A method and product for recovering phosphorus from wastewater using phosphogypsum in conjunction with sulfur bacteria

Abstract

The application provides a method and product for recovering phosphorus by using phosphogypsum and sulfur bacteria to treat wastewater, and belongs to the technical field of solid waste disposal and resource utilization. The phosphogypsum and microbial inoculum containing sulfur bacteria are put into wastewater for anaerobic and anoxic reaction for a certain time. The method adds industrial waste phosphogypsum into the wastewater treatment process, replaces the strong acid anion sulfate in the phosphogypsum into the medium-strong acid anion phosphate by the action of microorganisms, and achieves the purposes of waste control and phosphorus resource recovery. At the same time, with the reaction, the phosphorus in the microorganism is released into the sewage under anaerobic conditions; the residual phosphorus in the phosphogypsum lattice is also gradually released into the sewage due to the decomposition of the phosphogypsum; finally, all the released phosphorus will be combined with calcium ions in priority, and through the action of microorganisms, the hydroxyapatite (main component is calcium phosphate) precipitate with lower solubility product and more stable properties is formed.

Description

Technical Field

[0001] This invention relates to the field of solid waste disposal and resource utilization technology, and in particular to a method and product for treating wastewater and recovering phosphorus using phosphogypsum in conjunction with sulfur bacteria. Background Technology

[0002] Phosphogypsum (PG) is a byproduct of the wet process for producing phosphoric acid, specifically, phosphoric acid and phosphogypsum produced by the reaction of phosphate rock and sulfuric acid. The main component of phosphogypsum is calcium sulfate dihydrate (CaSO4·2H2O), with a small amount of phosphoric acid impurities. Approximately 5 tons of phosphogypsum are produced for every ton of phosphoric acid produced. Globally, approximately 185 million to 215 million tons of phosphogypsum are produced annually, with about 3 to 4 billion tons currently stockpiled. This large-scale stockpiling of phosphogypsum not only occupies significant land resources but also poses safety and environmental risks. Therefore, the harmless disposal and resource utilization of phosphogypsum have become a bottleneck affecting the production of phosphate chemical enterprises, and the comprehensive utilization of phosphogypsum is crucial for the sustainable development of the phosphate industry. Currently, only 15% of the PG produced annually is recycled, mainly concentrated in five areas: phosphogypsum building materials, underground backfilling, soil conditioner production, cement retarder use, and acid production. However, these methods primarily rely on physicochemical recovery methods. In recent years, microbial treatment methods have attracted much attention due to their advantages such as environmental safety, economic feasibility, high efficiency, and greenness.

[0003] Currently, phosphorus recovery from wastewater mainly involves chemical precipitation, crystallization, and biological phosphorus removal. However, these methods are limited to single physical, chemical, and biological principles and cannot simultaneously utilize multiple principles. Some scholars have proposed using calcium sulfate to adsorb phosphorus from wastewater. However, since calcium sulfate is a solid and a strong acid-base salt, its chemical properties are relatively stable. Therefore, when calcium sulfate is directly added to wastewater, phosphorus removal can only be achieved through physical adsorption, with phosphorus adsorbed onto the surface of calcium sulfate crystals. Consequently, the total amount of phosphorus adsorbed and recovered is relatively small. The academic paper "Study on the Simultaneous Removal of Soluble Pollutants by Microbial Decomposition of Phosphogypsum" reports the simultaneous removal of soluble pollutants by decomposing phosphogypsum using sulfate-reducing bacteria. It shows that a certain concentration of calcium ions in phosphogypsum can promote the activity of sulfate-reducing bacteria, and the small amount of phosphate present in phosphogypsum combines with calcium ions to form calcium phosphate precipitate. However, this study mainly focuses on the precipitation of a small amount of phosphorus in phosphogypsum, which is essentially a chemical precipitation, and the resulting loose calcium phosphate is difficult to recover.

