Method for removing inhibitors in fermentation liquor of kitchen waste and application of nitrogen and phosphorus synergistic recovery

Abstract

The application discloses a method for removing inhibitors in kitchen waste fermentation liquor and cooperatively recovering nitrogen and phosphorus and application thereof. The method comprises the following steps: (1) inoculating a complex bacterial liquid into pretreated kitchen waste fermentation liquor and aerating to obtain a degradation liquid; the complex bacterial liquid is a mixed liquid of Pseudomonas maltophilia and Bacillus subtilis; (2) adding MgCl2·6H2O into the degradation liquid, stirring for 20-40 min, then separating, and then blowing off ammonia nitrogen from the supernatant after separation to obtain a treated liquid; (3) adding a PEI-MNP adsorbent into the treated liquid, stirring for 15-30 min, and then performing magnetic separation to obtain treated fermentation liquor. The method can not only realize targeted removal of inhibitors in kitchen waste fermentation liquor and cooperatively recover nitrogen and phosphorus, but also can harvest high-quality carbon sources. The treated fermentation liquor can be applied to sewage treatment as a carbon source, so that the denitrification rate can be improved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a method and application for removing inhibitors and co-recovering nitrogen and phosphorus from fermentation liquid of kitchen waste. Background Technology

[0002] With continuous social development and the sustained improvement of people's living standards, the amount of food waste generated is showing a serious increasing trend. Food waste is characterized by high moisture content, high organic matter content, easy decomposition and odor, and easy biodegradability. Improper handling will lead to resource waste and environmental pollution. The most common method of food waste disposal in my country is sanitary landfill, but this method generates a series of environmental pollution problems such as landfill leachate, greenhouse gases, and odors. Furthermore, landfills require large land areas, have high processing costs, and result in a significant waste of organic matter. Other methods of food waste disposal, such as ocean disposal, incineration, and use as animal feed and fertilizer, are being prohibited due to increasingly stringent environmental laws and regulations. Therefore, in today's society with extreme energy shortages, the effective resource utilization of food waste is of great practical significance.

[0003] Denitrification, a core step in wastewater nitrogen removal, refers to the process by which denitrifying bacteria, under anaerobic conditions, utilize organic carbon sources as electron donors to gradually reduce nitrate nitrogen to nitrogen gas. In this process, the sufficiency and quality of the carbon source directly determine the denitrification rate and nitrogen removal efficiency; only by adding sufficient carbon sources to the wastewater can complete nitrogen removal be achieved. Currently, many commercial wastewater treatment plants commonly use ethanol, acetate, and methanol to improve nitrogen removal efficiency. Due to its low cost, methanol has long been the most commonly used external carbon source; however, it tends to cause slow start-up of methanol denitrification systems. While ethanol and acetate can immediately improve the denitrification reaction, their costs are relatively high. Therefore, researchers have developed many other carbon sources suitable for denitrification, such as crude syrup, industrial wastewater from ice cream production or beet sugar processing, and solid carbon sources like wheat straw and plant pruning. However, using these carbon sources for wastewater treatment involves complex and time-consuming pretreatment processes, and most are still at the laboratory level, hindering industrialization.

[0004] Microorganisms are used to convert organic matter in food waste into volatile fatty acids, including acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, and valeric acid, which have higher added value than biological hydrogen and methanogenesis. These volatile acids have wide applications, such as serving as endogenous carbon for denitrification and phosphorus removal bacteria in wastewater treatment plants, improving denitrification efficiency. When food waste fermentation broth is used as a carbon source for wastewater denitrification, the high concentrations of ammonia nitrogen, capsaicin, and heavy metals it contains significantly reduce the activity of denitrifying bacteria. While the struvite process can recover nitrogen and phosphorus, it is not effective in removing organic inhibitors such as capsaicin present in the fermentation broth. These organic inhibitors still negatively impact the activity of denitrifying bacteria, thus affecting the wastewater treatment effect. Although activated carbon adsorption can utilize the rich pore structure and strong adsorption properties of activated carbon to adsorb and remove heavy metals from the fermentation broth, the loss rate of sugars during adsorption is high. This not only wastes resources but may also affect the quality and utilization efficiency of the fermentation broth as a carbon source. Therefore, existing technologies cannot simultaneously remove multiple inhibitors and harvest high-quality carbon sources, making it difficult to meet the needs of food waste fermentation liquid treatment and resource recycling in practical applications. Summary of the Invention

