Hydrogen production method for treating etching solution wastewater by using light-assisted single-chamber microbial electrolysis cell

Abstract

The invention discloses a hydrogen production method for treating etching solution wastewater by using a photo-assisted single-chamber microbial electrolytic cell, and relates to the technical field of microbial electrochemistry and photocatalysis, and the hydrogen production method comprises the following steps: S1, mixing an anolyte of a stably operated double-chamber microbial fuel cell with etching solution tail end wastewater, adding the mixture into a reactor, and regularly replacing the solution until the anode potential is stable; s2, domesticating two ends of the electrode by using a direct-current power supply and external voltage until the potential of the cathode is reduced, and completing the domestication of the anode; and S3, the photocathode adopts a photocatalytic material, and organic matters are mineralized and nickel ions are removed while hydrogen is produced under an external voltage condition. The photo-assisted microbial electrolytic tank integrates the advantages of water electrolysis hydrogen production, photocatalytic hydrogen production and microbial electrolytic tank hydrogen production, overcomes the defect that a photocatalyst for photocatalytic hydrogen production is unstable, reduces the energy consumption required by microbial electrolytic tank hydrogen production, and recovers heavy metal mineralized refractory organics in etching liquid tail end wastewater. The method is a clean, efficient and low-consumption mode for treating wastewater and simultaneously producing hydrogen.

Description

Technical Field

[0001] The invention relates to microbial catalysis, photoelectric effect, wastewater treatment and electrocatalysis, belonging to the technical field of microbial electrochemistry and photocatalysis, and in particular to a method for producing hydrogen by treating etching liquid wastewater using a light-assisted single-chamber microbial electrolytic cell. Background Art

[0002] Microbial electrolysis cells produce hydrogen by applying a small external voltage, using electroactive bacteria growing on the anode to oxidize organic matter in wastewater into carbon dioxide and protons, and then transfer electrons through an external circuit to the cathode to combine with protons to generate clean energy - hydrogen. Therefore, microbial electrolysis cells show broad prospects in the field of wastewater treatment, recycling chemical energy in sewage and producing clean energy (such as hydrogen) simultaneously with valuable products.

[0003] The main factors that limit the hydrogen production rate of microbial electrolysis cells include electrode materials, reactor configuration, and the physical and chemical properties of the electrolyte. Electrode materials affect the internal resistance of the system, the overpotential of the hydrogen evolution reaction, and the reaction rate. Platinum has a high catalytic activity for the hydrogen evolution reaction and can reduce the overpotential of hydrogen production at the cathode. However, platinum is a precious metal with low production and high price. It is easy to react with sulfides in the presence of sulfides, resulting in reduced catalytic activity.

[0004] With the increasing demand for electronic products, the circuit board industry has developed rapidly. In the process of circuit board production, sulfur-containing compounds and organic matter are used to maintain the stability of the etching process, and etching liquid is needed to remove unnecessary metals on the circuit board. After repeated use, the etching liquid loses its etching ability, thus forming etching liquid wastewater. At present, the main methods for treating this type of water are physical and chemical methods. The physical method is mainly reverse osmosis, ultrasound, etc. to remove heavy metals in water. The chemical method is mainly electrochemistry and flotation. The electrochemical method recycles heavy metals in water through primary cells or electrolytic cells. At present, the treatment methods for the end wastewater of etching liquid focus more on the treatment of heavy metals, and organic matter, nitrogen, sulfide and other substances in the wastewater need to be further treated by other methods. Direct discharge of wastewater to sewage treatment plants will have an impact on conventional treatment, and additional fees will also be charged.

[0005] At present, photo-assisted microbial electrolysis cells are limited to the recovery of simple refractory organic matter or simple heavy metals, and there is no research on the mixed situation of refractory organic matter and heavy metals, especially the method of treating the actual etching liquid end wastewater mixed with refractory organic matter and heavy metals while producing hydrogen. Summary of the invention

[0006] The purpose of the present invention is to provide a method for producing hydrogen by treating etching liquid wastewater with a photo-assisted single-chamber microbial electrolysis cell, so as to solve the problems raised in the above-mentioned background technology. The photo-assisted microbial electrolysis cell of the present invention combines the advantages of water electrolysis to produce hydrogen, photocatalytic hydrogen production and hydrogen production in a microbial electrolysis cell, overcomes the disadvantage of the instability of the photocatalyst for photocatalytic hydrogen production and reduces the energy consumption required for hydrogen production in the microbial electrolysis cell, and at the same time recovers the heavy metal mineralization and refractory organic matter in the wastewater at the end of the etching liquid, which is a clean, efficient and low-consumption method for treating wastewater and producing hydrogen at the same time.

