Method and system for synchronously removing nitrate nitrogen in wastewater and hydrogen sulfide in biogas based on iron circulation

Abstract

The invention discloses a method and system for synchronously removing nitrate nitrogen in wastewater and hydrogen sulfide in biogas based on iron circulation, and belongs to the technical field of industrial sewage treatment and biogas purification. According to the invention, iron ions are used as a medium to construct a closed cycle, and biogas and wastewater are synchronously purified; the method comprises the following steps: oxidizing hydrogen sulfide in biogas by using a ferric sulfate solution to generate ferrous sulfide, elemental sulfur and sulfuric acid; then sulfuric acid is separated from a mixture of ferrous sulfide and elemental sulfur through solid-liquid separation, then the ferrous sulfide and the elemental sulfur are subjected to autotrophic denitrification with nitrate in the wastewater under the action of thiobacillus denitrificans, and ferric hydroxide, nitrogen and sulfate are generated; and then the ferric hydroxide reacts with the separated sulfuric acid to regenerate a ferric sulfate solution which is reused in the desulfurization step. In the whole process, cyclic utilization of iron ions is achieved, hydrogen sulfide and nitrate nitrogen are synchronously converted into harmless nitrogen, elemental sulfur and sulfate, and the purposes of treating waste with waste and recycling resources are achieved.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment and biogas purification technology, and particularly relates to a method and system for the simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron circulation. Background Technology

[0002] In the process of treating high-concentration organic industrial wastewater using anaerobic biological technology, sulfates or sulfur-containing organic matter in the wastewater are reduced, producing a large amount of hydrogen sulfide that enters biogas. Hydrogen sulfide is highly corrosive and toxic, and must be desulfurized before biogas utilization. While mainstream chemical absorption methods (such as iron-based and alkali-based treatments) are effective in desulfurization, they are costly to operate, and the desulfurization agents can cause secondary pollution, increasing the difficulty of treatment. Furthermore, the effluent after anaerobic treatment often still requires biological denitrification processes to remove nitrogen pollutants. For high-nitrate wastewater, traditional heterotrophic denitrification processes typically require an external carbon source, resulting in high operating costs. Existing technologies include research on using autotrophic denitrifying thiobacilli to reduce nitrates using sulfides or elemental sulfur as electron donors, but these studies are mostly limited to the laboratory stage. Coupled with waste gas desulfurization and wastewater denitrification—two independent processes—and achieving the recycling of key agents (such as iron) to form a highly efficient and low-cost closed-loop process, no mature and feasible industrial-scale solutions have yet been reported. Therefore, developing a process that can simultaneously remove hydrogen sulfide and nitrate nitrogen, achieve reagent recycling, and is environmentally friendly and efficient has become an urgent technical problem to be solved in this field. Summary of the Invention

[0003] To address the problems of simultaneous nitrogen and sulfur removal, high reagent consumption, and secondary pollution in existing technologies, this invention proposes a method and system for the simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling. This method achieves simultaneous removal of nitrate nitrogen and hydrogen sulfide, as well as resource recycling, and reduces operating costs.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for the simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling, comprising the following steps:

[0006] (1) Pass biogas containing hydrogen sulfide into the desulfurization tower, add ferric sulfate solution into the desulfurization tower to carry out oxidation-reduction reaction, and obtain desulfurization tower products and desulfurized biogas;

[0007] (2) The desulfurization tower product obtained in step (1) is subjected to solid-liquid separation to obtain a mixed solid of ferrous sulfide and elemental sulfur and a filtrate containing sulfuric acid;

[0008] (3) The mixed solid of ferrous sulfide and elemental sulfur obtained in step (2) is transported to the denitrifying thiobacillus pool, and at the same time, wastewater containing nitrate is introduced to carry out an autotrophic denitrification reaction, and ferric hydroxide suspension, nitrogen gas and sulfate are obtained respectively.

[0009] (4) The ferric hydroxide suspension obtained in step (3) is transported to the regeneration reactor, and then the sulfuric acid filtrate obtained in step (2) is added to the regeneration reactor for neutralization reaction to obtain regenerated ferric sulfate solution;

[0010] (5) The regenerated ferric sulfate solution obtained in step (4) is returned to the desulfurization tower in step (1), and steps (1)-(4) are repeated to realize the recycling of ferric sulfate and sulfuric acid.

