A method for two-cycle treatment of high ammonia nitrogen and recalcitrant antibiotics in pig biogas slurry using microalgae biofilm.

Abstract

This invention belongs to the field of biotechnology, specifically relating to a method for the two-cycle cyclic treatment of high ammonia nitrogen and recalcitrant antibiotics in pig farm biogas slurry using a microalgae biofilm. This invention utilizes *Chlorella vulgaris* to construct a microalgae biofilm and adds an organic carbon source and sodium chloride (from saline wastewater) to the actual biogas slurry to adjust its carbon-to-nitrogen ratio and salinity. Under the obtained optimal carbon source, carbon-to-nitrogen ratio, and salinity conditions, the actual biogas slurry is purified using a two-cycle cyclic treatment method (i.e., after the first stage of treatment and harvesting of microalgae, the same concentration of microalgae is inoculated, and the remaining wastewater is treated in the second stage). The addition of an organic carbon source and salinity in this invention has a positive impact on the removal of high concentrations of ammonia nitrogen and recalcitrant antibiotics. Based on this, the optimal carbon source, carbon-to-nitrogen ratio, and salinity are obtained, and the purification characteristics of the microalgae biofilm on actual biogas slurry under optimal environmental conditions are studied, enabling the treated biogas slurry wastewater to meet discharge standards, providing theoretical support for the treatment of actual biogas slurry wastewater using microalgae biofilms.

Description

Technical Field

[0001] This invention belongs to the field of biotechnology, specifically relating to a method for two-cycle cyclic treatment of high ammonia nitrogen and recalcitrant antibiotics in pig biogas slurry using microalgae biofilm. Background Technology

[0002] In today's society, with the accelerated development of industrialization and the improvement of living standards, per capita consumption of meat, eggs, and dairy products is constantly increasing, which has promoted a gradual shift in the food structure towards animal-based diets. Pig farming accounts for a large proportion of my country's agricultural development, and livestock and poultry farming has become a pillar industry of rural economic development; however, the environmental hazards it generates are also very serious. According to data from the 2020 Second National Pollution Source Census Bulletin, the discharge of pollutants from intensive livestock and poultry farms amounted to 6.0483 million tons of chemical oxygen demand (COD), 370,000 tons of total nitrogen (TN), and 80,400 tons of total phosphorus (TP), accounting for 60.5%, 62.0%, and 67.2% of the total emissions from livestock and poultry farming, respectively. If these pollutants are discharged directly without treatment, they will cause irreversible harm to the surrounding environment and human health. Therefore, the resource utilization and harmless treatment of livestock and poultry wastewater are of great significance for promoting ecological protection and environmental governance in the Yellow River Basin and further implementing the goals of carbon peaking and carbon neutrality.

[0003] Using microalgae to treat pig farm biogas slurry wastewater is a method of achieving harmlessness, stabilization, and resource recovery. However, this method still faces some problems in practical application, mainly including the following aspects: the wastewater quality is complex; biogas slurry usually contains some antibiotics, which are widely used in pig farming, but their absorption rate is extremely low and they cannot be effectively degraded by anaerobic fermentation; the biogas slurry wastewater contains a high concentration of NH4. + -N, when NH4 + Excessive N concentration can affect the osmotic pressure of microalgae and thus have a toxic effect on them. The C / N ratio of biogas slurry is low, resulting in poor biodegradability. An unbalanced C / N ratio is not conducive to the absorption and transformation of nutrients in wastewater by microorganisms. Traditional microalgae treatment systems are mainly suspension systems, in which microalgae cells are suspended in water, resulting in low biological density and a low tolerance threshold to pollutants. Harvesting is difficult and the cost is high.

[0004] Microalgae biofilm treatment is a microalgae treatment technology with advantages such as easy harvesting, high biological density, high tolerance to pollutants, and high mass transfer rate. In addition, this technology can also accumulate a certain amount of biomass energy from wastewater, providing a new approach for the resource utilization of pig biogas slurry. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for two-cycle cyclic treatment of high ammonia nitrogen and recalcitrant antibiotics in pig farm biogas slurry using microalgae biofilm. This method utilizes the addition of organic carbon sources and salinity (derived from saline wastewater) to improve the treatment efficiency of the microalgae biofilm for high concentrations of ammonia nitrogen and antibiotics, thus solving the aforementioned problems of low C / N ratio, antibiotic recalcitrantness, low microalgae biomass density leading to low tolerance thresholds for pollutants, and difficulty in harvesting microalgae. This method simultaneously treats biogas slurry wastewater and obtains microalgae biomass energy.

