A biological process for recovering elemental sulfur from sulfur paste

Abstract

The present application provides a kind of biological method for recovering elemental sulfur from sulfur paste, belongs to environmental microbiological technology and solid waste resource technology field.The biological method includes the following steps: inoculating sulfur-oxidizing bacteria in sulfur paste, then carrying out oxidation reaction under aerobic condition, to obtain mixture A;Mixture A is subjected to solid-liquid separation, to obtain acidic supernatant and sulfur mud containing elemental sulfur;The pH value of acidic supernatant is adjusted to 6.5-8.5, then mixed with sulfur mud, to obtain mixture B;Inoculate sulfur-reducing bacteria in mixture B to obtain reaction system;Reaction system is reacted under anaerobic condition, to generate elemental sulfur precipitate.The present application utilizes the synergistic coupling of sulfur-oxidizing bacteria and sulfur-reducing bacteria, realizes efficient removal of impurities in sulfur paste and directional enrichment and recovery of elemental sulfur, and the purity of recovered elemental sulfur is high.

Description

Technical Field

[0001] This invention relates to the fields of environmental microbiology technology and solid waste resource utilization technology, specifically to a biological method for recovering elemental sulfur from sulfur paste. Background Technology

[0002] Sulfur paste, a byproduct of biogas production, has a complex composition. Traditional physicochemical methods, such as melting, are energy-intensive and prone to generating sulfur dioxide pollution, while solvent extraction methods pose solvent toxicity and safety risks. Biological treatment of sulfur-containing waste has advantages such as mild conditions, low cost, and environmental friendliness. However, current methods mainly focus on treating soluble sulfides (such as hydrogen sulfide and thiosulfates). Direct biological treatment is inefficient for sulfur paste, which has a complex composition and is rich in solid elemental sulfur.

[0003] Existing technologies include methods that utilize sulfur-oxidizing bacteria to directly oxidize sulfur in sulfur paste. However, this method aims to completely oxidize sulfur into sulfuric acid, failing to recover elemental sulfur resources and instead generating highly concentrated acidic wastewater that requires further treatment. Other methods utilize sulfur-reducing bacteria to reduce sulfate to hydrogen sulfide, which is then chemically converted back to sulfur. However, this process is lengthy and involves the generation and control of the toxic gas hydrogen sulfide, posing a higher risk.

[0004] Chinese patent application publication number CN116621367A discloses a method for preparing elemental sulfur based on sulfate-reducing bacteria, used to treat high-sulfate industrial wastewater. The method steps are as follows: adjusting the COD / SO4 ratio in the wastewater. 2- The ratio and pH value were used to cultivate sulfate-reducing bacteria in an anaerobic tank to produce S. 2- and utilize the generated S 2- The process involves precipitating metal ions from wastewater in an anaerobic tank; adding a catalyst to the remaining wastewater and selectively oxidizing sulfides to elemental sulfur using an oxidant. The catalyst comprises nitrogen-rich materials of transition metals and their oxides, wherein the transition metals include one or more of Cu, Ni, Fe, Co, Mn, Pt, and Pd, and the nitrogen-rich materials include nitrogen-rich biochar and nitrogen-rich covalent organic framework materials (CFOS); the oxidant includes at least one of air, oxygen, and hydrogen peroxide. This method carries the risk of hydrogen sulfide release and requires the addition of both a catalyst and an oxidant to obtain elemental sulfur, necessitating subsequent catalyst recovery, thus increasing production steps and costs.

[0005] Chinese patent document authorization announcement number CN103667096B discloses a sulfur-oxidizing bacterium and a method for removing sulfides using it. The method employs *Themithiobacillus tepidarius* JNU-2 to oxidize reduced sulfur compounds, yielding elemental sulfur and sulfate. However, if this method is used to prepare elemental sulfur from sulfur paste, it suffers from problems such as low recovery rate and low purity of the obtained elemental sulfur. Furthermore, the elemental sulfur is often encapsulated with bacterial cells and impurities, making it difficult to purify and recover.

