Method for recovering high-purity sulfur from wastewater based on electrochemical coupling organisms

Abstract

The invention relates to the technical field of water treatment, and discloses a method for recovering high-purity sulfur from wastewater based on electrochemical coupling organisms, which comprises the following steps: 1) reducing SO4 < 2-> in wastewater into HS <-> in a cathode of an electrolytic hydrogen production reactor by using hydrogen autotrophic sulfate reducing bacteria; (2) CO2 is introduced as a carbon source, HS <-> in catholyte is blown off into a delocalized electrochemical oxidation unit containing a Fe (CN) 63 <-> / Fe (CN) 64 <-> redox mediator in the form of H2S by regulating and controlling the pH of a cathode and the internal circulation gas speed, H2S is selectively oxidized into S0 by Fe (CN) 63 <-> and collected, and the generated Fe (CN) 64 <-> is introduced into the anode and oxidized back to Fe (CN) 63 <->. According to the invention, efficient removal of SO4 < 2-> in wastewater and synchronous recovery of high-purity S0 are realized in an electrically-driven low-carbon mode, and the problems of low S0 purity, excessive oxidation and electrode passivation in a traditional bioelectrochemical method are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a method for recovering high-purity sulfur from wastewater based on electrochemical coupling biology. Background Art

[0002] With the surge in demand for phosphate fertilizers and chemical raw materials, the gap between supply and demand of sulfur as a basic industrial raw material continues to widen. Traditional production processes (Frasch and Claus processes) are gradually restricted by environmental regulations, and there is an urgent need to develop sustainable sulfur production technology. In high-salt wastewater generated by industries such as petrochemicals (such as catalytic cracking desulfurization wastewater), SO4 2- Concentrations exceeding 20,000 mg L -1 If S can be recovered from sulfate wastewater in a green and low-carbon way, it will cause ecological risks and harm human health. 0 , which can not only solve the problem of pollution control, but also build a sustainable supply path for sulfur resources.

[0003] At present, biological method is the main technology for recovering sulfur from sulfate wastewater. Its core is sulfate-reducing bacteria (SRB) that convert SO4 2- Restore to S 2- , and then oxidized to generate S 0 Compared with the heterotrophic process that requires an external organic carbon source, the autotrophic SRB uses CO2 / CO3 2- The advantages of using hydrogen as a carbon source and H2 / CO as electron donors are clear. H2 is the most commonly used electron donor, and electrolytic hydrogen production coupled with an autotrophic SRB system can avoid H2 storage and transportation risks. However, due to bottlenecks such as low H2 solubility and poor gas-liquid mass transfer efficiency, SRB still faces problems such as inefficient H2 utilization.

[0004] In addition, sulfides are oxidized to S with high selectivity. 0 Compared with chemical oxidation which requires precise control of oxygen delivery and biological oxidation which requires continuous feeding, electrochemical oxidation is convenient for coupling the cathode sulfate reduction process, thereby constructing a simple and easy-to-control wastewater resource system. 2- to S 0 Conversion, but there is excessive oxidation to SO4 2- Finally, high purity S 0 The recovery of sulfur is also facing challenges. The sludge and microorganisms in the wastewater are easily mixed with the recovered sulfur products, reducing the S 0 purity. Summary of the Invention

[0005] The present invention provides a method for recovering high-purity sulfur from wastewater based on electrochemical coupling. The present invention achieves SO4 recovery from wastewater in a low-carbon mode driven by electricity by constructing a microbial sulfate reduction coupled with sulfide delocalized electrochemical oxidation system mediated by electrolytic hydrogen production. 2- High efficiency removal and high purity S 0 The synchronous recovery of S 0 Problems of low purity, excessive oxidation and electrode passivation.

[0006] The specific technical solution of the present invention is: a method for recovering high-purity sulfur from wastewater based on electrochemical coupled biology, which comprises the following steps:

[0007] 1) Using hydrogen autotrophic sulfate reducing bacteria to reduce SO4 in wastewater at the cathode of electrolytic hydrogen production reactor 2- Restore to HS - .

[0008] 2) CO2 is introduced as a carbon source, and the HS in the cathode liquid is converted to - In the form of H2S, it is stripped to the Fe(CN)6 3- / Fe(CN)6 4- In the delocalized electrochemical oxidation unit of the redox mediator, H2S is converted to Fe(CN)6 3- Selective oxidation to S 0 And collect the generated Fe(CN)6 4- Passed to the anode and oxidized back to Fe(CN)6 3- , thereby achieving the cyclic regeneration of the redox mediator.

