MEC biocathode to treat nickel-containing wastewater, it was found that low potential nickel (Ni 2+ ) has a treatment efficiency of up to 70%, in which microbial electrochemical reduction is the main reaction process for nickel removal; for example, MEC technology is used to generate hydrogen and recover or treat cobalt ions (Co) from wastewater generated in simulated or actual lithium battery production processes. 3+), where a stainless steel mesh was used as the cathode, and the cobalt removal rate reached 75.4% at an applied voltage of 0.5V. MEC technology can also be used to treat cadmium (Cd)-containing wastewater. Different external power sources and carbon sources have varying degrees of impact on Cd removal. Using sodium acetate increased the removal rate by 20% compared to using sodium bicarbonate as the carbon source, achieving a cadmium removal efficiency of 7.33±0.37mg / L / h. Furthermore, MEC technology can also be used to treat acidic mine drainage, achieving good removal results for sulfate and heavy metals in acidic mine drainage. These research results demonstrate the great research potential and practical feasibility of MEC technology in the field of heavy metal wastewater treatment.

[0005] The development direction of uranium pollution control technology is to achieve harmlessness, resource utilization, and energy conversion. MEC is a new electrochemical technology that uses a low applied voltage to induce the reduction of heavy metals such as cadmium, nickel, and cobalt. Therefore, the establishment of a biocathode through MEC is of great significance for the treatment of uranium-containing wastewater. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a microbial electrolysis cell and a method for treating uranium-containing wastewater. The treatment method uses a microbial electrolysis cell with high treatment efficiency, is green and environmentally friendly, is simple to operate, and can simultaneously produce hydrogen.

[0007] The present invention provides a microbial electrolysis cell, comprising:

[0008] An electrolytic cell; an electrolyte solution and uranium-containing wastewater are provided in the electrolytic cell;

[0009] A bioanode and a biocathode are provided in the electrolytic cell; the bioanode comprises an anode current collector and a microbial membrane provided on the surface of the anode current collector; the biocathode comprises a cathode current collector, a Ni-Cu / CeO2 catalytic layer provided on the surface of the cathode current collector, and a microbial membrane provided on the surface of the Ni-Cu / CeO2 catalytic layer;

[0010] An external circuit connecting the bioanode to the biocathode.

[0011] The present invention also provides a method for treating uranium-containing wastewater, comprising:

[0012] The microbial electrolysis cell according to claim 1 is used to carry out microbial electrochemical reduction of uranium-containing wastewater.

[0013] Preferably, the mass ratio of Ni, Cu and Ce in the Ni-Cu / CeO2 catalytic layer of the biocathode is (15-25): (3-6): (1-3).

[0014] Preferably, the biocathode is prepared according to the following steps:

[0015] The cathode current collector is immersed in a solution containing nickel ions, cerium ions and copper ions, dried, and then sintered to obtain a cathode electrode;

[0016] The cathode electrode is acclimated in an electrolyte solution containing electrogenic bacteria and a carbon source by reversing the electrode polarity under an applied voltage condition to obtain a biocathode.

[0017] Preferably, the loading amount of Ni element in the cathode electrode is 15-25 wt%; the loading amount of Cu element is 3-6 wt%; and the loading amount of Ce element is 1-3 wt%.

[0018] Preferably, the drying temperature is 100° C. to 120° C.; the drying time is 1 to 3 hours; the sintering temperature is 300° C. to 550° C.; the sintering time is 3 to 5 minutes; and the sintering heating rate is 5 to 15° C. / min.

[0019] Preferably, the cathode current collector is selected from stainless steel mesh, platinum mesh or titanium foam; the electrogenic bacteria are derived from one or more of anaerobic sludge from a sewage treatment plant cultured with uranium-containing wastewater, the effluent from a microbial fuel cell and a microbial electrolysis cell; the carbon source is selected from one or more of glucose, sodium acetate, starch and protein; and the electrolyte solution is one or more of potassium ferricyanide solution, phosphate solution and borate solution.

[0020] Preferably, the bioanode is prepared according to the following steps:

[0021] The anode current collector is acclimated in an electrolyte solution containing electrogenic bacteria and a carbon source to obtain a bioanode;

[0022] The anode current collector is selected from carbon materials.

[0023] Preferably, the voltage of the microbial electrochemical reduction is 0.4 to 1.6V.

[0024] Preferably, during the microbial electrochemical reduction, the pH value of the electrolyte solution and the uranium-containing wastewater in the electrolytic cell is 4-8; and the concentration of hexavalent uranium ions in the uranium-containing wastewater is greater than or equal to 0.5 mg / L.

[0025] The present invention provides a microbial electrolysis cell and a method for treating uranium-containing wastewater. The microbial electrolyte comprises: an electrolysis cell; an electrolyte solution and uranium-containing wastewater are disposed within the electrolysis cell; a bioanode and a biocathode disposed within the electrolysis cell; the bioanode comprises an anode current collector and a microbial membrane disposed on the surface of the anode current collector; the biocathode comprises a cathode current collector, a Ni-Cu / CeO2 catalytic layer disposed on the surface of the cathode current collector, and a biofilm disposed on the surface of the Ni-Cu / CeO2 catalytic layer; an external circuit connecting the bioanode and the biocathode; and the microbial electrolysis cell is used to perform microbial electrochemical reduction of uranium-containing wastewater. Compared with the prior art, the present invention uses a microbial electrolysis cell to treat uranium-containing wastewater, can reduce hexavalent uranium ions at a low concentration by applying a low external voltage, and has a wide pH range of applicability. Furthermore, by establishing a biocathode, the treatment process of uranium-containing wastewater is accelerated, the treatment efficiency of uranium-containing wastewater is improved, and operating costs are reduced. Furthermore, the microbial electrolysis cell can produce a large amount of hydrogen while treating uranium-containing wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of the microbial electrolysis cell provided by the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] The present invention provides a microbial electrolysis cell, comprising:

[0029] An electrolytic cell; an electrolyte solution and uranium-containing wastewater are provided in the electrolytic cell; a bioanode and a biocathode are provided in the electrolytic cell; the bioanode comprises an anode current collector and a microbial membrane provided on the surface of the anode current collector; the biocathode comprises a cathode current collector, a Ni-Cu / CeO2 catalytic layer provided on the surface of the cathode current collector, and a microbial membrane provided on the surface of the Ni-Cu / CeO2 catalytic layer;

[0030] An external circuit connecting the bioanode to the biocathode.