[0005] In view of this, one object of the present invention is to provide a method for removing inhibitors and co-recovering nitrogen and phosphorus from food waste fermentation broth. This method can not only achieve targeted removal of inhibitors and co-recovery of nitrogen and phosphorus from food waste fermentation broth, but also harvest a high-quality carbon source. Another object of the present invention is to provide an application of the fermentation broth treated by the above method as a carbon source in wastewater treatment to improve the denitrification rate. The present invention achieves the above technical objectives through the following technical solutions.

[0006] This invention provides a method for removing inhibitors and co-recovering nitrogen and phosphorus from fermentation liquid of kitchen waste, comprising the following steps: (1) Inoculate the pretreated kitchen waste fermentation liquid with compound bacterial liquid and aerate to obtain degradation liquid; the compound bacterial liquid is a mixture of Pseudomonas maltophilia and Bacillus subtilis; (2) Add MgCl2·6H2O to the degradation solution, stir and react for 20-40 min, then separate, and then strip the ammonia nitrogen from the supernatant after separation to obtain the treatment solution; (3) Add PEI-MNP adsorbent to the treatment liquid, stir for 15-30 min and then perform magnetic separation to obtain the treated fermentation liquid.

[0007] In step (1) of this invention, a compound bacterial solution is inoculated into the pretreated kitchen waste fermentation liquid and aerated to degrade capsaicin, resulting in a degradation liquid. The compound bacterial solution is a mixture of *Pseudomonas maltophilia* and *Bacillus subtilis*. *Pseudomonas maltophilia* has a strong ability to degrade organic inhibitors, such as capsaicin, and can decompose these organic inhibitors into small molecules under specific conditions. *Bacillus subtilis* surfactants (such as lipopeptides) disrupt the hydrophobic structure of capsaicin, reducing its toxicity to *Pseudomonas maltophilia*; simultaneously, the spore structure of *Bacillus subtilis* allows for higher survival rates in high ammonia nitrogen environments, maintaining bacterial community stability. The combination of the two can better exert a synergistic effect.

[0008] In step (2) of this invention, MgCl2·6H2O is added to the degradation solution, and Mg²⁺ combines with PO₄³⁻ in the degradation solution to form struvite precipitate. The reaction environment can be adjusted to a suitable pH range using alkaline solution. After stirring for 20-40 minutes, the precipitate is separated to obtain struvite precipitate. If the stirring reaction time is less than 20 minutes, Mg²⁺ and PO₄³⁻ may not react sufficiently, resulting in a decrease in phosphorus recovery rate; if the stirring reaction time is greater than 40 minutes, it will not only increase the processing time and cost, but may also cause the already formed struvite precipitate to redissolve. After separation, the supernatant is stripped to remove ammonia nitrogen from the solution, thereby achieving the purpose of removing ammonia nitrogen from the fermentation broth.

[0009] In step (3) of the present invention, PEI-MNP adsorbent is added to the treatment liquid for stirring and magnetic separation, which can achieve the effect of targeted removal of heavy metals in fermentation liquid, improvement of carbon source quality and synergistic recovery of nitrogen and phosphorus.

[0010] According to the method of the present invention, preferably, the volume ratio of *Pseudomonas maltophilia* solution to *Bacillus subtilis* solution in the composite bacterial solution is 1:0.5-2.

[0011] In this invention, the volume ratio of *Pseudomonas maltophilia* suspension to *Bacillus subtilis* suspension in the compound bacterial solution can be 1:0.5–2, preferably 1:0.8–1.5, and more preferably 1:1–1.5. Within this range, the two strains exhibit a significant synergistic degradation effect, which can better improve the degradation effect of capsaicin.

