A modified sulfur autotrophic bacteria agent capsule with structural reinforcement, a preparation method and application thereof

Abstract

The present application relates to a kind of modified sulfur autotrophic bacteria agent capsules with structural reinforcement, its preparation method and application, the preparation method is by carrying out thiol modification to alginates, then mixed with polyvinyl alcohol to obtain gel solution;Add aqueous polyurethane in gel solution to obtain porous modified gel;Add sulfur powder and iron-rich sludge biochar and stir to mix, obtain modified reinforced gel with reinforced network structure and contain inorganic electron donor;Then mixed with sulfur autotrophic bacteria liquid, crosslinking fixation is carried out to obtain composite capsule.The capsule is based on the mechanical and mass transfer performance of reinforced hydrogel, improves the bioavailability of sulfur, improves the denitrification effect by immobilized active microorganism.The removal effect of nitrate nitrogen and nitrite nitrogen in sewage can be significantly optimized, and it has reusability and impact stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water treatment, and particularly relates to a modified sulfur autotrophic bacteria agent capsule with reinforced structure, a preparation method and application thereof. BACKGROUND

[0002] Sulfur autotrophic denitrification (SAD) is a process in which sulfur-oxidizing bacteria (SOB) use inorganic sulfur compounds as electron donors to reduce nitrate. This process has excellent denitrification effect, does not require organic carbon, has low sludge production and operation cost, and emits less greenhouse gases, and is expected to achieve carbon neutralization in wastewater treatment plants. However, the SAD denitrification load is usually 0.5~2.5 kg N / m 3 / d, which is much lower than that of heterotrophic denitrification process (3.0~6.0 kg N / m 3 / d), the main reasons are: ① insufficient SOB biomass can be retained in the SAD process; ② the uptake rate of microorganisms to solid sulfur is slow.

[0003] Considering the slow growth rate of SOB (0.04~0.27 h–1), immobilization of SOB to form biofilm or granules is an effective way to enrich biomass and improve electron transfer rate.

[0004] At present, the embedding method is the main means of microbial immobilization technology, which is simple to operate and has less impact on microbial activity. The commonly used microbial embedding materials are mainly sodium alginate (SA) and polyvinyl alcohol (PVA). The SA molecular skeleton has rich hydroxyl and carboxyl groups, which can easily form gel particles, but the mechanical strength is low and the biodegradability is poor. The PVA-derived carriers have three main problems: ① the formed gel particles are prone to agglomeration; ② the cross-linking speed is slow, and the survival rate of immobilized microorganisms decreases sharply under strong acid conditions (pH<4); ③ the generated PVA carrier lacks sufficient pore structure, affecting the mass transfer of nutrients in wastewater and the discharge of microbial metabolites, and is prone to swelling and breaking after long-term use.

[0005] In addition, when using SA as embedding material, increasing the content of SA will increase the viscosity of the capsule and make it difficult to form a ball, and excessive SA will affect the activity of microorganisms; when using PVA as embedding material, increasing the content of PVA will increase the mechanical strength of the capsule, but at the same time, it will also reduce the porosity and mass transfer performance. On the other hand, there is a lack of research on the long-term use performance of the bacteria agent capsule and the bioavailability of sulfur, and the large-scale application may face restrictions.

[0006] Therefore, modification of PVA / SA carriers to strengthen the mechanical strength and mass transfer performance of the carriers, increase the types and number of active groups, and improve the bioavailability of sulfur can further promote the large-scale application of SAD process. SUMMARY

[0007] The primary purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and provide a structure-reinforced modified sulfur autotrophic bacteria agent capsule and a preparation method thereof. By effectively fixing the SOB biomass in particles with high mechanical strength and excellent mass transfer performance, the bioavailability of sulfur is improved, thereby improving the denitrification effect of the sulfur autotrophic denitrification process.

[0008] Another purpose of the present application is to provide the use of the structure-reinforced modified sulfur autotrophic bacteria agent capsule.

[0009] The purpose of the present application is achieved by the following technical solutions:

[0010] In a first aspect of the present application, a preparation method of a structure-reinforced modified sulfur autotrophic bacteria agent capsule is provided, comprising the following steps:

[0011] S1. Dissolve polyvinyl alcohol and thiolated alginate in water at 90°C to obtain a gel solution, wherein the content of polyvinyl alcohol is 6-10 wt%, and the content of thiolated alginate is 0.5-2 wt%.