[0011] Further, in step (1), the Fe in the ferric sulfate solution 3+ The concentration of the ferric sulfate solution is ≥0.5 mol / L; the pH value of the ferric sulfate solution is 2.5-3.5.

[0012] Further, in step (1), the Fe in the ferric sulfate solution 3+ The molar ratio of H2S in the biogas containing hydrogen sulfide is 1:3.

[0013] Furthermore, in step (1), the temperature of the redox reaction is 25-40℃, the pH value is 5.0-6.0, and the time is 20-40 min.

[0014] Furthermore, in step (2), before the solid-liquid separation, there is also a step of adding polyacrylamide flocculant; the dosage of the polyacrylamide flocculant is 10 mg / L.

[0015] Further, in step (3), the sludge concentration in the denitrifying thiobacillus pond is 5 g / L; the mass ratio of the total mass of the mixed solids of ferrous sulfide and elemental sulfur to the mass of the nitrate-containing wastewater (calculated as N) is 20:1-30:1.

[0016] Furthermore, in step (3), the temperature of the autotrophic denitrification reaction is 25-35℃, the time is 12-24h, the dissolved oxygen is <0.5mg / L, and the pH value is 7.0-8.0.

[0017] Further, in step (4), the temperature of the neutralization reaction is 25-40℃, the time is 10-15min, and the stirring intensity is ≥300r / min; the molar ratio of Fe(OH)3 in the ferric hydroxide suspension and H2SO4 in the sulfuric acid filtrate is 2:3.

[0018] The present invention also provides a circulation system for the method described in the above technical solution, the circulation system comprising a primary desulfurization tower, a secondary desulfurization tower, a filter press system, a denitrifying thiobacillus pool, and a regeneration reactor.

[0019] Furthermore, both the primary desulfurization tower and the secondary desulfurization tower are packed tower structures, with a packing layer height of 4.0m.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] The present invention provides a method for the simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling. This method comprises five steps: desulfurization reaction, solid-liquid separation, biological denitrification and desulfurization reaction, regeneration reaction, and recycling. It constructs a closed-loop cycle using iron ions as a medium to simultaneously purify biogas and wastewater. First, ferric sulfate solution is used to oxidize hydrogen sulfide in biogas, generating ferrous sulfide, elemental sulfur, and sulfuric acid. Then, solid-liquid separation is used to separate the sulfuric acid from the mixture of ferrous sulfide and elemental sulfur. Next, ferrous sulfide and elemental sulfur undergo autotrophic denitrification with nitrates in the wastewater under the action of denitrifying thiobacters, generating ferric hydroxide, nitrogen gas, and sulfate. Finally, the ferric hydroxide reacts with the separated sulfuric acid to regenerate ferric sulfate solution, which is then reused in the desulfurization step. The entire process achieves the recycling of iron ions, simultaneously converting hydrogen sulfide and nitrate nitrogen into harmless nitrogen gas, elemental sulfur, and sulfate, thus achieving the goal of treating waste with waste and recycling resources.

[0022] The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling provided by this invention has the following advantages: (1) Waste treatment with waste, synergistic efficiency: Hydrogen sulfide in waste gas is used as an electron donor source for wastewater denitrification, solving the two pollutants at once and reducing the cost of separate treatment; (2) Closed-loop recycling, green economy: Iron reagent is regenerated and recycled within the system, greatly reducing the consumption of fresh reagents and the generation of chemical sludge, realizing "waste resource utilization"; (3) Stable process and strong adaptability: It can adapt to fluctuations in hydrogen sulfide concentration (2%-7%) and nitrate nitrogen concentration (300-600mg / L), and is suitable for various scenarios such as industrial wastewater treatment and biogas purification; (4) High degree of harmlessness of products: The final products are nitrogen, sulfate and a small amount of elemental sulfur (recyclable), which meets environmental protection requirements. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1The circulating system provided by this invention for the simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron circulation includes: 1-primary desulfurization tower, 2-secondary desulfurization tower, 3-filtration system, 4-denitrifying thiobacillus pool, 5-regeneration reactor, 6-biogas inlet, 7-primary desulfurization biogas outlet, 8-ferric sulfate reagent inlet, 9-primary circulating spray system, 10-desulfurization packing, 11-primary sedimentation outlet, 12-primary desulfurization biogas inlet, 13-secondary circulating spray system, 14-secondary desulfurization biogas outlet, 15-secondary sedimentation outlet, 16-nitrate-containing wastewater inlet, 17-filter layer of ferrous sulfide and elemental sulfur, 18-ferric hydroxide sedimentation outlet, 19-sulfuric acid inlet, 20-stirring device, 21-regenerated ferric sulfate solution outlet, 22-treated water outlet, 23-ferric sulfate reagent outlet, and 24-sludge cake outlet. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This invention provides a method for the simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling, comprising the following steps:

[0028] (1) Pass biogas containing hydrogen sulfide into the desulfurization tower, add ferric sulfate solution into the desulfurization tower to carry out oxidation-reduction reaction, and obtain desulfurization tower products and desulfurized biogas;

[0029] (2) The desulfurization tower product obtained in step (1) is subjected to solid-liquid separation to obtain a mixed solid of ferrous sulfide and elemental sulfur and a filtrate containing sulfuric acid;

[0030] (3) The mixed solid of ferrous sulfide and elemental sulfur obtained in step (2) is transported to the denitrifying thiobacillus pool, and at the same time, wastewater containing nitrate is introduced to carry out an autotrophic denitrification reaction, and ferric hydroxide suspension, nitrogen gas and sulfate are obtained respectively.

[0031] (4) The ferric hydroxide suspension obtained in step (3) is transported to the regeneration reactor, and then the sulfuric acid filtrate obtained in step (2) is added to the regeneration reactor for neutralization reaction to obtain regenerated ferric sulfate solution;

[0032] (5) The regenerated ferric sulfate solution obtained in step (4) is returned to the desulfurization tower in step (1), and steps (1)-(4) are repeated to realize the recycling of ferric sulfate and sulfuric acid.

[0033] In a preferred embodiment, in step (1), the Fe in the ferric sulfate solution 3+ The concentration is ≥0.5mol / L, specifically determined based on the solubility of ferric sulfate and practical operability, and more preferably 0.5-1.2mol / L; the pH value of the ferric sulfate solution is 2.5-3.5.

[0034] In a preferred embodiment, in step (1), the Fe in the ferric sulfate solution 3+ The molar ratio of H2S in the biogas containing hydrogen sulfide is 1:3; the mass concentration of hydrogen sulfide in the biogas containing hydrogen sulfide is 2-7%.

[0035] In a preferred embodiment, in step (1), the temperature of the redox reaction is 25-40℃, the pH value is 5.0-6.0, and the time is 20-40 min. In this invention, after adding ferric sulfate solution to the desulfurization tower, ferric sulfate reacts with hydrogen sulfide in biogas to produce ferrous sulfide, elemental sulfur, and sulfuric acid. The reaction equation is: Fe2(SO4)3 + 3H2S = 2FeS↓ + S↓ + 3H2SO4.

[0036] In a preferred embodiment, in step (1), after the redox reaction is completed, the removal rate of hydrogen sulfide is ≥90%, and the concentration of hydrogen sulfide in the desulfurized biogas is ≤100ppm.

[0037] In a preferred embodiment, in step (2), the solid-liquid separation is performed by plate and frame filtration; the water content of the mixed solid of ferrous sulfide and elemental sulfur is ≤80%; and the sulfuric acid concentration of the sulfuric acid-containing filtrate is ≥10%.

[0038] In a preferred embodiment, step (2) further includes the addition of polyacrylamide (PAM) flocculant before solid-liquid separation; the dosage of the polyacrylamide flocculant is 10 mg / L. The addition of polyacrylamide flocculant is beneficial to enhancing the separation effect.

[0039] In a preferred embodiment, in step (3), the sludge concentration in the denitrifying thiobacillus pond is 5 g / L; the mass ratio of the total mass of the mixed solids of ferrous sulfide and elemental sulfur to the mass of the nitrate-containing wastewater (calculated as N) is 20:1-30:1; and the concentration of nitrate in the nitrate-containing wastewater is 300-600 mg / L.