[0009] In the method of the present invention, hydrogen autotrophic sulfate reducing bacteria use H2 as electron donor and CO2 as carbon source under anaerobic environment to convert electron acceptor SO4 2- By adjusting the pH of the cathode and the internal circulation gas velocity, the sulfide in the solution is blown out in the form of H2S. The H2S is blown out to the inner circulation gas system of the electrolytic hydrogen production reactor to contain Fe(CN)6 3- In the delocalized oxidation device, H2S is oxidized to S 0 , the unreacted H2 and CO2 are introduced into the cathode again to improve gas-liquid mass transfer and gas utilization. 3- After being reduced by H2S, Fe(CN)6 is generated 4- , and then oxidized to Fe(CN)6 after being pumped into the anode chamber. 3- , realizing the cyclic regeneration of redox mediator and the continuous and efficient oxidation of H2S. 0The present invention utilizes H2S stripping to couple sulfate reduction with sulfide delocalized oxidation to achieve efficient desulfurization of wastewater and S 0 Synchronous recycling.

[0010] The cathode reaction equation is as follows:

[0011] 8H + +8e - →4H2

[0012] SO4 2- +4H2+H + →HS - +4H2O

[0013] HS - +CO2+H2O→H2S+HCO3 -

[0014] The reaction equation of the delocalized electrochemical oxidation unit is as follows:

[0015] H2S+2Fe(CN)6 3- →S 0 +2Fe(CN)6 4- +2H +

[0016] The reaction equation at the anode is as follows:

[0017] 2Fe(CN)6 4- →2Fe(CN)6 4- +2e -

[0018] 3H2O→6H + +6e - +3 / 2O2

[0019] As mentioned in the background technology section, in the traditional electrochemical oxidation method coupled with the cathode biological sulfate reduction system, direct oxidation at the anode can achieve S 2- to S 0 Conversion, but there is excessive oxidation to SO4 2- The present invention uses delocalized electrochemical oxidation technology to passivate Fe 3+ / Fe 2+ Redox mediators such as HO can achieve indirect electrochemical conversion, selectively oxidizing H2S to S in a delocalized unit that is spatially separated from the electrode. 0 , which solves the problem of direct electrochemical oxidation. However, Fe 3+ / Fe 2+It is necessary to maintain stability in a strong acid environment, otherwise it is easy to generate FeS precipitation or Fe(OH)3 colloid. Therefore, the selection of a suitable mediator becomes the key breakthrough of this technology. The present invention selects Fe(CN)6 3- / Fe(CN)6 4- Redox mediators can solve the above technical problems.

[0020] In addition, the sludge and microorganisms in the wastewater are easily mixed with the recovered sulfur products, which reduces the S 0 To this end, the present invention removes the sulfide in the solution in the form of H2S by adjusting the pH, and then converts H2S into S by delocalized electrochemical oxidation. 0 , it is possible to avoid the contact of sulfur products with wastewater and obtain high-purity S 0 .

[0021] Preferably, in step 1), a PU@RGO@MnO2 modified filler is added to the cathode, which includes polyurethane (PU) as a carrier, and redox graphene (RGO) and MnO2 nanoparticles supported in the polyurethane.

[0022] In order to further increase SO4 2- Reduction efficiency can be enhanced by adding functional fillers to enhance the mass transfer effect of the gas-liquid-microorganism interface, thereby improving the efficiency of hydrogen autotrophic sulfate-reducing bacteria in utilizing H2. The PU@RGO@MnO2 modified filler of the present invention is beneficial to enhancing H2 mass transfer and sulfate reduction performance. The modified filler has a three-dimensional porous skeleton, provides a high specific surface area, and can promote the miniaturization and dispersion of large bubbles through shearing, expand the gas-liquid-microorganism contact interface area, and prolong the residence time of H2 bubbles at the cathode, thereby improving mass transfer efficiency. MnO2 can promote the metabolic activity of microorganisms in anaerobic sludge, and at the same time promote the expression of cytochrome C content. Cytochrome C plays an important role in electron transfer in the process of sulfate-reducing bacteria utilizing H2. The introduction of MnO2 is beneficial to enhancing the electron transfer process in H2 utilization. Therefore, the addition of PU@RGO@MnO2 lays the foundation for building an efficient sulfate reduction system.

[0023] Preferably, in step 1), the preparation method of the PU@RGO@MnO2 modified filler comprises: immersing polyurethane (PU) in a suspension containing graphite oxide (GO) and a reducing agent, heating, so that the graphite oxide is adsorbed in the polyurethane and reduced to redox graphene to obtain PU@RGO; immersing PU@RGO in a MnO2 precursor solution and heating, growing MnO2 nanoparticles in the polyurethane through an in situ redox reaction between the redox graphene and the MnO2 precursor; washing and drying the product to obtain PU@RGO@MnO2.

[0024] Preferably, in step 1), the PU@RGO@MnO2 modified filler occupies 10-20% of the cathode volume.

[0025] Preferably, in step 1), the hydrogenotrophic sulfate-reducing bacteria are inoculated into the cathode in the form of anaerobic sludge as a carrier.