[0012] The thiolated alginate can be thiolated sodium alginate, thiolated calcium alginate, thiolated potassium alginate, or other common alginate thiolated to obtain.

[0013] Preferably, the thiolated alginate is prepared by activating the alginate solution with 1-ethyl-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide at room temperature; then, adding cysteine, adjusting the pH to about 4.0, and stirring at room temperature for reaction; then, increasing the pH to 6.0, and stirring at room temperature for 0.5-2 h; finally, purifying the obtained reaction solution by dialysis, and freeze-drying to obtain.

[0014] In a preferred embodiment, the thiolated alginate is thiolated sodium alginate, and the preparation method of the thiolated sodium alginate comprises: preparing a 0.5-1 wt% sodium alginate (SA) solution, adding 1-ethyl-(3-dimethylaminopropyl)-carbodiimide hydrochloride with a final concentration of 50 mmol / L and N-hydroxysuccinimide with a final concentration of 100 mmol / L, respectively, stirring at room temperature for 30-60 min to convert the activated carboxyl groups of sodium alginate into active ester products; then, adding 2 times the weight of sodium alginate of cysteine, adjusting the pH to about 4.0, and stirring at room temperature for 2 h; then, increasing the pH to 6.0, and stirring at room temperature for 1 h; purifying the thiolated sodium alginate by dialysis of the obtained reaction solution, and collecting the sample by freeze-drying.

[0015] S2. After the gel solution is cooled to room temperature, 1-5 wt% of anionic waterborne polyurethane with a solid content of 30% is added and stirred to obtain a porous modified gel.

[0016] S3. Adding 10-20 wt% of sulfur powder and 1-5 wt% of iron-rich sludge biochar into the porous modified gel, stirring and mixing to obtain a modified and reinforced gel.

[0017] Preferably, the particle size of the sulfur powder and sludge biochar is 200-300 mesh.

[0018] Preferably, the iron-rich sludge biochar is prepared by anaerobic thermal decomposition of iron-rich sludge at 500-700°C, and the iron-rich sludge contains 20wt%-40wt% of iron and 20wt%-30wt% of organic matter (both are dry weight). The iron-rich sludge can be obtained from residual sludge using inorganic iron salt flocculants or residual sludge from Advanced Oxidation Processes (AOPs) involving iron-based catalysts.

[0019] S4. Adding 30-40 wt% of sulfur autotrophic bacteria liquid into the modified and reinforced gel, stirring and mixing uniformly to obtain a gel-bacteria liquid mixture, and then dropping the gel-bacteria liquid mixture into a cross-linking solution to obtain the structure-reinforced modified sulfur autotrophic bacteria agent capsule.

[0020] Preferably, the total number of viable bacteria in the sulfur autotrophic bacteria liquid is ≥2×10 8 CFU / g, and the sulfur autotrophic bacteria liquid is Thiobacillus denitrificans and / or Sulfococcus bacteria liquid.

[0021] Preferably, the cross-linking solution is a 2-4 wt% calcium chloride solution.

[0022] Alginate has good biocompatibility, biodegradability, and non-toxicity, etc. Its performance can be further improved through chemical modification or physical blending. In this application, cysteine is used to functionalize alginate to form thiolated alginate, which is then mixed with PVA. With the increase of alginate functional groups (carboxyl, hydroxyl, thiol, and amide groups) and the formation of disulfide bonds, the conversion of solid sulfur to soluble sulfur can be accelerated: for example, hydrophilic groups (such as carboxyl groups) make it easier for sulfur particles to be absorbed into bacterial cells, accelerating the transport of sulfur at the solid phase interface; disulfide bonds and thiol groups can open the S-S single bond in elemental sulfur through nucleophilic attack.

[0023] The addition of aqueous polyurethane can promote the formation of outer surface pores and walls and expand the internal three-dimensional network structure. The honeycomb-like pore structure can provide abundant attachment sites for microorganisms, protect microorganisms from external toxic effects, and the dense outer and loose internal pore structure can ensure the transport of nutrients and metabolites and prevent the loss of immobilized microorganisms.

