A method for recovering high-purity sulfur from wastewater based on electrochemical coupling biology

Abstract

The application relates to the technical field of water treatment, and discloses a method for recovering high-purity sulfur from wastewater based on electrochemical coupling biology, which comprises the following steps: 1) hydrogen autotrophic sulfate-reducing bacteria are used to reduce SO4 2‑ in wastewater into HS ‑ in a cathode of an electrolytic hydrogen production reactor; 2) CO2 is introduced as a carbon source, HS ‑ in cathode liquid is blown off in the form of H2S into a Fe(CN)6 3‑ / Fe(CN)6 4‑ delocalized electrochemical oxidation unit of a redox mediator, H2S is selectively oxidized into S 3‑ in the unit, the generated Fe(CN)6 0 is collected, and the generated Fe(CN)6 4‑ is introduced into an anode to be oxidized into Fe(CN)6 3‑ . The application realizes efficient removal of SO4 2‑ in wastewater and synchronous recovery of high-purity S 0 under the condition of low-carbon mode driven by electricity, and solves the problems of low S 0 purity, excessive oxidation and electrode passivation in traditional bioelectrochemical methods.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for recovering high-purity sulfur from wastewater based on electrochemically coupled biological processes. Background Technology

[0002] With the surge in demand for phosphate fertilizers and chemical raw materials, the supply-demand gap for sulfur, a fundamental industrial raw material, continues to widen. Traditional production processes (Frasch and Claus processes) are increasingly constrained by environmental regulations, necessitating the development of sustainable sulfur production technologies. In high-salinity wastewater generated by industries such as petrochemicals (e.g., catalytic cracking desulfurization wastewater), SO4... 2- Concentration exceeding 20000 mg / L -1 Improper discharge of sulfur dioxide can pose ecological risks and harm human health. If sulfur dioxide can be recovered from sulfate wastewater in a green and low-carbon manner... 0 This approach can not only solve the problem of pollution control, but also build a sustainable supply path for sulfur resources.

[0003] Currently, biological methods are the main technology for recovering sulfur from sulfate wastewater. The core of this technology is sulfate-reducing bacteria (SRB) which metabolize SO42- through heterotrophic / autotrophic metabolism. 2- Restore to S 2- Then it is oxidized to produce S 0 Compared to heterotrophic processes that require an external organic carbon source, autotrophic SRB utilize CO2 / CO3... 2- The characteristics of H2 as a carbon source and H2 / CO as an electron donor have obvious advantages. Among them, H2 is the most commonly used electron donor. The electrolytic hydrogen production coupled with the autotrophic SRB system can avoid the risks of H2 storage and transportation. However, due to bottlenecks such as the low solubility of H2 and poor gas-liquid mass transfer efficiency, there are still problems such as the low efficiency of SRB in utilizing H2.

[0004] Furthermore, sulfides are selectively oxidized to S. 0 This is a crucial step. Compared to chemical oxidation, which requires precise control of oxygen delivery, and biological oxidation, which requires continuous feeding, electrochemical oxidation is easier to couple with the cathode sulfate reduction process, thereby constructing a simple and easily controllable wastewater resource recovery system. However, while traditional direct anode oxidation can achieve S... 2- To S 0 The conversion occurs, but there is a risk of over-oxidation to SO4. 2- And the issue of electrode passivation. Finally, high-purity S... 0 The recycling process also faces challenges. Sludge and microorganisms in the wastewater can easily contaminate the recovered sulfur products, reducing their sulfur content. 0 Purity. Summary of the Invention

[0005] This invention provides a method for recovering high-purity sulfur from wastewater based on electrochemical coupling with biological processes. This invention constructs a microbial sulfate reduction coupled with delocalized electrochemical oxidation of sulfides, mediated by electrolytic hydrogen production, thereby achieving SO4 recovery from wastewater in a low-carbon, electrically driven mode. 2- Highly efficient removal and high purity S 0 Simultaneous recovery solves the problem of S in traditional bioelectrochemical methods. 0 Problems include low purity, excessive oxidation, and electrode passivation.

[0006] The specific technical solution of this invention is as follows: a method for recovering high-purity sulfur from wastewater based on electrochemical coupling with biological processes, comprising the following steps:

[0007] 1) Utilizing hydrogen autotrophic sulfate-reducing bacteria at the cathode of an electrolytic hydrogen production reactor to remove SO42- from wastewater. 2- Restore to HS - .