[0026] Preferably, in step 1), the electrolytic hydrogen production reactor uses a tubular cation exchange membrane to separate the cathode and the anode; the cathode is located in the middle of the electrolytic hydrogen production reactor, and the anode is arranged around the cathode.

[0027] Preferably, in step 1), the temperature of the cathode is controlled to be 20-40°C.

[0028] Preferably, in step 1), the cathode is controlled to be in anoxic conditions, the constant current applied to the electrolytic hydrogen production reactor is 200-400 mA, and the hydraulic retention time (HRT) during operation in continuous flow mode is 1-2 days.

[0029] Preferably, in step 2), the flow rate of CO2 is controlled at 2.65-4.10 mL / min; the internal circulation gas rate is controlled at 120-160 mL / min; and the pH of the cathode is controlled at 6-7.

[0030] Preferably, in step 2), the Fe(CN)6 3- The initial concentration is 0.3-0.7M;

[0031] Preferably, in step 2), the Fe(CN)6 3- / Fe(CN)6 4- The circulation flow rate is 0.3-0.7Lh -1 ;

[0032] Preferably, in step 2), the pH of the anode is controlled at 5.5-6.5.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The method of the present invention is based on bioelectrochemistry and constructs a microbial sulfate reduction coupled with sulfide delocalized electrochemical oxidation system mediated by electrolytic hydrogen production. Sulfate-reducing bacteria use CO2 as a carbon source at the cathode and use the H2 generated by electrolysis as an electron donor to convert SO4 2- Restore to HS - , and then HS - Blowing off Fe(CN)6 with gaseous H2S 3- / Fe(CN)6 4- The delocalized electrochemical oxidation unit further produces S with a purity of up to 99.15%. 0 . Solve the problem of S in traditional technology0 The problem of low purity. High purity S 0 It can be applied to lithium-sulfur batteries, realizing the connection between environmental remediation and energy storage applications.

[0035] (2) The method of the present invention is highly efficient in treating sulfate wastewater, SO4 2- The removal rate reached 92.6±1.3~94.1±2.5%, S 0 The recovery rate reached 88.7±2.8~90.1±2.1%, and the S 0 Separation can be carried out in solution by gravity sedimentation, which reduces processing costs.

[0036] (3) The method of the present invention solves the problems of excessive sulfide oxidation and electrode passivation in direct electrochemistry, achieving 100% conversion of H2S to S 0 The conversion of Fe(CN)6 3- / Fe(CN)6 4- It has good recycling performance, avoids the addition of large amounts of chemicals, and improves economic and environmental benefits.

[0037] (4) The electrolytic hydrogen production reactor designed by the method of the present invention and the use of modified fillers are conducive to prolonging the residence time of H2 in the cathode, thereby improving the utilization efficiency of H2 by SRB and achieving efficient sulfate reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the sulfate reduction coupled sulfide delocalized electrochemical oxidation system of Example 1;

[0039] Figure 2 is a graph showing changes in sulfur species concentration in the cathode effluent and the delocalized oxidation unit of the system of Example 1;

[0040] Figure 3 This is a graph showing changes in the coulombic efficiency and hydrogen utilization efficiency of the system in Example 1;

[0041] Figure 4 This is a graph showing changes in energy consumption for the system in Example 1;

[0042] Figure 5 is a schematic diagram of a sulfate reduction coupled sulfide direct electrochemical oxidation system according to Example 2;

[0043] Figure 6 It is SO4 of system I and system II of embodiment 2 2- Remove and S 0 Recycling performance comparison chart;

[0044] Figure 7are the SEM images and EDS spectra of System I and System II of Example 2;

[0045] Figure 8 This is a comparison chart of energy consumption for recovering elemental sulfur between System I and System II in Example 2;

[0046] Figure 9 is a comparison chart of the power efficiency of system I and system II in Example 2;

[0047] Figure 10 is the XRD pattern of the sample sulfur recovered by system I and system II in Example 3;

[0048] Figure 11 is a graph showing the settling performance and purity of sample sulfur recovered by system I and system II in Example 3;

[0049] Figure 12 is a particle size distribution diagram of the sulfur samples recovered by system I and system II in Example 3;

[0050] Figure 13 is the EDS layered image and spectrum of the sample sulfur recovered by system I in Example 3;

[0051] Figure 14 Figure 3 is a lithium-sulfur battery performance test diagram of the sample sulfur recovered by System I in Example 3 compared with commercial sulfur: (a) charge and discharge specific capacity at different rates and (b, c) charge and discharge curves. DETAILED DESCRIPTION

[0052] The present invention will be further described below with reference to the following examples and accompanying drawings. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0053] The materials involved in the embodiments of the present invention are as follows:

[0054] (1) Anaerobic sludge rich in hydrogen-autotrophic sulfate-reducing bacteria, with a solid concentration of 14 g L -1 :Including desulfurization bacteria, acetic acid bacteria and other bacteria, among which the relative abundance of each bacteria is as follows: Desulfurization bacteria is 33.9%, Firmicutes is 34.2%, Campylobacter is 13.1%, Proteobacteria is 7.1%), Bacteroidetes is 6.1%, Actinobacteria is 2.0%, and other miscellaneous bacteria is 3.6%. You can also directly choose commercially available pure bacteria products (commonly used hydrogen autotrophic sulfate-reducing bacteria strains in industry include Desulfovibrio and Desulfobacter). Hydrogen autotrophic sulfate-reducing bacteria use H2 as electron donor and CO2 as carbon source in anaerobic environment, and can convert electron acceptor SO4 2- Reduced to sulfide. Lower pH and higher gas velocity are conducive to the stripping of sulfide in the solution in the form of H2S. H2S is stripped to the Fe(CN)6 3-In the delocalized oxidation device, H2S is oxidized to S 0 , the unreacted H2 and CO2 are introduced into the cathode again to improve gas-liquid mass transfer and gas utilization. 3- After being reduced by H2S, Fe(CN)6 is generated 4- , and then oxidized to Fe(CN)6 after being pumped into the anode chamber. 3- , realizing the cyclic regeneration of redox mediator and the continuous and efficient oxidation of H2S. 0 Collect it, wash it repeatedly with deionized water until the filtrate is clear, and dry the residue in a 60°C oven for 24 h.

[0055] (2) Simulated wastewater: The solvent was deionized water, and the composition included: sodium sulfate 1479.2, 2958.4, or 4437.6 mg L -1 , ammonium chloride 100 mg L -1 , sodium chloride 50mg L -1 , disodium hydrogen phosphate dodecahydrate 300mg L -1 , potassium dihydrogen phosphate 150mg L -1 , trace element solution 1ml L -1 ; The trace element solution includes 400mg L of ferric chloride hexahydrate -1 , cobalt chloride hexahydrate 150 mg L -1 , Manganese chloride tetrahydrate 120mg L -1 Calcium chloride dihydrate 200 mg L -1 , nickel chloride hexahydrate 30 mg L -1 , copper sulfate pentahydrate 20 mg L -1 , magnesium chloride hexahydrate 600mg L -1 , zinc chloride 100mg L -1 , Boric acid 150mg L -1 , sodium molybdate dihydrate 40mg L -1 , EDTA 1000mg L -1 .

[0056] (3) PU@RGO@MnO2 modified filler: The specific preparation method is as follows:

[0057] (3.1) Graphite oxide (GO) was first prepared using the Hummers method: 2 g of graphite powder (325 mesh) was added to a 250 mL beaker. 1 g of NaNO₃ and 46 mL of H₂SO₄ were then added while stirring in an ice bath. 6 g of KMnO₄ was then slowly added to the beaker while stirring, keeping the temperature below 20°C. After 5 min, the ice bath was removed, and the system was heated at 35°C for 30 min. 92 mL of deionized water was then added and stirred for 15 min. 80 mL of a 3% H₂O₂ solution at 60°C was then added to reduce the excess KMnO₄ until no bubbles were visible and the solution turned yellow. The mixture was centrifuged and washed several times with 10% hydrochloric acid to remove metal ions. The solution was centrifuged at 6000 rpm for 20 min, and the solid was repeatedly washed with warm water until the pH of the upper layer of the suspension approached 7. The resulting product was redispersed in deionized water and gently sonicated for 8 h. The suspension was then freeze-dried to yield GO.

[0058] (3.2) GO was then dissolved in deionized water (3 mg mL -1 ), vitamin C (3 mg mL -1 ), and a uniform suspension was obtained after ultrasonic treatment for 30 minutes. After ultrasonic cleaning of polyurethane (PU) with deionized water and ethanol and complete drying at 60 ° C for 24 hours, it was immersed in the suspension (PU: suspension = 1:1, volume ratio), and then heated at 65 ° C for 6 hours. During this period, GO was adsorbed on PU and reduced to RGO by vitamin C to obtain PU@RGO. Finally, PU@RGO was immersed in KMnO4 solution (10 mg mL -1 ) and heated at 80°C for 10 minutes (until the solution turned from purple-red to brown). MnO2 nanoparticles were grown on the PU via an in situ redox reaction between RGO and KMnO4. The resulting PU@RGO@MnO2 was washed with copious deionized water and dried at 60°C for 24 hours.

[0059] (4) Electrolytic hydrogen production reactor: The specific construction method is as follows: The reactor is made of polyvinyl chloride and includes a bottom electrolytic cell and an extended cathode part in the middle. The tubular cation exchange membrane in the electrolytic cell divides the reactor into a cathode chamber and an anode chamber. The cathode chamber has a total height of 82 cm and a working volume of 2 L. It contains a stainless steel mesh cylinder (304L, 9 cm × 5 cm; pore size 4 mm; thickness 0.5 mm) as the cathode. The extended cathode part has a diameter of 10 cm and a height of 52 cm. An inner cylinder with a diameter of 6.6 cm and a height of 35 cm is added to connect to the cathode part with a diameter of 6.6 cm and a height of 30 cm in the electrolytic cell. The cathode is designed with an internal circulation gas system from top to bottom to achieve gas recycling and solution disturbance. The anode chamber has a diameter of 11 cm and a height of 20 cm, a working volume of 0.6 L, and a tubular Ti mesh (8.5 cm × 9 cm) coated with IrO2 as the anode.