[0024] The iron-based sludge biochar is introduced into the polymer network structure of the carrier by physical blending, and the main effects are: ① improving the mechanical strength of the carrier, the unique structure is firmly combined with the polymer molecules to form a hybrid material, the water swelling performance of the capsule is gradually reduced, and the mechanical strength is significantly improved; ② S-Fe co-electron donors are generated in the system through the Fe (II) / Fe (III) cycle; ③ phosphorus is removed to a certain extent. The iron contained in the iron-based sludge biochar mainly exists in the form of Fe (III) due to thermal decomposition. Although Fe (III) cannot directly act as an electron donor to participate in the denitrification process, it can generate Fe (II) / Fe (III) cycle through microbial action, that is, under anaerobic conditions, Fe (III) acts as the final electron acceptor of iron-reducing bacteria, and Fe (II) acts as the electron donor of iron-oxidizing bacteria. Different forms of Fe can promote the performance of SAD denitrification. The hydrogel obtained has a reinforced network structure and contains inorganic electron donors, which is beneficial to the nitrification reaction.

[0025] The second aspect of the present application also provides a modified and reinforced sulfur autotrophic composite microbial agent capsule prepared by the preparation method. The sulfur autotrophic microbial agent capsule is based on the mechanical and mass transfer performance of the reinforced hydrogel, the improvement of the biological availability of sulfur, and the improvement of the denitrification effect by immobilized active microorganisms. Under suitable working conditions, the composite microbial agent capsule can significantly optimize the removal effect of nitrate nitrogen and nitrite nitrogen in wastewater, and has certain reusability and impact stability.

[0026] The third aspect of the present application also provides the application of the modified and reinforced sulfur autotrophic composite microbial agent capsule in water treatment. For example, it is used for treating domestic sewage containing nitrate nitrogen and nitrite nitrogen, aquaculture tail water, industrial tail water, surface water and underground water, etc.

[0027] In some embodiments, a circulating biological fluidized bed reactor is used, the loading ratio of the composite microbial agent capsule of the present application is 40-60% (v / v), the composite microbial agent capsule is suspended and fluidized by an external circulating waterway or inert gas charging, which can increase the contact frequency of the microbial agent and the flowing water, and strengthen the absorption and utilization of pollutants in the wastewater.

[0028] In some embodiments, a column reactor with a fixed bed filler is used, and the composite microbial agent capsule of the present application can be used as filler or supplementary material, which can be used once or in batches, and can strengthen the removal efficiency of pollutants.

[0029] The fourth aspect of the present application provides a water treatment agent comprising the modified and reinforced sulfur autotrophic composite microbial agent capsule.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] The application obtains a gel solution by modifying alginate with mercaptan and mixing with polyvinyl alcohol; a porous modified gel is prepared by adding water-based polyurethane to the gel solution; a modified reinforced gel with a reinforced network structure and containing inorganic electron donors is obtained by adding sulfur powder and stirring with iron-rich sludge biochar; and then mixed with sulfur autotrophic bacteria liquid to prepare a composite capsule by cross-linking and fixing. The capsule improves the bioavailability of sulfur based on the mechanical and mass transfer properties of the reinforced hydrogel, and improves the denitrification effect through immobilized active microorganisms. The removal effect of nitrate nitrogen and nitrite nitrogen in wastewater can be significantly optimized, and the capsule has certain reusability and impact stability. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Appearance characteristics of the sulfur autotrophic bacteria capsule prepared in this example;

[0033] Figure 2 Mass transfer efficiency comparison curve of the sulfur autotrophic bacteria capsules prepared in the examples and comparative examples 1-3;

[0034] Figure 3 Trend of the concentration of nitrate nitrogen and nitrite nitrogen in the influent and effluent after the sulfur autotrophic bacteria capsules prepared in the examples and comparative examples 1-3 are loaded into a fluidized bed reactor;

[0035] Figure 4 Comparison chart of the removal effect of nitrate nitrogen in wastewater by the sulfur autotrophic bacteria capsules prepared in the examples and comparative example 4 loaded into an upflow denitrification packed bed. DETAILED DESCRIPTION

[0036] The application will be further described in conjunction with specific examples, but the examples do not limit the application in any form. Unless otherwise specified, the reagents, methods and equipment used in the application are conventional reagents, methods and equipment in the technical field.

[0037] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0038] EXAMPLE

[0039] S1. 8g of polyvinyl alcohol and 1g of mercaptan alginate sodium were added to 100ml of distilled water, and stirred at 90℃ in a water bath until completely dissolved to obtain a gel solution.