[0040] In a preferred embodiment, in step (3), the temperature of the autotrophic denitrification reaction is 25-35℃, the time is 12-24h, the dissolved oxygen is <0.5mg / L, and the pH value is 7.0-8.0. Ferrous sulfide and elemental sulfur act as electron donors, reacting with nitrates in wastewater under the action of denitrifying thiobacilli to produce ferric hydroxide, nitrogen gas, and sulfate. The overall reaction equation is: 10FeS + 5S + 24NO3 - +18H2O=10Fe(OH)3↓+12N2↑+15SO4 2- +6H + .

[0041] In a preferred embodiment, after the autotrophic denitrification reaction is completed in step (3), the removal rate of nitrate in the wastewater is ≥85%. The nitrogen generated by the autotrophic denitrification reaction in this invention can be emitted non-toxically, and the sulfate can be recycled without secondary pollution, thus achieving effective removal of nitrate nitrogen from wastewater.

[0042] In a preferred embodiment, in step (4), the neutralization reaction is carried out at a temperature of 25-40°C for 10-15 minutes, with a stirring intensity ≥300 r / min; the molar ratio of Fe(OH)3 in the ferric hydroxide suspension to H2SO4 in the sulfuric acid-containing filtrate is 2:3. In this invention, after adding the sulfuric acid-containing filtrate to the regeneration reactor, ferric hydroxide and sulfuric acid undergo a neutralization reaction to generate ferric sulfate solution. The reaction equation is: 2Fe(OH)3 + 3H2SO4 = Fe2(SO4)3 + 6H2O, thus achieving the regeneration of ferric sulfate.

[0043] In a preferred embodiment, in step (4), the Fe in the regenerated ferric sulfate solution 3+ The concentration of the ferric sulfate solution is ≥0.5mol / L, and the pH value of the regenerated ferric sulfate solution is 2.5-3.5, which can meet the requirements of the desulfurization reaction.

[0044] In a preferred embodiment, during step (5), the loss rate of ferric sulfate is ≤5% during the repetition of steps (1)-(4), and ferric sulfate needs to be replenished periodically.

[0045] This invention also provides a circulation system for the method described in the above technical solution, the circulation system comprising a primary desulfurization tower 1, a secondary desulfurization tower 2, a filter press system 3, a denitrifying thiobacillus pool 4, and a regeneration reactor 5.

[0046] The technical solution of the present invention will be described in detail below through specific embodiments.

[0047] In the following embodiments, the circulating system used includes a primary desulfurization tower 1, a secondary desulfurization tower 2, a filter press system 3, a denitrifying thiobacillus pool 4, and a regeneration reactor 5; wherein, the primary desulfurization tower 1 has a biogas inlet 6 and a ferric sulfate reagent inlet 8 at its lower left, a ferric sulfate reagent outlet 23 at its lower right, and a primary desulfurization biogas outlet 7 at its top; the primary desulfurization tower 1 is equipped with desulfurization packing 10, and a primary circulating spray system 9 is correspondingly installed above the desulfurization packing 10; a primary sedimentation outlet 11 is opened at the bottom of the primary desulfurization tower 1; the secondary desulfurization tower 2 has a primary desulfurization biogas inlet 12 at its lower left, which is connected to the primary desulfurization biogas outlet 7; the secondary desulfurization... Tower 2 is equipped with a two-stage circulating spray system 13, with a two-stage desulfurization biogas outlet 14 at the top and a two-stage sedimentation outlet 15 at the bottom; the filter press system 3 has a sludge cake outlet 24 on the right side, which is connected to the denitrifying thiobacterium pool 4; the denitrifying thiobacterium pool 4 has a nitrate-containing wastewater inlet 16 on top, and is equipped with a filter layer 17 of ferrous sulfide and elemental sulfur inside, with a ferric hydroxide sedimentation outlet 18 at the bottom; the regeneration reactor 5 has a sulfuric acid inlet 19 at the top, which is connected to the filter press system 3, and is equipped with a stirring device 20 inside, with a regenerated ferric sulfate solution outlet 21 at the bottom, which is connected to the ferric sulfate reagent inlet 8 through a pipeline.

[0048] In a preferred embodiment, both the primary desulfurization tower 1 and the secondary desulfurization tower 2 are packed tower structures, with a packing layer height of 4.0m.

[0049] In this embodiment of the invention, room temperature refers to "25±2℃".

