Bioreactor for treating wastewater based on algae-bacteria symbiosis and wastewater treatment method

Abstract

The invention relates to the technical field of pig farm wastewater treatment, in particular to a bioreactor for treating wastewater based on algae-bacteria symbiosis and a wastewater treatment method.The bioreactor comprises activated sludge and algae, and stable bacteria-algae floc is formed in the bioreactor through self-attachment of the algae to a double-layer concentric carrier; removing nutrient substances in the wastewater; the wastewater is pig farm wastewater. The bioreactor provided by the invention promotes algae self-adhesion and floc formation through the algae self-adhesion double-layer concentric carrier, systematically guides bacterial-algae symbiosis, realizes synergistic metabolism, significantly improves COD, TN and TP removal efficiency, and realizes efficient removal of nutrients in pig farm wastewater treatment under extreme conditions of high ammonia nitrogen, high TP and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pig farm wastewater treatment, and particularly relates to a biological reactor for treating wastewater based on alga-bacteria symbiosis and a wastewater treatment method. BACKGROUND

[0002] Pig farm wastewater is a typical wastewater with high nutrient level and low carbon-nitrogen ratio. Although the upflowing air biological reactor has shown high nutrient removal efficiency (COD 89.5%, TN 61.1% and TP 57.3%), there are still many nutrients discharged into the effluent. In order to meet the increasingly stringent emission standards, it is necessary to provide a new method for removing nutrients in pig farm wastewater. SUMMARY

[0003] To solve the above problems, the present application provides a biological reactor for treating wastewater based on alga-bacteria symbiosis and a wastewater treatment method.

[0004] The present application is realized by the following technical solutions: A biological reactor for treating wastewater based on alga-bacteria symbiosis, comprising: A reactor main body, a gas-lifting pipe is built-in the reactor main body, a blade mixer is installed on the inner side of the gas-lifting pipe, a double-layer concentric carrier is arranged in the reactor main body, the double-layer concentric carrier is located above the blade mixer, a ring-shaped aeration strip is installed on the outer side of the gas-lifting pipe in the annular area at the bottom of the reactor main body, an aeration pump is arranged on the side of the reactor main body, and the aeration pump is in communication with the ring-shaped aeration strip; the double-layer concentric carrier comprises an inner ring, a middle ring and an outer ring from inside to outside, the inner ring, the middle ring and the outer ring are fixed on snowflake-shaped plastic branches, polyester fiber filaments are fixed on the outer ring and radiate outward from the outer ring.

[0005] A water inlet pool, which is in through connection with the bottom of the reactor main body and is provided with a first peristaltic pump between the reactor main body and the water inlet pool.

[0006] A water outlet pool, which is in through connection with the reactor main body and is provided with a second peristaltic pump between the reactor main body and the water outlet pool.

[0007] A method for treating pig farm wastewater by using the biological reactor of claim 1, comprising the following steps: Preparation stage: algae, activated sludge and double-layer concentric carriers are placed in the reactor main body.

[0008] Water inlet stage: pretreated pig farm wastewater is pumped into the reactor main body from the water inlet pool through the first peristaltic pump.

[0009] Reaction stage: air is delivered to the annular aeration strip through the aeration pump, aeration is started, an aerobic stage is formed, and pollutants in the pig wastewater are removed by activated sludge and algae in the aerobic stage; stop aeration, form an anoxic stage, and carry out denitrification and algae use NO3 - ; by controlling the opening and closing of the aeration pump, an alternating aerobic environment and anoxic environment is formed in the annular area above the annular aeration strip, and an anaerobic environment is formed in the internal area of the gas lift pipe.

[0010] Precipitation stage: the liquid in the reactor body is stationary, and the sludge and suspended matter are settled.

[0011] Drainage stage: the supernatant is discharged from the reactor body to the effluent tank through the second peristaltic pump.

[0012] Compared with the prior art, the present application has the following beneficial effects: The present application provides a kind of based on algae-bacteria symbiosis treatment wastewater bioreactor, including: The reactor body is internally provided with a gas lift pipe, a blade mixer is installed on the inner side of the gas lift pipe, a double-layer concentric carrier is arranged in the reactor body, the double-layer concentric carrier is located above the blade mixer, an annular aeration strip is installed on the outer side of the gas lift pipe in the bottom of the reactor body, an aeration pump is arranged on the side of the reactor body, and the aeration pump is communicated with the annular aeration strip;The double-layer concentric carrier includes an inner ring, a middle ring and an outer ring from inside to outside, the inner ring, the middle ring and the outer ring are fixed on snowflake-shaped plastic branches, polyester fiber filaments are fixed on the outer ring and radiate outwardly from the outer ring;The water inlet tank is connected with the bottom of the reactor body in a penetrating manner, and a first peristaltic pump is arranged between the water inlet tank and the reactor body;The effluent tank is connected with the reactor body in a penetrating manner, and a second peristaltic pump is arranged between the effluent tank and the reactor body.