[0008] 2) Introduce CO2 as a carbon source, and by adjusting the pH of the cathode and the internal circulation gas rate, remove the HS from the catholyte. - Stripped in the form of H2S to a solution containing 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 it, the generated Fe(CN)6 4- The anode is oxidized back to Fe(CN)6. 3- This enables the cyclic regeneration of the redox mediator.

[0009] In the method of this invention, hydrogen autotrophic sulfate-reducing bacteria use H2 as an electron donor and CO2 as a carbon source under anaerobic conditions, and can convert SO4 into an electron acceptor. 2- The solution is reduced to sulfides. Sulfides in the solution are stripped out as H2S by adjusting the pH at the cathode and the internal circulation gas rate. The H2S is then stripped to a concentration of Fe(CN)6 through the internal circulation gas system of the electrolysis hydrogen production reactor. 3- In the delocalized oxidation device, H2S is oxidized to S 0 Unreacted H2 and CO2 are then reintroduced into the cathode to improve gas-liquid mass transfer and gas utilization. Fe(CN)6 3- After being reduced by H2S, Fe(CN)6 is generated. 4- After being pumped into the anode chamber, it is re-oxidized to Fe(CN)6. 3- This enables the cyclic regeneration of the redox mediator and the continuous, efficient oxidation of H2S. The resulting S... 0Collect the residue and wash it repeatedly with deionized water until the filtrate is clear. Dry the filter residue. This invention utilizes H2S stripping coupled with sulfate reduction and delocalized sulfide oxidation to achieve efficient desulfurization and sulfur removal from wastewater. 0 Synchronous recycling.

[0010] The reaction equation for the cathode is as follows:

[0011] 8H + +8e - →4H2

[0012] SO4 2- +4H2+H + →HS - +4H2O

[0013] HS - +CO2 +H2O →H2S +HCO3 -

[0014] The reaction equations for the delocalized electrochemical oxidation unit are 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 described in the background section, in traditional electrochemical oxidation coupled with cathode bio-sulfate reduction systems, although direct anodic oxidation can achieve S... 2- To S 0 The conversion occurs, but there is a risk of over-oxidation to SO4. 2- This invention addresses the issue of electrode passivation. It employs delocalized electrochemical oxidation technology using Fe... 3+ / Fe 2+ Redox mediators can achieve indirect electrochemical conversion, selectively oxidizing H2S to S within delocalized units spatially separated from the electrode. 0 This solved the problem of direct electrochemical oxidation. However, Fe 3+ / Fe 2+Stability must be maintained in a strongly acidic environment; otherwise, FeS precipitate or Fe(OH)3 colloid is easily formed. Therefore, the selection of a suitable mediator is a key breakthrough in this technology. This invention selects Fe(CN)6. 3- / Fe(CN)6 4- Redox mediators can solve the above-mentioned technical problems.

[0020] Furthermore, sludge and microorganisms in wastewater can easily become mixed with recovered sulfur products, reducing sulfur content. 0 To ensure the purity of the solution, this invention removes sulfides from the solution as H2S by adjusting the pH, and then converts the H2S to S through delocalized electrochemical oxidation. 0 This avoids contact between sulfur products and wastewater, resulting in high-purity sulfur. 0 .

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

[0022] To further enhance SO4 2- The reduction efficiency can be improved by adding functional fillers to enhance the mass transfer effect at the gas-liquid-microorganism interface, thereby increasing the efficiency of hydrogen autotrophic sulfate-reducing bacteria in utilizing H2. The PU@RGO@MnO2 modified filler of this invention is beneficial for enhancing H2 mass transfer and sulfate reduction performance. The modified filler possesses a three-dimensional porous framework, providing a high specific surface area. It can promote the micro-dispersion of large bubbles through shearing action, expanding the gas-liquid-microorganism contact interface area and prolonging the residence time of H2 bubbles at the cathode, thus improving mass transfer efficiency. MnO2 can promote the metabolic activity of microorganisms in anaerobic sludge and also promote the expression of cytochrome C. Cytochrome C plays a crucial role in electron transfer during the utilization of H2 by sulfate-reducing bacteria; the introduction of MnO2 is beneficial for enhancing the electron transfer process in H2 utilization. Therefore, the addition of PU@RGO@MnO2 lays the foundation for constructing a highly efficient sulfate reduction system.