[0050] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0051] Example 1

[0052] A method for simultaneously removing nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling, with a treatment capacity of 200 m³ / day of nitrate wastewater. 3 (NO3) - The concentration of -N is 500 mg / L), the biogas contains 5% H2S (mass concentration), and the total H2S is 0.2 tons / day. A schematic diagram of the circulating system is shown below. Figure 1 The specific steps are as follows:

[0053] (1) Desulfurization reaction: Biogas enters the primary desulfurization tower 1 from the biogas inlet 6, and at the same time, ferric sulfate reagent with a mass concentration of 10% is added into the primary desulfurization tower 1 through the ferric sulfate reagent inlet 8. 3+ A Fe2(SO4)3 solution with a concentration ≥0.5 mol / L and a pH value of 2.5-3.5, the Fe in the Fe2(SO4)3 solution 3+The molar ratio of H2S in the biogas is 1:3. The temperature of the primary desulfurization tower 1 is controlled at 25-40℃, the pH value at 5.0-6.0, and the biogas residence time at 20-40 min. The primary circulating spray system 9 is started to carry out the oxidation-reduction reaction, obtaining the primary desulfurization tower product and primary desulfurized biogas. The obtained primary desulfurized biogas is led out through the primary desulfurized biogas outlet 7 and then enters the secondary desulfurization tower 2 through the primary desulfurized biogas inlet 12. At the same time, the unreacted ferric sulfate solution from the primary desulfurization enters the secondary desulfurization tower 2 through the ferric sulfate reagent outlet 23. The desulfurization tower continues to react. The secondary desulfurization tower is set with the same parameters as the primary desulfurization tower. After the primary desulfurized biogas comes into contact with the desulfurization packing 10 through the secondary circulating spray system 13, it generates secondary desulfurization tower products and secondary desulfurized biogas. The secondary desulfurized biogas is discharged and collected from the secondary desulfurized biogas outlet 14. At this time, the H2S removal rate is >99.5%, and the concentration of hydrogen sulfide in the secondary desulfurized biogas is <50ppm. Both the primary and secondary desulfurization towers adopt a packed tower structure, which is filled with Pall ring packing with a packing layer height of 4.0m.

[0054] (2) Solid-liquid separation: The product of the first-stage desulfurization tower in step (1) is discharged through the first-stage sedimentation outlet 11, and the product of the second-stage desulfurization tower is discharged through the second-stage sedimentation outlet 15. Both are sent to the filter press system 3 and are filtered in the filter press at an operating pressure of 0.7 MPa. At the same time, 10 mg / L of PAM flocculant is added to obtain a mixed solid of ferrous sulfide and elemental sulfur with a water content of 78% and a sulfuric acid filtrate with a sulfuric acid concentration of 12%.

[0055] (3) Biological denitrification and desulfurization reaction: The mixed solid of ferrous sulfide and elemental sulfur obtained in step (2) is introduced into the denitrification thiobacterium tank 4 through the sludge cake outlet 24 as a filter layer. The sludge concentration of the denitrification thiobacterium tank 4 is 5 g / L. The mass ratio of the total mass of the mixed solid of ferrous sulfide and elemental sulfur to the mass of nitrate-containing wastewater (calculated as N) is 20:1. At the same time, nitrate wastewater is introduced through the nitrate-containing wastewater inlet 16. The hydraulic retention time is controlled at 12 h, the reaction temperature is 30 °C, the dissolved oxygen in the tank is <0.5 mg / L, and NaHCO3 is added to maintain the pH value of the reaction system at about 7.0. After the reaction is completed, ferric hydroxide suspension, nitrogen and sulfate are obtained respectively. NO3 in the effluent - -N removal rate is 85%, and effluent is discharged from treated water outlet 22;

[0056] (4) Regeneration reaction: The ferric hydroxide suspension generated in step (3) flows out through the ferric hydroxide precipitate outlet 18 and enters an effective volume of 30m³. 3In the regeneration reactor 5, the sulfuric acid-containing filtrate generated in step (2) is simultaneously added through the sulfuric acid inlet 19 (the molar ratio of Fe(OH)3 in the ferric hydroxide suspension and H2SO4 in the sulfuric acid-containing filtrate is controlled to be 2:3). The reaction temperature is controlled at 35℃, the residence time is 12min, and the stirring intensity of the stirring device 20 is 350r / min to carry out the neutralization reaction, generating Fe. 3+ A regenerated ferric sulfate solution with a concentration of 0.58 mol / L and a pH of 3.2;