[0013] (1) The bioreactor for treating wastewater based on algae-bacteria symbiosis constructed for the first time has a double-layer concentric carrier structure, the carrier algae has strong self-attachment ability, can prevent floating and loss, forms stable "bacteria-algae flocs", improves sludge settling property, and the carrier surface promotes microecological partition, and aerobic, anoxic and anaerobic environments coexist.(2) The algae in the application are green algae (such as Chlorella, Scenedesmus), which have better nitrogen and phosphorus removal; the composition of the bacterial flora (such as Campylobacteria, Desulfuromonadia) is regulated to realize multi-stage nitrogen cycle; the microbial structure is optimized and domesticated for a long period to form a stable synergistic metabolic network.(3) The specific light intensity, photoperiod, algal concentration parameters are screened for the first time using Box-Behnken design, and the chlorophyll a concentration, light intensity and time; (4) It is specially designed for pig farm wastewater treatment, the treatment object TN is as high as 2000+mg / L, and COD is as high as 3000+mg / L; the system can stably operate in high salt and high load conditions, and bacteria and algae show high adaptability; the effluent TN and TP are significantly better than those of the traditional reactor by 20.6% / 39.3% or more.

[0014] (5) Through the design and operation control of the reactor structure, the synergistic occurrence of nitrification-denitrification-phosphorus accumulating bacteria reaction is realized; through "airlift+intermittent aeration+light", the reaction space and time are multi-dimensionally controlled; the number of equipment and the land occupation are significantly reduced, and the engineering adaptability is improved.

[0015] In summary, the bioreactor of the application introduces algae and carriers into the sequencing batch reactor and intermittent air-lift biological reactor for the first time, promotes the self-attachment and floc formation of algae, systematically guides the symbiosis of bacteria and algae, realizes synergistic metabolism, and accurately regulates the operation parameters through the Box-Behnken response surface model, evaluates the nutrient removal performance, and classifies the relationship between microorganisms and wastewater treatment efficiency, which significantly improves the removal efficiency of COD (92%), TN (81.7%) and TP (89.3%), and realizes the efficient performance of nutrient removal in the treatment of pig farm wastewater under extreme conditions such as high ammonia nitrogen and high TP. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 It is a schematic diagram of the A-SBIAB system and the algae-bacteria symbiotic system of the application; wherein A is a schematic diagram of the A-SBIAB reactor; B is a schematic diagram of the double-layer concentric carrier with attached algae.

[0018] Figure 2 COD, TN, TP removal rate of the present application with the response of chlorophyll a concentration, light intensity and light time variation chart; wherein, A is the COD removal rate with the response of chlorophyll a concentration, light intensity and light time variation chart; B is the TN removal rate with the response of chlorophyll a concentration, light intensity and light time variation chart; C is the TP removal rate with the response of chlorophyll a concentration, light intensity and light time variation chart.

[0019] Figure 3 The nitrogen concentration variation chart of the system outflow of the present application.

[0020] Figure 4 SOUR and outflow MLSS concentration chart of the present application.

[0021] Figure 5 The best area fitting chart of the present application.

[0022] Figure 6 COD removal rate, TN removal rate and TP removal rate of the present application, the predicted data and the actual data comparison chart; wherein, A is the COD removal rate, the predicted data and the actual data comparison chart; B is the TN removal rate, the predicted data and the actual data comparison chart; C is the TP removal rate, the predicted data and the actual data comparison chart.

[0023] Figure 7 The bacterial community analysis chart of different samples of the present application; Figure 7 A is the sparse curve analysis chart, the curve is constructed by the serial number and the number of its representative genus, and the flat curve reflects the reasonable data; B is the genus level hierarchical clustering tree chart; C is the Venn diagram; two samples are marked with different colors, and the numbers represent the unique and shared genera in the first chart; chart B shows the clustering of different samples; the number of genera is shown in chart C.