[0006] To achieve the above-mentioned objectives, the present invention includes the following technical solutions:

[0007] A method for treating high ammonia nitrogen and recalcitrant antibiotics in pig farm biogas slurry using a two-cycle microalgae biofilm, specifically including the following steps:

[0008] (1) Chlorella vulgaris was cultured in a light incubator with BG11 medium until the logarithmic phase, and then concentrated by centrifugation to obtain seed culture.

[0009] (2) First cycle treatment: Mix 100 mL of seed liquid and 800 mL of biogas slurry with adjusted carbon-nitrogen ratio and salinity, and let it flow on the biofilm carrier. The microalgae biofilm formed during the flow process treats the actual biogas slurry.

[0010] (3) Second cycle treatment: Collect the biogas slurry after the first cycle treatment, scrape off the algal film that has entered the decline stage in the first cycle, and inoculate again with the same concentration of seed liquid to continue the second cycle of wastewater recycling treatment. The treatment is completed.

[0011] Further, the biomass in the seed liquid described in step (1) is 0.8-1.0 g / L; preferably 1.0 g / L.

[0012] Furthermore, the cultivation conditions described in step (1) are 25±1℃ and 5000 lux.

[0013] Furthermore, the carbon source mentioned in step (2) is selected from at least one of glucose, sodium acetate, starch and sucrose; preferably sodium acetate.

[0014] Further, the carbon-nitrogen ratio C / N in step (2) is 18-22; preferably 20.

[0015] Further, the salinity mentioned in step (2) is 130-150 mM; preferably 140 mM; and the salinity adjustment is performed using saline wastewater.

[0016] Furthermore, the biogas slurry mentioned in step (2) is pig biogas slurry.

[0017] Furthermore, the treatment conditions described in step (2) are as follows: light intensity of 4000-6000 lux, cultivation under continuous light, and flow rate of the mixture of seed liquid and biogas slurry of 20-30 mL / min.

[0018] Furthermore, the processing time described in step (2) is at least 6 days; preferably at least 8 days.

[0019] Further, the biomass in the seed liquid described in step (3) is 0.8-1.0 g / L; preferably 1.0 g / L.

[0020] Furthermore, the treatment conditions described in step (3) are as follows: light intensity of 4000-6000 lux, cultivation under continuous light, and flow rate of the mixture of seed liquid and biogas slurry of 20-30 mL / min.

[0021] Furthermore, the processing time described in step (3) is at least 6 days; preferably at least 8 days.

[0022] Furthermore, 50 mL samples were taken every 48 hours during each culture cycle, filtered through a 0.45 μm filter membrane, and the filtrate was used to detect TN, TP, and NH4 in the water. + The concentrations of -N and COD were measured; after filtration through a 0.22 μm filter membrane, the concentration of SM2 in the filtrate was determined.

[0023] Furthermore, at the end of each cultivation cycle, a certain amount of dried algal powder was weighed, and the contents of lipids, total sugars, and proteins accumulated by the microalgae in the two stages were determined.

[0024] Furthermore, after a two-stage treatment process, the biogas slurry wastewater can meet the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001).

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] This invention provides a two-cycle cyclic treatment method for high ammonia nitrogen and recalcitrant antibiotics in pig farm biogas slurry using a microalgae biofilm. The method utilizes the addition of organic carbon sources and salinity (derived from saline wastewater) to improve the treatment efficiency of the microalgae biofilm for high concentrations of ammonia nitrogen and antibiotics. This solves the problems of low C / N ratio, recalcitrant antibiotics, low microalgae biomass density leading to low tolerance thresholds for pollutants, and difficulty in harvesting microalgae in pig farm biogas slurry. Simultaneously, microalgae biomass energy can be obtained while treating the biogas slurry wastewater. After cyclic treatment using the method described in this invention, the pollutants in the pig farm biogas slurry not only meet emission standards, but also increase the oil content accumulated by the microalgae to over 34%, polysaccharide content to over 18%, and protein content to over 31%. Attached Figure Description

[0027] Figure 1 In Example 4, after two cycles of treatment using microalgae biofilm, the TN and NH4+ levels in the actual pig farm biogas slurry wastewater were... + -N, TP, COD and SM2 variation trends;