[0012] According to the method of the present invention, preferably, the dosage of the PEI-MNP adsorbent is 0.5 to 1.5 g / L.

[0013] In this invention, the dosage of PEI-MNP adsorbent can be 0.5-1.5 g / L, preferably 0.8-1.2 g / L, and more preferably 0.9-1.1 g / L. When the dosage is below 0.5 g / L, firstly, the number of active sites (amino groups on PEI) provided by the adsorbent is limited, which cannot fully complex all target heavy metal ions (such as Pb²⁺, Cu²⁺) and adsorb some organic inhibitors. This not only leads to excessive heavy metal concentration in the effluent, but the residual inhibitors also affect the activity of subsequent denitrifying bacteria. Secondly, in the complex fermentation broth system, in addition to the target pollutants, there are many other organic molecules. Sufficient adsorbent concentration can ensure that it can preferentially capture target pollutants when competing with non-target substances. When the dosage is greater than 1.5 g / L, firstly, the non-specific adsorption of small molecule organic acids (such as acetic acid and propionic acid) that serve as carbon sources in the fermentation broth by PEI-MNP will increase significantly, which will lead to an increase in COD loss rate. Secondly, excessive and dense magnetic nanoparticles may not be completely separated during the magnetic separation process due to the aggregation effect, resulting in a small number of nanoparticles remaining in the treated liquid, causing some secondary pollution.

[0014] According to the method of the present invention, preferably, the PEI-MNP adsorbent is prepared by the following method: S1: Fe3O4 magnetic nanoparticles were dispersed in an alcohol solution, and ethyl silicate and ammonia were added to react and separate to obtain SiO2@Fe3O4 microspheres; S2: SiO2@Fe3O4 microspheres were dispersed in an alcohol solution, 3-aminopropyltriethoxysilane was added and reacted, and then separated to obtain NH2-SiO2@Fe3O4; S3: NH2-SiO2@Fe3O4 is dispersed in deionized water, polyethyleneimine is added, and then a crosslinking agent is added to react. After separation, washing, and drying, PEI-MNP adsorbent is obtained.

[0015] In this invention, PEI-MNP adsorbents are used for targeted removal of heavy metal ions. A protective SiO2 layer is constructed using TEOS, followed by amination modification with APTES to introduce reaction sites. Finally, PEI grafting is used to achieve targeted and efficient adsorption of heavy metal ions. This multilayer structure design, through the synergistic effect of its components, solves the technical problem of selective detoxification and carbon source retention in complex fermentation broth environments.

[0016] According to the method of the present invention, preferably, in step (1), the reaction temperature is 35-40°C, the reaction time is 10-15h, and the dissolved oxygen is 1.0-1.5mg / L.

[0017] In this invention, the preferred reaction temperature for capsaicin degradation is 35–40°C, and the preferred reaction time is 10–15 h. If the temperature is below 35°C, the growth and metabolic rate of the compound bacteria will slow down, reducing the degradation efficiency of the inhibitors. If the temperature is above 40°C, it may adversely affect the activity of the compound bacteria, even leading to the death of some strains. If the reaction time is less than 10 h, the inhibitors may not be completely degraded; if the reaction time is greater than 15 h, it will increase processing costs and may lead to the loss of beneficial components in the fermentation broth. If dissolved oxygen is below 1.0 mg / L, the growth of aerobic bacteria will be limited, affecting capsaicin degradation; if dissolved oxygen is above 1.5 mg / L, it will not only waste energy but may also affect the growth of the compound bacteria. The reaction temperature, reaction time, and dissolved oxygen range of this invention are more suitable for the growth and metabolism of the compound bacteria. After inoculation with the compound bacterial solution, the synergistic effect of the two bacteria in the compound bacterial solution is utilized to comprehensively degrade the inhibitors in the fermentation broth under suitable temperature and time conditions.

[0018] According to the method of the present invention, preferably, in step (1), the molar ratio of Mg²⁺:PO₄³⁻ in the degradation solution is controlled to be 1 to 1.5:1.