[0023] Preferably, in step 1), the preparation method of the PU@RGO@MnO2 modified filler includes: immersing polyurethane (PU) in a suspension containing graphene oxide (GO) and a reducing agent, heating to allow the graphene oxide to be adsorbed into the polyurethane and reduced to graphene oxide-reduced, thus obtaining PU@RGO; immersing PU@RGO in a MnO2 precursor solution and heating to grow MnO2 nanoparticles in the polyurethane through an in-situ redox reaction between graphene oxide-reduced and MnO2 precursor; and washing and drying the product to obtain PU@RGO@MnO2.

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

[0025] Preferably, in step 1), the hydrogen autotrophic 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 from 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 at 20-40°C.

[0028] Preferably, in step 1), the cathode is controlled to be under oxygen-free conditions, the constant current applied to the electrolytic hydrogen production reactor is 200-400mA, and the hydraulic residence time (HRT) during continuous flow operation 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 was 0.3-0.7 M;

[0031] Preferably, in step 2), the Fe(CN)6 3- / Fe(CN)6 4- The circulation rate is 0.3-0.7 L / h. -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 beneficial effects of the present invention are:

[0034] (1) The method of this invention is based on bioelectrochemistry, and constructs a microbial sulfate reduction coupled with delocalized electrochemical oxidation of sulfides mediated by electrolytic hydrogen production. Sulfate-reducing bacteria use CO2 as a carbon source at the cathode and utilize the H2 generated by electrolysis as an electron donor to reduce SO42-. 2- Restore to HS - Then HS - Gas-phase H2S was used to strip the Fe(CN)6 3- / Fe(CN)6 4- The mediated delocalized electrochemical oxidation unit further produces S with a purity of up to 99.15%. 0 It solves the problem of S in traditional technology.0 The problem is 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 obtained S 0 Separation can be achieved through gravity sedimentation in solution, reducing processing costs.

[0036] (3) The method of this invention solves the problems of excessive oxidation of sulfides and electrode passivation in direct electrochemistry, and achieves 100% H2S to S 0 The conversion process avoids electrode deactivation and improves system stability. The Fe(CN)6 used... 3- / Fe(CN)6 4- It has excellent recycling performance, avoiding the addition of large amounts of chemicals and improving economic and environmental benefits.

[0037] (4) The electrolytic hydrogen production reactor designed by the method of the present invention and the addition of modified packing are conducive to extending the residence time of H2 in the cathode, thereby improving the utilization efficiency of SRB for H2 and realizing efficient sulfate reduction. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the sulfate reduction coupled with sulfide delocalized electrochemical oxidation system in Example 1;

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

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

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

[0042] Figure 5 This is a schematic diagram of the sulfate reduction coupled with direct electrochemical oxidation of sulfides system in Example 2;

[0043] Figure 6 SO4 in System I and System II of Example 2 2- Remove and S 0 Comparison chart of recycling performance;

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

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

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

[0047] Figure 10 These are XRD patterns of sulfur recovered from samples in System I and System II of Example 3;

[0048] Figure 11 This is a graph showing the sedimentation properties and purity of sulfur recovered from samples in System I and System II of Example 3;

[0049] Figure 12 This is a particle size distribution diagram of sulfur recovered from samples in System I and System II of Example 3;

[0050] Figure 13 These are EDS layered images and spectra of sulfur recovered from the sample by System I in Example 3;

[0051] Figure 14 The following are lithium-sulfur battery performance test graphs comparing the sample sulfur recovered from System I in Example 3 with commercial sulfur: (a) charge-discharge specific capacity at different rates and (b, c) charge-discharge curves. Detailed Implementation

[0052] The present invention will be further illustrated below with reference to the embodiments and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

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

[0054] (1) Anaerobic sludge rich in hydrogen autotrophic sulfate-reducing bacteria, with a solids concentration of 14 g / L. -1 The microbial community includes desulfurizing bacteria and acetic acid bacteria, with the following relative abundance: desulfurizing bacteria 33.9%, Firmicutes 34.2%, Campylobacteria 13.1%, Proteobacteria 7.1%, Bacteroidetes 6.1%, Actinobacteria 2.0%, and other miscellaneous bacteria 3.6%. Alternatively, commercially available pure bacterial products can be selected (commonly used industrial hydroautotrophic sulfate-reducing bacteria strains include *Desulfovibrio* and *Desulfobacterium*). Hydroautotrophic sulfate-reducing bacteria, under anaerobic conditions, use H2 as an electron donor and CO2 as a carbon source, and can convert SO42-, an electron acceptor... 2- The solution is reduced to sulfides. Lower pH and higher gas velocities favor the stripping of sulfides from the solution as H₂S. H₂S is stripped to a Fe(CN)₆ content via the internal circulation gas system of the electrolytic hydrogen production reactor. 3-In the delocalized oxidation device, H2S is oxidized to S 0 Unreacted H2 and CO2 are then reintroduced into the cathode to improve gas-liquid mass transfer and gas utilization. Fe(CN)6 3- After being reduced by H2S, Fe(CN)6 is generated. 4- After being pumped into the anode chamber, it is re-oxidized to Fe(CN)6. 3- This enables the cyclic regeneration of the redox mediator and the continuous, efficient oxidation of H2S. The resulting S... 0 Collect the residue and wash it repeatedly with deionized water until the filtrate is clear. Place the residue in a 60℃ oven and dry for 24 hours.

