Bioelectrochemical-assisted sulfur conversion to promote sulfur-based denitrification and sulfate discharge reduction method

Abstract

The application discloses a biological electrochemical auxiliary sulfur conversion promoting sulfur-based denitrification and sulfate emission reduction method and belongs to the field of water treatment. ‑ Nitrogen-containing wastewater enters an elemental sulfur denitrification system, and NO3 0 is reduced to N2 by sulfur autotrophic denitrifying bacteria, and elemental sulfur (S 2‑ ) is converted into SO4 2‑ . Effluent enters a cathode chamber of an electrochemical auxiliary sulfate reduction system, and hydrogen autotrophic sulfate reducing bacteria utilize cathode hydrogen production to reduce SO4 ‑ to HS 2‑ , and meanwhile, alkalinity produced by cathode hydrogen production neutralizes acidity produced in the denitrification process in the elemental sulfur denitrification system. ‑ HS 2‑ / supernatant is returned to the elemental sulfur denitrification system to react with S 0 to generate polysulfide (S n 2‑ ), S n 2‑ , which is used as an efficient electron donor to participate in denitrification, thereby significantly improving denitrification efficiency. The application does not need to add an organic carbon source, sludge production is small, high-concentration nitrogen-containing wastewater is efficiently treated, and the content of sulfate in effluent is simultaneously reduced, thereby realizing sulfur resource recycling, and the application is an economic and environment-friendly autotrophic denitrification method.

Description

Technical Field

[0001] This invention relates to a bioelectrochemical-assisted sulfur conversion method to promote sulfur-based denitrification and sulfate emission reduction, belonging to the fields of environmental technology and water treatment. Background Technology

[0002] Nitrate pollution in aquatic ecosystems primarily originates from agricultural runoff and industrial wastewater, posing a serious threat to global water security. Traditional heterotrophic denitrification processes heavily rely on the supplementation of organic carbon (such as methanol or acetate), which inevitably increases operating costs and the risk of secondary effluent pollution. As a promising alternative, sulfur-based autotrophic denitrification (SAD) utilizes elemental sulfur (S)... 0 Using sulfur as an electron donor to drive nitrate reduction offers advantages such as minimized sludge production and greenhouse gas emissions, no organic carbon requirement, and low operating costs. Despite the significant potential of the SAD process, its practical application in wastewater treatment plants still faces several challenges. First, elemental sulfur has extremely low solubility in water (5 μg / L at 25 °C), resulting in poor bioavailability and consequently low nitrate removal efficiency and rate. Furthermore, two other fundamental limitations of the SAD process are: 1) the generation of excessive H₂ during denitrification. + 1) It is necessary to continuously add alkali to maintain pH stability; 2) and the accumulation of sulfate as a terminal byproduct may violate emission standards and further promote pipeline corrosion.

[0003] To overcome the low nitrate removal rate in the SAD process, the bioavailability of elemental sulfur must be significantly improved. Under neutral or alkaline conditions, sulfur reacts with sulfides (HS-H2O). - / S 2- Abiotic interactions between these elements can produce polysulfides (S... n 2- These soluble compounds are relative to insoluble elemental sulfur (S). 0 Polysulfides exhibit higher bioavailability and act as extracellular electron mediators, thereby promoting sulfur utilization by autotrophic denitrifying bacteria. It has been reported that polysulfides (S...) n 2- The use of ) can significantly improve the denitrification effect of the SAD process, but sulfides (HS) - / S 2- The source and potential risks of sulfate (SAD) remain a concern. To prevent over-acidification, limestone is typically used to buffer the pH of SAD systems. The addition of limestone inevitably leads to an increase in effluent hardness, thus gradually reducing the effective working volume of the reactor through accumulation. However, given that WHO guidelines recommend a maximum sulfate concentration of 250 mg / L in drinking water, and based on 1 mg NO3... - -N reduction produces 7.54 mg of SO4.2- The stoichiometric relationship of NO3 in wastewater - The -N concentration must be limited to ≤33.2 mg / L, which significantly restricts the applicability and scope of the SAD process.