[0031] See also Figure 1 , Figure 1 This is a schematic structural diagram of the microbial electrolysis cell provided by the present invention.

[0032] The microbial electrolysis cell provided by the present invention includes an electrolysis cell; the electrolysis cell can be a single-chamber electrolysis cell or a dual-chamber electrolysis cell; when the electrolysis cell is a dual-chamber electrolysis cell, it preferably also includes an ion exchange membrane, and the two chambers are separated by the ion exchange membrane; the ion exchange membrane is preferably a proton exchange membrane, an anion exchange membrane or a cation exchange membrane; in the embodiment provided by the present invention, the ion exchange membrane is specifically a proton exchange membrane.

[0033] The electrolytic cell is provided with an electrolyte solution and uranium-containing wastewater, which is the place where the microbial electrochemical reduction reaction occurs; when the electrolytic cell is a single-chamber electrolytic cell, the electrolyte solution preferably includes nutrients, phosphate buffer solution, trace elements and a carbon source; the nutrients preferably include ammonium chloride and potassium chloride; the concentration of nutrients in the electrolyte solution is preferably 0.3-0.8 g / L, more preferably 0.4-0.5 g / L, and more preferably includes 0.31 g / L of ammonium chloride and 0.13 g / L of potassium chloride; the trace elements preferably include calcium chloride, magnesium sulfate, sodium chloride, manganese sulfate, sodium molybdate, boric acid and zinc chloride; the carbon source is preferably one or more of glucose, sodium acetate, starch and protein, and in the embodiment provided by the present invention, specifically sodium acetate; the amount of the carbon source added is preferably such that the concentration of the carbon source in the electrolyte is 1-1.5 g / L, more preferably 1.28 g / L; when the electrolytic cell is In the case of a dual-chamber electrolytic cell, the uranium-containing wastewater is arranged in an electrolytic cell arranged at a biological cathode, and the anolyte solution preferably includes nutrients, trace elements, a carbon source and a phosphate buffer; the cathode electrolyte solution preferably includes nutrients, a phosphate buffer solution, trace elements and a carbon source; the nutrients preferably include ammonium chloride and potassium chloride; the concentration of nutrients in the electrolyte solution is preferably 0.3-0.8 g / L, more preferably 0.4-0.5 g / L, and more preferably includes 0.31 g / L of ammonium chloride and 0.13 g / L of potassium chloride; the trace elements preferably include calcium chloride, magnesium sulfate, sodium chloride, manganese sulfate, sodium molybdate, boric acid and zinc chloride; the carbon source is preferably one or more of glucose, sodium acetate, starch and protein, and in the embodiment provided by the present invention, specifically sodium acetate; the amount of the carbon source added preferably makes the concentration of the carbon source in the electrolyte 1-1.5 g / L, more preferably 1.28 g / L. In the present invention, the phosphate buffer preferably includes sodium dihydrogen phosphate and disodium hydrogen phosphate; the concentration of the sodium dihydrogen phosphate is preferably 5-6 g / L, more preferably 5.54 g / L; the concentration of the disodium hydrogen phosphate is preferably 22-24 g / L, more preferably 23.1 g / L.

[0034] A bioanode and a biocathode are also provided in the electrolytic cell, and the bioanode and the biocathode are immersed in the electrolyte solution and the uranium-containing wastewater.

[0035] The bioanode comprises an anode current collector and a microbial film arranged on the surface of the anode current collector; the anode current collector is preferably a carbon material, more preferably a carbon cloth; the rough surface of the carbon cloth is more conducive to the formation of a film of mixed bacteria on the surface, and the film is not easy to fall off after forming; the area ratio of the anode current collector to the volume of the electrolytic cell is preferably 5 to 15 cm 2 : 150-250 mL, more preferably 8-12 cm 2 : 150~250mL, preferably 9cm 2 : 150-250mL; a microbial film is provided on the surface of the anode current collector. The microbial film is preferably formed by electrogenic bacteria; the electrogenic bacteria are preferably derived from one or more of anaerobic sludge from a sewage treatment plant cultivated with uranium-containing wastewater, the effluent of a microbial fuel cell, and a microbial electrolysis cell. In the embodiment provided by the present invention, it is specifically anaerobic sludge from a sewage treatment plant cultivated with uranium-containing wastewater; microorganisms attach to the surface of the anode current collector to form a bioanode, which can oxidize and metabolize organic matter in the electrolyte solution in the anode region to produce electrons and protons, and the electrons are transferred to the anode through electron carriers outside the microorganisms; the anode reaction formula is:

[0036] CH3COO - +2H2O→CO2+8e - +7H +

[0037] The biocathode comprises a cathode current collector, a Ni-Cu / CeO2 catalytic layer arranged on the surface of the cathode current collector, and a microbial membrane arranged on the surface of the Ni-Cu / CeO2 catalytic layer; the cathode current collector is preferably a stainless steel mesh, a platinum mesh or titanium foam; the surface area of ​​the cathode current collector is preferably 5 to 15 cm 2 , more preferably 8 to 12 cm 2 , and preferably 9cm 2 The area of ​​the cathode current collector and the volume ratio of the electrolytic cell are preferably 5 to 15 cm 2 : 150-250 mL, more preferably 8-12 cm 2 : 150~250mL, preferably 9cm 2:150~250mL;The surface of the cathode current collector is provided with a Ni-Cu / CeO2 catalytic layer, wherein the mass ratio of Ni, Cu and Ce is preferably (15~25):(3~6):(1~3), more preferably (18~22):(4~6):2, and more preferably 20:5:2; if the mass of the microbial film is ignored, the loading amount of Ni element in the biocathode is preferably 15~25wt%, more preferably 18~22wt%, and more preferably 20wt%; the loading amount of Cu element is preferably 3~6wt%, more preferably 4~6wt%, and more preferably 5wt%; the loading amount of Ce element is preferably 1~3wt%, and more preferably 2wt%; The surface is provided with a Ni-Cu / CeO2 catalytic layer, which is more conducive to microbial growth, improves electron acceptance efficiency, accelerates the establishment of the biocathode and reduces overpotential; The surface of the Ni-Cu / CeO2 catalytic layer is provided with a microbial film to form a biocathode, which acts as a catalyst for the cathode reaction and can accelerate the reduction of hexavalent uranium and the generation of hydrogen; The cathode reaction formula is:

[0038] UO2 2+ +2e - →U 4+

[0039] 2H + +e - →H2

[0040] The three metals of the loaded nano Ni-Cu / CeO2 catalytic electrode selected by the present invention are irreplaceable. Among them, the addition of non-precious metal Ni improves the catalytic activity of the electrode, reduces the overpotential of the reactor and increases the hydrogen production rate of the reactor. Due to the synergistic electronic effect between metals, the performance of nickel alloy in catalytic hydrogen production is better than that of single nickel metal. Therefore, Ni-Cu alloy is used; the auxiliary Ce inorganic salt and Ni-Cu alloy are loaded on the formed stainless steel mesh / foam titanium, and finally the nano Ni-Cu / CeO2 catalytic electrode is obtained by various means. Compared with the ordinary cathode electrode, the catalyst electrode under this metal ratio accelerates the startup of the reactor, improves the removal efficiency of uranium and other metal ions, and improves the removal efficiency of COD and ammonia nitrogen in the reactor.

[0041] In addition, the microorganisms attached to the anode and cathode are widely available, have extremely low costs, and have excellent adaptability to various environments.

[0042] The bioanode and the biocathode are connected through an external circuit; the external circuit includes a power supply and a fixed resistor; the power supply is preferably a DC regulated power supply; the fixed resistor is preferably connected in series between the positive pole of the power supply and the bioanode; the resistance value of the fixed resistor is preferably 10Ω.

[0043] The microbial electrolysis cell provided by the present invention preferably further includes a data collector; the data collector is connected to both ends of the fixed resistor and is used to record the voltage across the fixed circuit and then calculate the current value in the circuit using Ohm's law.

[0044] The cathode region of the microbial electrolysis cell provided by the present invention is preferably further provided with a reference electrode; the reference electrode is preferably Ag / AgCl.

[0045] The present invention also provides a method for treating uranium-containing wastewater, comprising: applying the above-mentioned microbial electrolysis cell to perform microbial electrochemical reduction on the uranium-containing wastewater.

[0046] The present invention has no particular limitation on the sources of all raw materials, and any commercially available raw materials may be used.

[0047] The composition of the microbial electrolysis cell is the same as described above and will not be repeated here.

[0048] The biocathode is preferably prepared according to the following steps: the cathode current collector is immersed in a solution containing nickel ions, cerium ions and copper ions, dried, and then sintered to obtain a cathode electrode; the cathode electrode is acclimated in an electrolyte solution containing electrogenic bacteria and a carbon source by reversing the electrode polarity under an applied voltage condition to obtain a biocathode.

[0049] The cathode current collector is preferably a stainless steel mesh, a platinum mesh or titanium foam; the surface area of ​​the cathode current collector is preferably 5 to 15 cm 2 , more preferably 8 to 12 cm 2 , and preferably 9cm 2 ; The nickel ions are preferably provided by an inorganic salt of nickel, more preferably by nickel nitrate; the cerium ions are preferably provided by an inorganic salt of cerium, more preferably by cerium nitrate; the copper ions are preferably provided by a soluble inorganic salt of copper, preferably by copper nitrate; the drying temperature is preferably 100°C to 120°C, specifically 110°C in the present invention; the drying time is preferably 1 to 3 hours, and in the embodiment provided by the present invention, the drying time is specifically 2 hours; in the present invention, the impregnation and drying steps are repeated until a predetermined load is reached; the sintering temperature is preferably 300°C to 550°C; the sintering time is preferably 3 to 5 minutes; the sintering heating rate is preferably 5 to 15°C / min, more preferably 8 to 12°C / min.