[0055] (2) Simulated wastewater: The solvent is deionized water, and the composition includes: sodium sulfate 1479.2, 2958.4, or 4437.6 mg / L. -1 100 mg / L of ammonium chloride -1 Sodium chloride 50mg / L -1 300 mg / L of disodium hydrogen phosphate dodecahydrate -1 Potassium dihydrogen phosphate 150mg / L -1 1 ml / L of trace element solution -1 The trace element solution includes 400 mg / L ferric chloride hexahydrate. -1 150 mg / L cobalt chloride hexahydrate -1 120 mg / L manganese chloride tetrahydrate -1 Calcium chloride dihydrate 200mg / L -1 Nickel chloride hexahydrate 30mg / L -1 Copper sulfate pentahydrate 20mg / L -1 Magnesium chloride hexahydrate 600 mg / L -1 100mg / L of zinc chloride -1 Boric acid 150mg / L -1 Sodium molybdate dihydrate 40mg / L -1 1000 mg / L of ethylenediaminetetraacetic acid -1 .

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

[0057] (3.1) First, graphite oxide (GO) was prepared using the Hummers method: 2 g of graphite powder (325 mesh) was added to a 250 mL beaker, followed by the addition of 1 g of NaNO3 and 46 mL of H2SO4 under stirring in an ice bath. Then, 6 g of KMnO4 was slowly added to the beaker under stirring, controlling the system temperature to not exceed 20 °C. After 5 min, the ice bath was removed, and the system was heated at 35 °C for 30 min. Next, 92 mL of deionized water was added and stirred for 15 min. Then, 80 mL of 3% H2O2 solution at 60 °C was added to reduce excess KMnO4 until no obvious bubbles were observed and the solution turned yellow. The mixture was centrifuged and washed several times with 10% hydrochloric acid to remove metal ions from the solution. 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 was close to 7. The obtained product was redispersed in deionized water, gently sonicated for 8 h, and the suspension was freeze-dried to obtain GO.

[0058] (3.2) Then dissolve GO in deionized water (3 mg / mL) -1 Add vitamin C (3mg / mL) -1 After ultrasonic treatment for 30 min, a homogeneous suspension was obtained. Polyurethane (PU) was ultrasonically cleaned with deionized water and ethanol and completely dried at 60℃ for 24 h. It was then immersed in the suspension (PU:suspension = 1:1, volume ratio) and heated at 65℃ for 6 h. During this time, GO was adsorbed onto the PU and reduced to RGO by vitamin C, yielding PU@RGO. Finally, PU@RGO was immersed in KMnO4 solution (10 mg / mL). -1 MnO2 nanoparticles were grown on PU via an in-situ redox reaction between RGO and KMnO4 by heating at 80°C for 10 minutes (until the solution changed from purple-red to brown). The resulting PU@RGO@MnO2 was washed with plenty of 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 section in the middle. The tubular cation exchange membrane inside the electrolytic cell divides the reactor into a cathode chamber and an anode chamber. The cathode chamber has a total height of 82cm and a working volume of 2L. It contains a stainless steel mesh cylinder (304L, 9cm×5cm; pore size 4mm; thickness 0.5mm) as the cathode. The extended cathode section has a diameter of 10cm and a height of 52cm, and an inner cylinder with a diameter of 6.6cm and a height of 35cm is added, which is connected to the cathode section inside the electrolytic cell with a diameter of 6.6cm and a height of 30cm. The cathode is designed with a top-to-bottom internal circulation gas path system to realize the recycling of gas and the disturbance of the solution. The anode chamber has a diameter of 11cm and a height of 20cm, with a working volume of 0.6L. It contains an IrO2-plated tubular Ti mesh (8.5cm×9cm) as the anode.