[0024] Figure 8 The abundance result chart of bacterial community at the class level and the heat analysis chart of community at the genus level of the present application; wherein, A is the abundance result chart of bacterial community at the class level; B is the heat analysis chart of community at the genus level.

[0025] Figure 9 Algal community analysis chart of different samples of the present application; A is the rare curve analysis chart; B is the genus level hierarchical clustering tree chart; C is the Venn diagram; two samples are marked with different colors, and the numbers represent the unique and shared genera in the first chart; chart B shows the clustering of different samples; the number of genera is shown in chart C.

[0026] Figure 10The fungal abundance result chart at the class level and the community heat map analysis chart at the genus level of two samples of the application; wherein A is the fungal abundance result chart at the class level of two samples; and B is the community heat map analysis chart at the genus level. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present application, the present application will be described more fully below, and preferred embodiments of the present application will be given. However, the present application can be realized in many different forms and is not limited to the embodiments described in the present application. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0028] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the present application in the specification of the present application are only for the purpose of describing the specific embodiments of the present application, and are not intended to limit the present application.

[0029] The inventive concept of the present application is as follows: Pig farm wastewater is a typical wastewater with high nutrient level and low carbon-nitrogen ratio. Although the upflowing air biological reactor has shown high nutrient removal efficiency (COD 89.5%, TN 61.1% and TP 57.3%), but there are still many nutrients discharged into the effluent. In order to meet the increasingly stringent emission standards, it is necessary to provide a new method for removing nutrients in pig farm wastewater.

[0030] Based on this, the present application provides a method for treating wastewater based on algal-bacterial symbiosis, which provides a double-layer annular fixed carrier to provide a stable surface to promote the "self-attachment" of algae; aeration disturbance + shear force to promote the formation of algal-bacterial flocs, improve the solid-liquid separation performance of the system; solves the technical bottlenecks such as loss of suspended algae, uneven illumination, and growth cycle of bacteria and algae not coordinated in the traditional algal system. Solving the problems of easy floating of algae in the traditional reactor, serious loss, limited light penetration, uneven distribution of algae, and difficulty in forming a stable "bacteria-algae symbiotic" system. Significantly enhance the stability of algal colonization, reduce the operating energy consumption, and improve the denitrification and phosphorus removal efficiency.

[0031] The three-in-one integrated reactor of "sequencing batch + intermittent aeration + gas stripping structure" is used to realize the single reaction system with alternating aerobic / anoxic / anaerobic conditions; the built-in gas lifting pipe and annular isolation structure are arranged, and the oxygen concentration gradient in the spatial distribution is realized by means of aeration switch and liquid level control, so that different microecological environments are created; the double-ring plastic carrier structure is arranged outside the reactor, and the polyester fiber material is matched, which can promote the self-attachment of algae, sludge flocculation and mass transfer efficiency; the multistage denitrification and phosphorus removal reaction path (nitrification, denitrification, phosphorus release / absorption of phosphorus bacteria) is completed in the single reaction system. The problems of complex structure, large occupation and difficult to form effective oxygen gradient, which limit the denitrification and phosphorus bacteria activity, are solved in the traditional system which needs to be connected by multiple pool bodies to realize aerobic / anaerobic / anoxic conditions. The land occupation is reduced, the equipment structure is simplified, and the integrated denitrification and phosphorus removal is realized.

[0032] The Box-Behnken response surface analysis method is adopted to systematically optimize three key parameters: algal concentration (1000 mg / m 3 ), light intensity (6000 lux) and light time (10 h / d). Under the optimal conditions, the removal efficiencies of COD, TN and TP are 92.0%, 81.7% and 89.3% respectively, which are significantly better than those of the traditional gas lifting reactor. The key threshold relationship between algal concentration and light intensity is proposed for the first time, which can inhibit the nitrogen cycle process and the activity of phosphorus bacteria. The problems of the traditional algal-bacterial system, such as rough parameter control, high light / algal amount inhibiting the function of bacterial flora, lack of strong replicable operation interval standard and difficult actual promotion, are solved. The optimal parameter interval which can be replicated in engineering is formed to realize stable and efficient denitrification and phosphorus removal and reduce the risk of system collapse.