[0060] Example 1: Construction of a sulfate reduction coupled sulfide delocalized electrochemical oxidation system

[0061] The construction of sulfate reduction coupled sulfide delocalized electrochemical oxidation system is as follows: Figure 1 As shown in the figure, denoted as System I. Anaerobic sludge rich in hydrogen-autotrophic sulfate-reducing bacteria was inoculated into the cathode of the electrolytic hydrogen production reactor, and 0.6 L PU@RGO@MnO2 was added. The cathode was controlled to be anaerobic, and the reactor was operated in continuous flow mode. A constant current of 300 mA was applied using a DC power supply, and a peristaltic pump was used to pump 1000-3000 mg L -1 SO4 2- The simulated wastewater was introduced from the bottom of the cathode, the HRT was controlled at 1 to 2 days, the cathode temperature was 30°C, and the cathode inlet and outlet water and the delocalized oxidation unit were sampled regularly. 2- Reduced to HS by hydrogenotrophic sulfate-reducing bacteria at the cathode - The cathode pH was maintained at 6.5 by adjusting the CO2 (99.9%) flow rate, thereby - In a delocalized electrochemical oxidation unit connected to the cathode internal circulation gas path (containing 0.5L 0.5M Fe(CN)6 3- solution) to carry out delocalized electrochemical oxidation of H2S, and adjust the internal circulation gas velocity to blow H2S from the cathode to Fe(CN)6 3- In the solution, H2S is oxidized to S 0 , while Fe(CN)6 3- Reduced to Fe(CN)6 4- Use peristaltic pump to pump Fe(CN)6 3- / Fe(CN)6 4- The medium passes through S 0 The precipitation bottle (0.5L) was transferred to the anode chamber for Fe(CN)63- The electrochemical regeneration was followed by 0.5 L h -1 The anode solution is recirculated to the delocalized electrochemical oxidation unit at a constant rate. The pH of the anode solution is controlled at 6.0 using 5M NaOH. The cathode effluent is sequentially passed through a 0.25L sedimentation bottle and a hollow fiber membrane before being discharged. The sludge in the sedimentation bottle and the bacterial solution filtered through the hollow fiber membrane are regularly circulated to the cathode to prevent significant loss of microorganisms.

[0062] The reactor was operated for a total of 103 days to explore the SO4 removal performance of the coupled system under different influent sulfate loads. 2- And recycle S 0 The performance includes three stages, such as Figure 2 shown.

[0063] Stage 1 (Day 1 to 30), SO4 in the cathode water 2- The concentration is 1000 mg L -1 , HRT is 1d, influent SO4 2- Loading is 333mg SO4 2- -SL -1 d -1 The CO2 flow rate was 2.65 mL min -1 , the circulating gas rate is 120 mL min -1 As the operation time increases, the SO4 2- The concentration decreased, S 2- The concentration decreased, but S 0 The concentration increases. This indicates that the cathode's sulfate removal performance is gradually enhanced, and more and more S 2- It is blown off in the form of H2S to the delocalized electrochemical oxidation unit and oxidized to S 0 In the stable stage, the SO4 2- Concentration is 19.6±8.6mg SO4 2- -SL -1 , SO4 2- The removal rate (SRR) is 314.0±9.0mgSO4 2- -SL -1 d -1 , the removal efficiency is 94.1±2.5%. At this time, the S 0 The concentration was 299.8±9.7 mg S 0 -SL -1 , S 0 The production rate (SPR) was 299.8±9.7 mg S 0 -SL -1 d -1 , the recovery efficiency was 90.1±2.1%.

[0064] Stage 2 (31st to 63rd day), increasing the SO4 content of cathode influent 2- The concentration is 2000 mg L -1 , while increasing the HRT to 2d and keeping the influent load unchanged. In the stable stage, the SRR of the system is 306.7±10.1mg SO4 2- -SL -1 d -1 , SPR was 293.6±11.3 mg S 0 -SL -1 d -1 , SO4 2- Removal efficiency and S 0 The recovery efficiencies were 92.7±2.2% and 88.7±2.8%, respectively. Compared to the previous stage, the performance did not change much, which was attributed to the influent SO4 2- The load remains unchanged.