[0004] Therefore, there is an urgent need to provide a simple, convenient, efficient, and environmentally friendly method for phosphorus recovery. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned shortcomings of existing technologies by providing a method and product for treating wastewater and recovering phosphorus using phosphogypsum in conjunction with sulfur bacteria. The related microbial agents and sludge provide usable microorganisms, represented by sulfur bacteria; the wastewater and sludge provide sufficient carbon sources and other trace elements necessary for microbial growth; and the phosphogypsum provides electron acceptors and donors required for sulfur bacteria growth. Sulfur bacteria enhance the decomposition efficiency of calcium sulfate in phosphogypsum, resulting in a phosphorus recovery product (Ca...). 2+ Through biological and chemical processes, it preferentially combines with phosphates in wastewater to form highly crystalline hydroxyapatite precipitate, thereby achieving the goal of recovering phosphorus resources from wastewater.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a method for treating wastewater and recovering phosphorus using phosphogypsum in conjunction with sulfur bacteria. Phosphogypsum and a sulfur-containing microbial agent are added to the wastewater for an anaerobic-anoxic reaction. Phosphate in the wastewater is first adsorbed by phosphogypsum through physicochemical adsorption, and then converted into hydroxyapatite through microbial action, thus achieving phosphorus recovery. The amount of phosphogypsum added is not less than 1:20, based on the molar ratio of calcium ions in the phosphogypsum to phosphate ions in the wastewater; the abundance of sulfur bacteria in the microbial agent is greater than 1%.

[0007] Furthermore, sulfur-containing microbial agents include sludge containing sulfate-reducing bacteria and sulfur-oxidizing bacteria.

[0008] Furthermore, the sulfur bacteria include sulfate-reducing bacteria and sulfur-oxidizing bacteria, wherein the sulfate-reducing bacteria include at least one of the genera *Desulfovibrio*, *Desulfomonas*, *Desulfophyllum*, *Desulfenterobacter*, *Desulfobacterium*, *Desulfococcus*, *Desulfococcus*, and *Desulfuricella*, and the sulfur-oxidizing bacteria include at least one of the genera *Thiobacillus*, *Thiospira*, and *Sulphophyllum*.

[0009] Furthermore, the sulfate concentration in the wastewater is 10~500000 mg / L, the biological oxygen demand is 10~100000 mg / L, the chemical oxygen demand is 50~500000 mg / L, and the total phosphorus content is 0.05~500 mg / L.

[0010] Furthermore, the reaction conditions are: pH 4-10, and reaction temperature 10-50℃.

[0011] Furthermore, the ratio of the amount of phosphogypsum added to the mass of phosphate in the wastewater is (100~500):(2~10).

[0012] Furthermore, the addition of phosphogypsum promotes the enrichment of sulfur bacteria and inhibits the growth of methanogens.

[0013] Furthermore, the addition of phosphogypsum promotes the growth of sulfur-oxidizing bacteria.

[0014] Furthermore, the anaerobic-anoxic reaction environment is provided by UASB, anaerobic contact process, upflow anaerobic sludge blanket, baffle anaerobic process, anaerobic biofilter, anaerobic expanded bed and fluidized bed, third-generation anaerobic process EGSB or IC anaerobic reactor.