[0006] Therefore, developing a new biotechnology that can directly, efficiently, and safely process sulfur paste and recover elemental sulfur has significant application value. Summary of the Invention

[0007] In view of this, the present invention provides a biological method for recovering elemental sulfur from sulfur paste, which utilizes the synergistic coupling of sulfur-oxidizing bacteria and sulfur-reducing bacteria to achieve efficient removal of impurities in sulfur paste and targeted enrichment and recovery of elemental sulfur, resulting in high purity of recovered elemental sulfur.

[0008] To achieve the above objective, the present invention provides a biological method for recovering elemental sulfur from sulfur paste, comprising the following steps: (1) Inoculate sulfur-oxidizing bacteria into sulfur paste, and then carry out an oxidation reaction under aerobic conditions to obtain mixture A; (2) The mixture A was subjected to solid-liquid separation to obtain an acidic supernatant and sulfur mud containing elemental sulfur; (3) Adjust the pH of the acidic supernatant to 6.5-8.5, and then mix it with sulfur mud to obtain mixture B; (4) Inoculate sulfur-reducing bacteria into mixture B to obtain a reaction system; the reaction system reacts under anaerobic conditions to generate elemental sulfur precipitate.

[0009] Sulfur paste includes soluble reducing sulfides and solid elemental sulfur. Taking biogas sulfur paste as an example, biogas sulfur paste is a byproduct of biogas desulfurization. Biogas sulfur paste is mainly composed of three parts: elemental sulfur, water, and impurities. Elemental sulfur is the main component, while the content of impurities is relatively low, usually below 10%, such as about 5%. The impurities are complex in composition, mainly consisting of desulfurizing agent carriers (such as iron oxide, activated carbon, etc.) as well as a small amount of soluble reducing sulfides and a small amount of incompletely separated biomass particles.

[0010] Biogas is a renewable biological resource, and biogas sulfur paste is a bio-based sulfur paste. This type of sulfur paste contains elemental sulfur, and the recovery of elemental sulfur enables the green and sustainable utilization of biogas sulfur paste. The sulfur paste can also be from the petroleum industry or the coal industry, but petroleum industry sulfur paste and coal industry sulfur paste are both chemical sulfur pastes, which are non-renewable and have more complex compositions.

[0011] In step (1), sulfur-oxidizing bacteria are used to oxidize the soluble reducing sulfides in the sulfur paste. Specifically, sulfur-oxidizing bacteria are used to completely oxidize the soluble reducing sulfides such as thiosulfates and polysulfates in the sulfur paste into sulfuric acid. This step aims to eliminate impurity sulfur that interferes with subsequent reactions and to create an acidic environment.

[0012] In step (3), the pH value is adjusted using an alkaline substance such as NaOH or Ca(OH)2 solution. The reason for adjusting the pH value is as follows: the pH value of the acidic supernatant is extremely low (about 1.5), which is a strongly acidic environment; while the survival environment of sulfur-reducing bacteria in the subsequent step (4) is neutral or weakly alkaline, so it is necessary to adjust the pH value of the acidic supernatant here so that the sulfur-reducing bacteria can survive and play a role in step (4). If the pH value is not adjusted, a large number of sulfur-reducing bacteria will die after inoculation, making step (4) impossible. Optimally, the pH value of the acidic supernatant is adjusted to 6.5-7.5.

[0013] The mixing in step (3) refers to mixing the pH-adjusted supernatant and sulfur mud by stirring to obtain a slurry mixture B. The specific method of stirring and mixing includes: stirring at 100-300 rpm for 10-30 minutes under normal pressure and room temperature (e.g., 20-35℃) to make the sulfur mud uniformly suspended in the supernatant, forming a slurry with uniform solid-liquid mixing, which is mixture B.

[0014] In step (4), sulfur-reducing bacteria are used to convert SO4 into sulfur. 2- The sulfur is reduced to H2S, which reacts chemically with the pre-existing elemental sulfur in the reaction system to generate soluble polysulfides. The polysulfides decompose in situ in the reaction system, regenerating elemental sulfur precipitates. In short, the newly generated H2S chemically attacks and "dissolves" the existing elemental sulfur particles in the system, forming soluble polysulfides. These polysulfides are unstable in the reaction environment of step (4) and will decompose and recrystallize into new, purer elemental sulfur crystals. The original sulfur mud mainly contains elemental sulfur, as well as bacteria and impurities (mainly inorganic salt impurities) wrapped in elemental sulfur. When the elemental sulfur is "dissolved" by H2S to form soluble polysulfides, the bacteria, inorganic salts and other impurities that were originally wrapped or adsorbed in the sulfur particles are released into the solution, thereby achieving the separation of impurities. The newly precipitated elemental sulfur is a recrystallization, therefore it has higher purity and crystallinity. This is like a recrystallization purification process, where the old sulfur is dissolved and then recrystallized, thus generating new, purer elemental sulfur (S). 0 .