[0040] The preparation of mercaptan alginate includes the following steps:

[0041] S11. 1g of sodium alginate powder was added to 100ml of distilled water and stirred at 90℃ in a water bath until completely dissolved;

[0042] S12. After cooling to room temperature, 1-ethyl-(3-dimethylaminopropyl)-carbodiimide hydrochloride and 100 mmol / L N-hydroxysuccinimide with final concentrations of 50 mmol / L were added to the solution respectively, and the reaction was stirred at room temperature for 60 min;

[0043] S13. Cysteine was added to the reaction in an amount of 2 times the weight of sodium alginate, and the pH was adjusted to about 4.0, and the reaction was stirred at room temperature for 2 h;

[0044] S14. The pH of the reaction was raised to 6.0, and the reaction was stirred at room temperature for 1 h;

[0045] S15. The reaction solution was dialyzed with 1 mmol / L hydrochloric acid solution, dialyzed twice with 1% NaCl in 1 mmol / L HCl solution, and purified again by dialysis with 1 mmol / L HCl aqueous solution. The sample was freeze-dried at -40℃, and stored at 4℃ for use.

[0046] S2. After cooling the gel solution obtained in S1 to room temperature, 1 wt% of an anionic aqueous polyurethane with a solid content of 30% was added and stirred for 5 min to obtain a porous modified gel.

[0047] S3. 15 wt% of sulfur powder and 2.5 wt% of iron-rich sludge biochar were added to the porous modified gel obtained in S2, and stirred and mixed to obtain a modified reinforced gel with a reinforced network structure and containing inorganic electron donors.

[0048] The preparation of the iron-rich sludge biochar includes the following steps:

[0049] S31. After drying the sludge from the sludge water of a water purification plant at 105℃, dry sludge was obtained, which contained 20 wt% to 40 wt% of iron elements and 20 wt% to 30 wt% of organic matter (both on a dry weight basis);

[0050] S32. The dry sludge was thermally decomposed at 700℃ under anoxic conditions for 4 h, and after cooling, it was ground to 200 to 300 mesh to obtain the iron-rich sludge biochar.

[0051] S4. 30 wt% of a sulfur autotrophic bacteria solution was added to the modified reinforced gel obtained in S3, and stirred uniformly to obtain a gel-bacteria solution mixture. The sulfur autotrophic bacteria solution was a mixed bacteria solution of Thiobacillus denitrificans and Sulfococcus, and the total number of viable bacteria was 3.50×10 8 CFU / g.

[0052] S5. 4 g of calcium chloride was completely dissolved in 200 ml of distilled water to prepare a 2 wt% calcium chloride cross-linking solution.

[0053] S6. The gel-bacteria liquid mixture obtained in S4 was dropped into a 2 wt% calcium chloride cross-linking solution using a pear-shaped separatory funnel or a perforated plate for immobilization, and recross-linked at 4°C for 12 h to obtain composite capsules with a diameter of 3-4 mm.

[0054] Comparative Example 1

[0055] The difference between the example and comparative example 1 is that sodium alginate is used instead of thiolated sodium alginate when preparing the microbial agent capsules in comparative example 1, and no aqueous polyurethane, iron-rich sludge biochar is added; the specific process is as follows:

[0056] S1. 8 g of polyvinyl alcohol and 1 g of sodium alginate were added to 100 ml of distilled water, and stirred at 90°C in a water bath until completely dissolved to obtain a gel solution;

[0057] S2. After the gel solution was cooled to room temperature, 30 wt% of the sulfur autotrophic bacteria liquid was added and stirred uniformly;

[0058] S3. 4 g of calcium chloride was completely dissolved in 200 ml of distilled water to prepare a 2 wt% calcium chloride cross-linking solution;

[0059] S4. The mixture was dropped into the cross-linking solution using a pear-shaped separatory funnel or a perforated plate for immobilization, and recross-linked at 4°C for 12 h to obtain composite capsules with a diameter of 3-4 mm.

[0060] Comparative Example 2

[0061] The preparation method of this comparative example is similar to that of the example, the difference being that no aqueous polyurethane modification is added.

[0062] Comparative Example 3

[0063] The preparation method of this comparative example is similar to that of the example, the difference being that no iron-rich sludge biochar is added.