[0057] (5) Recycling: The regenerated ferric sulfate solution generated in step (4) flows out through the regenerated ferric sulfate solution outlet 21 and then flows back to the primary desulfurization tower 1 through the ferric sulfate reagent inlet 8. In order to maintain the stable operation of the system, when the concentration of hydrogen sulfide in the biogas at the secondary desulfurization outlet is >50ppm, ferric sulfate with an iron mass content of 11% is added, and steps (1)-(4) are repeated to realize the recycling of ferric sulfate and sulfuric acid.

[0058] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling, characterized in that, Includes the following steps: (1) Pass biogas containing hydrogen sulfide into the desulfurization tower, add ferric sulfate solution into the desulfurization tower to carry out oxidation-reduction reaction, and obtain desulfurization tower products and desulfurized biogas; (2) The desulfurization tower product obtained in step (1) is subjected to solid-liquid separation to obtain a mixed solid of ferrous sulfide and elemental sulfur and a filtrate containing sulfuric acid; (3) The mixed solid of ferrous sulfide and elemental sulfur obtained in step (2) is transported to the denitrifying thiobacillus pool, and at the same time, wastewater containing nitrate is introduced to carry out an autotrophic denitrification reaction, and ferric hydroxide suspension, nitrogen gas and sulfate are obtained respectively. (4) The ferric hydroxide suspension obtained in step (3) is transported to the regeneration reactor, and then the sulfuric acid filtrate obtained in step (2) is added to the regeneration reactor for neutralization reaction to obtain regenerated ferric sulfate solution; (5) The regenerated ferric sulfate solution obtained in step (4) is returned to the desulfurization tower in step (1), and steps (1)-(4) are repeated to realize the recycling of ferric sulfate and sulfuric acid.

2. The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling according to claim 1, characterized in that, In step (1), the Fe in the ferric sulfate solution 3+ The concentration of the ferric sulfate solution is ≥0.5 mol / L; the pH value of the ferric sulfate solution is 2.5-3.

5.

3. The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling according to claim 2, characterized in that, In step (1), the Fe in the ferric sulfate solution 3+ The molar ratio of H2S in the biogas containing hydrogen sulfide is 1:

3.

4. The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling according to claim 1, characterized in that, In step (1), the temperature of the redox reaction is 25-40℃, the pH value is 5.0-6.0, and the time is 20-40min.

5. The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling according to claim 1, characterized in that, In step (2), before the solid-liquid separation, there is also a step of adding polyacrylamide flocculant; the dosage of polyacrylamide flocculant is 10 mg / L.

6. The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling according to claim 1, characterized in that, In step (3), the sludge concentration in the denitrifying thiobacillus pond is 5 g / L; the mass ratio of the total mass of the mixed solids of ferrous sulfide and elemental sulfur to the mass of the nitrate-containing wastewater (calculated as N) is 20:1-30:

1.

7. The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling according to claim 1, characterized in that, In step (3), the temperature of the autotrophic denitrification reaction is 25-35℃, the time is 12-24h, the dissolved oxygen is <0.5mg / L, and the pH value is 7.0-8.

0.

8. The method for simultaneous removal of nitrate nitrogen from wastewater and hydrogen sulfide from biogas based on iron recycling according to claim 1, characterized in that, In step (4), the temperature of the neutralization reaction is 25-40℃, the time is 10-15min, and the stirring intensity is ≥300r / min; the molar ratio of Fe(OH)3 in the ferric hydroxide suspension to H2SO4 in the sulfuric acid filtrate is 2:

3.

9. A cyclic system for use in the method according to any one of claims 1-8, characterized in that, The circulating system includes a primary desulfurization tower (1), a secondary desulfurization tower (2), a filter press system (3), a denitrifying thiobacillus pool (4), and a regeneration reactor (5).

10. The circulation system according to claim 9, characterized in that, Both the primary desulfurization tower (1) and the secondary desulfurization tower (2) are packed tower structures, with a packing layer height of 4.0m.

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