[0007] To achieve the above object, the present invention provides the following technical solutions: A method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell, comprising the following steps: S1: Use the anode liquid of the stable double-chamber microbial fuel cell to remove dissolved oxygen through nitrogen aeration, then mix it with the wastewater at the end of the etching solution and add it to the reactor to replace the solution regularly until the anode potential is stable; S2: Use a DC power supply to apply voltage at both ends of the electrode until the cathode potential decreases and the anode taming is completed; S3: The photocathode uses a photocatalytic material with a narrow bandgap width that can absorb visible light and has stable chemical properties, and another material with a wider bandgap to form a composite material. Under external voltage conditions, it produces hydrogen while mineralizing organic matter and removing nickel ions. Among them, the photocatalytic material is a composite material formed by mixing ZnFe2O4 and g-C3N4.

[0008] In the above-mentioned photo-assisted single-chamber microbial electrolysis cell method for producing hydrogen by treating etching liquid wastewater, S1 uses a microbial fuel cell anode liquid that has been stably operating for one year and etching liquid terminal wastewater to be added to the reactor in ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, and 10:0, respectively, wherein the solution is replaced in a cycle of 2-4 days for each ratio until the anode potential stabilizes at -0.22V to -0.26V.

[0009] In the aforementioned method for producing hydrogen by treating etching liquid wastewater with a photo-assisted single-chamber microbial electrolysis cell, the anode liquid of a microbial fuel cell that has been stably operated for one year is first mixed with a nutrient solution in a ratio of 1:1 and added to the reactor, and the solution is replaced every 2 days until the anode potential stabilizes at -0.24 V. Then, the anode liquid of a microbial fuel cell that has been cultured and has been stably operated for one year and the wastewater at the end of the etching liquid are added to the reactor in a ratio of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, and 10:0, respectively, wherein the solution is replaced every 3 days for each ratio until the anode potential stabilizes at -0.24 V.

[0010] In the aforementioned method for producing hydrogen by treating etching liquid wastewater with a photo-assisted single-chamber microbial electrolysis cell, the S2 is tamed by applying a 0.28-0.32 V voltage at both ends of the electrode using a DC power supply until the cathode potential is reduced to 0.45-0.55 V, and the anode taming is completed.

[0011] In the aforementioned method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell, a DC power supply is used to apply a 0.3V voltage to both ends of the electrode for domestication until the cathode potential is reduced to 0.5V, and the anode domestication is completed.

[0012] In the aforementioned method for producing hydrogen by treating etching liquid wastewater using a light-assisted single-chamber microbial electrolysis cell, in S3, the photocathode is made of a photocatalytic material whose conduction band energy is lower than the standard redox potential of hydrogen evolution.

[0013] In the aforementioned method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell, in S3, the applied voltage is 0.4-0.9V.

[0014] In the aforementioned method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell, the applied voltage is 0.6V.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The photo-assisted microbial electrolytic cell of the present invention combines the advantages of water electrolysis to produce hydrogen, photocatalytic hydrogen production and hydrogen production in a microbial electrolytic cell, overcomes the disadvantage of unstable photocatalysts in photocatalytic hydrogen production and reduces the energy consumption required for hydrogen production in a microbial electrolytic cell. At the same time, it recovers heavy metal mineralization and refractory organic matter in the wastewater at the end of the etching solution. It is a clean, efficient and low-consumption method for treating wastewater and producing hydrogen at the same time.

[0016] 2. Under the optimal voltage condition of 0.6V for maximizing solar energy utilization, the voltage has the highest effects on the energy recovery efficiency of metal nickel removal based on electrical energy and organic matter input and the energy recovery efficiency of hydrogen production based on electrical energy and organic matter input, which are (48.1±5.1%, 53.3±3.6%) respectively. The electrical energy utilization under higher external voltage is insufficient, resulting in a low recovery rate. Therefore, from the perspective of energy consumption, subsequent experiments all use an external voltage of 0.6V.