[0050] Under the condition of an applied voltage, the cathode electrode is acclimated in an electrolyte solution containing an electrogenic bacteria group and a carbon source by reversing the electrode polarity to obtain a biological cathode. The applied voltage is preferably 0.3-0.5V, more preferably 0.4V; the electrogenic bacteria group is derived from one or more of the anaerobic sludge of a sewage treatment plant cultivated with uranium-containing wastewater, the effluent of a microbial fuel cell, and a microbial electrolysis cell, and in the embodiment provided by the present invention, it is specifically the anaerobic sludge of a sewage treatment plant cultivated with uranium-containing wastewater; the amount of anaerobic sludge added to the volume of the electrolyte solution is preferably 1: (2-5), more preferably 1: 3; the carbon source is preferably one or more of glucose, sodium acetate, starch, and protein, and in the embodiment provided by the present invention, it is specifically sodium acetate; the carbon source is added to the electrolyte solution. The amount of carbon source introduced is preferably such that the concentration of the carbon source in the electrolyte is 1 to 1.5 g / L, more preferably 1.28 g / L; the cathode electrolyte solution of the microbial fuel cell MFC during the startup period is preferably a potassium ferricyanide solution; the concentration of the potassium ferricyanide solution is preferably 5 / 40 (i.e., 0.125) mmol / L; before acclimation, a protective gas is preferably introduced to remove oxygen contained in the electrolyte solution and maintain the operation under an anaerobic environment; the protective gas is preferably at least one of nitrogen, argon, and helium with a purity of not less than 99.999%, specifically nitrogen in the embodiment provided by the present invention. According to the present invention, microbial nutrient elements are preferably added to the electrolyte solution to provide minerals and nutrient elements required for microbial growth; the microbial nutrient elements are preferably one or more of CaCl2, MgSO4, NaCl, MnSO4, AlCl3, Na2MoO4·2H2O, H3BO3 and ZnCl2; the acclimation is specifically to use a data collector to monitor the voltage value of the fixed resistor in real time, when the voltage value of one cycle drops to about 0.1V, replace 70% to 80% of the electrolyte solution, and add an appropriate bacterial source at the same time, when the reactor stably and continuously outputs a maximum voltage of more than 0.5V for three consecutive cycles in the feeding cycle, and the COD removal rate in the reactor reaches more than 90% in each cycle, it indicates that the electrode sheet has successfully formed a biofilm; the amount of the bacterial source added is preferably such that its volume ratio to the electrolyte is maintained at 1: (2 to 5), more preferably 1:3.

[0051] The bioanode is preferably prepared according to the following steps: the anode current collector is acclimated in an electrolyte solution containing an electrogenic bacteria group and a carbon source to obtain a bioanode; the anode current collector is preferably a carbon material, more preferably a carbon cloth; the anode current collector is preferably subjected to a high-temperature ammonia treatment and then acclimated; the temperature of the high-temperature ammonia treatment is preferably 600°C to 900°C, more preferably 700°C, and the time is preferably 0.5 to 2h, more preferably 1h; the anode current collector is preferably acclimated in a dual-chamber microbial fuel cell; the electrogenic bacteria group is derived from one or more of the anaerobic sludge of a sewage treatment plant cultured with uranium-containing wastewater, the effluent of a microbial fuel cell and a microbial electrolysis cell, and in the embodiment provided by the present invention, it is specifically the anaerobic sludge of a sewage treatment plant cultured with uranium-containing wastewater; the volume ratio of the anaerobic sludge added to the electrolyte solution is preferably 1: (2 to 5), more preferably 1: 3; the dual-chamber microbial fuel cell The anode electrolyte solution preferably includes a carbon source, a nutrient salt, a trace element and a phosphate buffer; the carbon source is preferably one or more of glucose, sodium acetate, starch and protein, and in the embodiment provided by the present invention, it is specifically sodium acetate; the amount of the carbon source added is preferably such that the concentration of the carbon source in the electrolyte is 1 to 1.5 g / L, more preferably 1.28 g / L; the cathode electrolyte solution is preferably one or more of potassium ferricyanide solution, phosphate solution and borate solution; specifically, phosphate buffer or potassium ferricyanide solution; the concentration of the potassium ferricyanide solution is preferably 5 / 40 (i.e. 0.125) mmol / L; before acclimation, a protective gas is preferably introduced to exclude oxygen contained in the electrolyte solution and maintain the operation under an anaerobic environment; the protective gas is preferably at least one of nitrogen, argon and helium with a purity of not less than 99.999%, and in the embodiment provided by the present invention, it is specifically nitrogen. According to the present invention, trace elements are added to the electrolyte solution as microbial nutrients to provide minerals and nutrients required for microbial growth; the microbial nutrients are preferably one or more of CaCl2, MgSO4, NaCl, MnSO4, AlCl3, Na2MoO4·2H2O, H3BO3 and ZnCl2; according to the present invention, the nutrient salts in the electrolyte solution preferably include ammonium chloride and potassium chloride; the concentration of the nutrient salts in the electrolyte solution is preferably 0.3-0.8 g / L, more preferably 0 .4~0.5g / L, and preferably includes 0.31g / L ammonium chloride and 0.13g / L potassium chloride; the acclimation is specifically to use a data collector to monitor the voltage value of the fixed resistor in real time, when the voltage value of one cycle drops to about 0.1V, replace 70%~80% of the electrolyte solution, and at the same time add an appropriate bacterial source (to keep the content of the bacterial source constant), when the reactor stably and continuously outputs a maximum voltage of more than 0.5V for three consecutive cycles in the feeding cycle, and at the same time the COD removal rate in the reactor reaches more than 90% in each cycle, it means that the electrode film is successfully formed.

[0052] An electrolyte solution and uranium-containing wastewater are added to the electrolytic cell for microbial electrochemical reduction; the electrolyte solution is preferably one or more of potassium ferricyanide solution, phosphate solution and borate solution; specifically, potassium ferricyanide solution or phosphate buffer solution; the concentration of the potassium ferricyanide solution is preferably 5 / 40 (i.e., 0.125) mmol / L; the concentration of hexavalent uranium ions in the uranium-containing wastewater is preferably greater than or equal to 0.5 mg / L, more preferably greater than or equal to 5 mg / ml; in the embodiment provided by the present invention, the concentration of hexavalent uranium ions in the uranium-containing wastewater is specifically 5 mg / ml or 10 mg / L; during the microbial electrochemical reduction, The pH value of the electrolyte solution and the uranium-containing wastewater is preferably 4 to 8. In the embodiment provided by the present invention, the pH value of the electrolyte solution and the uranium-containing wastewater is specifically 7. In the present invention, anaerobic sludge cultured with uranium-containing wastewater is preferably added to the electrolytic cell; the volume ratio of the anaerobic sludge added to the electrolyte is preferably 1:(2 to 5), more preferably 1:3; the voltage of the microbial electrochemical reduction is preferably 0.4 to 1.6 V, more preferably 0.6 to 1.4 V. In the embodiment provided by the present invention, the voltage of the microbial electrochemical reduction is specifically 0.8 V or 1 V; the time of the microbial electrochemical reduction is preferably 40 to 120 h.