[0004] Overcoming these limitations is crucial for the widespread application of SAD processes. Various technologies have been developed for the remediation of sulfate-contaminated water, including traditional physicochemical methods such as ion exchange, membrane filtration, and chemical precipitation. These technologies can address sulfate accumulation in SAD processes, but typically require significant chemical reagents and energy inputs. In contrast, biological methods exhibit significant advantages, such as lower energy consumption, reduced sludge production, and the potential for recovering valuable elements. Sulfate-reducing bacteria (SRB) are used to reduce sulfate to sulfides (HS-) under anaerobic conditions. - / S 2- This process has been extensively studied. It can effectively alleviate sulfate accumulation in SAD effluent while simultaneously providing sulfides (HS). - / S 2- ) to support polysulfides (S n 2- The formation of SRB-mediated sulfate reduction (SRB) can be categorized into heterotrophic and autotrophic processes based on their metabolic pathways. Traditional heterotrophic SRB processes require organic substrates as both carbon and electron donors, increasing operating costs and posing potential secondary pollution risks. Bioelectrochemical autotrophic SRB processes offer an alternative electron supply pathway to organic substrate supplementation. In this process, SRB colonize the cathode surface to form a biocathode and catalyze sulfate reduction through two electron transfer pathways: direct cathode electron absorption or electron transfer mediated by electrochemically generated H2. Subsequently, the enrichment of hydrogen-trophic sulfate-reducing bacteria (SRB) on the biocathode efficiently generates sulfides (HS-). - / S 2- Crucially, this method utilizes proton (H⁺) reduction for in-situ hydrogen production, simultaneously achieving three key objectives: (i) consuming excess protons (H⁺) to buffer the solution pH; (ii) providing high-purity hydrogen as an electron donor to drive the in-situ reduction of sulfate to produce sulfides (HS-H⁺). - / S 2- (iii) The formation of sulfides (HS) - / S 2- ) and elemental sulfur (S) 0 ) combine to form polysulfides (S n 2- ), with S n 2- To carry out the denitrification reaction, it can solve the problem of the solubility of elemental sulfur and improve the denitrification efficiency. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art. This invention couples an elemental sulfur autotrophic denitrification system and an electrochemically assisted sulfate reduction system, and proposes a bioelectrochemically assisted sulfur conversion method to promote sulfur-based denitrification and sulfate emission reduction, thereby enhancing the treatment of nitrate wastewater by the elemental sulfur autotrophic denitrification process and reducing the sulfate content of the effluent at the same time.

[0006] According to a first aspect of the present invention, the present invention first provides a bioelectrochemical assisted sulfur conversion device for promoting sulfur-based denitrification and sulfate emission reduction, which includes an elemental sulfur self-oxygenation denitrification system, an electrochemical assisted sulfate reduction system, and a power source;

[0007] The elemental sulfur autoaerobic denitrification system is enriched with sulfur autotrophic denitrifying bacteria and filled with elemental sulfur (S). 0 The elemental sulfur autotrophic denitrification system is used to receive nitrate wastewater to be treated, and uses sulfur autotrophic denitrifying bacteria to remove NO3 from the nitrate wastewater. - Reduced to N2, and sulfides (HS-H2O) refluxed from the cathode chamber of the electrochemically assisted sulfate reduction system as elemental sulfur and / or electrochemically assisted sulfate reduction system. - / S 2- ) and / or elemental sulfur with HS - / S 2- The polysulfides formed (S n 2- (The electron source is used to convert it into SO4) 2- ;

[0008] The electrochemically assisted sulfate reduction system has a columnar nested structure, with an inner cathode chamber and an outer anode chamber, separated by a cation exchange membrane. The cathode chamber and anode chamber are connected to the negative and positive terminals of the power supply, respectively. Hydrogen autotrophic sulfate-reducing bacteria are enriched in the cathode chamber.

[0009] The elemental sulfur autogenous denitrification system has at least two outlets; one of these outlets is connected to the inlet of the cathode chamber of the electrochemically assisted sulfate reduction system, where hydrogen autotrophic sulfate-reducing bacteria reduce SO42-. 2- Reduced to sulfide (HS) - / S 2- And it produces hydroxide ions (OH-) through a hydrogen production reaction. - The outlet of the cathode chamber of the electrochemically assisted sulfate reduction system is connected to the reflux inlet of the elemental sulfur denitrification system, and the refluxed sulfides (HS-H2O) are then refluxed. - / S 2- ) and elemental sulfur (S) 0 ) forms polysulfides (S n 2-Hydroxide (OH-) can be used for denitrification or directly as an electron donor in denitrification. - It neutralizes the protons (H⁺) generated during the denitrification process in the elemental sulfur autotrophic denitrification system, maintaining the system pH.

[0010] Furthermore, the elemental sulfur particles inside the elemental sulfur auto-oxygenation denitrification system range from 6 to 12 mm in size, gradually decreasing in size as they accumulate from bottom to top. The elemental sulfur auto-oxygenation denitrification system has a columnar structure, with the wastewater inlet and return inlet located at the bottom or bottom; the outlet is located at the top or top, with at least one outlet for discharging treated wastewater; the elemental sulfur auto-oxygenation denitrification system is equipped with multiple sampling ports at different heights.