[0015] Simply put, it's SO4 2- +Organic carbon source→H2S→S 0The newly generated hydrogen sulfide will react chemically with the impure sulfur mud already present in the reaction system, like "dissolution and recrystallization", dissolving the old sulfur and then re-precipitating it, thereby generating new, purer elemental sulfur.

[0016] Further, in step (4), exogenous sulfate is added to the reaction system so that the molar ratio of sulfate to elemental sulfur is 1:1 to 1:5.

[0017] The exogenous sulfate is sodium sulfate, potassium sulfate, etc. The reason for adding exogenous sulfate is as follows: In mixture B of step (3), the molar ratio of sulfate to elemental sulfur (sulfur-sulfur ratio) is 1:5 to 1:20. The purpose of adding exogenous sulfate here is to provide sufficient and stable electron acceptors (sulfate ions) for sulfate-reducing bacteria in the system, so as to ensure that they can continue to metabolize and generate excess hydrogen sulfide.

[0018] By precisely controlling the initial sulfur-to-sulfur ratio in the reaction system, the purity and crystal form of elemental sulfur recrystallization can be significantly affected. The method described in this invention can be implemented in the following two ways: (1) Material recycling mode: After adjusting the pH value of all the acidic supernatant produced in the aerobic oxidation stage, it is mixed with all the sulfur sludge containing elemental sulfur in the anaerobic reduction stage. This method is simple to operate, and the molar ratio of sulfate to elemental sulfur (sulfur-sulfur ratio) naturally forms in the range of 1:5 to 1:20. It is suitable for treating conventional sulfur paste and can effectively recover high-purity elemental sulfur. (2) Optimized control mode: The sulfate concentration in the supernatant and the elemental sulfur content in the sulfur mud are determined by chemical analysis. By adding exogenous sulfate, the sulfur-to-sulfur ratio in the system is actively controlled within the range of 1:1 to 1:5 to optimize the metabolic environment of sulfur-reducing bacteria, thereby controlling the amount of hydrogen sulfide generated and achieving the optimal reaction ratio with the existing elemental sulfur in the system. This enables a more efficient and thorough 'dissolution-recrystallization' purification process of elemental sulfur, ultimately obtaining elemental sulfur products with higher purity and better crystallinity. This optimized mode is particularly suitable for processing complex sulfur pastes or scenarios with higher requirements for product appearance.

[0019] Further, in step (4), 5%-15% of the total volume of sulfur-reducing bacteria in logarithmic growth phase (also called activated bacterial solution) is inoculated into mixture B.

[0020] Furthermore, in step (4), the anaerobic conditions include: an oxidation-reduction potential below -300 mV. In addition, in step (4), the reaction temperature of the reaction system is 35-40℃ and the reaction time is 5-9 days; optimally, the reaction temperature is 35-37℃ and the reaction time is 5-7 days.

[0021] After adjustment in step (3), the initial pH of mixture B is 6.5-8.5, providing a suitable initial acid-base environment for the subsequent anaerobic reaction. In step (4), the pH of the reaction system will fluctuate naturally due to microbial metabolism, but based on the initial pH range set in step (3), it can usually maintain the activity requirements of sulfur-reducing bacteria, and no additional adjustment is required during the reaction process.

[0022] By setting the above conditions, an optimal working environment is created for sulfur-reducing bacteria, characterized by anaerobic conditions, suitable temperature, appropriate pH, and sufficient nutrients, to ensure that they can efficiently reduce sulfate.

[0023] Furthermore, in step (4), an organic carbon source needs to be added to the reaction system as an electron donor.

[0024] Furthermore, the organic carbon source is one or more of sodium lactate, ethanol, sodium acetate, methanol, glucose, and starch; preferably, the organic carbon source is sodium lactate or ethanol.