[0017] 3. The step S1 of the present invention is to mix the anode liquid of the microbial fuel cell that has been running stably for 1 year with the nutrient solution in a ratio of 1:1 and add it to the reactor, and replace the solution every 2 days until the anode potential stabilizes at -0.24V. This step uses the anode liquid of the microbial fuel cell that has been running stably and the nutrient solution to mix and add it to the reactor, and the solution is replaced regularly to provide nutrition to the power-producing microorganisms, so that they can secrete extracellular polymers to form a uniform and stable biofilm on the electrode. Since the strains come from microbial fuel cells without external voltage, and the microbial electrolysis cell is a device that requires external voltage, the voltage is an external environmental pressure for the original bacterial community, and the external voltage needs to be gradually applied to screen out the power-producing microbial flora that can survive in the presence of voltage. Enriching the bacterial community that can produce electricity under voltage conditions can increase the potential difference between the cathode and the anode, which is beneficial to hydrogen production. Therefore, after research, step S2 of the present invention is to use a DC power supply to apply a 0.3 V voltage to both ends of the electrode for taming, until the cathode potential is reduced to 0.5 V, and the anode taming is completed; wherein, the cathode voltage is reduced to 0.5 V, the DC power supply is applied with 0.3 V, and the anode voltage is 0.2 V, which is close to the theoretical 0.3 V, so it can be considered that the taming is completed.

[0018] 4. Step S1 of the present invention is to add the anode liquid of the microbial fuel cell which has been running stably for 1 year and the wastewater of the etching liquid to the reactor in the ratio of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, 10:0, respectively, wherein the solution is replaced every 2-4 days until the anode potential stabilizes at -0.22V to -0.26V. Since the anode electroactive bacteria oxidize organic matter to produce electricity, the anode potential is about -0.3V, Ni 2+ The standard redox potential of NI is -0.25 V. Considering the overpotential, a lower potential is applied to the cathode to reduce the NI 2+ Reduced to nickel.

[0019] 5. After 24 hours of operation, the mineralization rate of refractory organic matter in the light-assisted microbial electrolysis cell was 70.4±1.2%, and the effluent concentration was 97.6±3.82 mg / L; the nickel ion removal rate was 99.4±0.4%, and the effluent concentration was 0.7±0.4 mg / L, which met the national emission standards (GB39731-2020). Light is conducive to hydrogen production and mineralization of refractory organic matter.

[0020] 6. The stability of hydrogen production from the photo-assisted microbial electrolysis cell in treating the end wastewater of the etching solution was evaluated by intermittent operation for 12 cycles. The cycle was 24 hours, and the end wastewater of the etching solution was replaced at the end of each cycle. The results showed that while the system could stably and completely remove nickel ions, the mineralization rate, loop current and hydrogen production of refractory organic matter were significantly improved with the extension of the operation cycle.

[0021] 7. The photocathode uses a photocatalytic material with a conduction band energy lower than the standard redox potential of hydrogen evolution, and the photogenerated electrons can directly reduce electrons to generate hydrogen; the electrons generated by the electrochemically active bacteria at the anode oxidizing the organic matter in the wastewater combine with the photogenerated holes to enhance the separation efficiency of the carriers and further promote hydrogen production.

[0022] 8. As the operation time increases, more catalytic microorganisms are enriched on the cathode; at the same time, more nickel is deposited on the electrode. Nickel, as a transition metal, has a good catalytic hydrogen evolution effect whether it is a single substance, a nickel alloy, or even a nickel oxide. The mineralization rate, loop current and hydrogen production of difficult-to-degrade organic matter are significantly improved with the extension of the operation cycle.