[0053] In the present invention, the fixed stable period during the microbial electrochemical reduction process is preferably measured by the increase in system current. Specifically, it is preferably calculated by the voltage value of a 10Ω fixed resistor connected in series with the circuit. More preferably, real-time voltage data is recorded every 30 minutes. The purpose of measuring the voltage of the fixed external resistor is to calculate the system current. After the operation cycle is completed, electrochemical indicators are measured, including cathode output voltage, cathode current density, and CV curve.

[0054] After the microbial electrolysis reaction has run for several hours, the external circuit is disconnected, and the tetravalent uranium precipitate deposited at the bottom of the MEC reactor and on the cathode is preferably collected and placed in dilute nitric acid for oxidation recovery, thus completing the MEC uranium recovery process.

[0055] The present invention utilizes a microbial electrolytic cell to treat low-concentration uranium-containing wastewater based on the principle that dissolved hexavalent uranium ions in an aqueous environment can be reduced to precipitated tetravalent uranium ions by gaining electrons. The low-concentration hexavalent uranium ions can be reduced by applying a relatively low external voltage, with low power consumption and a wide applicable pH range. Furthermore, by establishing a biological cathode, the treatment process of the uranium-containing wastewater is accelerated, the treatment efficiency of the uranium-containing wastewater is improved, and the operating costs are reduced. Furthermore, the microbial electrolytic cell can generate a large amount of hydrogen while treating the uranium-containing wastewater.

[0056] In actual situations, the composition of uranium-containing wastewater is complex, containing not only radioactive elements such as uranium, but also other heavy metal ions and problems such as excessively high indicators such as ammonia nitrogen and COD. The microbial electrolysis technology adopted in the present invention can not only reduce the uranium and other heavy metals in the uranium-containing wastewater by controlling different external voltages to obtain electrons at the cathode in different time periods to generate precipitates and remove them, but also the COD and ammonia nitrogen in the uranium-containing wastewater can be consumed and removed as carbon sources and nutrients for microorganisms. Therefore, the microbial electrolysis cell technology provided by the present invention has a very wide treatment range.

[0057] Furthermore, the present invention injects anaerobic sludge that has been cultured and domesticated with uranium-containing wastewater during the treatment process of uranium-containing wastewater. The anaerobic sludge contains many anaerobic microorganisms that can oxidize and degrade organic matter to produce a large amount of electrons, which are transferred to the anode through the extracellular electron carriers of the microorganisms. Then, under the action of the potential difference provided by the external voltage, they are transferred to the cathode surface through the external circuit, providing electron acceptors for hexavalent uranium ions and other impurity metal ions in the cathode area. The dissolved hexavalent uranium ions and other impurity metal ions accept electrons and are reduced to a precipitated state, thereby achieving the purpose of removal.

[0058] To further illustrate the present invention, a microbial electrolysis cell and a method for treating uranium-containing wastewater provided by the present invention are described in detail below with reference to examples.

[0059] The reagents used in the following examples are all commercially available.

[0060] Example 1

[0061] The nano Ni-Cu / CeO2 catalytic electrode is prepared by impregnation sintering method, and the molar ratio of Ni / Ce / Cu is 7:2:1. The surface area is 9cm 2 A stainless steel mesh or nickel foam is used as a cathode current collector, and the cathode current collector is placed in a solution formed by dissolving and mixing 4.07106 g of nickel nitrate hexahydrate, 1.6964 g of cerium nitrate, and 0.59112 g of copper nitrate hexahydrate in an appropriate amount of deionized water, and then immersed, dried, and sintered in sequence to obtain a cathode electrode.

[0062] The number of impregnation and drying times is 15 times; the impregnation amount is sufficient to cover the electrode sheet; the amount of Ni(NO3)2·6H2O, Cu(NO3)2·6H2O and Ce(NO3)·6H2O is used to control the Cu loading to be 5wt%, the Ni loading to be 20wt%, and the Ce loading to be 2wt%.

[0063] The drying temperature is 110°C and the drying time is 2 hours;

[0064] The sintering temperature is 450° C., the heating rate is 10° C. / min, and the sintering time is 5 min.