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

[0061] Construction of a sulfate reduction coupled with sulfide delocalized electrochemical oxidation system, such as Figure 1 As shown, this is 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 of PU@RGO@MnO2 was added. The cathode was controlled to be under anaerobic conditions, and the reactor operated in continuous flow mode, using a constant current of 300 mA applied by a DC power supply. A peristaltic pump was used to deliver sludge containing 1000–3000 mg L... -1 SO4 2- Simulated wastewater was introduced from the bottom of the cathode, with an HRT (Heat Retention Time) of 1–2 days and a cathode temperature of 30°C. Samples were periodically taken from the cathode influent and effluent, as well as from the delocalized oxidation unit. SO4 2- In the cathode, it is reduced to H₂S by hydroautotrophic sulfate-reducing bacteria. - By adjusting the CO2 (99.9%) flow rate, the cathode pH was maintained at 6.5, thereby enabling HS... - It is converted to H2S. In the delocalized electrochemical oxidation unit (containing 0.5 L 0.5 M Fe(CN)6) connected to the cathode internal circulation gas path... 3- The delocalized electrochemical oxidation of H2S was carried out in the solution, and the internal circulation gas rate was adjusted to strip H2S from the cathode to Fe(CN)6. 3- In solution, H2S is oxidized to S. 0 At the same time, Fe(CN)6 3- Reduced to Fe(CN)6 4- A peristaltic pump was used to transport Fe(CN)6 3- / Fe(CN)6 4- medium through S 0 The precipitate bottle (0.5L) was transferred to the anode chamber for Fe(CN)6 precipitation.3- Electrochemical regeneration, followed by 0.5 L h -1 The solution is then recycled back to the delocalized electrochemical oxidation unit. The pH of the anolyte solution is maintained at 6.0 using 5M NaOH. The cathode effluent passes sequentially 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 periodically recycled back to the cathode to prevent significant loss of microorganisms.

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

[0063] Phase 1 (Days 1-30), SO4 in the cathode influent 2- The concentration is 1000 mg / L -1 HRT is 1 day, influent SO4 2- The load was 333 mg 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 operating time increases, the SO4 in the cathode effluent... 2- Concentration decreases, S 2- Concentration decreased, however S 0 The concentration increased. This indicates that the sulfate removal performance of the cathode gradually improved, and more and more S... 2- H2S is blown off into the delocalized electrochemical oxidation unit and oxidized to S. 0 During the steady-state phase, SO4 in the cathode effluent... 2- The concentration was 19.6 ± 8.6 mg SO4. 2- -SL -1 SO4 2- The single-removal rate (SRR) was 314.0 ± 9.0 mg SO4. 2- -SL -1 d -1 The removal efficiency was 94.1 ± 2.5%. At this point, the S in the delocalized electrochemical oxidation unit... 0 The concentration was 299.8 ± 9.7 mg S 0 -SL -1 S 0 The spontaneous generation rate (SPR) was 299.8 ± 9.7 mg S. 0 -SL -1 d -1 The recovery efficiency was 90.1 ± 2.1%.

[0064] Phase 2 (days 31-63): Increase SO4 levels in the cathode feed water. 2- The concentration is 2000 mg / L -1 Simultaneously, the HRT was increased to 2 days while maintaining a constant influent load. During the steady-state phase, the system's SRR was 306.7 ± 10.1 mg SO4. 2- -SL -1 d -1 The 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 change was minimal, which is attributed to the presence of SO4 in the influent. 2- The load remains unchanged.

[0065] Phase 3 (days 64-103): Further increase SO4 levels in the cathode feed water. 2- The concentration is 3000 mg / L -1 Keeping the HRT constant, the influent load is increased to 500 mg SO4. 2- -SL -1 d -1 Adjust the CO2 flow rate to 4.10 mL / min. -1 The pH was maintained at 6.5. However, during the first 8 days of this phase, the circulating gas rate was 120 mL / min. -1 At that time, the sulfide concentration in the cathode effluent was 36.3 ± 18.3 mgS. 2- -SL -1 Therefore, on day 9, the circulating gas rate was increased to 160 mL / min. -1 During the stable phase, the sulfide concentration in the cathode effluent decreased to zero. A concentration as high as 464.3 ± 7.1 mg SO4 was achieved. 2- -SL -1 d -1 The SRR and 450.6 ± 8.6 mg 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) were detected in the delocalized electrochemical oxidation unit during operation. 2- SO3 2- S2O3 2- ) and sulfides, further illustrating the conversion of H2S to S0 The conversion rate is close to 100%. This is attributed to the fact that delocalized electrochemical oxidation avoids the direct oxidation of sulfides at the anode, thus preventing the over-oxidation of sulfides into other higher-valence sulfur species. It also avoids secondary pollution from sulfides, confirming the effectiveness of H2S stripping coupled with delocalized electrochemical oxidation in recovering sulfur from high-concentration sulfate wastewater. 0 The effectiveness and feasibility of this.