[0028] Figure 2 The TN and NH4+ levels in the actual pig farm biogas slurry wastewater after two cycles of treatment with microalgae biofilm in Comparative Example 1 were... + -N, TP, COD and SM2 variation trends. Detailed Implementation

[0029] The present application will now be described in further detail by way of embodiments to enable those skilled in the art to practice the application. It should be understood that other implementations may be employed, and appropriate changes may be made without departing from the spirit or scope of the present application. To avoid unnecessary detail that would enable those skilled in the art to practice the application, certain information known to them may be omitted from the specification. Therefore, the following detailed description should not be construed in a limiting sense, and the scope of the invention is defined only by the appended claims. The following embodiments are intended to facilitate a better understanding of the present application, but are not intended to limit its scope.

[0030] The common Chlorella vulgaris (FACHB-32) used in this embodiment of the invention was purchased from the Freshwater Algae Bank of the Chinese Academy of Sciences, while the actual pig farm biogas slurry was taken from the effluent of an anaerobic digester in a pig farm in Shandong Province.

[0031] Examples 1-3 below screened the pollutant content detection results in simulated pig farm biogas slurry before and after wastewater treatment under different organic carbon source conditions, different carbon-nitrogen ratio conditions, and different salinity conditions.

[0032] Example 1

[0033] (1) Chlorella vulgaris was cultured in a light incubator (25±1℃, 5000 lux) with BG11 culture medium until the logarithmic phase, and then concentrated by centrifugation to obtain seed culture.

[0034] (2) Using simulated pig farming biogas slurry wastewater as the research substrate, 800 mL of wastewater and 100 mL of seed liquid were mixed and introduced into the microalgae biofilm system. The biomass of the seed liquid was about 1.0 g / L. Glucose, sucrose, starch and sodium acetate were added as organic carbon sources for the simulated wastewater. The treatment conditions were 5000 lux and continuous light, and the treatment cycle was 8 days.

[0035] (3) Take water samples every 48 hours to measure algal biomass, wastewater TN, TP, and NH4. +The concentrations of -N, COD, and SM2 were analyzed to assess the treatment of pollutants and the growth of microorganisms in the simulated biogas slurry wastewater.

[0036] Table 1 shows the data on the content of various pollutants in the wastewater before and after the experiment. The group with sodium acetate as the organic carbon source had the best treatment effect on ammonia nitrogen, total nitrogen and SM2 in the wastewater, which were 57.07%, 54.51% and 60.52%, respectively.

[0037] Table 1. Comparison of pollutant content before and after wastewater treatment under different organic carbon sources

[0038]

[0039] Example 2

[0040] (1) Chlorella vulgaris was cultured in a light incubator (25±1℃, 5000 lux) with BG11 culture medium until the logarithmic phase, and then concentrated by centrifugation to obtain seed culture.

[0041] (2) Using simulated pig farming biogas slurry wastewater as the research substrate, 800 mL of wastewater and 100 mL of seed liquid were mixed and introduced into the microalgae biofilm system. The biomass of the seed liquid was about 1.0 g / L. Sodium acetate was added to adjust the carbon-nitrogen ratio to 2.2 (original wastewater), 5, 10, 15, 20, and 30. The treatment conditions were 5000 lux and continuous light, and the treatment cycle was 8 days.

[0042] (3) Take water samples every 48 hours to measure algal biomass, wastewater TN, TP, and NH4. + The concentrations of -N, COD, and SM2 were analyzed to assess the treatment of pollutants and the growth of microorganisms in the simulated biogas slurry wastewater.

[0043] Table 2 shows the data on the content of various pollutants in the wastewater before and after the experiment. The group with a carbon-to-nitrogen ratio of 20 showed the best treatment effect on ammonia nitrogen and total nitrogen in the wastewater, with reductions of 89.13% and 90.12%, respectively. The removal efficiency of SM2 was not significantly different under different carbon-to-nitrogen ratios.

[0044] Table 2. Comparison of pollutant content before and after wastewater treatment under different carbon-nitrogen ratios.

[0045]

[0046] Experimental Example 3

[0047] (1) Chlorella vulgaris was cultured in a light incubator (25±1℃, 5000 lux) with BG11 culture medium until the logarithmic phase, and then concentrated by centrifugation to obtain seed culture.