[0065] Stage 3 (64th to 103rd day), further increase the SO4 content of cathode influent 2- The concentration is 3000 mg L -1 , keeping HRT unchanged, the influent load is increased to 500mg SO4 2- -SL -1 d -1 , adjust the CO2 flow rate to 4.10 mL min -1 The pH value was controlled at 6.5. However, during the first 8 days of this phase, the circulating gas rate was 120 mL / min. -1 When the cathode effluent sulfide concentration is 36.3±18.3mgS 2- -SL -1 Therefore, on day 9, the circulating gas rate was increased to 160 mL / min -1 , the sulfide concentration in the cathode effluent during the stable phase dropped to zero. Achieved a high of 464.3±7.1mg SO4 2- -SL -1 d -1 SRR and 450.6±8.6mg S 0 -SL -1 d -1 SPR(SO4 2- The removal efficiency was 92.6±1.3%, S 0 The recovery efficiency was 89.8±1.6%).

[0066] No soluble sulfur species (SO4 2- ,SO3 2- ,S2O3 2- ) and sulfides, further illustrating the H2S to S0 The conversion rate is close to 100%. This is attributed to the fact that delocalized electrochemical oxidation avoids direct oxidation of sulfide at the anode, thereby preventing excessive oxidation of sulfide to other high-valent sulfur species. At the same time, it avoids secondary pollution caused by sulfide, confirming the effectiveness of H2S stripping coupled with delocalized electrochemical oxidation to recover S from high-concentration sulfate wastewater. 0 effectiveness and feasibility.

[0067] In addition to SO4 2- Remove and S 0 The coupling performance of the electrolytic hydrogen production reactor and the H2 utilization efficiency are also analyzed. Figure 3 As shown in Figure 3, the optimal coulombic efficiency and H2 utilization efficiency were achieved in stage 3, which were 76.4±1.6% and 93.2±2.6%, respectively. The H2 utilization rate of 93.2±2.6% kept the gaseous H2 concentration in the cathode below 2.5%, which was outside the explosion limit range (4.0-75.6%), thus effectively avoiding safety risks. At this time, the optimal hydrogen evolution energy consumption was approximately 0.018 kWh d -1 , every 1kg S recovered 0 The energy consumption is about 20.1kwh kg -1 S 0 , which is about half of stage 1 and stage 2, such as Figure 4 This is because as sulfate reduction increases, more and more H2S is oxidized to S 0 , more Fe(CN)6 4- At the anodic oxidation point, Fe(CN)6 3- , which is beneficial to inhibiting the anode oxygen evolution reaction, thereby reducing energy consumption.

[0068] Example 2: Performance comparison of direct electrochemical sulfide oxidation systems coupled with sulfate reduction

[0069] The construction of sulfate reduction coupled sulfide direct electrochemical oxidation system is as follows Figure 5 As shown, it is called System II. The difference from System I is that SO4 2- Reduced to HS by hydrogenotrophic sulfate-reducing bacteria - , containing HS - The cathode effluent is passed through a 0.25L sedimentation bottle and a hollow fiber membrane and then into the bottom of the anode to further separate the HS - Direct electrochemical oxidation to S 0 , and finally the water comes out from the top of the anode. Regularly sample the cathode inlet and outlet water and the anode outlet water. Use a micro-regulating valve to control the CO2 flow rate to 0.57mLmin -1 , so that the theoretical H2 / CO2 flow rate is about 4:1, and the internal circulation gas rate is adjusted to 40mLmin using a gas circulation pump -1, the pH in the cathode and anode was controlled to 8.0 by adding 3 M HCl or 5 M NaOH using a pH controller.

[0070] The SO4 of system I and system II in three stages were compared and analyzed. 2- Remove and S 0 Recycling coupling performance, such as Figure 6 As shown. In the influent SO4 2- 1000mg L -1 In the stable stage, the SRR of system I is 314.0±9.0mg SO4 2- -SL -1 d -1 (removal efficiency of 94.1 ± 2.5%), compared with 310.9 ± 6.0 mg SO4 in system II 2- -SL -1 d -1 However, system I in S 0 The recovery was significantly better than that of System II, with an SPR of 299.8 ± 9.7 mg S 0 -SL -1 d -1 (recovery efficiency was 90.1 ± 2.1%), while the SPR of system II was 197.5 ± 11.4 mg S 0 -SL -1 d -1 (59.5±2.9%). This is because in the process of direct oxidation of HS- at the anode in System II, it will be over-oxidized into other high-valent sulfur species such as SO4 2- 、S2O3 2- , thus reducing the SPR.

[0071] When the influent SO4 2- Increased to 2000mg L -1 When the system I maintains a relatively stable coupling performance (SO4 2- The removal rate was 92.7±2.2%, S 0 The recovery rate was 88.7±2.8%). In contrast, the SO4 2- The removal efficiency dropped to 65.4±2.5% (SRR=217.4±8.5mg SO4 2- -SL -1 d -1 ), S 0 The recovery efficiency dropped to 45.9±2.8% (SPR=152.4±9.4 mg S 0 -SL -1 d -1The decrease in coupling performance may be due to the accumulation of sulfide in the catholyte. High concentrations of sulfide inhibit the activity of SRB, ultimately limiting the S 0 The production of.