[0065] Example 2: Electrode Acclimation

[0066] The area is 9cm 2 The carbon cloth and the cathode electrode prepared in Example 1 were placed in a stably operated dual-chamber microbial fuel cell. Anaerobic sludge was used as inoculum (the volume ratio of the added amount to the anolyte was 1:3), sodium acetate was used as the carbon source (mass concentration was 1.28 g / L), and an electrolyte solution (1.28 g / L sodium acetate, 0.31 g / L NH4Cl, 0.13 g / L KCl, 5.54 g / L NaH2PO4·2H2O, 23.1 g / L Na2HPO4·12H2O and 20 mg / L of trace elements were added to the anode chamber of the microbial fuel cell. The trace element formula was 0.01 g / L CaCl2, 1.2 g / L MgSO4, 2×10 -3 g / L NaCl, 7.6×10 -4 g / L MnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 - 3 g / L ZnCl2), and 5 / 40 (i.e., 0.125) mmol / L potassium ferricyanide solution was added to the cathode chamber. At the same time, the voltage value of the resistor was monitored in real time using a data logger. When the voltage value of one cycle dropped to about 0.1V, 80% of the electrolyte in the reactor and the yellowing sludge on the upper layer were replaced, and appropriate bacterial sources were added (always maintaining a sludge to electrolyte ratio of 1:3). When the reactor stably and continuously generated a maximum voltage of more than 0.5V for three consecutive cycles in the feeding cycle, and the COD removal rate in the reactor reached more than 90% in each cycle, it indicated that the carbon cloth was successfully biofilmed and a bioanode was obtained. The successfully biofilmed carbon cloth and cathode electrode were transferred to the anode and cathode of the MEC respectively to serve as the anode and cathode electrodes of the MEC. Nitrogen was introduced to remove oxygen in the reactor before adding the solution. Then 1.28g / L sodium acetate, trace elements (0.01g / L CaCl2, 1.2g / LMgSO4, 2×10 -3 g / L NaCl, 7.6×10 -4 g / L MnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 -3g / L ZnCl2) and 5mg / L uranium-containing wastewater, and then reverse the electrode polarity under an applied voltage of 0.8V to allow biofilm formation at the cathode. The signs of successful biofilm formation are the same as those for the anode of the microbial fuel cell.

[0067] Example 3: Treatment of low-concentration uranium-containing wastewater by dual-chamber MECs

[0068] The anode chamber and cathode chamber of the double-chamber MECs are both 100 mL, that is, the total volume of the MECs is 200 mL. The anode and cathode are separated by a diaphragm to form two chambers, and the diaphragm is a proton exchange membrane. The anode electrode is the bioanode obtained by domestication in Example 2, and the cathode electrode is the stainless steel mesh loaded with nano-Ni-Cu / CeO2 prepared in Example 1 after domestication. Nutrient salts containing 0.31 g / L NH4Cl, 0.13 g / L KCl, 5.54 g / L NaH2PO4·2H2O, 23.1 g / L Na2HPO4·12H2O and 20 mg / L trace elements (the trace element formula is: 0.01 g / L CaCl2, 1.2 g / L MgSO4, 2×10 -3 g / L NaCl, 7.6×10 -4 g / L MnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 -3 g / L ZnCl2), 0.64g / L sodium acetate solution, and finally the volume ratio of the added anaerobic sludge to the anolyte was kept at 1:3), the initial COD concentration of the anode chamber was 500mg / L, and the pH was about 7.0. The sludge cultured with uranium-containing wastewater (the volume ratio of the added amount to the catholyte was 1:3), nutrient salts containing 0.31g / L NH4Cl, 0.13g / L KCl and 20mg / L trace elements (trace element formula: 0.01g / L CaCl2, 1.2g / L MgSO4, 2×10 -3 g / L NaCl, 7.6×10 -4 g / L MnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 -3After startup, a 0.68 g / L sodium acetate solution containing 10.5 g / L ZnCl2 (0.68 g / L sodium acetate solution), a phosphate buffer solution (5.54 g / L NaH2PO4·2H2O, 23.1 g / L Na2HPO4·12H2O), and 10.0 mL of 1 g / L uranium-containing wastewater (with U(VI) added at a concentration of approximately 10.0 mg / L), with a pH of approximately 7.0, were added to the cathode chamber of the MECs. High-purity nitrogen was then introduced into the cathode chamber to expel dissolved oxygen from the cathode solution. Microorganisms at the anode oxidize organic matter in the anode chamber, releasing electrons and protons. Electrons are transferred to the cathode chamber through an external circuit under the influence of the potential difference provided by the external voltage, while protons pass through the ion exchange membrane and reach the cathode chamber. Microorganisms attached to the cathode act as catalysts, accelerating the reduction of hexavalent uranium ions to tetravalent precipitated uranium. The cathode and anode were connected by a titanium wire and connected to an external circuit. The applied voltage was maintained at 0.8V and the external resistance was 10Ω. After 48 hours of microbial electroreduction at room temperature and pressure, tetravalent uranium precipitate was accumulated on the cathode electrode surface. After 120 hours of microbial electrochemical reduction, the uranium concentration in the water dropped to 0.40 mg / L, achieving a uranium removal efficiency of 96%. The residual COD in the reactor was 60 mg / L, with a COD removal rate of 88%.

[0069] Example 4: Treatment of low-concentration uranium-containing wastewater by dual-chamber MECs

[0070] The anode chamber and cathode chamber of the double-chamber MECs are both 100 mL, that is, the total volume of the MEC is 200 mL. The anode and cathode are separated by a diaphragm to form two chambers, and the diaphragm can be a proton exchange membrane. The anode electrode is the bioanode obtained by domestication in Example 2, and the cathode electrode is the titanium foam electrode loaded with nano-Ni-Cu / CeO2 prepared in Example 1 after domestication. A buffer solution containing 0.31 g / L NH4Cl, 0.13 g / L KCl, 5.54 g / L NaH2PO4·2H2O, 23.1 g / L Na2HPO4·12H2O and 20 mg / L of trace elements (the trace element formula is: 0.01 g / L CaCl2, 1.2 g / L MgSO4, 2×10 -3 g / L NaCl, 7.6×10 -4 g / L MnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 -3g / L ZnCl2) and 0.64g / L sodium acetate solution and anaerobic sludge acclimated with uranium-containing wastewater (the volume ratio of the amount added to the cathode electrolyte was 1:3). The initial COD concentration in the anode chamber was 500mg / L and the pH was about 7.0. The sludge acclimated with uranium-containing wastewater (the volume ratio of the amount added to the cathode electrolyte was 1:3) and nutrient salts containing 0.31g / LNH4Cl, 0.13g / L KCl and 20mg / L trace elements (the trace element formula was: 0.01g / L CaCl2, 1.2g / LMgSO4, 2×10 -3 g / L NaCl, 7.6×10 -4 g / L MnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 -3 g / L ZnCl 2) After startup, 0.68 g / L of sodium acetate, a phosphate buffer solution (5.54 g / L NaH2PO4·2H2O, 23.1 g / L Na2HPO4·12H2O), and 10.0 mL of 1 g / L uranium-containing wastewater (U(VI) concentration approximately 10.0 mg / L), with a pH of approximately 7.0, were added to the MEC cathode chamber. High-purity nitrogen was then introduced into the cathode chamber to expel dissolved oxygen from the solution. Microorganisms attached to and grew on the anode surface, oxidizing organic matter in the anode chamber and releasing electrons and protons. Electrons were transferred to the cathode chamber through an external circuit under the potential difference provided by an external voltage, while protons passed through the ion exchange membrane to the cathode chamber. Microorganisms attached to the cathode acted as catalysts, accelerating the reduction of hexavalent uranium ions to tetravalent uranium precipitates. The cathode and anode were connected by a titanium wire and connected to an external circuit. The applied voltage was maintained at 0.8V and the external resistance was 10Ω. After 48 hours of microbial electroreduction at room temperature and pressure, tetravalent uranium precipitate was enriched on the cathode electrode surface. After 120 hours of microbial electrochemical reduction, the uranium concentration in the water dropped to 0.18 mg / L, achieving a uranium removal efficiency of 98.2%. The residual COD in the reactor was 47 mg / L, with a COD removal rate of 90.6%.