[0067] Besides SO4 2- Remove and S 0 The coupling performance of the recovery was also analyzed, as well as the coulombic efficiency and H2 utilization efficiency of the electrolytic hydrogen production reactor, such as... Figure 3 As shown, the optimal coulombic efficiency and H2 utilization efficiency were achieved in stage 3, at 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%, outside the explosion limits (4.0–75.6%), thus effectively avoiding safety risks. The optimal hydrogen evolution energy consumption at this stage was approximately 0.018 kWh / day. -1 For every 1kg of S recycled 0 Its energy consumption is approximately 20.1 kWh / kg. -1 S 0 It is about half of phases 1 and 2, such as Figure 4 As shown. This is because, with the increase of sulfate reduction, more and more H2S is oxidized to S. 0 More Fe(CN)6 4- It is anoly oxidized to Fe(CN)6 3- This helps to suppress the oxygen evolution reaction at the anode, thereby reducing energy consumption.

[0068] Example 2: Performance comparison of a direct electrochemical oxidation system for sulfides coupled with sulfate reduction

[0069] Construction of a sulfate reduction coupled with direct electrochemical oxidation of sulfides, such as... Figure 5 As shown, this is denoted as System II. The difference between System I and System II is that SO4... 2- Reduced to HS by hydrogen autotrophic sulfate-reducing bacteria - Contains HS - The cathode effluent passes sequentially through a 0.25L sedimentation bottle and a hollow fiber membrane before being introduced to the bottom of the anode, further purifying the H₂S. - Direct electrochemical oxidation to S 0 Finally, water exits from the top of the anode. Samples of the cathode inlet and outlet water, as well as the anode outlet water, are taken periodically. A micro-regulating valve is used to control the CO2 flow rate at 0.57 mL / min. -1 This resulted in a theoretical H2 / CO2 flow rate of approximately 4:1, and the internal circulation gas rate was adjusted to 40 mL / min using a gas circulation pump. -1Use a pH controller to add 3M HCl or 5M NaOH to control the pH in the cathode and anode to 8.0.

[0070] A comparative analysis of SO4 in System I and System II was conducted in three stages. 2- Remove and S 0 The coupling properties of the recovery, such as Figure 6 As shown. In the influent SO4 2- 1000mg L -1 During the stable phase, the SRR of system I was 314.0 ± 9.0 mg SO4. 2- -SL -1 d -1 (Removal efficiency was 94.1 ± 2.5%), compared to 310.9 ± 6.0 mg SO4 in System II. 2- -SL -1 d -1 Equivalent (92.7 ± 2.7%). However, system I in S 0 It showed significantly better recovery than System II, with a 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 during the direct anodic oxidation of HS- in System II, it is over-oxidized into other high-valence sulfur species such as SO4. 2- S2O3 2- This reduces the SPR.

[0071] When SO4 enters the water 2- Increase to 2000 mg L -1 At that time, system I maintained 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 recovery rate of SO4 in System II was... 2- The removal efficiency decreased to 65.4 ± 2.5% (SRR = 217.4 ± 8.5 mg SO4). 2- -SL -1 d -1 ), S 0 Recovery efficiency decreased 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 sulfides in the catholyte. High concentrations of sulfides inhibit the activity of the SRB, ultimately limiting the S... 0 The generation of.

[0072] Further reduce SO4 in the influent 2- Increase to 3000 mg L -1 It can be seen that the two systems have significant performance differences. System I achieved a high SO4 content of 464.3 ± 7.1 mg. 2- -SL -1 d -1 The SRR and 450.6 ± 8.6 mg 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 was 213.5 ± 11.4 mg SO4. 2- -SL -1 d -1 ) and SPR (146.7±11.1mg S 0 -SL -1 d -1 The change is very small, corresponding to SO4 2- Removal rate and S 0 The recoveries 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, through H2S stripping coupled with delocalized electrochemical oxidation, eliminated the inhibition of SRB activity by high sulfide concentration, avoided excessive oxidation of sulfides, and ensured efficient SO42- removal. 2- Restoration and S 0 The generation of.