[0011] Furthermore, the cathode in the cathode chamber is made of titanium sheet rolled into a tubular structure, and the cathode is connected to the negative terminal of the power supply via titanium sheet, while the anode in the anode chamber is made of DSA electrode.

[0012] Furthermore, the elemental sulfur self-oxygenation denitrification system and the cathode chamber are both under anoxic conditions, with dissolved oxygen (DO) < 0.5 mg / L; the anode chamber is under aerobic conditions, with dissolved oxygen (DO) > 0.5 mg / L.

[0013] Furthermore, an electrochemical oxygen production reaction occurs in the anode chamber, the oxygen produced by the reaction is discharged, and the electrons produced by the reaction flow to the cathode chamber through the external circuit. The protons (H⁺) produced migrate to the cathode chamber through the cation exchange membrane under the action of the electric field, providing a proton source for the cathode hydrogen production reaction.

[0014] According to a second aspect of the present invention, the present invention provides a method for promoting sulfur-based denitrification and sulfate emission reduction through bioelectrochemical-assisted sulfur conversion, comprising:

[0015] Nitrate-laden wastewater enters through the bottom of an elemental sulfur autotrophic denitrification system, where sulfur autotrophic denitrifying bacteria remove NO3 from the wastewater. - Reduced to N2, while simultaneously reacting with elemental sulfur (S) 0 ) and / or sulfides (HS-) recirculated from the cathode chamber of an electrochemically assisted sulfate reduction system - / S 2- ) and / or HS - / S 2- With S 0 The S produced by the reaction n 2- It is derived from electrons and converted into SO4. 2- ;

[0016] The effluent from the elemental sulfur autogenous denitrification system is partially discharged through the first outlet, while the remainder enters the cathode chamber of the electrochemically assisted sulfate reduction system through the second outlet. In the cathode chamber, hydrogen autotrophic sulfate-reducing bacteria carry out the sulfate reduction reaction, converting SO42- into sulfur dioxide.2- Restore to HS - / S 2- In addition, hydroxide ions (OH-) are generated in the cathode chamber along with the hydrogen production reaction. - );

[0017] The effluent from the cathode chamber then flows through the reflux inlet to the elemental sulfur autogenous denitrification system; HS - / S 2- With elemental sulfur (S) 0 ) forms polysulfides (S n 2- Hydroxide (OH-) can be used for denitrification or directly as an electron donor in denitrification. - This effectively neutralizes the large number of protons (H+) generated during the denitrification process in an elemental sulfur autotrophic denitrification system. + ), to maintain the system pH.

[0018] Furthermore, the volumetric flow rate ratio between the first outlet and the second outlet is 1:0.5 to 1:5.

[0019] Furthermore, the temperatures of the elemental sulfur autotrophic denitrification system, the cathode chamber, and the anode chamber are all controlled at 25 ± 5 °C, and the hydraulic retention time is 12~72h.

[0020] Furthermore, the power supply outputs a constant current to provide electrical assistance to the electrochemically assisted sulfate reduction system.

[0021] Furthermore, the constant current is 50 mA ~ 300 mA.

[0022] Furthermore, the present invention is applicable to the treatment of NO3. - Nitrogen wastewater with a concentration ≤600 mg / L, preferably containing NO3-. - The concentration is 50~600 mg / L.

[0023] This invention employs an electrochemically assisted sulfate reduction system coupled with an elemental sulfur denitrification system. In the sulfur autotrophic denitrification system, the main reaction is sulfur autotrophic denitrification (equation (1)). Elemental sulfur has extremely low solubility in water (5 μg L⁻¹ at 25 °C), severely affecting the nitrogen removal efficiency. Furthermore, it can be seen from reaction equation (1) that the effluent mainly contains SO₄²⁻. 2- and H +This can easily lead to two key problems: 1) excessive H+ is generated during denitrification, requiring continuous addition of alkali to maintain pH stability; 2) the accumulation of sulfate as a terminal byproduct, which may violate emission standards and further promote pipeline corrosion. This invention addresses this by diverting a portion of the effluent to a hydrogen autotrophic sulfate reduction system, where hydrogen production and sulfate reduction reactions mainly occur (equations (2) and (3)). The effluent from the hydrogen autotrophic sulfate reduction system is mainly HS-H+. - / S 2- and OH - This portion of the effluent is then returned to the sulfur autotrophic denitrification system, HS - It reacts with elemental sulfur to form polysulfides (S) n 2- (Equation (4)), and then denitrification reaction is carried out by replacing elemental sulfur with polysulfides (Equation (5)). Refluxed OH - Used to neutralize H2 produced during the denitrification process + .