[0025] Furthermore, in step (1), the aerobic conditions include: introducing sterile air and controlling dissolved oxygen at 2-4 mg / L. In addition, in step (1), the oxidation reaction temperature is 28-45℃ and the reaction time is 3-8 days; optimally, the temperature is 28-32℃, the pH decreases naturally (without adjustment), and the reaction time is 3-5 days.

[0026] The above conditions facilitate the efficient oxidation of soluble reducing sulfides in sulfur paste by sulfur-oxidizing bacteria. Sterile air is introduced to prevent interference from other microorganisms.

[0027] Further, in step (1), the sulfur-oxidizing bacteria are obligate acidophilic sulfur-oxidizing bacteria, which are one or more of the following: Thiobacillus thiooxidans, Thiobacillus acidophilus, Thiobacillus thermophilic sulfur oxidizing, Thiobacillus thermophilic acidophilus.

[0028] Obligatory acidophilic sulfur oxidizing bacteria oxidize reduced sulfides (such as thiosulfate) into sulfuric acid in an acidic environment.

[0029] Further, in step (4), the sulfur-reducing bacteria are sulfate-reducing bacteria, which are one or more of the following: desulfovibrio, desulfomonas, desulfophylloxera, desulfurenterobacteria, desulfococcus, desulfobacterium, and desulfonobacterium.

[0030] The genus *Desulfovibrio* includes *Vibrio vulnificus*, *Desulfovibrio desulfurization*, or *Desulfovibrio megaloblasticus*, etc. The genus *Desulfomonas* includes *Acetyloxydesulfomonas*, etc.

[0031] Furthermore, the sulfate-reducing bacteria are at least one of the genera *Desulfomonas* and *Desulfophyllum*, and one or more of the genera *Desulfovibrio*, *Desulfoenterobacter*, *Desulfococcus*, *Desulfobacterium*, and *Desulfonobacterium*.

[0032] One or more of the genera *Desulfovibrio*, *Desulfuric Enterobacter*, *Desulfococcus*, *Desulfobacterium*, and *Desulfuric Acidobacter* play a dominant role as the dominant microorganism, while at least one of the genera *Desulfomonas* and *Desulfophyllum* plays an auxiliary role as the auxiliary microorganism. Through the synergistic effect of the dominant and auxiliary microorganisms, a complex metabolic network is formed, which effectively promotes the dissolution-recrystallization process of elemental sulfur in the system. This is beneficial for accelerating and optimizing the purification process of elemental sulfur, thereby improving the purity and recovery rate of elemental sulfur.

[0033] Further, after the reaction in step (4) is completed, mixture C is obtained. Mixture C is subjected to solid-liquid separation to obtain sediment. The sediment is washed and dried to obtain elemental sulfur product.

[0034] The elemental sulfur product here is mainly the higher purity elemental sulfur precipitate regenerated in step (4). The sediment is washed with deionized water to remove attached salts and bacteria. Finally, it is vacuum dried at 80°C to obtain a light yellow, high-purity biological elemental sulfur product. If biogas sulfur paste is used as raw material, the sediment here is bio-based sulfur mud.

[0035] Further, in step (1), the sulfur paste is first mixed with water to make a slurry and then sterilized. Then, sulfur-oxidizing bacteria are inoculated into the slurry. 5%-10% of the volume of the logarithmic growth phase bacterial solution of sulfur-oxidizing bacteria (also called activated bacterial solution) is inoculated into the slurry.

[0036] Mix sulfur paste and sterile water to obtain a slurry with a solid content of 5%-16%. To eliminate interference from other microorganisms, pasteurize the slurry (80-85℃, hold for 30 minutes) or autoclave (121℃, 20 minutes), and cool it to room temperature (25-35℃) for later use.

[0037] The logarithmic growth phase bacterial suspension (also called activated bacterial suspension) of the present invention contains bacterial cells with high metabolic activity. Its preparation method includes the following steps: activating the standard strain of the desired bacterial species under its corresponding culture medium and culture conditions; after 2-3 consecutive subculturings, a bacterial cell density (OD) of high level is obtained in the late logarithmic growth phase. 600 The bacterial suspension has a concentration of 0.8–1.2, and a viable cell count concentration of 1 × 10⁻⁶. 8 ~ 5×10 8 CFU / mL.