[0023] 9. Compared with the prior art, the photocatalytic material is formed by mixing ZnFe2O4 and g-C3N4 to form a composite material, so that the composite material produces hydrogen and has a better metal removal rate in the process of treating the end wastewater of the etching solution than any of the photocatalytic materials used alone. The mixture is used for traditional photocatalytic hydrogen production, but the hydrogen production is low, only 200.77μmol / h / g; it uses photogenerated electrons to reduce heavy metal Cr(VI); and it uses light to generate strong oxidizing free radicals (hydroxyl, superoxide free radicals, hydrogen peroxide, etc.) to degrade typical difficult-to-degrade organic matter such as rhodamine, methyl orange, etc. At present, the composite photocatalytic material has not been used in the photo-assisted microbial electrolysis cell system to treat the end wastewater of the etching solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 This is a schematic diagram of a light-assisted single-chamber microbial electrolysis cell of the present invention; Figure 2 Schematic diagram of hydrogen production and loop current of the light-assisted single-chamber microbial electrolytic cell of the present invention in different control tests; Figure 3 It is a comparison chart of the removal rates of refractory organic matter and nickel ions in different control tests of the light-assisted single-chamber microbial electrolysis cell of the present invention; Figure 4 It is a comparison diagram of hydrogen production and loop current of the light-assisted single-chamber microbial electrolysis cell of the present invention at different cycles; Figure 5 It is a comparison chart of the mineralization rate of refractory organic matter and the removal rate of nickel ions in different cycles of the light-assisted single-chamber microbial electrolysis cell of the present invention; Figure 6 This is a comparison chart of the operating effect of the light-assisted single-chamber microbial electrolysis cell of the present invention as a function of voltage; Figure 7 Schematic diagram of transient light response of the light-assisted single-chamber microbial electrolysis cell of the present invention under different photocatalytic materials; Figure 8 This is a comparison chart of the hydrogen production and metal removal rate of the light-assisted single-chamber microbial electrolysis cell of the present invention under different photocatalytic materials. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments 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 creative work are within the scope of protection of the present invention.

[0027] Example 1. A method for producing hydrogen by treating etching wastewater using a photo-assisted single-chamber microbial electrolysis cell. The structure of the photo-assisted single-chamber microbial electrolysis cell is shown in FIG. Figure 1 , the steps of hydrogen production are as follows: S1: The anode liquid of the microbial fuel cell that has been running stably for one year and the wastewater from the etching liquid were added to the reactor in the ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, and 10:0, respectively. The solution was replaced every 3 days for each ratio until the anode potential stabilized at -0.24V. S2: Apply a 0.3 V voltage to both ends of the electrode with a DC power supply until the cathode potential drops to 0.5 V, and the anode taming is completed; S3: The photocathode uses a photocatalytic material with a narrow bandgap that can absorb visible light and has stable chemical properties, and another material with a wide bandgap. Under the condition of an applied voltage, it can mineralize organic matter and remove nickel ions while producing hydrogen. The photocatalytic material is a material formed by a mixture of ZnFe2O4 and g-C3N4. Hydrogen is produced under an applied voltage of 0.6V; photogenerated electrons can directly reduce electrons to generate hydrogen, and the electrons generated by the oxidation of organic matter by electrochemically active bacteria at the anode combine with photogenerated holes to enhance the separation efficiency of carriers and further promote hydrogen production.

[0028] In step S1, the stably operating microbial fuel cell anode liquid refers to the mixture of the nutrient solution and the domesticated electrochemically active bacteria in the anode chamber of the dual-chamber microbial fuel cell; theoretically, all types of microbial fuel cell anode liquids meet the requirements; the nutrient solution is adjusted according to the basic formula of the microbial culture medium, and the specific components are: (NH4)2SO4 (2.94mM), K2SO4 (0.84mM), NaH2PO4∙2H2O (46mM), Na2HPO4∙12H2O (4.2mM), complex vitamins 12.5mL / L, minerals 12.5mL / L, sodium acetate (12.0mM); the reactor is a container where the hydrogen production reaction occurs. According to whether there is a diaphragm in the container, it is divided into a double-chamber reactor and a single-chamber reactor. The one with a diaphragm is a double-chamber reactor and the one without a diaphragm is a single-chamber reactor. Compared with the double-chamber reactor, the single-chamber reactor has a simpler structure. Since there is no proton exchange membrane, the cost is greatly reduced. Figure 1 As shown, a single-chamber reactor was used, the reactor was made of organic glass, and the working solution volume was 26 mL. Figure 1 The anode shown is composed of a carbon felt (size 2cm×2cm×0.25cm) pre-inoculated with electroactive bacteria, and the cathode is composed of a carbon felt (size 2cm×2cm×0.25cm) loaded with a photocatalyst. The cathode and the anode are connected to the negative and positive electrodes of a DC power supply, respectively. A 10Ω resistor is connected in series to the external circuit, and the loop current is calculated based on the voltage drop across the resistor. A saturated calomel electrode (0.24Vvs.SHE) is inserted into the reactor, and a gas collecting pipe is inserted on the side close to the cathode to collect gas. The cathode can be operated with a 100W iodine tungsten lamp as the light source to simulate the intensity of sunlight, and the light intensity is 23.3mW / cm 2 Before the nutrient solution is transferred to the reactor, nitrogen is aerated for 15 minutes to remove dissolved oxygen to ensure an anaerobic environment in the system; In step S3, the photocatalytic material with a conduction band energy lower than the standard redox potential of hydrogen evolution has a catalytic effect on hydrogen production due to its use at the cathode, such as (TiO2, Cu2O, g-C3N4), and in the light-assisted microbial electrolysis cell hydrogen production in this embodiment, a composite material of g-C3N4 and ZnFe2O4 that has not been used before is required. Among them, the photocatalytic material is a photocatalytic material with a narrow band gap that can absorb visible light, stable chemical properties, easy synthesis, and low cost, combined with another material with a wide band gap to form a heterojunction (ZnFe2O4 / g-C3N4). This mixture is used for traditional photocatalytic hydrogen production, but the hydrogen production is low, only 200.77μmol / h / g; using photogenerated electrons to reduce heavy metal Cr(VI); and using light to generate strong oxidizing free radicals (hydroxyl, superoxide free radicals, hydrogen peroxide, etc.) to degrade typical refractory organics such as rhodamine, methyl orange, etc. At present, this composite photocatalytic material has not been used in the photo-assisted microbial electrolysis cell system to treat the end wastewater of etching solution.