[0019] In this invention, the molar ratio of Mg²⁺ to PO₄³⁻ in the degradation solution can be 1–1.5:1, preferably 1.1–1.4:1, and more preferably 1.2–1.3:1. This ensures effective phosphorus recovery.

[0020] According to the method of the present invention, preferably, in step (2), the supernatant is passed into a membrane contactor to strip ammonia nitrogen and the pH is adjusted to 10.5 to 11.5; wherein the stripping temperature is 35 to 45°C and the gas-liquid ratio is 250 to 350:1.

[0021] In this invention, the supernatant enters the membrane contactor to strip ammonia nitrogen, and the pH value of the environment is adjusted to 10.5–11.5, so that the ammonia nitrogen exists in a free state, thereby improving the stripping efficiency. The stripping temperature is preferably 35–45°C, and the gas-liquid ratio can be 250–350:1, preferably 280–320:1. If the stripping temperature is below 35°C, the ammonia nitrogen stripping efficiency will decrease; if the stripping temperature is above 45°C, energy consumption will increase. When the gas-liquid ratio is less than 250:1, the ammonia nitrogen stripping is insufficient; when the gas-liquid ratio is greater than 350:1, the gas consumption and treatment cost will increase.

[0022] According to the method of the present invention, preferably, in step (2), sulfuric acid is used to absorb the stripped tail gas; the concentration of the sulfuric acid is 0.5 to 1 mol / L.

[0023] In this invention, sulfuric acid is used to absorb the stripped exhaust gas to form an ammonium sulfate solution, thereby achieving nitrogen recovery.

[0024] According to the method of the present invention, preferably, step (3) further includes the following step: filtering the treated fermentation broth with an ultrafiltration membrane, wherein the turbidity of the filtered fermentation broth is <1 NTU.

[0025] In this invention, the treated fermentation broth can also be filtered. The ultrafiltration membrane has a certain pore size, which can trap suspended particles and other substances in the fermentation broth, making the turbidity of the filtered fermentation broth <1 NTU, further improving the clarity and quality of the fermentation broth. This allows the treated fermentation broth to play a better role as a carbon source in wastewater treatment, improving the denitrification rate, while also reducing problems such as clogging of wastewater treatment equipment, further enhancing the stability and effectiveness of the entire treatment process.

[0026] On the other hand, the present invention also provides an application of the fermentation broth obtained by the method described above as a carbon source to improve the denitrification rate in wastewater treatment.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects: (1) This invention combines steps such as inoculation with a compound bacterial solution, struvite-ammonia stripping, and PEI-MNP adsorbent to achieve targeted removal of inhibitors and synergistic recovery of nitrogen and phosphorus in the fermentation liquid of kitchen waste. The synergistic effect of the compound bacterial solution has a significant degradation effect on capsaicin in the fermentation liquid of kitchen waste. Struvite crystallization and ammonia stripping effectively recover nitrogen and phosphorus resources. The PEI-MNP adsorbent can target and remove heavy metals in the fermentation liquid while further improving the quality of the carbon source, thereby reducing the inhibitory effect of the fermentation liquid on denitrifying bacteria and providing a high-quality carbon source for wastewater treatment. At the same time, struvite (containing P2O5) and ammonium sulfate can also be recovered, improving resource recovery efficiency.

[0028] (2) The method of the present invention has high overall processing efficiency, and reduces capsaicin, ammonia nitrogen, and Pb in the fermentation liquid of kitchen waste. 2+ and Cu 2+ The removal rates can reach 99.1%, 87%, 99.4% and 98.9% respectively, the total phosphorus removal rate is over 90%, the COD loss rate is <4%, and the BOD5 / COD ratio of the liquid carbon source can reach 0.7, indicating that the harvested carbon source is of good quality.