[0015] The second objective of this invention is to provide a kit for treating wastewater and recovering phosphorus using phosphogypsum in conjunction with sulfur bacteria. The kit contains phosphogypsum and sulfur bacteria. The phosphogypsum is a byproduct of industrial wet phosphoric acid production. The abundance of sulfur bacteria in the kit is greater than 1%. The dosage of the phosphogypsum, calculated based on the molar ratio of calcium ions in the phosphogypsum to phosphate ions in the wastewater, is not less than 1:20. The dosage of the kit is greater than 20 grams per cubic meter of wastewater.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention provides a method for synergistic phosphorus recovery from wastewater using phosphogypsum. Phosphogypsum and sulfur-containing bacteria microbial agents are added to wastewater and reacted under anaerobic-anoxic conditions for a certain period of time. In the initial stage of the reaction, phosphate in the wastewater is mainly adsorbed by physicochemical means, forming adsorbed phosphate on the surface of phosphogypsum. In the later stage of the reaction, the strong acid anion sulfate in phosphogypsum is replaced by medium-strong acid anion phosphate through microbial action, thereby converting the adsorbed phosphate into bound hydroxyapatite (mainly composed of calcium phosphate) precipitate, so as to realize the recovery of phosphate in wastewater and achieve the purpose of treating waste with waste and recovering phosphorus resources. At the same time, as the reaction proceeds, the polyphosphate accumulated in the microorganisms will be released into the wastewater under anaerobic conditions; the soluble phosphorus, eutectic phosphorus and insoluble phosphorus remaining in the phosphogypsum lattice will also be gradually released into the wastewater due to the decomposition of phosphogypsum; finally, all the released phosphate will preferentially combine with the calcium ions produced by the decomposition of phosphogypsum, forming hydroxyapatite precipitate (mainly composed of calcium phosphate) with lower solubility product and more stable properties through microbial action. In addition, sulfur-oxidizing bacteria in sulfur bacteria can further oxidize and remove sulfides, while also contributing to the production of hydroxyapatite, thereby promoting the precipitation of highly crystalline hydroxyapatite, increasing the phosphate removal rate, and facilitating phosphorus recovery.

[0017] (2) Unlike traditional methods of comprehensive utilization of phosphogypsum, which mainly rely on physicochemical recycling, this invention proposes a biological utilization method. Considering the huge volume of wastewater to be treated, this invention will greatly promote the reduction and resource utilization of phosphogypsum, reduce the harm caused by phosphogypsum stockpiling to water bodies, the atmosphere and the earth's surface, and improve the quality of human life.

[0018] (3) Unlike traditional methods for phosphorus recovery from wastewater, which are limited to single physical, chemical, and biological principles and cannot simultaneously utilize multiple principles, this invention first utilizes the physical adsorption of phosphate by calcium sulfate itself to remove phosphate from wastewater; it also leverages the characteristic of microorganisms releasing polyphosphates under anaerobic-anoxic conditions to further recover phosphorus from the microorganisms; finally, it utilizes the decomposition products of phosphogypsum (Ca... 2+ This method uses biological and chemical precipitation to treat all phosphates in wastewater, thereby utilizing physical, chemical, and biological principles to achieve the goal of phosphorus recovery from wastewater and phosphogypsum.

[0019] (4) Since phosphogypsum has an inhibitory effect on methanogens, it can reduce the production of CH4 in wastewater treatment. Therefore, this invention can, on the one hand, make sulfur bacteria gradually become the dominant species, improve their decomposition efficiency and utilization of calcium sulfate; on the other hand, it can improve the utilization efficiency of carbon sources in wastewater and reduce greenhouse gas emissions. Attached Figure Description

[0020] Figure 1 The graph shows the changes in phosphorus content in wastewater after the addition of 0.1g PG, following physicochemical (a) and biological reactions (b). Figure 2 The graph shows the proportion of phosphorus forms after physicochemical reaction for different PG addition amounts. After the physicochemical reaction, the phosphate binding forms are mainly weakly bound and iron and aluminum oxide bound, while the calcium bound forms are 1%, 1%, 7%, 50% and 65% in different phosphogypsum addition amounts, respectively. Figure 3 The graph shows the proportion of phosphorus forms after bioreaction for different PG addition amounts. After bioreaction, the bound form of phosphate gradually transforms into calcium-bound and residual forms with higher crystallinity. Among them, the content of calcium-bound form increases to 6%, 5%, 28%, 59% and 83% respectively in different phosphogypsum addition amounts. Figure 4 XRD characterization diagrams of different PG addition amounts after bioreaction; Figure 5 A comparative graph showing the effects of different PG addition amounts on the content of sulfate-reducing bacteria and methanogens; Figure 6 A comparative graph showing the effect of different PG addition amounts on the growth of sulfur-oxidizing bacteria. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] The phosphogypsum used in this invention is a chemical product with CaSO4 as its main component. It is not limited to a byproduct of industrial wet phosphoric acid production, but also includes industrial byproducts such as flue gas desulfurization gypsum, citric acid gypsum, salt gypsum, monosodium glutamate gypsum, copper gypsum, fluorine gypsum, titanium gypsum, nickel gypsum, chromium gypsum, boron gypsum, mirabilite gypsum, tartaric acid gypsum, lactic acid gypsum, and natural gypsum.