[0029] The applied voltage was 0.6V, the operating cycle was 12 hours, and ZnFe2O4 and g-C3N4 were used for the experiment. Figure 7 As shown, the photoresponse current of ZnFe2O4 is 1.5 microamperes, and the photoresponse current of g-C3N4 is 2 microamperes; after the composite material is formed, the photoresponse current is 6.5 microamperes, indicating that the composite is conducive to carrier separation.

[0030] The experimental results are as follows Figure 8 As shown, ZnFe2O4\g-C3N4 is used as cathode material to treat the end wastewater of etching solution, and the hydrogen production is (ZnFe2O4: 0.19±0.01, g-C3N4: 0.09±0.01, ZnFe2O4\g-C3N4: 0.36±0.04), and the metal removal rates are (ZnFe2O4: 41.5±3.4, g-C3N4: 21.6±2.8, ZnFe2O4\g-C3N4: 69.8±3.6).

[0031] In summary, ZnFe2O4\g-C3N 4的 The composite material has better hydrogen production and metal removal rate in the process of treating etching liquid wastewater than any of the photocatalytic materials used alone, so the composite material was used as a photocathode catalyst in subsequent experiments.

[0032] Example 2. A method for producing hydrogen by treating etching wastewater using a photo-assisted single-chamber microbial electrolysis cell. The structure of the photo-assisted single-chamber microbial electrolysis cell is shown in FIG. Figure 1 , the steps of hydrogen production are as follows: S1: The anode liquid of the microbial fuel cell that has been running stably for 1.2 years and the wastewater from the etching liquid are added to the reactor in the ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, and 10:0, respectively. The solution is replaced every 2 days for each ratio until the anode potential stabilizes at -0.26V; S2: Apply a 0.28V voltage to both ends of the electrode with a DC power supply until the cathode potential drops to 0.55V, and the anode taming is completed; S3: The photocathode uses a photocatalytic material with a conduction band energy lower than the standard redox potential of hydrogen evolution to produce hydrogen under an applied voltage of 0.4V.

[0033] Example 3. A method for producing hydrogen by treating etching wastewater using a photo-assisted single-chamber microbial electrolysis cell. The structure of the photo-assisted single-chamber microbial electrolysis cell is shown in FIG. Figure 1 , the steps of hydrogen production are as follows: S1: The anode liquid of the microbial fuel cell that has been running stably for 1.1 years and the wastewater from the etching liquid are added to the reactor in the ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, and 10:0, respectively. The solution is replaced every 2 days for each ratio until the anode potential stabilizes at -0.22V; S2: Apply a 0.32V voltage to both ends of the electrode with a DC power supply until the cathode potential drops to 0.45V, and the anode taming is completed; S3: The photocathode uses a photocatalytic material with a conduction band energy lower than the standard redox potential of hydrogen evolution to produce hydrogen under an applied voltage of 0.6V.