[0072] Further SO4 2- Increased to 3000mg L -1 It can be seen that the two systems have significant performance differences. System I achieved up to 464.3±7.1mg SO4 2- -SL -1 d -1 SRR and 450.6±8.6mg S 0 -SL -1 d -1 SPR(SO4 2- The removal efficiency was 92.6±1.3%, S 0 The recovery efficiency was 89.8±1.6%). However, the SRR of system II (213.5±11.4 mg SO4 2- -SL -1 d -1 ) and SPR (146.7±11.1 mg S 0 -SL -1 d -1 ) changes very little, and the corresponding SO4 2- Removal rate and S 0 The recovery rates were 42.0±2.9% and 29.3±2.1%, respectively. This indicates that the performance of System II has reached its limit, while System I eliminates the inhibition of high sulfide concentration on SRB activity by coupling H2S stripping with delocalized electrochemical oxidation, avoids excessive oxidation of sulfide, and ensures efficient SO4 2- Reduction and S 0 The production of.

[0073] In order to study the phenomenon of electrode passivation in the two systems, the anode materials were characterized by SEM and EDS after the operation. Figure 7 As shown. No sulfur particles were observed on the anode surface of system I, and the surface was mainly composed of Ti, O and Ir elements, while the anode was a Ti mesh coated with IrO2. This shows that SEM and EDS mainly revealed the element information of IrO2 coating and titanium mesh, because no S 0 The deposition on the anode surface avoids electrode passivation. In contrast, the anode surface of system II contains a large number of sulfur particles, mainly S elements, which leads to severe electrode passivation.

[0074] Since system I avoids electrode passivation, the energy consumption of operation at the same stage is lower, e.g. Figure 8 It is worth noting that in the influent SO4 2-3000mg L -1 When system I recycles S 0 The energy consumption is 20.1kWh kg -1 S 0 , about 1 / 5 of System II (97.4kWh kg -1 S 0 ), significantly reducing the cost of electricity. The energy efficiency of the two systems was further evaluated, such as Figure 9 As shown. Influent SO4 2- 1000 and 2000 mg L -1 When the power efficiency of system I is 40.2±2.1% and 39.3±1.7%, respectively, which is higher than 24.9±1.4% and 17.3±1.4% of system II. 2- The concentration is 3000 mg L -1 , the power efficiency of system I is increased to 62.5±1.9%, which is about 3.8 times that of system II (16.5±1.6%). The above results show that the power efficiency of system I is significantly higher than that of system II. This is because the S 0 The recovery rate is higher, so more electricity is used in resource treatment of sulfate wastewater. 2- With the increase of concentration, the SPR of system II gradually decreases, resulting in a gradual decrease in power efficiency. The SPR of system I is between 1000 and 2000 mg L -1 When the concentration is basically unchanged, at 3000mg L -1 Therefore, the power efficiency remains unchanged at first and then increases significantly. Overall, System I efficiently recovers S 0 The mechanism is mainly to relieve the inhibition of high concentration of sulfide on SRB, avoid electrode passivation and excessive oxidation, and improve S 0 Selectivity and electrical efficiency, thus achieving high SO4 efficiency in high-concentration sulfate wastewater 2- Remove and synchronize S 0 Recycle.

[0075] Example 3: Characteristics and applicability of elemental sulfur recovery from wastewater based on electrochemical coupled biological

[0076] First, the characteristics of elemental sulfur recovered from wastewater based on electrochemical coupled biological recovery were evaluated. The phase analysis of sulfur samples obtained from the two systems was performed by XRD, as shown in Figure 2. Figure 10 Compared with the standard spectrum of S8, it is verified that the crystal structure and composition of sulfur in the two samples are consistent with S 0 . For S in solution 0 Sedimentation performance, S 0 The purity was analyzed as Figure 11After 5 minutes of sedimentation, the system I obtained 0 The solution was separated into solid and liquid by gravity sedimentation, and then washed with deionized water to obtain S with a purity of up to 99.15%. 0 , which means that the theoretical contamination level of sulfur by impurities is ≤0.85%. In contrast, the S-containing 0 The solution is still turbid and needs to be separated by centrifugation or filtration. Since it is difficult to completely separate the microorganisms and sludge, the S recovered from system II 0 The purity is only 88.4%. This shows that System I can effectively separate and recover high-purity S from sulfate wastewater in a more economical way. 0 .