[0048] (2) Using simulated pig farming biogas slurry wastewater as the research substrate, 800 mL of wastewater and 100 mL of seed liquid were mixed and introduced into the microalgae biofilm system. The biomass of the seed liquid was about 1.0 g / L. The carbon-nitrogen ratio of the wastewater was kept at 20. Then sodium chloride (taken from saline wastewater) was added to adjust the salinity to 0, 50, 80, 11, 140 and 170 mM. The treatment conditions were 5000 lux and continuous light, and the treatment cycle was 8 days.

[0049] (3) Take water samples every 48 hours to measure algal biomass, wastewater TN, TP, and NH4. + The concentrations of -N, COD, and SM2 were analyzed to assess the treatment of pollutants and the growth of microorganisms in the simulated biogas slurry wastewater.

[0050] Table 3 shows the data on the content of various pollutants in the wastewater before and after the experiment. The group with a salinity of 140 mM had the best treatment effect on ammonia nitrogen, total nitrogen and SM2 in the wastewater, with reductions of 94.82%, 93.85% and 82.50%, respectively.

[0051] Table 3. Detection results of pollutant content in wastewater before and after treatment under different salinity conditions.

[0052]

[0053] Example 4

[0054] (1) Chlorella vulgaris was cultured in a light incubator (25±1℃, 5000 lux) with BG11 culture medium until the logarithmic phase was reached, and then concentrated by centrifugation to obtain seed culture. The biomass of the microalgae seed culture was 1.0 g / L.

[0055] (2) First cycle treatment: Sodium acetate and sodium chloride were added to adjust the carbon-nitrogen ratio and salinity of the actual wastewater to 20 and 140 mM, respectively. 100 mL of seed liquid and 800 mL of actual biogas slurry wastewater were mixed and introduced into the microalgae biofilm. The treatment conditions were 5000 lux and continuous light. The treatment cycle was 8 days.

[0056] (3) Second cycle of treatment: After 8 days, scrape off the algal film on the microalgae biofilm, collect the remaining wastewater as the culture medium for the second cycle, and re-inoculate 100mL of seed liquid with a biomass of 1.0g / L to continue the second cycle of treatment of the wastewater; the treatment conditions are 5000 lux and continuous light, and the treatment cycle is 8 days.

[0057] (4) Take water samples every 48 hours to measure algal biomass, wastewater TN, TP, and NH4. + The concentrations of -N, COD, and SM2 were measured to analyze the treatment of pollutants and the growth of microorganisms in the biogas slurry wastewater. After the two stages, a certain amount of algal powder was weighed to determine the content of oil, total sugar, and protein accumulated by microalgae.

[0058] Table 4 shows that, after two treatment cycles, the microalgal biofilm system under optimal environmental conditions significantly reduced TN, TP, and NH4 levels in the wastewater. + The removal rates of -N, COD, and SM2 were 96.28%, 90.67%, 98.40%, 96.39%, and 90.76%, respectively, ultimately meeting the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001); the biomass rate was 4.54 g / m³. 2 / d, and produced 35.66%, 18.44%, and 32.56% of oil, polysaccharide, and protein biomass energy, respectively.

[0059] Table 4. Detection results of various pollutants before and after wastewater treatment.

[0060]

[0061]

[0062] Example 5

[0063] (1) Chlorella vulgaris was cultured in a light incubator (25±1℃, 5000 lux) with BG11 culture medium until the logarithmic phase, and then centrifuged and concentrated to obtain seed culture. The biomass of the seed culture was 0.8 g / L.

[0064] (2) First cycle treatment: Sodium acetate and sodium chloride were added to adjust the carbon-nitrogen ratio and salinity of the actual wastewater to 22 and 150 mM, respectively. 100 mL of seed liquid and 800 mL of actual wastewater were mixed and introduced into the microalgae biofilm. The treatment conditions were 5000 lux and continuous light. The treatment cycle was 8 days.

[0065] (3) Second cycle of treatment: After 8 days, scrape off the algal film on the microalgae biofilm, collect the remaining wastewater as the culture medium for the second cycle, and re-inoculate 100mL of seed liquid with a biomass of 0.8g / L to continue the second cycle of treatment of the wastewater; the treatment conditions are 5000 lux and continuous light, and the treatment cycle is 8 days.