[0038] The above-described technical solution of the present invention has at least the following beneficial effects: 1. Green and environmentally friendly: The entire process is carried out at normal temperature and pressure, the reaction is mild and the energy consumption is extremely low; it uses the metabolism of microorganisms as the driving force of the reaction, without adding harmful chemicals, catalysts and oxidants, without secondary pollution and with low cost.

[0039] 2. Thorough resource recovery: Through a coupled biological process of "oxidation and purification-reduction", soluble sulfur impurities in sulfur paste are converted into sulfuric acid, which is then reduced in situ and directionally converted into elemental sulfur, ultimately obtaining high-purity sulfur products, thus realizing a closed-loop cycle of sulfur elements.

[0040] 3. High product purity and safety: The sulfur produced by bio-generation has high purity, and the process avoids the accumulation and emission of toxic hydrogen sulfide gas, resulting in good production safety.

[0041] 4. The object of treatment is solid waste, realizing its resource utilization: This invention targets the difficult-to-treat solid sulfur paste and realizes its deep resource utilization through microbial coupling, providing a brand-new technical path for sulfur paste treatment.

[0042] 5. High recovery rate and good resource utilization: This invention achieves efficient and targeted conversion and recovery of sulfur through a coupled process. For example, when using the method of this invention to treat typical biogas sulfur paste, the recovery rate of elemental sulfur can reach over 85%, and the purity can reach over 98%. The recovery rate of elemental sulfur (%) = (mass of elemental sulfur in the final product / mass of total sulfur in the raw sulfur paste) × 100%. Attached Figure Description

[0043] Figure 1 The light yellow sulfur powder of Example 1; Figure 2 The product is a dark brown to black solid, as shown in Comparative Example 2. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0045] Example 1 A biological method for recovering elemental sulfur from sulfur paste includes the following steps: (1) Take 1.0 kg of biogas sulfur paste with a moisture content of 30%, mix it with 5.0 L of sterile water to form a slurry, paste it at 85℃ for 30 minutes, cool it to 30℃ to obtain a slurry; transfer the slurry to an aerobic reactor, inoculate it with 10% of the slurry volume of logarithmic growth phase bacterial solution of Thiobacillus thiooxidans, pass sterile air (DO=3mg / L), react at 30℃ for 4 days to obtain mixture A; (2) Centrifuge mixture A to obtain a supernatant with a pH of approximately 1.5 and sulfur mud containing elemental sulfur; (3) Adjust the pH of the supernatant to 7.0 with NaOH, and then stir and mix it with the sulfur mud so that the sulfur mud is evenly suspended in the supernatant to form a slurry with uniform solid-liquid mixture. This slurry is mixture B. (4) Transfer mixture B to an anaerobic reactor, inoculate 10% of the total volume of mixture B with logarithmic growth phase of ordinary desulfovibrio (belonging to the genus Desulfovibrio), and add sodium lactate (molar ratio of sodium lactate (calculated as COD) to sulfate is 4-5:1) as carbon source to obtain a reaction system. The molar ratio of sulfate to elemental sulfur in the reaction system is controlled at 1:10. The reaction is carried out at 37℃ under strict anaerobic conditions (oxidation-reduction potential is below -300 mV) for 6 days. During the reaction, the pH value in the reaction system fluctuates naturally. After the reaction is completed, mixture C is obtained. (5) Centrifuge mixture C, collect the solid (settled material), wash three times with deionized water, and vacuum dry at 80℃ to obtain light yellow sulfur powder. Using the test method of national standard GB / T 2449.1-2021, the sulfur purity reached 98.5%.