[0024] (1)

[0025] (2)

[0026] (3)

[0027] (4)

[0028] (5)

[0029] Based on the above coupling, the following key performance improvements are expected to be achieved:

[0030] (i) By replacing equation (1) with equations (4) and (5) as the main denitrification reaction, the efficiency of elemental sulfur utilization is greatly improved by using polysulfides as an intermediate product as a "bridge", while improving the system denitrification efficiency and denitrification rate.

[0031] (ii) Using equation (3) to process part of the nitrogen produced during the denitrification process With HS - / S 2- The form of recirculation reduces the amount of wastewater in the final system drainage. content;

[0032] (iii) Reflux OH through equation (2) - Neutralize the H produced during the denitrification process + Reduce the amount of added alkalinity. Attached Figure Description

[0033] Figure 1 A schematic diagram of a device for treating nitrate wastewater using a bioelectrochemical-assisted sulfur conversion process to promote sulfur-based denitrification and reduce sulfate emissions;

[0034] Figure 2 The results of the domestication of sulfur autotrophic denitrifying bacteria in Example 1;

[0035] Figure 3 The results of domestication of hydrogen autotrophic sulfate-reducing bacteria in Example 1;

[0036] Figure 4 The results are from the microbial community analysis.

[0037] Figure 5 The graph shows the changes in nitrate nitrogen and sulfur production when using an autotrophic denitrification system of elemental sulfur to treat wastewater with different concentrations of nitrate nitrogen.

[0038] Figure 6 The graph shows the pH changes of influent and effluent when using an autotrophic denitrification system of elemental sulfur to treat wastewater with different concentrations of nitrate nitrogen.

[0039] Figure 7 Figure 1. Changes in nitrate nitrogen and sulfur production in an electrochemically assisted sulfate reduction coupled with elemental sulfur autotrophic denitrification system when treating wastewater with different concentrations of nitrate nitrogen.

[0040] Figure 8 Figure 1. pH variation of influent and effluent in an electrochemically assisted sulfate reduction coupled with elemental sulfur autotrophic denitrification system when treating wastewater with different concentrations of nitrate nitrogen.

[0041] Figure 9 The graph shows the changes in nitrate nitrogen when using an autotrophic denitrification system of elemental sulfur to continuously treat wastewater with different concentrations of nitrate nitrogen in batch processing.

[0042] Figure 10 The graph shows the variation of nitrite nitrogen when using an autotrophic denitrification system of elemental sulfur to treat wastewater with different concentrations of nitrate nitrogen in a batch process.

[0043] Figure 11 The graph shows the changes in sulfide content when using an autotrophic denitrification system of elemental sulfur to continuously treat wastewater with different concentrations of nitrate nitrogen in batch processing.

[0044] Figure 12 The graph shows the change in nitrate nitrogen in a batch treatment system of elemental sulfur autotrophic denitrification with added sulfides when treating wastewater with different concentrations of nitrate nitrogen.

[0045] Figure 13 This is a graph showing the changes in sulfide content during batch treatment of wastewater with different concentrations of nitrate nitrogen in an elemental sulfur autotrophic denitrification system with added sulfides.

[0046] Figure 14 This is a graph showing the changes in polysulfides in an elemental sulfur autotrophic denitrification system when treating wastewater with different concentrations of nitrate nitrogen in a batch process with added sulfides. Detailed Implementation

[0047] To better understand the present invention, further explanation is provided below with reference to the accompanying drawings and specific embodiments.

[0048] Reference Figure 1 This is a schematic diagram of a bioelectrochemical-assisted sulfur conversion device to promote sulfur-based denitrification and sulfate emission reduction. The device illustrated in this embodiment operates in a continuous flow manner. The device includes: an elemental sulfur self-oxygenation denitrification system, an electrochemically assisted sulfate reduction system, and a power source.

[0049] The electrochemically assisted sulfate reduction system has a columnar nested structure, with an inner cathode chamber and an outer anode chamber, separated by a cation exchange membrane. The cathode and anode chambers are connected to the negative and positive terminals of a power source, respectively. The cathode chamber is enriched with hydrogen autotrophic sulfate-reducing bacteria. In one specific embodiment, the cathode in the cathode chamber is formed into a tubular structure using titanium sheets, with the cathode connected to the negative terminal of the power source. The anode in the anode chamber is a DSA electrode. Both the cathode and anode chambers are also equipped with gas outlets.

[0050] The elemental sulfur autoaerobic denitrification system is enriched with sulfur autotrophic denitrifying bacteria and filled with elemental sulfur. This system receives nitrate-laden wastewater and uses sulfur autotrophic denitrifying bacteria to remove NO3- from the wastewater. - Reduced to N2, and HS is refluxed from the cathode chamber of the sulfate reduction system as elemental sulfur and / or electrochemically assisted sulfate reduction system. - / S 2- and / or elemental sulfur with HS - / S 2- The formed S n 2- It is derived from electrons and converted into SO4. 2- .