[0073] To investigate the electrode passivation phenomenon in both systems, the anode material was characterized by SEM and EDS after operation. Figure 7 As shown. No deposited sulfur particles were observed on the anode surface of System I, and the surface mainly consisted of Ti, O, and Ir elements, while the anode was a Ti mesh plated with IrO2. This indicates that SEM and EDS primarily revealed the elemental information of the IrO2 coating and the titanium mesh, as no sulfur particles were observed. 0 The deposition on the anode surface prevents electrode passivation. In contrast, the anode surface in System II contains a large number of sulfur particles, mainly S, resulting in severe electrode passivation.

[0074] Because System I avoids electrode passivation, it consumes less energy during operation in the same phase, such as... Figure 8 As shown. It is worth noting that in the influent SO4 2-3000mg L -1 At that time, the system I reclaims S 0 The energy consumption is 20.1 kWh / kg. -1 S 0 It is approximately 1 / 5 of System II (97.4 kWh kg) -1 S 0 This significantly reduced electricity costs. Further evaluation of the energy efficiency of the two systems, such as… Figure 9 As shown. Influent SO4 2- For 1000 and 2000 mg L -1 At that time, the energy efficiency of system I was 40.2±2.1% and 39.3±1.7%, respectively, which was higher than that of system II (24.9±1.4% and 17.3±1.4%). This increased the SO4 content of the influent. 2- The concentration is 3000 mg / L -1 The energy efficiency of system I increased to 62.5 ± 1.9%, approximately 3.8 times that of system II (16.5 ± 1.6%). These results indicate that the energy efficiency of system I is significantly higher than that of system II. This is because system I has a higher S... 0 The recovery rate is higher, thus utilizing more electricity in the resource-based treatment of sulfate wastewater. Furthermore, with the reduction of SO4 in the influent... 2- As the concentration increases, the SPR of System II gradually decreases, leading to a gradual reduction in energy efficiency. In contrast, the SPR of System I is highest at 1000 and 2000 mg / L. -1 The time remained basically unchanged at 3000 mg / L -1 The efficiency initially remains constant, then increases significantly, resulting in a substantial improvement in energy efficiency. Overall, system I efficiently recovers S. 0 The mechanism mainly involves relieving the inhibition of SRB by high concentrations of sulfides, avoiding electrode passivation and excessive oxidation, and improving S... 0 Selectivity and energy efficiency, thus achieving high-efficiency SO42- in high-concentration sulfate wastewater. 2- Remove and synchronize S 0 Recycle.

[0075] Example 3: Characteristics and applicability of elemental sulfur recovered from wastewater based on electrochemically coupled biological processes.

[0076] First, the characteristics of elemental sulfur recovered from wastewater based on electrochemically coupled biological processes were evaluated. Phase analysis of sulfur samples obtained from both systems was performed using XRD, such as... Figure 10 As shown. Comparison with the standard spectrum of S8 verifies that the crystal structure and composition of sulfur in both samples conform to S8. 0 For S in solution 0 Settlement performance, S 0 Purity was analyzed, such as Figure 11As shown. After 5 minutes of settling, system I obtained a solution containing S. 0 The solution underwent effective solid-liquid separation via gravity sedimentation, followed by washing with deionized water to obtain S with a purity of up to 99.15%. 0 This indicates that the theoretical pollution level of sulfur by impurities is ≤0.85%. In contrast, System II yielded S... 0 The solution remained turbid and required centrifugation or filtration for separation. Due to the difficulty in completely separating microorganisms and sludge, S recovered from System II... 0 The purity was only 88.4%. This indicates 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 significant differences in sulfur particle morphology and aggregation behavior, such as Figure 12 As shown. S in System I 0 The particles are regularly baseball-shaped, exhibiting significant aggregation behavior, with a particle size of 6.7 ± 2.1 μm. In contrast, System II produces irregularly shaped S particles. 0 The particles are loosely distributed and small in size, with a particle size of 4.8 ± 2.2 μm. In system I, S... 0 The larger particle size of sulfur reduces the specific surface area, thereby lowering the surface energy of each particle. This minimizes electrostatic repulsion between sulfur particles and promotes aggregation through van der Waals forces or electrostatic shielding, resulting in easily sedimentable aggregates. Conversely, the smaller sulfur particles in System II... 0 The particles have a higher specific surface area and surface energy, which in turn promotes S 0 The stability of colloids hinders S based on gravity sedimentation. 0 Separation. Furthermore, the oxidizing conditions in System II may cause sulfur particles to adsorb more charged ions or impurities (such as biological solids), which enhances electrostatic repulsion and improves the stability of the colloidal suspension, further inhibiting S… 0 Settling properties.