[0066] (4) Take water samples every 48 hours to measure algal biomass, wastewater TN, TP, and NH4. + The concentrations of -N, COD, and SM2 were measured to analyze the treatment of pollutants and the growth of microorganisms in the biogas slurry wastewater. After the two stages, a certain amount of algal powder was weighed to determine the content of oil, total sugar, and protein accumulated by microalgae.

[0067] Table 4 shows that, after two treatment cycles, the microalgal biofilm system under optimal environmental conditions significantly reduced TN, TP, and NH4 levels in the wastewater. +The removal rates of -N, COD, and SM2 were 95.14%, 84.29%, 96.30%, 96.16%, and 85.30%, respectively, ultimately meeting the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001); and 35.74%, 18.03%, and 32.03% of oil, polysaccharides, and protein biomass energy were generated.

[0068] Table 5. Detection results of pollutant content before and after wastewater treatment

[0069]

[0070] Example 6

[0071] (1) Chlorella vulgaris was cultured in a light incubator (25±1℃, 5000 lux) with BG11 culture medium until the logarithmic phase, and then concentrated by centrifugation to obtain seed culture.

[0072] (2) First cycle treatment: The biomass of the inoculated microalgae seed solution was 1.0 g / L. Sodium acetate and sodium chloride were added to adjust the carbon-nitrogen ratio and salinity of the actual wastewater to 18 and 130 mM, respectively. 100 mL of seed solution and 800 mL of actual wastewater were mixed and introduced into the microalgae biofilm. The treatment conditions were 5000 lux and continuous light. The treatment cycle was 8 days.

[0073] (3) Second cycle of recycling: After 8 days, scrape off the algal film on the microalgae biofilm, collect the remaining wastewater as the culture medium for the second cycle, re-inoculate with seed liquid with a biomass of 1.0 g / L, and continue to recycle the wastewater for the second cycle; the treatment conditions are 5000 lux and continuous light, and the treatment cycle is 8 days.

[0074] (4) Take water samples every 48 hours to measure algal biomass, wastewater TN, TP, and NH4. + The concentrations of -N, COD, and SM2 were measured to analyze the treatment of pollutants and the growth of microorganisms in the biogas slurry wastewater. After the two stages, a certain amount of algal powder was weighed to determine the content of oil, total sugar, and protein accumulated by microalgae.

[0075] Table 4 shows that, after two treatment cycles, the microalgal biofilm system under optimal environmental conditions significantly reduced TN, TP, and NH4 levels in the wastewater. + The removal rates of -N, COD, and SM2 were 95.56%, 85.31%, 97.18%, 96.23%, and 87.53%, respectively, ultimately meeting the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001); and generated 34.92%, 18.79%, and 31.36% of oil, polysaccharides, and protein biomass energy.

[0076] Table 6. Detection results of pollutant content before and after wastewater treatment

[0077]

[0078] Comparative Example 1

[0079] (1) Chlorella vulgaris was cultured in a light incubator (25±1℃, 5000 lux) with BG11 culture medium until the logarithmic phase, and then concentrated by centrifugation to obtain seed culture.

[0080] (2) First cycle treatment: The biomass of the seed liquid was 1.0 g / L. 800 mL of actual wastewater without sodium acetate and sodium chloride was mixed with 100 mL of seed liquid and introduced into the microalgae biofilm. The treatment conditions were 5000 lux and continuous light. The treatment cycle was 8 days.

[0081] (3) Second cycle of recycling: After 8 days, scrape off the algal film on the microalgae biofilm, collect the remaining wastewater as the culture medium for the second cycle, re-inoculate with seed liquid with a biomass of 1.0 g / L, and continue to recycle the wastewater for the second cycle; the treatment conditions are 5000 lux and continuous light, and the treatment cycle is 8 days.

[0082] (4) Take water samples every 48 hours to measure algal biomass, wastewater TN, TP, and NH4. + The concentrations of -N, COD, and SM2 were measured to analyze the treatment of pollutants and the growth of microorganisms in the biogas slurry wastewater. After the two stages, a certain amount of algal powder was weighed to determine the content of oil, total sugar, and protein accumulated by microalgae.

[0083] The results shown in Table 5 indicate that, after the two-stage treatment, the microalgal biofilm system without adjusting the carbon-to-nitrogen ratio and salinity significantly reduced TN, TP, and NH4+ levels in the wastewater. + The removal rates of nitrogen (N), COD, and SM2 were 72.78%, 77.50%, 75.03%, 74.83%, and 68.84%, respectively. Neither ammonia nitrogen nor COD met the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001). Biomass accumulated at 4.44 g / m³. 2 / d, and produced 26.51%, 34.34%, and 22.67% of oil, polysaccharide, and protein biomass energy, respectively.