[0029] (3) The fermentation broth obtained by the method of the present invention can be used as a carbon source in wastewater treatment. The denitrification efficiency is above 92% and the denitrification rate can reach 12.1 NO3⁻-N / (g VSS·h), which is comparable to commercial carbon source sodium acetate. It can replace sodium acetate and save costs. Detailed Implementation

[0030] Preparation Example 1 (1) Weigh 2.16 g FeCl3·6H2O and 0.795 g FeCl2·4H2O, dissolve them in 80 mL of deionized water, and stir mechanically (500 rpm) and heat to 80 °C under nitrogen protection. Quickly add 5 mL of ammonia water, and react for 1 hour. The solution quickly turns black. After the reaction is complete, separate the black precipitate with a strong magnet, and wash it alternately with deionized water and anhydrous ethanol until neutral to obtain Fe3O4 magnetic nanoparticles (MNP).

[0031] (2) Fe3O4 magnetic nanoparticles were dispersed in 50 mL of anhydrous ethanol and ultrasonically dispersed for 10 min. 2 mL of LTEOS (ethyl silicate) and 10 mL of ammonia were added. The mixture was stirred continuously at room temperature for 6 h. After magnetic separation, the nanoparticles were washed three times with ethanol to obtain SiO2@Fe3O4 microspheres.

[0032] (3) Disperse SiO2@Fe3O4 microspheres in 50 mL of anhydrous ethanol, then add 2 mL of APTES (3-aminopropyltriethoxysilane), reflux and stir at 70 °C for 8 h, then magnetically separate, and wash thoroughly with ethanol to obtain NH2-SiO2@Fe3O4.

[0033] (4) Disperse 0.1g NH2-SiO2@Fe3O4 in 40 mL of deionized water, add 0.2g PEI (polyethyleneimine), sonicate to dissolve completely, then add 2 mL of glutaraldehyde solution dropwise, stir and react at room temperature for 12 h. After the reaction is complete, collect the product by magnetic separation, and wash repeatedly with deionized water until no free PEI is found. Dry the final product under vacuum at 50℃ for 6 h, grind it to obtain PEI-functionalized magnetic adsorbent (PEI-MNP). Example 1

[0034] (1) The fermentation liquid of kitchen waste was filtered to obtain the pretreated fermentation liquid. The COD concentration of the pretreated fermentation liquid was 52.2 g / L, the ammonia nitrogen concentration was 850 mg / L, the capsaicin concentration was 32 mg / L, and the total phosphorus concentration was 120 mg / L.

[0035] (2) Inoculate the pretreated fermentation broth with compound bacterial solution and aerate it. React at 37℃ and DO of 1.2 mg / L for 12 h to obtain degradation solution; wherein, the volume ratio of Pseudomonas maltophilia solution (accession number CCTCC M 2020013) to Bacillus subtilis solution (accession number CGMCC No.20543) in the compound bacterial solution is 1:1.

[0036] (3) Add 1.5 g / L of MgCl2·6H2O (Mg²⁺:PO4³⁻ molar ratio 1.2:1) to the degradation solution, and adjust the pH to 9.0 with NaOH. After stirring for 30 min, the precipitate is separated to obtain struvite precipitate. Then, the supernatant after precipitation is passed into the membrane contactor, and the pH of the supernatant is adjusted to 11.0. The ammonia nitrogen is stripped at 40℃ and a gas-liquid ratio of 300:1 to obtain the treatment solution. At the same time, the tail gas is absorbed by 0.5 mol / L H2SO4 to obtain ammonium sulfate solution.

[0037] (4) Add 1 g / L of the PEI-MNP adsorbent obtained in Preparation Example 1 to the treatment liquid, stir for 30 min and then perform magnetic separation to obtain the treated fermentation liquid. Example 2

[0038] (1) Inoculate the pretreated fermentation broth (same as in Example 1) with compound bacterial solution and aerate. React at 37°C and DO of 1.2 mg / L for 12 h to obtain degradation solution; wherein, the volume ratio of Pseudomonas maltophilia solution to Bacillus subtilis solution in compound bacterial solution is 1:0.5.