[0023] In this invention, wastewater refers to wastewater treated by processes such as UASB, anaerobic contact process, upflow anaerobic sludge blanket, baffle anaerobic process, anaerobic biological filter, anaerobic expanded bed and fluidized bed, as well as third-generation anaerobic processes such as EGSB and IC anaerobic reactor.

[0024] In their research, the applicant discovered that the production of calcium phosphate significantly increased with different PG addition levels after biological treatment, and that PG could inhibit the growth of methanogens. Therefore, PG promotes the enrichment of sulfur bacteria, thereby enabling them to decompose more calcium sulfate and promote the formation of hydroxyapatite; at the same time, it can improve the carbon source utilization efficiency of sulfur bacteria and reduce greenhouse gas emissions.

[0025] The method for detecting phosphate in this invention employs the molybdenum-antimony spectrophotometric method.

[0026] The phosphogypsum used in the following examples is a byproduct of industrial wet phosphoric acid production in Hubei Province, and the abundance of sulfur bacteria in the sludge used is not less than 1%.

[0027] Example 1 0.02 g of phosphogypsum was taken from the phosphogypsum storage site and added to 80 mL of sulfur-containing wastewater; the initial phosphate concentration was 25 mg / L; the dosage was 2 g of anaerobic activated sludge (sludge concentration of 3000~8000 mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provided sulfur-providing bacteria, the initial pH was 7, nitrogen was purged for 30 min to ensure an anaerobic-anoxic environment, and cultured at room temperature until the phosphate content stabilized. The final recovered phosphate was 5% of the original addition.

[0028] Example 2 Take 0.1g of phosphogypsum from the phosphogypsum storage site and add it to 80mL of sulfur-containing wastewater; the initial phosphate concentration is 25mg / L; the dosage is 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provides sulfate-providing bacteria, the initial pH is 7, nitrogen is introduced for 30min to ensure an anaerobic-anoxic environment, and culture is carried out at room temperature until the phosphate content stabilizes. Figure 1 As shown. The final recovered phosphate was 28% of the original addition.

[0029] Example 3 0.5g of phosphogypsum was taken from the phosphogypsum storage site and added to 80mL of sulfur-containing wastewater; the initial phosphate concentration was 25mg / L; the dosage was 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provided sulfur-providing bacteria, the initial pH was 7, nitrogen was purged for 30min to ensure an anaerobic-anoxic environment, and cultured at room temperature until the phosphate content stabilized. The final recovered phosphate was 59% of the original added phosphate.

[0030] Example 4 2.5g of phosphogypsum was taken from the phosphogypsum storage site and added to 80mL of sulfur-containing wastewater; the initial phosphate concentration was 25mg / L; the dosage was 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provided sulfur-providing bacteria, the initial pH was 7, nitrogen was purged for 30min to ensure an anaerobic-anoxic environment, and cultured at room temperature until the phosphate content stabilized. The final recovered phosphate was 83% of the original added phosphate.

[0031] Example 5 2.5g of phosphogypsum was taken from the phosphogypsum storage site and added to 80mL of sulfur-containing wastewater; the initial phosphate concentration was 5mg / L; the dosage was 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provided sulfur-providing bacteria, the initial pH was 7, nitrogen was purged for 30min to ensure an anaerobic-anoxic environment, and cultured at room temperature until the phosphate content stabilized. The final recovered phosphate was 86% of the original added phosphate.