[0064] Comparative Example 4

[0065] The preparation method of this comparative example is similar to that of the example, the difference being that no sulfur autotrophic bacteria liquid is added.

[0066] Performance test:

[0067] The appearance characteristics of the sulfur autotrophic bacteria agent capsules of the example are shown in FIG. 1, and the capsules are spherical, without tailing, aggregation, etc. Figure 1

[0068] 2. Mechanical properties

[0069] ​Randomly selected quantitative examples and comparative examples of the microbial agent capsules were placed on a balance and pressed slowly with a plate. The reading at the time of breaking was recorded as the compressive strength index. Another quantitative capsule was placed in 40 mL of distilled water and stirred at 500 rpm / min for 120 min at room temperature. The retention rate of the unbroken capsule was measured as the mechanical strength index. According to the experimental results, Comparative Example 1 without the addition of waterborne polyurethane and sludge biochar had the worst physical properties. Comparative Example 2 using biochar as an adsorption substrate did not significantly improve the mechanical strength of the capsule. Comparative Example 3 modified with waterborne polyurethane had a three-dimensional network structure inside the capsule, and the retention rate of the capsule after high-speed stirring reached 70%. Further, the examples reduced the water swelling properties of the capsule by using biochar, significantly improving the mechanical strength of the material, with a compressive strength of 252.35 g and a capsule retention rate of 82%.

[0070] Table 1 Physical properties of microbial agent capsules

[0071]

[0072] 3. Mass transfer efficiency

[0073] A quantitative microbial agent capsule of the examples and comparative examples was placed in a 0.01% methylene blue solution, and the mass transfer efficiency of the carrier was determined by detecting the change in absorbance at 660 nm at the sampling time. Figure 2 As can be seen from the comparison, the examples and Comparative Example 3 with the addition of waterborne polyurethane had better effects, with a maximum mass transfer efficiency of about 93%. The maximum mass transfer efficiencies of Comparative Examples 1 and 2 were 31.79% and 31.12%, respectively. Waterborne polyurethane is beneficial to the formation of a porous structure in the capsule, improving the mass transfer efficiency and swelling properties. On the other hand, although the addition of iron-rich sludge biochar increased the mass transfer equilibrium time of the capsule from 1.5 h to 4 h, it did not ultimately affect the mutual exchange of the capsule and the simulated nutrients.

[0074] Application Example: Sulfur autotrophic microbial agent capsule treatment of simulated wastewater experiment

[0075] The composite microbial agent capsules prepared in the examples and Comparative Examples 1 to 3 were loaded into four identical fluidized bed reactors. A water flow rate of 5 L / min was provided by an external circulating water circuit to fluidize the particles, and the HRT was adjusted to 2.5 h. Sodium bicarbonate was added to the wastewater to supplement alkalinity, and the pH value was about 7.60. Potassium nitrate was added to supplement nitrate nitrogen, and the concentration was about 35 mg / L.

[0076] From the comparison, it can be seen that the waterborne polyurethane modified in the examples had a better effect on the removal of nitrogen and phosphorus in the wastewater. The removal rates of nitrogen and phosphorus in the examples were 73.6% and 73.2%, respectively, which were significantly higher than those of Comparative Examples 1 to 3. Figure 3It can be seen that the example has a short start-up time and exhibits excellent denitrification effect after starting operation. The immobilized microorganisms grow rapidly, the denitrification performance of the system gradually improves, and the effluent nitrate concentration remains consistently below 8 mg / L during stable operation, with no nitrite nitrogen accumulation. In contrast, the effluent nitrate concentration of Comparative Example 1 is close to 20 mg / L, and the highest nitrite nitrogen concentration reaches 2.69 mg / L. Under the combined action of thiolated sodium alginate, waterborne polyurethane, and iron-rich sludge biochar, the composite microbial agent capsules significantly enhance the denitrification process.

[0077] Specifically, Comparative Example 3 performed better than Comparative Examples 1 and 2 in the initial stage of operation, but its denitrification performance subsequently declined, with an average effluent nitrate nitrogen concentration (16.23 mg / L) higher than that of Comparative Example 2 (13.87 mg / L). These observations indicate that introducing waterborne polyurethane into the gel can increase the microbial loading, but the lack of iron-rich sludge biochar to supplement electron donors leads to incomplete denitrification. The accumulation of low nitrite nitrogen (average effluent concentration of 0.37 mg / L during the stable period) in Comparative Example 3 can be attributed to the following reasons: ① The iron-rich sludge biochar system is more conducive to the growth of iron-reducing bacteria, promoting the reduction of Fe(III) to Fe(II); ② Fe(II) can react with nitrate nitrogen under the action of microorganisms, enriching the electron donor combination within the system.