[0077] SEM and particle size distribution analysis further revealed obvious differences in the morphology and aggregation behavior of sulfur particles, such as Figure 12 As shown. S in System I 0 The particles were regular baseball-shaped with obvious aggregation behavior and the particle size was 6.7 ± 2.1 μm. In contrast, system II produced irregularly shaped S 0 The particles are loosely distributed and small in size, with a particle size of 4.8±2.2μm. 0 The larger particle size of S decreases the specific surface area, thereby reducing the surface energy of each particle. This minimizes the electrostatic repulsion between sulfur particles and promotes aggregation through van der Waals forces or electrostatic screening, thus forming easily sedimentable aggregates. In contrast, the smaller S in System II 0 The particles have higher specific surface area and surface energy, which promotes S 0 The stability of the colloids hinders the gravity-based sedimentation of S 0 In addition, the oxidative conditions in System II may cause the sulfur particles to adsorb more charged ions or impurities (such as biosolids), which enhances the electrostatic repulsion and improves the stability of the colloidal suspension, further suppressing the S 0 Sedimentation.

[0078] In order to evaluate the contamination of sulfur recovery by cyanide, the S recovered from system I was 0 EDS characterization was performed, such as Figure 13 As shown. According to the EDS layered image and spectrum, it can be seen that S 0 The main element is S, and Fe and N are not detected, which indicates that the recovered S 0 After simple rinsing with deionized water, there is basically no Fe(CN)6 3- / Fe(CN)6 4- .

[0079] Finally, the S recovered by system I was tested by constant current charge and discharge. 0With commercial standard S 0 The electrochemical performance of the cathode materials was compared. Figure 14 (a) The two materials exhibit similar specific capacities at rates of 0.2–2.0 C. Figure 14 (b) and (c) show that the charge-discharge curves of the two are almost the same at 0.2-0.8C, and therefore have similar polarization voltages. However, at higher rates (1.0-2.0C), the recovered S 0 Compared to the standard S 0 has a slightly lower charging voltage. This indicates that the recovered S 0 It has lower electrochemical impedance and better electrochemical performance under high rate conditions, and is used as a standard S in lithium-sulfur batteries. 0 It has shown great potential as an alternative to

[0080] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for recovering high-purity sulfur from wastewater based on electrochemical coupled biological reactions, characterized in that: The following steps are involved: 1) Using hydrogen autotrophic sulfate reducing bacteria to reduce SO4 in wastewater at the cathode of electrolytic hydrogen production reactor 2- Restore to HS - ; 2) CO2 is introduced as a carbon source, and the HS in the cathode liquid is converted to - In the form of H2S, it is stripped to the Fe(CN)6 3- / Fe(CN)6 4- In the delocalized electrochemical oxidation unit of the redox mediator, H2S is converted to Fe(CN)6 3- Selective oxidation to S 0 And collect the generated Fe(CN)6 4- Passed to the anode and oxidized back to Fe(CN)6 3- .

2. The method according to claim 1, wherein: In step 1), a PU@RGO@MnO2 modified filler is added to the cathode, which includes polyurethane as a carrier, and redox graphene and MnO2 nanoparticles supported in the polyurethane.

3. The method according to claim 2, wherein: In step 1), the preparation method of the PU@RGO@MnO2 modified filler includes: immersing polyurethane in a suspension containing graphite oxide and a reducing agent, heating, so that the graphite oxide is adsorbed in the polyurethane and reduced to redox graphene, to obtain PU@RGO; immersing PU@RGO in a MnO2 precursor solution and heating, growing MnO2 nanoparticles in the polyurethane through an in situ redox reaction between the redox graphene and the MnO2 precursor; washing and drying the product to obtain PU@RGO@MnO2.

4. The method according to claim 2 or 3, wherein: In step 1), the PU@RGO@MnO2 modified filler occupies 10-20% of the cathode volume.

5. The method according to claim 1, wherein: In step 1), the hydrogenotrophic sulfate-reducing bacteria are inoculated into the cathode in the form of anaerobic sludge as a carrier.

6. The method according to claim 1, wherein: In step 1), the electrolytic hydrogen production reactor uses a tubular cation exchange membrane to separate the cathode and the anode; the cathode is located in the middle of the electrolytic hydrogen production reactor, and the anode is arranged around the cathode.

7. The method according to claim 1, wherein: In step 1), the temperature of the cathode is controlled to be 20-40°C.

8. The method according to claim 1, wherein: In step 1), the cathode is controlled to be in an anaerobic condition, the constant current applied to the electrolytic hydrogen production reactor is 200-400 mA, and the hydraulic retention time during the continuous flow mode operation is 1-2 days.

9. The method according to claim 1, wherein: In step 2), The flow rate of the CO2 is controlled at 2.65-4.10 mL / min; The internal circulation gas velocity is controlled at 120-160 mL / min; The pH of the cathode is controlled at 6-7.

10. The method according to claim 1 or 9, wherein: In step 2), The Fe(CN)6 3- The initial concentration is 0.3-0.7M; The Fe(CN)6 3- / Fe(CN)6 4- The circulation flow rate is 0.3-0.7Lh -1 ; The pH of the anode is controlled at 5.5-6.5.

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