[0078] To assess the contamination effect of cyanide on the recovered sulfur, the sulfur recovered by System I was analyzed. 0 EDS characterization was performed, such as Figure 13 As shown. Based on the EDS layered image and spectrum, S... 0 The main element was sulfur (S), and no fe or nitrogen was detected, indicating that the recovered S... 0 After a simple rinse with deionized water, it contains virtually no Fe(CN)6. 3- / Fe(CN)6 4- .

[0079] Finally, through constant current charge-discharge testing, the S recovered by System I was... 0With commercial standard S 0 The electrochemical performance when used as a cathode material was compared. For example... Figure 14 As shown in (a), the two materials exhibit similar specific capacities at rates ranging from 0.2 to 2.0 C. Figure 14 (b) and (c) show that their charge-discharge curves are almost identical at 0.2–0.8 C, thus exhibiting similar polarization voltages. However, at higher rates (1.0–2.0 C), the recovered S... 0 Compared to standard S 0 It has a slightly lower charging voltage. This indicates that the recycled S 0 It exhibits lower electrochemical impedance and better electrochemical performance under high-rate conditions, making it a standard S in lithium-sulfur batteries. 0 It has shown great potential as an alternative.

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

Claims

1. A method for recovering high-purity sulfur from wastewater based on electrochemically coupled biological processes, characterized in that: Includes the following steps: 1) Utilizing hydrogen autotrophic sulfate-reducing bacteria at the cathode of an electrolytic hydrogen production reactor to remove SO42- from wastewater. 2- Restore to HS - The electrolytic hydrogen production reactor uses a tubular cation exchange membrane to separate the cathode and anode. The cathode is located in the middle of the electrolysis hydrogen production reactor, and the anode is arranged around the cathode; 2) By introducing CO2 as a carbon source and adjusting the pH of the cathode and the internal circulation gas rate, the H₂S in the cathode solution is reduced. - Stripped in the form of H2S to a solution containing 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- The solution is introduced into the anode and oxidized back to Fe(CN)6. 3- .

2. The method as described in claim 1, characterized in that: In step 1), the cathode is filled with PU@RGO@MnO2 modified filler, which includes polyurethane as a carrier, and redox graphene and MnO2 nanoparticles loaded in polyurethane.

3. The method as described in claim 2, characterized in that: In step 1), the preparation method of the PU@RGO@MnO2 modified filler includes: immersing polyurethane in a suspension containing graphene oxide and a reducing agent, heating it to allow the graphene oxide to be adsorbed into the polyurethane and reduced to graphene oxide, thus obtaining PU@RGO; immersing PU@RGO in a MnO2 precursor solution and heating it to grow MnO2 nanoparticles in the polyurethane through an in-situ redox reaction between graphene oxide and the MnO2 precursor; washing and drying the product to obtain PU@RGO@MnO2.

4. The method as described in claim 2 or 3, characterized in that: In step 1), the PU@RGO@MnO2 modified filler accounts for 10-20% of the cathode volume.

5. The method as described in claim 1, characterized in that: In step 1), the hydrogen autotrophic sulfate-reducing bacteria are inoculated into the cathode in the form of anaerobic sludge as a carrier.

6. The method as described in claim 1, characterized in that: In step 1), the temperature of the cathode is controlled at 20-40℃.

7. The method as described in claim 1, characterized in that: In step 1), the cathode is controlled to be under oxygen-free conditions, the constant current applied to the electrolysis hydrogen production reactor is 200-400 mA, and the hydraulic residence time during continuous flow operation is 1-2 days.

8. The method as described in claim 1, characterized in that: In step 2), The CO2 flow rate 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.

9. The method as described in claim 1 or 8, characterized in that: In step 2), The Fe(CN)6 3- The initial concentration was 0.3-0.7 M; The Fe(CN)6 3- / Fe(CN)6 4- The circulation rate is 0.3-0.7 L / h. -1 ; The pH of the anode is controlled between 5.5 and 6.5.

Images