[0071] Example 5: Single-chamber MEC treatment of low-concentration uranium-containing wastewater

[0072] The volume of the single-chamber MEC is 200 mL. The anode electrode is the carbon cloth domesticated in Example 2, and the cathode electrode is the stainless steel mesh electrode loaded with nano-Ni-Cu / CeO2 domesticated in Example 2. Fix the anode and cathode to complete the assembly of the MEC. Anaerobic sludge cultured with uranium-containing wastewater was used as inoculum (the volume ratio of the added amount to the entire electrolytic cell electrolyte was 1:3), sodium acetate was used as the carbon source (the amount added was 0.64 g / L), 0.31 g / L NH4Cl, 0.13 g / L KCl nutrient salts and 20 mg / L mineral elements were added (the element ratio was: 0.01 g / L CaCl2, 1.2 g / L MgSO4, 2×10 -3 g / L NaCl, 7.6×10 -4 g / LMnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 -3 The researchers used a microbial electrolyte solution composed of 5.54 g / L ZnCl2 and phosphate buffer (5.54 g / L NaH2PO4·2H2O, 23.1 g / L Na2HPO4·12H2O) with an initial COD concentration of 500 mg / L. The solution was then injected into a MEC, where high-purity nitrogen was introduced to remove all dissolved oxygen. After MEC startup, uranium-containing wastewater (U(VI) concentration of approximately 5.0 mg / L) was injected into the MEC. The pH in the MEC reactor was adjusted to 7.0, and an external circuit was connected, maintaining an applied voltage of 1.0 V and an external resistance of 10 Ω. After 48 hours of microbial electroreduction at room temperature and pressure, tetravalent uranium precipitate was enriched on the cathode electrode surface. After 120 hours of microbial electrochemical reduction, the uranium concentration in the water dropped to 0.1 mg / L, achieving a uranium removal efficiency of 98%.

[0073] Example 6: Single-chamber MEC treatment of low-concentration uranium-containing wastewater

[0074] The volume of the single-chamber MEC is 200 mL. The anode electrode is the carbon cloth domesticated in Example 2, and the cathode electrode is the titanium foam electrode loaded with nano-Ni-Cu / CeO2 domesticated in Example 2. Fix the anode and cathode to complete the assembly of the MEC. Anaerobic sludge cultured with uranium-containing wastewater was used as inoculum (the volume ratio of the added amount to the entire electrolytic cell electrolyte was 1:3), sodium acetate was used as the carbon source (the amount added was 0.64 g / L), 0.31 g / L NH4Cl, 0.13 g / L KCl nutrient salts and 20 mg / L mineral elements (the element ratio was 0.01 g / L CaCl2, 1.2 g / L MgSO4, 2×10 -3g / L NaCl, 7.6×10 -4 g / L MnSO4, 5×10 -4 g / L AlCl3、3×10 -3 g / L Na2MoO4·2H2O, 1×10 -3 g / L H3BO3 and 1×10 -3 The researchers used a microbial electrolyte solution composed of 5.54 g / L ZnCl2 and phosphate buffer (5.54 g / L NaH2PO4·2H2O, 23.1 g / L Na2HPO4·12H2O) with an initial COD concentration of 500 mg / L. The solution was then injected into a MEC, where high-purity nitrogen was introduced to remove all dissolved oxygen. After MEC startup, uranium-containing wastewater (U(VI) concentration of approximately 5.0 mg / L) was injected into the MEC. The pH in the MEC reactor was adjusted to 7.0, and an external circuit was connected, maintaining an applied voltage of 1.0 V and an external resistance of 10 Ω. After 48 hours of microbial electroreduction at room temperature and pressure, tetravalent uranium precipitate was enriched on the cathode electrode surface. After 120 hours of microbial electrochemical reduction, the uranium concentration in the water dropped to 0.01 mg / L, achieving a uranium removal efficiency of 98%.