[0039] (2) Add 1.5 g / L of MgCl2·6H2O to the degradation solution, and adjust the pH to 9.0 with NaOH. After stirring for 30 min, the precipitate is separated to obtain struvite precipitate (containing 5.8% N and 12.3% P). Then, pass the supernatant after precipitation into the membrane contactor, adjust the pH of the supernatant to 11.0, and strip ammonia nitrogen at 40℃ and a gas-liquid ratio of 300:1 to obtain the treatment solution. At the same time, the tail gas is absorbed by 0.5 mol / L H2SO4 to obtain ammonium sulfate solution.

[0040] (3) Add 1.5 g / L of the PEI-MNP adsorbent obtained in Preparation Example 1 to the treatment liquid, stir for 30 min and then perform magnetic separation to obtain the treated fermentation liquid. Example 3

[0041] (1) Inoculate the pretreated fermentation broth (same as in Example 1) with compound bacterial solution and aerate. React at 37°C and DO of 1.2 mg / L for 12 h to obtain degradation solution; wherein, the volume ratio of Pseudomonas maltophilia solution to Bacillus subtilis solution in compound bacterial solution is 1:2.

[0042] (2) Add 1.5 g / L of MgCl2·6H2O to the degradation solution, and adjust the pH to 9.0 with NaOH. After stirring for 30 min, the precipitate is separated to obtain struvite precipitate (containing 5.8% N and 12.3% P). Then, pass the supernatant after precipitation into the membrane contactor, adjust the pH of the supernatant to 11.0, and strip ammonia nitrogen at 40℃ and a gas-liquid ratio of 300:1 to obtain the treatment solution. At the same time, the tail gas is absorbed by 0.5 mol / L H2SO4 to obtain ammonium sulfate solution.

[0043] (3) Add 0.5 g / L of the PEI-MNP adsorbent obtained in Preparation Example 1 to the treatment liquid, stir for 30 min and then perform magnetic separation to obtain the treated fermentation liquid.

[0044] Comparative Example 1 The bacterial suspension was only *Pseudomonas maltophilia* suspension, and the rest was the same as in Example 1.

[0045] Comparative Example 2 The bacterial solution used was only Bacillus subtilis solution, and the rest was the same as in Example 1.

[0046] Comparative Example 3 The PEI-MNP adsorbent was replaced with activated carbon with a particle size of 0.5~1mm, and the rest was the same as in Example 1.

[0047] The removal rates of each component in the treated fermentation broth and the BOD5 / COD ratio of the carbon source are shown in Table 1.

[0048]

[0049] Table 1 shows that both Comparative Examples 1 and 2 used a single bacterial strain to degrade capsaicin. As can be seen from Table 1, the degradation effect of a single bacterial strain on capsaicin is limited. In Comparative Example 3, activated carbon was used to adsorb heavy metals, but not only was its adsorption effect on heavy metals limited, but it also resulted in the loss of carbon source during the adsorption process. The method of this application was used to degrade capsaicin, ammonia nitrogen, and Pb in the fermentation liquid of kitchen waste. 2+ and Cu 2+ The removal rates can reach 99.1%, 87%, 99.4% and 98.9% respectively, which have a good removal effect on inhibitors. At the same time, the removal rate of total phosphorus in the fermentation broth after treatment also reaches more than 90%, the COD loss rate is <4%, and the BOD5 / COD ratio of the liquid carbon source can reach 0.7, indicating that the quality of the harvested carbon source is good.

[0050] Experimental Example Seven 1L sealed glass reactors were used as reactors. Each reactor was filled with 250mL of inoculum sludge (after a 10-day acclimatization period) and 750mL of synthetic wastewater as the basic system. The seven reactors were respectively filled with the fermentation broth treated in Example 1 (Experimental Group 1), the fermentation broth treated in Example 2 (Experimental Group 2), the fermentation broth treated in Example 3 (Experimental Group 3), the fermentation broth treated in Comparative Example 1 (Comparative Group 1), the fermentation broth treated in Comparative Example 2 (Comparative Group 2), the fermentation broth treated in Comparative Example 3 (Comparative Group 3), and sodium acetate (commercial carbon source, Comparative Group 4).