[0051] In one specific embodiment of the present invention, the elemental sulfur self-oxidative denitrification system and the cathode chamber are both under anoxic conditions, with dissolved oxygen (DO) < 0.5 mg / L; the anode chamber is under aerobic conditions, with dissolved oxygen (DO) > 0.5 mg / L.

[0052] like Figure 1As shown, the elemental sulfur denitrification system has a columnar structure, filled with elemental sulfur particles of 6-12 mm in diameter, with the particle size gradually decreasing from bottom to top. In this embodiment, three sampling ports (P1 / P2 / P3) are provided at different locations on its sidewall for easy sampling and analysis. It should be noted that the sampling ports are not strictly necessary. The upper sidewall of the elemental sulfur denitrification system has at least two outlets, with outlet E2 connected to the inlet of the cathode chamber of the electrochemically assisted sulfate reduction system; outlet E1 is used for discharging treated wastewater. A nitrogen outlet is located at the top of the elemental sulfur denitrification system, and a nitrate / nitrogen wastewater inlet and a return inlet are located on the lower sidewall or bottom. The outlet of the cathode chamber of the electrochemically assisted sulfate reduction system is connected to the return inlet of the elemental sulfur denitrification system.

[0053] The cathode chamber of the electrochemically assisted sulfate reduction system receives wastewater from outlet E2, and hydrogen autotrophic sulfate-reducing bacteria remove SO4 from the wastewater. 2- It is reduced to sulfide and produces hydroxide ions (OH-) through a hydrogen production reaction. - An electrochemical oxygen production reaction occurs in the anode chamber, producing oxygen which is then released. Electrons generated flow through the external circuit to the cathode chamber, where protons (H⁺) migrate through the cation exchange membrane under the influence of the electric field, providing a proton source for the cathode hydrogen production reaction. Sulfides flowing back from the cathode chamber to the elemental sulfur self-oxygenation denitrification system react with elemental sulfur to form polysulfides for denitrification, or directly act as electron donors for denitrification, producing hydroxide ions (OH⁻). - It neutralizes the protons (H⁺) generated during the denitrification process in the elemental sulfur autotrophic denitrification system, maintaining the system pH.

[0054] The process for treating nitrate wastewater according to this invention is as follows: Nitrate wastewater (50 mg / L ≤ NO3) - (Concentration ≤ 600 mg / L) enters through the bottom of the elemental sulfur autotrophic denitrification system. Under completely mixed conditions, sulfur autotrophic denitrifying bacteria remove NO3 from the wastewater. - Reduced to N2 (exhausted from the top vent) and HS returned to the cathode chamber of the elemental sulfur and / or electrochemically assisted sulfate reduction system. - / S 2- and / or elemental sulfur with HS - / S 2- The formed S n 2- It is derived from electrons and converted into SO4. 2- ;

[0055] The effluent from the elemental sulfur denitrification system is discharged through the first outlet E1, while the remainder enters the cathode chamber of the electrochemically assisted sulfate reduction system through the second outlet E2. To prevent interference between ion migration in the cathode and anode chambers, a cation exchange membrane is used to separate the anode and cathode chambers. In the cathode chamber, hydrogen autotrophic sulfate-reducing bacteria carry out the sulfate reduction reaction, converting SO42- into sulfur dioxide. 2- Restore to HS - / S 2- Then, the effluent from the cathode chamber flows to the return inlet of the elemental sulfur autotrophic denitrification system; HS - / S 2- After entering the autotrophic elemental sulfur denitrification system, it can form polysulfides with elemental sulfur for denitrification, or it can directly act as an electron donor for denitrification. An electrochemical oxygen production reaction occurs in the anode chamber, releasing the produced oxygen. Electrons generated flow through the external circuit to the cathode chamber, while protons (H⁺) migrate through the cation exchange membrane to the cathode chamber under the influence of the electric field, providing a proton source for the cathode hydrogen production reaction. Furthermore, a large amount of hydroxide ions (OH⁻) are generated in the cathode chamber along with the hydrogen production reaction. - This system effectively neutralizes the large number of protons (H⁺) generated during the denitrification process in the elemental sulfur autotrophic denitrification system, maintaining the system pH. The effluent E1 from the elemental sulfur autotrophic denitrification system is directly discharged. The E2 return flow rate and E1 discharge rate can be adjusted according to actual water quality conditions, with a volumetric flow rate ratio of 1:0.5 to 1:5. The temperatures of the elemental sulfur autotrophic denitrification system, cathode chamber, and anode chamber are all controlled at 25 ± 5 °C, and the hydraulic retention time is 12–72 h. The power supply output constant current, ranging from 50 mA to 300 mA, provides electrical assistance to the electrochemically assisted sulfate reduction system.