[0032] Example 6 2.5g of phosphogypsum was taken from the phosphogypsum storage site and added to 80mL of sulfur-containing wastewater; the initial phosphate concentration was 125mg / L; the dosage was 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provided sulfur-providing bacteria, the initial pH was 7, nitrogen was purged for 30min to ensure an anaerobic-anoxic environment, and cultured at room temperature until the phosphate content stabilized. The final recovered phosphate was 75% of the original added phosphate.

[0033] Example 7 2.5g of phosphogypsum was taken from the phosphogypsum storage site and added to 80mL of sulfur-containing wastewater; the initial phosphate concentration was 25mg / L; the dosage was 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provided sulfur-providing bacteria, the initial pH was 5.5, nitrogen was purged for 30min to ensure an anaerobic-anoxic environment, and cultured at room temperature until the phosphate content stabilized. The final recovered phosphate was 63% of the original added phosphate.

[0034] Example 8 2.5g of phosphogypsum was taken from the phosphogypsum storage site and added to 80mL of sulfur-containing wastewater; the initial phosphate concentration was 25mg / L; 10% sulfur bacteria microbial agent was added, the initial pH was 7, nitrogen was purged for 30min to ensure an anaerobic-anoxic environment, and cultured at room temperature until the phosphate content stabilized. The final recovered phosphate was 88% of the original added phosphate.

[0035] Example 9 0.1 g of phosphogypsum was taken from the phosphogypsum storage site and added to 80 mL of sulfur-containing wastewater; the initial phosphate concentration was 25 mg / L; 10% sulfur bacteria microbial agent was added, the initial pH was 7, nitrogen was purged for 30 min to ensure an anaerobic-anoxic environment, and the mixture was incubated at room temperature until the phosphate content stabilized. The final recovered phosphate was 34% of the original added phosphate.

[0036] Example 10 Take 2.5g of natural gypsum and add it to 80mL of sulfur-containing wastewater; the initial phosphate concentration is 25mg / L; the dosage is 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provides sulfur-producing bacteria, nitrogen is purged for 30min to ensure an anaerobic-anoxic environment, and culture is carried out at room temperature until the phosphate content stabilizes. The final recovered phosphate is 78% of the original added phosphate.

[0037] Example 11 Take 2.5g of desulfurized gypsum from the desulfurization gypsum site and add it to 80mL of sulfur-containing wastewater; the initial phosphate concentration is 25mg / L; the dosage is 2g of anaerobic activated sludge (sludge concentration of 3000~8000mg / L, sludge from the anaerobic stage of the AAO process after concentration); the sludge provides sulfur-providing bacteria, nitrogen is purged for 30min to ensure an anaerobic-anoxic environment, and culture is carried out at room temperature until the phosphate content stabilizes. The final recovered phosphate is 66% of the original added phosphate.

[0038] Example 12 0.1g of phosphorus desulfurization gypsum was taken from the desulfurization gypsum site and added to 80mL of sulfur-containing wastewater; the initial phosphate concentration was 25mg / L; 10% of a microbial agent containing different sulfur bacteria (sulfate-reducing bacteria + sulfur-oxidizing bacteria) was added, and nitrogen was purged for 30min to ensure an anaerobic-anoxic environment. The mixture was then incubated at room temperature until the phosphate content stabilized. The final recovered phosphate was 41% of the original added amount.

[0039] Comparative Example 1 This comparative example provides a method for phosphorus recovery without the addition of phosphogypsum.

[0040] Take 0g of phosphogypsum from the phosphogypsum storage site and add 80mL of sulfur-containing wastewater; the initial phosphate concentration is 25mg / L; the dosage is 2g of anaerobic activated sludge (sludge concentration is 3000~8000mg / L, the sludge comes from the anaerobic section of the AAO process after concentration); the initial pH is 7, nitrogen is purged for 30min to ensure anaerobic conditions, and the mixture is cultured at room temperature for 45 days.