[0046] Example 2 A biological method for recovering elemental sulfur from sulfur paste includes the following steps: (1) Take 1.5 kg of biogas sulfur paste with a moisture content of about 35%, mix it with 7 L of deionized water to make a slurry, and sterilize it with high pressure steam at 121℃ for 20 minutes to completely eliminate the interference of miscellaneous bacteria. After cooling to 30℃, the slurry is obtained; the slurry is transferred to an aerobic bioreactor, and 10% (v / v) of the slurry volume of logarithmic growth phase bacterial solution of Thiobacillus thiooxidans is inoculated. Sterile air is introduced and dissolved oxygen is controlled at 3 mg / L. The reaction is stirred at 30℃ for 4 days to oxidize soluble impurities such as thiosulfate. After the reaction is completed, mixture A is obtained. (2) The mixture A was centrifuged to obtain an acidic supernatant and sulfur mud containing elemental sulfur; (3) Neutralize the acidic supernatant with calcium carbonate powder to pH 7.0, and then mix it with sulfur mud to obtain mixture B; (4) Transfer mixture B into an anaerobic reactor, inoculate with 15% (v / v) of the total volume of supernatant and sulfur mud with logarithmic growth phase of Vibrio desulfurization, and use ethanol (molar ratio of ethanol (calculated as COD) to sulfate 4-5:1) as electron donor to obtain a reaction system. Control the molar ratio of sulfate to elemental sulfur in the reaction system at 1:8. React the reaction system at 35℃ under absolute anaerobic (ORP<-350mV) conditions for 6 days. During the reaction, the pH value in the reaction system fluctuates naturally. After the reaction is completed, mixture C is obtained. (5) The mixture C was centrifuged to obtain bio-sulfur mud. The bio-sulfur mud was washed three times with deionized water and dried under vacuum at 80°C to obtain a light yellow bio-sulfur product with a purity of 98.2%.

[0047] Example 3 A biological method for recovering elemental sulfur from sulfur paste includes the following steps: (1) To verify the adaptability of the process of the present invention to extreme materials, the complex sulfur paste with high solid content (40%) and high organic matter content produced by an industrial biogas project was optimized. First, 2.0 kg of the sulfur paste was diluted to a uniform slurry with a solid content of 5%, and then sterilized at 121°C for 20 minutes to eliminate interference from miscellaneous bacteria and obtain the slurry; In the aerobic oxidation stage, thermophilic sulfur oxidizing bacteria were used as inoculum. 10% of the volume of thermophilic sulfur oxidizing bacteria in logarithmic growth phase was inoculated into the slurry. The enhanced oxidation was carried out for 5 days under the conditions of 40℃ and natural pH decrease. This high temperature condition effectively improved the decomposition efficiency of soluble sulfur impurities and organic matter. After the reaction was completed, mixture A was obtained. (2) Mixture A is subjected to solid-liquid separation to obtain acidic supernatant and sulfur mud; (3) The obtained acidic supernatant was precisely neutralized to neutral (pH=7.0) with sodium hydroxide, and then mixed with sulfur mud to obtain mixture B; (4) In the anaerobic reduction stage, logarithmic growth phase bacterial solution of common desulfurization Vibrio and logarithmic growth phase bacterial solution of desulfurization leaf bacteria were inoculated into mixture B. The inoculation amount of the two bacterial solutions was 5% of the total volume of mixture B, and the total inoculation amount of the two bacterial solutions was 10%. Sodium lactate was added as an electron donor to obtain the reaction system. The initial sulfur-to-sulfur ratio in the reaction system was precisely controlled. The sulfate concentration in the clear liquid and the elemental sulfur content in the sulfur mud were measured. By adding exogenous sodium sulfate, the molar ratio of sulfate to elemental sulfur in the reaction system was controlled at 1:1.5. The reaction system was subjected to 7 days of reaction at 37℃ under strict anaerobic conditions (ORP below -300mV). During the reaction, the pH value in the reaction system fluctuated naturally, successfully inducing the formation of sulfur crystals with regular morphology, and obtaining mixture C. (5) The mixture C was centrifuged, washed with deionized water and vacuum dried at 80°C to obtain a high-purity elemental sulfur product in the form of light yellow, flaky crystals. The purity was tested to be 99.0%, which is significantly better than the treatment effect of ordinary sulfur paste. This proves that the purity and appearance of the final product can be further improved by optimizing the combination of strains and reaction parameters.

[0048] The high-organic-matter complex sulfur paste of this embodiment has a much higher organic matter content than conventional sulfur paste. It typically contains high concentrations of residual biomass such as oils, proteins, and carbohydrates. These substances constitute a complex mixed system with strong reducing properties and easy biodegradation. This extremely high organic background not only fiercely competes with functional bacteria for electron donors and nutrients but also easily leads to abnormal proliferation of miscellaneous bacteria, thereby severely interfering with and inhibiting the target sulfur conversion pathway. If only a single bacterial species, such as common desulfurizing Vibrio, is used for treatment, problems such as low anaerobic reaction efficiency, long cycle, poor product purity, and poor appearance will be encountered, making it difficult to achieve efficient sulfur resource recovery.