[0051] The denitrification experiment was conducted at pH 7.5 and a temperature of 25±1℃. Initially, the COD / TN ratio was set to 5.5, and the reaction cycle was set to 24 hours. Once the effluent quality indicators stabilized, the reaction cycle was shortened to 12 hours. This included a 30-minute influent treatment period, a 22.5-hour anoxic reaction period, a 30-minute settling period, and a 30-minute effluent treatment period.

[0052] The results of nitrogen removal efficiency and denitrification rate are shown in Table 2.

[0053]

[0054] As shown in Table 2, the denitrification efficiency of experimental groups 1 to 3 is all above 92%, and the denitrification rate can reach 12.1 NO3⁻-N / (g VSS·h), which is comparable to that of sodium acetate and can replace sodium acetate.

[0055] Both Comparative Group 1 and Comparative Group 2 used a single bacterial strain, which had limited effect on capsaicin degradation, thus affecting the denitrification rate in subsequent applications. In Comparative Group 3, activated carbon was used to adsorb heavy metals, but some carbon source was lost during the adsorption process, affecting the denitrification rate in subsequent applications and consequently the nitrogen removal efficiency.

[0056] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for removing inhibitors and co-recovering nitrogen and phosphorus from fermentation liquid of kitchen waste, characterized in that, Includes the following steps: (1) Inoculate the pretreated kitchen waste fermentation liquid with compound bacterial liquid and aerate to obtain degradation liquid; the compound bacterial liquid is a mixture of Pseudomonas maltophilia and Bacillus subtilis; (2) Add MgCl2·6H2O to the degradation solution, stir and react for 20-40 min, then separate, and then strip the ammonia nitrogen from the supernatant after separation to obtain the treatment solution; (3) Add PEI-MNP adsorbent to the treatment liquid, stir for 15-30 min and then perform magnetic separation to obtain the treated fermentation liquid.

2. The method according to claim 1, characterized in that, The volume ratio of *Pseudomonas maltophilia* solution to *Bacillus subtilis* solution in the compound bacterial solution is 1:0.5-2.

3. The method according to claim 1, characterized in that, The dosage of the PEI-MNP adsorbent is 0.5–1.5 g / L.

4. The method according to claim 1, characterized in that, The PEI-MNP adsorbent was prepared by the following method: S1: Fe3O4 magnetic nanoparticles were dispersed in an alcohol solution, and ethyl silicate and ammonia were added to react and separate to obtain SiO2@Fe3O4 microspheres; S2: SiO2@Fe3O4 microspheres were dispersed in an alcohol solution, 3-aminopropyltriethoxysilane was added and reacted, and then separated to obtain NH2-SiO2@Fe3O4; S3: NH2-SiO2@Fe3O4 is dispersed in deionized water, polyethyleneimine is added, and then a crosslinking agent is added to react. After separation, washing, and drying, PEI-MNP adsorbent is obtained.

5. The method according to claim 1, characterized in that, In step (1), the reaction temperature is 35-40℃, the reaction time is 10-15h, and the dissolved oxygen is 1.0-1.5mg / L.

6. The method according to claim 1, characterized in that, In step (2), the molar ratio of Mg²⁺:PO₄³⁻ in the degradation solution is controlled to be 1 to 1.5:

1.

7. The method according to claim 1, characterized in that, In step (2), the supernatant is passed into the membrane contactor to strip ammonia nitrogen and the pH is adjusted to 10.5-11.5; wherein the stripping temperature is 35-45℃ and the gas-liquid ratio is 250-350:

1.

8. The method according to claim 1, characterized in that, In step (2), sulfuric acid is used to absorb the stripped tail gas; the concentration of the sulfuric acid is 0.5 to 1 mol / L.

9. The method according to claim 1, characterized in that, Step (3) also includes the following steps: using an ultrafiltration membrane to filter the treated fermentation broth, and the turbidity of the filtered fermentation broth is <1 NTU.

10. The application of the treated fermentation broth obtained by the method according to any one of claims 1 to 9 as a carbon source in wastewater treatment to improve the denitrification rate.

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