[0034] Experimental Example 4. To verify the effectiveness of this method at different voltages, a catalyst loading ratio of 15% and a loading amount of 5 mg / cm 2 The cathode was used and the applied voltage (0V, 0.3V, 0.6V, 0.9V) was changed to explore the hydrogen production performance at various voltages.

[0035] The treatment cycle was 12 hours, and the effects of voltage on the energy recovery efficiency of metallic nickel removal based on electrical energy and organic matter input and the energy recovery efficiency of hydrogen production based on electrical energy and organic matter input were investigated.

[0036] from Figure 6 It can be seen that: Under the condition of 0.6 V, the energy recovery efficiency of metallic nickel removal based on electrical energy and organic matter input and the energy recovery efficiency of hydrogen production based on electrical energy and organic matter input were the highest (48.1 ± 5.1%, 53.3 ± 3.6%), respectively. The electrical energy under higher external voltage was not fully utilized, resulting in a low recovery rate. Therefore, from the perspective of energy consumption, subsequent experiments all used an external voltage of 0.6 V.

[0037] Experimental example 5.

[0038] The whole experiment was carried out in a single-chamber reactor made of plexiglass. Figure 1 The anode shown is composed of carbon felt pre-inoculated with electroactive bacteria, and the cathode is composed of carbon felt loaded with photocatalysts. The cathode and anode are connected to the negative and positive electrodes of a DC power supply, respectively. A 10Ω resistor is connected in series to the external circuit, and the loop current is calculated based on the voltage drop across the resistor. The reference electrode is inserted into the reactor, and a gas collecting pipe is inserted on the side close to the cathode to collect the gas. The cathode simulates the intensity of sunlight. Before the wastewater at the end of the etching solution (Table 1) is transferred to the reactor, nitrogen is aerated to remove dissolved oxygen to ensure an anaerobic environment in the system. A DC power supply is used to provide an external voltage to the reactor, and the data acquisition board collects the voltage data across the electrode and the resistor.

[0039] Table 1 Main parameters of etching liquid wastewater parameter Etching liquid wastewater pH 5.43 ± 0.01 Conductivity (mS / cm) 9.80 ± 1.3 Refractory organic matter (mg / L) 330 ± 1.2 Nickel (mg / L) 106.0 ± 1.5 Sulfate (mg / L) 0.67 ± 0.11 Nitrate nitrogen (mg / L) 3.25 ± 0.12 Nitrite nitrogen (mg / L) 0.11 ± 0.03 Ammonia nitrogen (mg / L) 6.62 ± 0.22 Total chlorine (mg / L) 0.52 ± 0.05 The applied voltage was 0.6 V and the running time was 24 h. The interaction between light, electricity and biology in the treatment of etching liquid wastewater on mineralized organic matter, hydrogen production and metal removal was determined under the conditions of light and no light, biological and non-biological, open circuit and closed circuit.

[0040] like Figure 2As shown in Figure 3, in the light-assisted microbial electrolysis cell, the mineralization rate of refractory organic matter was 70.4±1.2%, and the effluent concentration was 97.6±3.82 mg / L; the nickel ion removal rate was 99.4±0.4%, and the effluent concentration was 0.7±0.4 mg / L, which met the national emission standards (GB39731-2020). Light significantly increased hydrogen production (0.4±0.0m 3 / m 3 / d vs. 0.2±0.0m 3 / m 3 / d, p=0.01) and mineralization rate of refractory organic matter (9.7±0.2 mg / L / h vs.6.2±0.2 mg / L / h, p=0.001). The control experiment showed that the mineralization rates of refractory organic matter in the electrolysis cells with only microorganisms, only light, only electricity, and light-assisted microorganisms were 26.0±1.8%, 20.8±1.1%, 15.8±1.7%, and 70.4±1.2%, respectively.