[0049] Example 4 This embodiment is basically the same as embodiment 1, except that: in step (1), the sulfur oxidizing bacteria is acidophilic sulfobacterium, and 8% of the volume of the logarithmic growth phase bacterial solution of acidophilic sulfobacterium is inoculated into the slurry. The aerobic conditions include: introducing sterile air, controlling dissolved oxygen at 2 mg / L, the oxidation reaction temperature at 45°C, and the reaction time at 3 days. In step (3), the pH of the acidic supernatant is adjusted to 6.5; In step (4), 5% of the total volume of the logarithmic growth phase of the desulfurized enterobacteria spp. in the mixture B is inoculated into the mixture B. The reaction temperature of the reaction system is 35°C and the reaction time is 9 days.

[0050] Example 5 This embodiment is basically the same as embodiment 3, except that: in step (1), the sulfur oxidizing bacteria is acidophilic sulfur bacteria, and 5% of the volume of the logarithmic growth phase bacterial solution of sulfur oxidizing bacteria is inoculated into the slurry. The aerobic conditions include: introducing sterile air, controlling dissolved oxygen at 4 mg / L, the oxidation reaction temperature at 28°C, and the reaction time at 3 days. In step (3), the pH of the acidic supernatant is adjusted to 7.0; In step (4), 8% of the total volume of logarithmic growth phase bacterial solution (including 4% logarithmic growth phase bacterial solution of Desulfurized Enterobacteriaceae and 4% logarithmic growth phase bacterial solution of Desulfurized Monoclonal B) is inoculated into mixture B. The reaction temperature of the reaction system is 35°C and the reaction time is 9 days.

[0051] Comparative Example 1 A biological method for recovering elemental sulfur from sulfur paste includes the following steps: Take 1.0 kg of biogas sulfur paste from the same source as in the example, prepare sterilized slurry in the same manner, and then inoculate it with Thiobacillus thiooxidans for aerobic treatment (under the same conditions as in Example 1), that is, only perform step (1) of Example 1. The results show that the pH of the reaction system eventually drops below 1.0, but the target product is not elemental sulfur. Chemical analysis shows that more than 95% of the total sulfur in the slurry was completely oxidized to sulfate and entered the liquid phase, and only a very small amount of sulfur mud was obtained in the end, which was wrapped by bacteria and had a purity of less than 70%. This process not only failed to recover sulfur resources, but also generated a large amount of high-concentration acidic sulfur-containing wastewater that needed to be neutralized, which fully proves that a single sulfur oxidation path will lead to the loss of sulfur resources and secondary pollution, thus highlighting the rationality and superiority of the "oxidation and impurity removal-reduction and sulfur extraction" coupled process of the present invention.

[0052] Comparative Example 2 A biological method for recovering elemental sulfur from sulfur paste includes the following steps: (1) Take 1.0 kg of biogas sulfur paste from the same source as in the example, mix it with 5.0 L of sterile water to form a slurry, paste it at 85°C for 30 minutes, and cool it to 30°C to obtain a slurry; (2) Without aerobic oxidation treatment, the obtained slurry is directly centrifuged to obtain supernatant (pH close to neutral) and original sulfur mud containing a large number of impurities; (3) Adjust the pH of the obtained supernatant to 7.0 with NaOH; mix the original sulfur mud with the obtained neutral supernatant to obtain mixture B; (4) Transfer mixture B to an anaerobic reactor, inoculate 10% of the total volume of mixture B with logarithmic growth phase of ordinary desulfurization Vibrio, and add sodium lactate as a carbon source. React for 6 days at 37°C under strict anaerobic conditions (oxidation-reduction potential below -300 mV). The reaction mixture was centrifuged, the solid was collected, washed three times with deionized water, and dried under vacuum at 80°C to obtain a dark brown to black solid product, such as... Figure 2 As shown.