[0084] Table 7. Detection results of pollutant content before and after wastewater treatment

[0085]

[0086] Results analysis:

[0087] This invention, through experimental verification, shows that the optimal environmental conditions for treating pig farm wastewater using microalgae biofilms are: adjusting the carbon-to-nitrogen ratio to 18-20 using sodium acetate, and simultaneously adjusting the salinity to 130-150 mM. When the wastewater carbon-to-nitrogen ratio is 20, the microalgae biofilm effectively treats NH4+. + The microalgae biofilm exhibited the highest removal rates for NH4+, TN, COD, TP, and SM2, at 80.19%, 80.40%, 80.65%, 89.13%, and 59.16%, respectively, significantly improving the removal of pollutants from wastewater compared to the absence of a carbon source. Furthermore, when the salinity was adjusted to 140 mM at the optimal carbon-to-nitrogen ratio, the microalgae biofilm showed the best removal rate for NH4+. + The removal rates of -N, TN, COD, TP and SM2 were the highest, at 94.82%, 93.85%, 95.80%, 95.11% and 82.54%, respectively. Compared with the case where the salinity was not adjusted, the microalgae’s ability to degrade SM2 was greatly improved.

[0088] After undergoing two cycles of treatment using microalgae biofilm under optimal environmental conditions, the pollutant indicators in the biogas slurry wastewater all met the discharge standards for livestock and poultry farming wastewater. Furthermore, SM2 was also efficiently removed. After 16 days of cyclic treatment, the remaining NH4 in the wastewater... + The minimum concentrations of -N, TN, COD, TP, and SM2 were only 9.31 mg / L, 22.64 mg / L, 367.04 mg / L, 4.10 mg / L, and 0.93 mg / L, respectively. This demonstrates that using microalgae biofilms for two-cycle treatment of pig farm biogas slurry can ensure that its pollution indicators meet the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001), while also efficiently degrading SM2 and accumulating a certain amount of biomass energy.

Claims

1. A method for treating high ammonia nitrogen and recalcitrant antibiotics in pig farm biogas slurry using a two-cycle microalgae biofilm, characterized in that, Specifically, the following steps are included: (1) Chlorella vulgaris was cultured in a light incubator with BG11 medium until the logarithmic phase, and then concentrated by centrifugation to obtain seed culture. (2) First cycle treatment: Mix the seed liquid described in step (1) with the pig biogas slurry after adjusting the carbon-nitrogen ratio and salinity, and let the mixture flow on the biofilm carrier. The microalgae biofilm formed during the flow process treats the pig biogas slurry. (3) Second cycle treatment: Collect the pig biogas slurry after the first cycle treatment, scrape off the algal film that has entered the decline period in the first cycle, and inoculate again with the seed liquid described in step (1) to continue the second cycle of pig biogas slurry treatment. The treatment is completed. The carbon-nitrogen ratio mentioned in step (2) is 18-22; The salinity mentioned in step (2) is 130-150 mM; Step (2) Sodium acetate is used to adjust the carbon-nitrogen ratio of the pig biogas slurry.

2. The method according to claim 1, characterized in that, The biomass of the seed solution mentioned in step (1) is 0.8- 1.0g / L.

3. The method according to claim 1, characterized in that, The seed solution in step (2) and the adjusted carbon-nitrogen ratio The volume ratio of the pig biogas slurry after salinity reduction is 1:

8.

4. The method according to claim 1, characterized in that, The treatment conditions in step (2) are as follows: light intensity of 4000-6000 lux, culture under continuous light, flow rate of the mixture of seed liquid and pig biogas slurry of 20-30 mL / min; treatment time of at least 6 days.

5. The method according to claim 4, characterized in that, The processing time in step (2) is at least 8 days.

6. The method according to claim 1, characterized in that, The processing condition in step (3) is light intensity. Cultivate under continuous light at 4000-6000 lux, with a flow rate of 20-30 mL / min for the mixture of seed liquid and pig biogas slurry; the treatment time should be at least 6 days.

7. The method according to claim 6, characterized in that, The processing time in step (3) is at least 8 days.

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