[0075] Comparative Example 1: Treatment of low-concentration uranium-containing wastewater by dual-chamber MEC (cathode is ordinary stainless steel / foam titanium electrode)

[0076] The dual-chamber MECs have a 100mL anode and cathode chambers, each with a total volume of 200mL. The anode and cathode are separated by a proton exchange membrane, forming two chambers. The anode electrode is carbon cloth acclimated according to the method in Example 2, and the cathode electrode is stainless steel mesh acclimated according to the method in Example 2. The uranium-containing wastewater treatment process is the same as in Example 3. Compared to the former, the MEC using stainless steel mesh electrodes without nano-Ni-Cu / CeO2 loading has a longer cathode startup period and a lower system voltage. This MEC startup period lasts approximately five weeks, with the system voltage maintained at approximately 0.1V. The MEC loaded with a catalytic electrode has a startup period of three weeks, with the system voltage reaching approximately 0.5V. Ultimately, at a uranium concentration of 10mg / L, at the end of one cycle, the residual uranium content in the reactor was 4.3mg / L, with a removal efficiency of 57%. The residual COD in the reactor was 130mg / L, with a COD removal rate of 74%.

[0077] Comparative Example 2: Single-chamber MEC treatment of low-concentration uranium-containing wastewater (cathode is ordinary stainless steel / foam titanium electrode)

[0078] The volume of the single-chamber MEC is 200mL. The carbon cloth is acclimated according to the method of Example 2, and the cathode electrode is an ordinary stainless steel mesh electrode acclimated according to the method of Example 2. The anode and cathode are fixed to complete the assembly of the MEC. The process of treating uranium-containing wastewater is consistent with that of Example 5. Compared with the former, the MEC cathode startup cycle of the stainless steel mesh electrode without nano-Ni-Cu / CeO2 loading is long and the system voltage is not high. The startup cycle of this MEC is about 5 weeks, and the system voltage is maintained at about 0.1V; while the startup cycle of the MEC loaded with catalytic electrode is 3 weeks, and the system voltage can also reach about 0.5V. Finally, for a uranium concentration of 10mg / L, at the end of one cycle, the residual uranium content in the reactor is 4.8mg / L, and its removal efficiency is 52%. The residual COD in the reactor is 150mg / L, and the COD removal rate is 70%.

[0079] Comparative Example 3

[0080] Changing the metal loading ratio, such as increasing the Ce ratio to 8wt%, the Cu ratio to 15wt%, and the Ni ratio to 40wt%, shows that the nano-Ni-Cu / CeO2 catalytic electrode with this ratio has no benefit in treating uranium-containing wastewater in the MEC reactor compared to ordinary stainless steel / foam titanium electrodes. For example, the treatment efficiency of a single-chamber ordinary electrode MEC for uranium-containing wastewater is 52%, while the removal efficiency of this single-chamber MEC is only 43%. It is speculated that the excessive Ce dosage inhibits microbial activity, affecting the long-term stability and efficiency of the MEC system. Excessive Ni content also affects the stability and catalytic activity of the electrode.

Claims

1. A microbial electrolysis cell, characterized in that: include: An electrolytic cell; an electrolyte solution and uranium-containing wastewater are provided in the electrolytic cell; A bioanode and a biocathode are arranged in an electrolytic cell, and the bioanode and the biocathode are immersed in an electrolyte solution and uranium-containing wastewater; the bioanode includes an anode current collector and a microbial membrane arranged on the surface of the anode current collector; the biocathode includes a cathode current collector, a Ni-Cu / CeO2 catalytic layer arranged on the surface of the cathode current collector, and a microbial membrane arranged on the surface of the Ni-Cu / CeO2 catalytic layer; the mass ratio of Ni, Cu and Ce in the Ni-Cu / CeO2 catalytic layer of the biocathode is (15-25):(3-6):(1-3); An external circuit connecting the bioanode and the biocathode; the external circuit includes a power supply and a fixed resistor; the fixed resistor is connected in series between the positive electrode of the power supply and the bioanode.

2. A method for treating uranium-containing wastewater, characterized in that: include: The microbial electrolysis cell according to claim 1 is used to carry out microbial electrochemical reduction of uranium-containing wastewater.

3. The processing method according to claim 2, characterized in that The biocathode is prepared according to the following steps: The cathode current collector is immersed in a solution containing nickel ions, cerium ions and copper ions, dried, and then sintered to obtain a cathode electrode; The cathode electrode is acclimated in an electrolyte solution containing electrogenic bacteria and a carbon source by reversing the electrode polarity under an applied voltage condition to obtain a biocathode.

4. The processing method according to claim 3, characterized in that The loading amount of Ni element in the cathode electrode is 15-25 wt %; the loading amount of Cu element is 3-6 wt %; and the loading amount of Ce element is 1-3 wt %.

5. The processing method according to claim 3, characterized in that: The drying temperature is 100° C. to 120° C., the drying time is 1 to 3 hours, the sintering temperature is 300° C. to 550° C., the sintering time is 3 to 5 minutes, and the sintering heating rate is 5 to 15° C. / min.

6. The processing method according to claim 3, characterized in that: The cathode current collector is selected from stainless steel mesh, platinum mesh or titanium foam; the electrogenic bacteria are derived from one or more of anaerobic sludge from a sewage treatment plant cultured with uranium-containing wastewater, the effluent from a microbial fuel cell and a microbial electrolysis cell; the carbon source is selected from one or more of glucose, sodium acetate, starch and protein; and the electrolyte solution is one or more of potassium ferrocyanide solution, phosphate solution and borate solution.

7. The processing method according to claim 2, characterized in that The bioanode is prepared according to the following steps: The anode current collector is acclimated in an electrolyte solution containing electrogenic bacteria and a carbon source to obtain a bioanode; The anode current collector is selected from carbon materials.

8. The processing method according to claim 2, characterized in that: The voltage of the microbial electrochemical reduction is 0.4-1.6V.

9. The processing method according to claim 2, characterized in that: During the microbial electrochemical reduction, the pH values ​​of the electrolyte solution and the uranium-containing wastewater in the electrolytic cell are 4-8; and the concentration of hexavalent uranium ions in the uranium-containing wastewater is greater than or equal to 0.5 mg / L.

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