[0041] Examples 1-12 all showed phosphorus recovery effects, accompanied by the formation of hydroxyapatite.

[0042] refer to Figure 1 The applicant investigated the changes in phosphorus content in wastewater after adding 0.1g of PG through physicochemical and biological reactions. When phosphogypsum was added directly to the wastewater, the phosphate content decreased slowly because phosphogypsum mainly adsorbed phosphate ions through physicochemical processes, forming adsorbed phosphate only on the surface of the phosphogypsum. It took 10 days for the phosphate content to decrease from 20.98 mg / L to 15.03 mg / L, a reduction of only 28.36%. After the biological reaction, the first 14 days were the adaptation period for the organisms. After 6 days of biological reaction, the phosphate content rapidly decreased from 14.21 mg / L to 5.19 mg / L, a reduction of 63.47%. Therefore, the biological reaction significantly accelerated phosphate precipitation, and the calcium phosphate after the biological reaction became the more stable hydroxyapatite.

[0043] refer to Figure 2The applicant investigated experiments on the promotion of calcium phosphate formation by different PG addition amounts and found that the more PG added, the more calcium-bound phosphorus was generated. Compared with the physicochemical reaction group, the proportion of calcium-bound phosphorus in the bioreaction group was further increased. Further XRD mineral morphology characterization revealed that the product of the bioreaction group was mainly phosphate rock, and the crystallinity was significantly higher than that of the physicochemical reaction group.

[0044] refer to Figure 3 The applicant investigated the effects of different PG addition amounts on the microbial composition and found that the higher the PG addition, the higher the abundance of sulfate-reducing bacteria in the system, with the highest abundance of sulfate-reducing bacteria in the 2.5g PG addition group. Furthermore, while the abundance of sulfate-reducing bacteria increased, the abundance of methanogens remained suppressed and consistently low.

[0045] Depend on Figure 1 , Figure 2 and Figure 3 It can be seen that calcium-bound phosphorus increases significantly after the biological reaction, and as... Figure 4 The XRD characterization shown indicates the formation of hydroxyapatite in the system. When the amount of PG added is ≤0.1g, the hydroxyapatite peak shape is obvious and the crystallinity is high. However, when the amount of PG added is >0.1g, the hydroxyapatite peak shape is not obvious due to the high PG content.

[0046] refer to Figure 5 Without the addition of PG, the ratio of sulfate-reducing bacteria to methanogens was 38.09. With the addition of a small amount of PG, this ratio increased to 60.38 and 53.41 at additions of 0.02 and 0.1 g, respectively. Therefore, the addition of a small amount of PG significantly promoted the growth of sulfate-reducing bacteria and inhibited methanogen production. Further increasing the PG dosage resulted in a decrease in the ratio to methanogens to 31.02 and 42.79 at additions of 0.5 and 2.5 g, respectively, due to the inhibitory effect of calcium ions in PG on sulfate-reducing bacteria. This indicates that sulfur bacteria significantly inhibited the growth of methanogens, making them the dominant bacteria in the system, while sulfate-reducing bacteria and sulfur-oxidizing bacteria coexisted.

[0047] refer to Figure 6 The addition of 0.1 g PG significantly promoted the growth of sulfur-oxidizing bacteria.

[0048] To better illustrate the application effect of the method for phosphorus recovery from wastewater in conjunction with phosphogypsum provided in this application, a detailed explanation is given below based on a specific engineering project.

[0049] Practical engineering applications of using phosphogypsum in wastewater treatment for phosphorus recovery can be achieved through in-situ addition of phosphogypsum. The phosphogypsum is sprinkled into the anaerobic-anoxic tank of the wastewater treatment process. Due to the long hydraulic retention time in the anaerobic-anoxic tank, sulfate-reducing bacteria can fully reduce the sulfate in the phosphogypsum, releasing calcium ions for phosphorus recovery from the wastewater. Simultaneously, sulfur-oxidizing bacteria can oxidize sulfides, promoting the formation of hydroxyapatite. Furthermore, due to the competitive advantage of sulfate-reducing bacteria for carbon sources, this reaction system can inhibit the growth of methanogenic bacteria, reducing greenhouse gas emissions.