[0056] Example 1

[0057] Enrichment culture of sulfur-autotrophic denitrifying bacteria and hydrogen-autotrophic sulfate-reducing bacteria

[0058] Sulfur-containing autotrophic denitrifying bacteria activated sludge was used as an inoculum for acclimatization and enrichment culture. The activated sludge concentration (MLSS) was 24.5 g / L, and the simulated wastewater treatment target was NO3. - The -N concentration was 50 mg / L, the sulfur packing density was 1 kg / L, and the elemental sulfur particle size ranged from 6 to 12 mm. The initial pH was ~8.2. The hydraulic retention time was controlled at 24 h, and the system operating temperature was controlled at 25 ± 5 °C. NO3 in the effluent was measured daily. - -N and SO4 2- -S changes, NO3 - -N steadily decreases, SO4 2-When the concentrations of sulfur-autotrophic denitrifying bacteria steadily increase and both concentrations tend to stabilize, the acclimatization and enrichment of these bacteria is considered successful. The acclimatization results are as follows: Figure 2 As shown, during the more than 20-day acclimatization process, the effluent NO3... - -N and NO2 - The -N concentration gradually stabilized at around 0, SO42- 2- -S concentration remained stable at around 100 mg / L.

[0059] Activated sludge containing sulfate-reducing bacteria was used as an inoculum for acclimatization and enrichment culture. The activated sludge concentration (MLSS) was 14 g / L, and the simulated wastewater treatment target was SO4. 2- The -S concentration was 333 mg / L, and the operating current was controlled at 150 mA. The initial pH was ~7.0. The hydraulic retention time was controlled at 24 h, and the system operating temperature was controlled at 25 ± 5 °C. SO4 levels in the effluent were measured daily. 2- -S and HS - -S and S2O3 2- -S changes, SO4 2- -S steadily decreases, HS - -S and S2O3 2- When the concentrations of -S steadily increase and all three (sulfate, sulfate-reducing bacteria, and thiosulfate) tend to stabilize, the domestication and enrichment of hydrogen autotrophic sulfate-reducing bacteria is considered successful. Domestication results are as follows: Figure 3 As shown, during the more than 40 days of acclimatization, cultivation, and enrichment process, the effluent HS... - -S gradually stabilized at around 100 mg / L, SO4 2- -S remains stable at around 200 mg / L, S2O3 2- -S remains stable at around 100 mg / L.

[0060] To further clarify the enrichment and culture status of sulfur autotrophic denitrifying bacteria and hydrogen autotrophic sulfate-reducing bacteria, we collected activated sludge samples after the system stabilized for microbial community detection and analysis. Samples were taken before and after coupling. The sulfur-based denitrifying bacteria samples were named SAD1 and SAD2 before and after coupling, respectively, and the hydrogen autotrophic sulfate-reducing bacteria samples were named ASRB1 and ASRB2 before and after coupling, respectively. The results of the microbial community analysis are as follows: Figure 4 As shown, Thiobacillus and Ignavibacterium were identified as the main sulfur autotrophic denitrifying bacteria, accounting for 44.9% and 15.7% respectively in SAD1, and 10.7% and 61.6% respectively in SAD2; Desulfomicrobium was identified as the main hydrogen autotrophic sulfate-reducing bacteria, accounting for 6.2% in ASRB1 and 12.8% in ASRB2.

[0061] Example 2

[0062] Application Cases of Sulfur Autotrophic Denitrification Systems

[0063] Wastewater treatment target is NO3 - The -N concentrations were 50 mg / L, 60 mg / L, 70 mg / L, and 80 mg / L, respectively; the sulfur packing density was 1 kg / L; and the particle size range of elemental sulfur was 6–12 mm. The initial pH was ~8.2.

[0064] Wastewater was treated using only an elemental sulfur autotrophic denitrification system (sulfur autotrophic denitrifying bacteria were enriched according to the method in Example 1; subsequent examples all used systems and devices that had been enriched with the corresponding bacteria, and will not be described again). The hydraulic retention time was controlled at 24 h, and the system operating temperature was controlled at 25 ± 5 °C.

[0065] Treatment results of wastewater with different concentrations, as follows: Figure 5 and Figure 6 As shown, with the influent NO3 - As the NO3- concentration increases, the sulfate concentration in the effluent also increases. - When the NO3- concentration reaches 80 mg / L, nitrite begins to accumulate, denitrification efficiency decreases significantly, and sulfate levels in the effluent also decrease. This indicates that the sulfur autotrophic denitrification system struggles to operate at high NO3- concentrations. - The denitrification effect was better under -N conditions. The pH of the influent was significantly higher than that of the effluent, which indicates that the denitrification process of the sulfur autotrophic denitrification system is indeed an acid-producing process, and long-term operation requires the addition of alkali solution to maintain pH stability.