[0078] 10Fe 2+ +2NO3 - +24H₂O→N₂+10Fe(OH)₃+2 ... +

[0079] The composite microbial agent capsules prepared in Examples 1 and 2 (Comparative Example 4) were respectively added to two upflow packed filter beds with identical structures, at a dosage of 10% of the filter media volume. Both reactors were started up and in a steady state, with effluent nitrate nitrogen levels of approximately 8.79 mg / L. Figure 4 As shown, the composite microbial agent capsules prepared in this application can be directly used to enhance the denitrification effect of sulfur autotrophic fixed beds. Specifically, in the example, due to the immobilization of a large number of active microorganisms in the system, the denitrification rate is greatly accelerated, and the effluent nitrate nitrogen concentration can be lower than 1 mg / L; while in Comparative Example 4, although no active microorganisms were encapsulated, the bioavailability of sulfur was increased by modifying the gel, and the amorphous iron in the iron-rich sludge biochar improved the electron donor deficiency, resulting in a reduction of effluent nitrate nitrogen by about 40%.

[0080] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method of preparing a structurally reinforced modified sulphur autotrophic bacteria capsule, characterized by: The preparation method comprises the following steps: S1. Dissolving polyvinyl alcohol and thiolated alginate in water at 90℃ to obtain a gel solution, wherein the content of polyvinyl alcohol is 6-10wt%, and the content of thiolated alginate is 0.5-2wt%; the thiolated alginate is activated by reacting alginate solution with 1-ethyl-3-dimethylaminopropyl-carbodiimide hydrochloride and N-hydroxysuccinimide at room temperature; then, cysteine is added, the pH is adjusted to about 4.0, and the reaction is stirred at room temperature; then, the pH is increased to 6.0, and the reaction is stirred at room temperature for 0.5-2h; finally, the obtained reaction solution is purified by dialysis, and the obtained product is freeze-dried to obtain a thiolated alginate gel; S2. After the gel solution is cooled to room temperature, 1-5wt% of anionic waterborne polyurethane with a solid content of 30% is added and stirred to obtain a porous modified gel; S3. Adding 10-20wt% of sulfur powder and 1-5wt% of iron-rich sludge biochar to the porous modified gel, and stirring to mix to obtain a modified and strengthened gel; S4. Adding 30-40wt% of sulfur autotrophic bacteria liquid to the modified and strengthened gel, stirring to mix uniformly to obtain a gel-bacteria liquid mixture, and then dropping the gel-bacteria liquid mixture into a crosslinking liquid to obtain the structure-strengthened modified sulfur autotrophic bacteria agent capsule.

2. The production method according to claim 1, characterized by, The thiolated alginate is thiolated sodium alginate, thiolated calcium alginate or thiolated potassium alginate.

3. The preparation method according to claim 1, characterized in that, The particle size of the sulfur powder and the iron-rich sludge biochar is 200-300 mesh.

4. The method of claim 1, wherein, The iron-rich sludge biochar is prepared by anaerobic thermal decomposition of iron-rich sludge at 500-700℃; according to dry weight, the content of iron element in the iron-rich sludge is 20wt%-40wt%, and the content of organic matter is 20wt%-30wt%.

5. The preparation method according to claim 1, characterized in that, The total viable bacteria count in the sulfur autotrophic bacteria liquid is ≥2×10 8 CFU / g, and the sulfur autotrophic bacteria liquid is Thiobacillus denitrificans and / or Sulfomonas bacteria liquid.

6. The method of claim 1, wherein, The crosslinking liquid is a 2-4wt% calcium chloride solution.

7. The modified and strengthened sulfur autotrophic composite bacteria agent capsule prepared by the preparation method of any one of claims 1-6.

8. The application of the modified and strengthened sulfur autotrophic composite bacteria agent capsule of claim 7 in water treatment.

9. A water treatment agent, characterized by, The modified and strengthened sulfur autotrophic composite bacteria agent capsule of claim 7.

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