[0050] A phosphorus recovery experiment was conducted at a wastewater treatment plant in Hubei Province. The wastewater was anaerobic wastewater after AAO treatment, characterized by high organic matter and sulfur content, with a volume of 100 m³. 3 The anaerobic-anoxic tank had a BOD of 3270 mg / L, a COD of 5610 mg / L, a sulfate content of 5000 mg / L, a phosphate content of 25 mg / L, a hydraulic retention time of 10 h, and a sludge return ratio of 50%. When 200 kg of phosphogypsum was added to the tank, the conversion rate of phosphate to hydroxyapatite precipitate was over 85%.

[0051] For any points not covered above, existing technologies shall apply.

[0052] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating wastewater and recovering phosphorus using phosphogypsum in conjunction with sulfate-reducing bacteria, characterized in that, The microbial agent of phosphogypsum and sulfur-containing bacteria is added to the wastewater to carry out a biochemical reaction in an anaerobic-anoxic environment. In the initial stage of the reaction, the phosphate in the wastewater is first adsorbed by phosphogypsum through physicochemical adsorption. In the later stage of the reaction, the phosphate is converted into hydroxyapatite precipitate through microbial action, thereby realizing in-situ phosphorus recovery. The microbial agent is sludge containing sulfate-reducing bacteria and sulfur-oxidizing bacteria, and the abundance of sulfur bacteria in the microbial agent is greater than 1%. The dosage of the phosphogypsum is in the mass ratio of phosphate ions in the wastewater as (100~500):(2~10), and the dosage of the phosphogypsum, calculated based on the molar ratio of calcium ions in the phosphogypsum to phosphate ions in the wastewater, is not less than 1:

20. The reaction conditions are: pH 4-10, reaction temperature 10-50℃; During the reaction, sulfate-reducing bacteria reduce sulfate ions in phosphogypsum, thereby releasing calcium ions and producing sulfides. The added phosphogypsum inhibits the growth of methanogenic bacteria in the wastewater to improve carbon source utilization. The released calcium ions combine with phosphate ions in the wastewater and work with sulfur-oxidizing bacteria to oxidize and remove sulfides produced by sulfate-reducing bacteria, inducing the formation of highly crystalline hydroxyapatite precipitate.

2. The method as described in claim 1, characterized in that, The sulfate-reducing bacteria include at least one of the genera *Desulfovibrio*, *Desulfomonas*, *Desulfophyllum*, *Desulfurenterobacter*, *Desulfurobacterium*, *Desulfococcus*, *Desulfococcus*, and *Desulfuricula*, and the sulfur-oxidizing bacteria include at least one of the genera *Thiobacillus*, *Thiospira*, and *Sulphophyllum*.

3. The method as described in claim 1, characterized in that, The wastewater has a sulfate concentration of 10-500,000 mg / L, a biological oxygen demand of 10-100,000 mg / L, a chemical oxygen demand of 50-500,000 mg / L, and a total phosphorus content of 0.05-150 mg / L.

4. The method as described in claim 1, characterized in that, The anaerobic-anoxic reaction environment is provided by anaerobic contact process, upflow anaerobic sludge blanket, baffle anaerobic process, anaerobic biological filter, anaerobic expanded bed and fluidized bed, third-generation anaerobic process EGSB or IC anaerobic reactor.

5. A kit for treating wastewater and recovering phosphorus using the method described in any one of claims 1-4, characterized in that, The kit contains phosphogypsum and sulfur bacteria. The phosphogypsum is a byproduct of industrial wet phosphoric acid production, and the sulfur bacteria include sulfate-reducing bacteria and sulfur-oxidizing bacteria.

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