[0066] Example 3

[0067] Application Case of Electric-Assisted Sulfate Reduction Coupled with Sulfate Autotrophic Denitrification System

[0068] Wastewater treatment target is NO3 - The -N concentrations were 50 mg / L, 60 mg / L, 70 mg / L, and 80 mg / L, respectively, and the sulfur packing density was 1 kg / L. The initial pH was ~8.2.

[0069] Wastewater was treated using the bioelectrochemical-assisted sulfur conversion device provided by this invention to promote sulfur-based denitrification and reduce sulfate emissions (sulfur autotrophic denitrifying bacteria and hydrogen autotrophic sulfate-reducing bacteria were enriched according to the method in Example 1).

[0070] The hydraulic retention time of the elemental sulfur autotrophic denitrification system, cathode chamber, and anode chamber was controlled at 24 h, and the operating temperature was controlled at 25 ± 5 °C. The power supply output constant current provided electrical assistance to the electrochemically assisted sulfate reduction system, and the constant current was controlled at 100 mA.

[0071] The results are as follows Figure 7 and Figure 8 As shown, with the influent NO3 - As the NO3- concentration increased, the effluent sulfate concentration also increased, but the overall effluent sulfate concentration remained lower than that of a standalone sulfur autotrophic denitrification system under the same conditions. Furthermore, no nitrite accumulation was observed, indicating that the coupled system can effectively handle high NO3- concentrations. - The denitrification effect was better under -N conditions, and the improvement was obvious. The overall pH fluctuation of the influent and effluent was also smaller than that of a standalone sulfur autotrophic denitrification system, and the pH drop was also significantly smaller, indicating that the pH regulation effect was obvious.

[0072] Example 4

[0073] Case Study of Batch Processing of Sulfur Autotrophic Denitrification System

[0074] Wastewater treatment target is NO3 - -N concentrations were 50 mg / L, 60 mg / L, 70 mg / L, and 80 mg / L, respectively, and the sulfur packing density was 1 kg / L. The initial pH was ~8.0-8.5.

[0075] The sampling time for subsequent batches is controlled within 36 hours, and the system operating temperature is controlled at 25 ± 5 °C.

[0076] The results are as follows Figures 9 to 11 As shown, besides the NO3 in the influent - When -N is 50 mg / L, NO3 in the effluent during the follow-up batch cycle - -N is almost zero, with the inflow of NO3 - The concentration of -N continuously increases, leading to increased NO3 in the effluent. - -N also continues to rise. And NO3 is emitted from the water. - -N concentrations generally stopped decreasing after 12 hours. Meanwhile, significant NO2 was detected. - -N accumulation peaked at 8 hours, then gradually decreased, and no polysulfides (S) were detected throughout the process. n 2- The presence of ) indicates that the electron transfer of elemental sulfur is too low, resulting in low denitrification efficiency.

[0077] Example 5

[0078] Case Study of Batch Processing of Sulfur Autotrophic Denitrification System

[0079] Wastewater treatment target is NO3 - -N concentrations were 50 mg / L, 60 mg / L, 70 mg / L, and 80 mg / L, respectively; sulfur filler density was 1 kg / L; and the added Na₂S·9H₂O concentration was 60 mg S / L (the added sulfide was used to verify the sulfide (HS)). - / S 2- ) and elemental sulfur (S)0 The reaction produces polysulfides (S) n 2- (This is an enhanced denitrification process). The initial pH is ~8.0-8.5.

[0080] The sampling time for subsequent batches is controlled within 36 hours, and the system operating temperature is controlled at 25 ± 5 °C.

[0081] The results are as follows Figures 12 to 14 As shown, all influent NO3 - At -N concentration, NO3 in the effluent - -N concentration decreased to almost zero within 2 hours. The simultaneous reaction of sulfides decreased to almost zero within 1 hour, and polysulfides (S...) were detected within 2 hours of the reaction. n 2- The rise followed by a fall indicates that elemental sulfur is converted into polysulfides (S). n 2- This greatly improves electron transfer efficiency, resulting in a significant increase in both denitrification efficiency and rate.