[0041] Similarly, in terms of hydrogen production, the control system without microorganisms produced no hydrogen, and the pure electrical process produced 0.01±0.0 m3 / m 3 / d, hydrogen production from pure light process 0.01±0.0m3 / m 3 / d, and the above controls were significantly lower than the hydrogen production of the photo-assisted microbial electrolysis cell by 0.4±0.0 m 3 / m 3 / d. The nickel ion removal rates in the control group with only microorganisms, only light, and only electricity were 10.4±4.8%, 11.4±3.4%, and 25.5±4.1%, respectively, which were significantly lower than the nickel ion removal rate of the photo-assisted microbial electrolysis cell (99.4±0.4%). Therefore, light, electricity, and microorganisms play a synergistic role not only in the mineralization of organic matter and the removal of nickel ions, but also in the hydrogen production process.

[0042] The stability of the photo-assisted microbial electrolysis cell in treating the wastewater at the end of the etching solution was evaluated by replacing the wastewater at the end of each cycle for a total of 12 cycles. 24 hours is the cycle of the reactor treating wastewater and producing hydrogen. Due to the actual wastewater used, the present invention takes into account that at the end of a reaction cycle, the wastewater should reach the pollutant emission limit specified in the "Copper, Nickel, and Cobalt Industrial Pollution Emission Standard" (GB 25467-2010). After 24 hours of operation, nickel and refractory organic matter meet the emission standards, so 24 hours is a reaction cycle.

[0043] The results show that the system can stably and completely remove nickel ions while the mineralization rate of refractory organic matter (p=0.000), such as Figure 5 As shown in Figure 2, the loop current (p = 0.001) and hydrogen production (p = 0.000) are Figure 4 As shown in the figure, they all increase significantly with the extension of the operating cycle. The possible reasons are: the extended operating time makes more catalytic microorganisms accumulate on the cathode; at the same time, more nickel is deposited on the electrode, and nickel, as a transition metal, has a good catalytic hydrogen evolution effect whether it is a single substance, a nickel alloy, or even a nickel oxide.

[0044] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell, characterized in that: The steps include: S1: Use the anode liquid of the stable double-chamber microbial fuel cell to remove dissolved oxygen through nitrogen aeration, then mix it with the wastewater at the end of the etching solution and add it to the reactor to replace the solution regularly until the anode potential is stable; S2: Use a DC power supply to apply voltage at both ends of the electrode until the cathode potential decreases and the anode taming is completed; S3: The photocathode uses a photocatalytic material with a narrow bandgap width that can absorb visible light and has stable chemical properties, and another material with a wider bandgap to form a composite material. Under external voltage conditions, it produces hydrogen while mineralizing organic matter and removing nickel ions. Among them, the photocatalytic material is a composite material formed by mixing ZnFe2O4 and g-C3N4.

2. The method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell according to claim 1, characterized in that: The S1 is a reactor in which the anode liquid of a microbial fuel cell that has been stably operating for one year and the wastewater from the etching liquid are added in ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, and 10:0, respectively, wherein the solution is replaced in a cycle of 2-4 days for each ratio until the anode potential stabilizes at -0.22V to -0.26V.

3. The method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell according to claim 2, characterized in that: In the above-mentioned method for producing hydrogen by treating etching liquid wastewater with a photo-assisted single-chamber microbial electrolysis cell, the anode liquid of a microbial fuel cell that has been stably operated for one year and the end wastewater of the etching liquid are added to the reactor in ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:5, 3:7, 2:8, 1:9, and 10:0, respectively, wherein the solution is replaced every 3 days until the anode potential stabilizes at -0.24V.

4. The method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell according to claim 1, characterized in that: The S2 is tamed by applying a 0.28-0.32 V voltage to both ends of the electrode using a DC power supply until the cathode potential drops to 0.45-0.55 V, and the anode taming is completed.

5. The method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell according to claim 4, characterized in that: A DC power supply is used to apply a 0.3 V voltage to both ends of the electrode for domestication until the cathode potential drops to 0.5 V, and the anode domestication is completed.

6. The method for producing hydrogen by treating etching liquid wastewater using a photo-assisted single-chamber microbial electrolysis cell according to claim 1, characterized in that: In S3, the photocathode is made of a photocatalytic material whose conduction band energy is lower than the standard redox potential of hydrogen evolution.

7. The method for producing hydrogen by treating etching wastewater using a photo-assisted single-chamber microbial electrolysis cell according to claim 6, characterized in that: In the S3, the applied voltage is 0V-0.9V.

8. The method for producing hydrogen by treating etching wastewater using a photo-assisted single-chamber microbial electrolysis cell according to claim 7, characterized in that: The external voltage is 0.6V.

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