[0053] The purity of elemental sulfur in the obtained solid product was 75%. Compared with the light yellow high-purity sulfur (98.5%) in Example 1, the comparative product was darker in color, lower in purity, and of poorer appearance. The fundamental reason is that soluble reducing sulfides (such as thiosulfates) in the original sulfur paste compete with sulfate-reducing bacteria for electron donors during the anaerobic reduction stage, or are directly reduced to H2S. These prematurely and disorderly generated H2S interfere with the orderly precipitation and purification process of elemental sulfur. At the same time, unoxidized organic matter and other impurities in the sulfur mud are also directly mixed into the final product, resulting in the inability to improve purity.

[0054] This comparative example demonstrates that the lack of a pretreatment step of "aerobic oxidation for impurity removal" fails to effectively remove soluble sulfur impurities and some organic matter from sulfur paste. This results in a complex substrate environment and numerous competing reactions in the subsequent reduction and purification steps, ultimately failing to obtain high-purity, high-grade elemental sulfur products. This, conversely, fully demonstrates the necessity and synergy of coupling the "aerobic oxidation for impurity removal" and "anaerobic reduction for sulfur extraction" steps in this invention; neither can be omitted.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the implementation of the invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A biological method for recovering elemental sulfur from sulfur paste, characterized in that, Includes the following steps: (1) Inoculate sulfur-oxidizing bacteria into sulfur paste, and then carry out an oxidation reaction under aerobic conditions to obtain mixture A; (2) The mixture A was subjected to solid-liquid separation to obtain an acidic supernatant and sulfur mud containing elemental sulfur; (3) Adjust the pH of the acidic supernatant to 6.5-8.5, and then mix it with sulfur mud to obtain mixture B; (4) Inoculate sulfur-reducing bacteria into mixture B to obtain a reaction system; the reaction system reacts under anaerobic conditions to generate elemental sulfur precipitate.

2. The biological method for recovering elemental sulfur from sulfur paste according to claim 1, characterized in that, In step (4), exogenous sulfate is added to the reaction system so that the molar ratio of sulfate to elemental sulfur is 1:1 to 1:

5.

3. A biological method for recovering elemental sulfur from sulfur paste according to claim 1 or 2, characterized in that, In step (1), the aerobic conditions include: dissolved oxygen 2-4 mg / L; in step (4), the anaerobic conditions include: oxidation-reduction potential below -300mV.

4. A biological method for recovering elemental sulfur from sulfur paste according to claim 1 or 2, characterized in that, In step (4), an organic carbon source is added to the reaction system as an electron donor.

5. A biological method for recovering elemental sulfur from sulfur paste according to claim 4, characterized in that, The organic carbon source is one or more of sodium lactate, ethanol, sodium acetate, methanol, glucose, and starch.

6. A biological method for recovering elemental sulfur from sulfur paste according to claim 1 or 2, characterized in that, In step (1), the sulfur-oxidizing bacteria are obligate acidophilic sulfur-oxidizing bacteria, which are one or more of the following: Thiobacillus thiooxidans, Thiobacillus acidophilus, Thiobacillus thermophilic sulfur oxidizing, Thiobacillus thermophilic acidophilus.

7. A biological method for recovering elemental sulfur from sulfur paste according to claim 1 or 2, characterized in that, In step (4), the sulfur-reducing bacteria are sulfate-reducing bacteria, which are one or more of the following genera: desulfovibrio, desulfomonas, desulfophylloxera, desulfenterobacteria, desulfococcus, desulfobacterium, and desulfonobacterium.

8. A biological method for recovering elemental sulfur from sulfur paste according to claim 7, characterized in that, Sulfate-reducing bacteria are at least one of the genera *Desulfomonas* and *Desulfophyllum*, and one or more of the genera *Desulfovibrio*, *Desulfoenterobacter*, *Desulfococcus*, *Desulfobacterium*, and *Desulfonobacterium*.

9. A biological method for recovering elemental sulfur from sulfur paste according to claim 1 or 2, characterized in that, After the reaction in step (4) is completed, mixture C is obtained. Mixture C is subjected to solid-liquid separation to obtain precipitate. The precipitate is washed and dried to obtain elemental sulfur product.

10. A biological method for recovering elemental sulfur from sulfur paste according to claim 1 or 2, characterized in that, In step (1), sulfur paste is first mixed with water to form a slurry and then sterilized before being inoculated with sulfur-oxidizing bacteria.

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