[0082] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A bioelectrochemical-assisted sulfur conversion device to promote sulfur-based denitrification and sulfate emission reduction, characterized in that: This includes an elemental sulfur self-oxidation denitrification system, an electrochemically assisted sulfate reduction system, and a power source; The elemental sulfur auto-oxidative denitrification system is enriched with sulfur autotrophic denitrifying bacteria and filled with elemental sulfur. This system receives nitrate-nitrogen wastewater and uses the sulfur autotrophic denitrifying bacteria to remove NO3- from the wastewater. - Reduced to N2, and HS is refluxed from the cathode chamber of the sulfate reduction system as elemental sulfur and / or electrochemically assisted sulfate reduction system. - / S 2- and / or elemental sulfur with HS - / S 2- The formed S n 2- It is derived from electrons and converted into SO4. 2- ; The electrochemically assisted sulfate reduction system has a columnar nested structure, with an inner cathode chamber and an outer anode chamber, separated by a cation exchange membrane. The cathode chamber and anode chamber are connected to the negative and positive terminals of the power supply, respectively. Hydrogen autotrophic sulfate-reducing bacteria are enriched in the cathode chamber. The elemental sulfur autogenous denitrification system has at least two outlets; one of these outlets is connected to the inlet of the cathode chamber of the electrochemically assisted sulfate reduction system, where hydrogen autotrophic sulfate-reducing bacteria reduce SO42-. 2- Restore to HS - / S 2- It generates hydroxide ions through a hydrogen production reaction; the outlet of the cathode chamber of the electrochemically assisted sulfate reduction system is connected to the reflux inlet of the elemental sulfur denitrification system, and the refluxed HS... - / S 2- Forms S with elemental sulfur n 2- Hydroxide ions can be used to neutralize protons generated during the denitrification process in an autotrophic denitrification system of elemental sulfur, either by carrying out the denitrification reaction or directly by acting as an electron donor. This helps maintain the pH of the system.

2. The apparatus according to claim 1, characterized in that, The elemental sulfur particles inside the self-oxygenating denitrification system range from 6 to 12 mm in size, gradually decreasing in size as they accumulate from bottom to top. The system has a columnar structure, with the wastewater inlet and return inlet located at the bottom or bottom; the outlet is located at the top or top, with at least one outlet for discharging treated wastewater. The system also has multiple sampling ports at different heights.

3. The apparatus according to claim 1, characterized in that, The cathode in the cathode chamber is made of titanium sheet rolled into a tubular structure, and the cathode is connected to the negative terminal of the power supply via titanium sheet. The anode in the anode chamber is made of DSA electrode.

4. The apparatus according to claim 1, characterized in that, The elemental sulfur self-oxygenation denitrification system and the cathode chamber are both under anoxic conditions, with dissolved oxygen (DO) < 0.5 mg / L; the anode chamber is under aerobic conditions, with dissolved oxygen (DO) > 0.5 mg / L.

5. A method for promoting sulfur-based denitrification and sulfate emission reduction through bioelectrochemical-assisted sulfur conversion, characterized in that, include: Nitrate-laden wastewater enters through the bottom of an elemental sulfur autotrophic denitrification system, where sulfur autotrophic denitrifying bacteria remove NO3 from the wastewater. - Reduced to N2, while HS is refluxed from the cathode chamber of the sulfate reduction system with elemental sulfur and / or electrochemically assisted sulfate reduction. - / S 2- and / or elemental sulfur with HS - / S 2- The formed S n 2- It is derived from electrons and converted into SO4. 2- ; The effluent from the elemental sulfur autogenous denitrification system is partially discharged through the first outlet, while the remainder enters the cathode chamber of the electrochemically assisted sulfate reduction system through the second outlet. In the cathode chamber, hydrogen autotrophic sulfate-reducing bacteria carry out the sulfate reduction reaction, converting SO42- into sulfur dioxide. 2- Restore to negative HS - / S 2- In addition, hydroxide ions are generated in the cathode chamber along with the hydrogen production reaction; The effluent from the cathode chamber then flows through the reflux inlet to the elemental sulfur autogenous denitrification system; HS - / S 2- Forms S with elemental sulfur n 2- Hydroxide ions can be used to carry out denitrification reactions or directly as electron donors for denitrification reactions. Hydroxide ions can effectively neutralize the large number of protons generated during the denitrification process in the elemental sulfur autotrophic denitrification system, thus maintaining the system pH.

6. The method according to claim 5, characterized in that, The volumetric flow rate ratio between the first outlet and the second outlet is 1:0.5 to 1:

5.

7. The method according to claim 5, characterized in that, The temperature of the elemental sulfur autotrophic denitrification system, the cathode chamber, and the anode chamber are all controlled at 25 ± 5 °C, and the hydraulic retention time is 12~72h.

8. The method according to claim 5, characterized in that, The power supply outputs a constant current to provide electrical assistance to the electrochemically assisted sulfate reduction system.

9. The method according to claim 8, characterized in that, The constant current is 50 mA ~ 300 mA.

10. The method according to claim 5, characterized in that, NO3 in nitrile wastewater - The concentration is 50~600 mg / L.

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