[0033] The structure of bacterial flora and algal flora is coordinated to improve the reaction efficiency: the dominant bacteria in the reactor are Campylobacteria, Desulfuromonadia, Spirochaetia and Bacteroidia, which are responsible for ammonium nitrate, nitrogen fixation, nitric acid reduction and organic matter degradation respectively; the dominant algal community is Chlorophyceae (98.21%), Scenedesmus, Chlorella and Coelastrum, which have strong stability and can assist in denitrification and phosphorus removal and wastewater decolorization; the dynamic regulation mechanism of light-oxygen concentration gradient-nutrient load-microbial distribution is emphasized. The problems of the traditional reactor, such as poor stability of functional microorganisms, easy to be washed out or eliminated by competition, and difficult to improve the long-period operation performance of the system through bacterial flora management, are solved. The strong functional microorganisms dominate to realize higher system resilience and impact resistance, which is especially suitable for pig farm wastewater with high ammonia nitrogen and high load.

[0034] The beneficial effects of the present application are illustrated by specific examples.

[0035] Example 1 A kind of biological reactor based on algae-fungus symbiosis treatment wastewater, comprising: The reactor body 4 is built-in gas-lift pipe 7, the inner side of the gas-lift pipe 7 is equipped with two vane mixers 8, the reactor body 4 is provided with double-layer concentric carrier 5, the double-layer concentric carrier 5 is located above the vane mixer 8, the bottom of the reactor body 4 is installed with annular aeration strip 9 in the outer side annular area of the gas-lift pipe 7, the reactor body 4 side is equipped with aeration pump 15, the explosive gas pump 14 is communicated with the annular aeration strip 9;The double-layer concentric carrier 5 includes inner ring 1-1, middle ring 2-1 and outer ring 3-1 in turn from inside to outside, the inner ring 1-1, middle ring 2-1 and outer ring 3-1 are fixed on snowflake-shaped plastic branch 5-1, polyester fiber filament 4-1 is fixed on the outer ring 3-1 and radiates to the outer side of the outer ring 3.

[0036] Preferably, the reactor body 4 is cylindrical, made of glass, and has an effective volume of 8 liters, a diameter of 18 centimeters and a liquid level of 32 centimeters. Preferably, the vane mixer 8 has two. The gas-lift pipe 7 is a hard pipe or a hose, and has a diameter of 9 centimeters and a liquid level of 25 centimeters. Preferably, the inner ring 1-1, the middle ring 2-1 and the outer ring 3-1 are circular and made of plastic; the polyester fiber filament 4-1 is made of polyester fiber. Preferably, the first timer 2 is connected above the first peristaltic pump 3; the second timer 10 is connected below the aeration pump 15; the third timer 13 is connected above the second peristaltic pump 12.

[0037] The water inlet pool 1 is connected with the bottom of the reactor body 4 in a through manner, and a first peristaltic pump 3 is arranged therebetween. The water outlet pool 14 is connected with the reactor body 4 in a through manner, and a second peristaltic pump 12 is arranged therebetween.

[0038] The biological reactor contains activated sludge and algae, and in the biological reactor, stable fungus-algae floc is formed by the self-attachment of the algae to the double-layer concentric carrier, so as to remove the nutrients in the wastewater; the wastewater is pig farm wastewater.

[0039] Example 2 (1) Pretreatment of pig farm wastewater: the pig farm wastewater is filtered through a chemical analysis filter paper with a pore size of 20 μm to remove sand, hair and fecal impurities, to obtain pretreated pig farm wastewater. The composition and characteristics of the pig farm wastewater are shown in Table 1.

[0040] Table 1 Water quality characteristics of pig wastewater (2) Preparation of activated sludge: The inoculated sludge was from a sewage treatment plant in Wenchang, Harbin. The activated sludge was first acclimated with synthetic wastewater for 20 days. Subsequently, the synthetic wastewater was gradually replaced with filtered pig farm wastewater. After one month, the removal rates of COD and NH4+-N were increased to 85% and 80%, respectively, indicating that the activated sludge had the ability to degrade the nutrients in the wastewater. The microbial community in the activated sludge contained species in the phylum Campilobacterota, Desulfobacterota, Spirochaetota, or Bacteroidota. The activated sludge was represented by MLSS.

[0041] (3) Preparation of attached algae and double-layer concentric carriers: The inoculated algae were collected from a pond near the pig wastewater sedimentation tank and were first enriched in unsterilized BG11 medium. Subsequently, raw pig farm wastewater was gradually mixed into the medium (BG11). When the concentration of algal chlorophyll a reached 1000 mg / m 3 , it indicated that the inoculation of algae was successful. The algae were green algae. The double-layer concentric carriers are shown in B of FIG. 1. Figure 1

[0042] (4) Preparation of the sequencing batch and intermittent air-lift bioreactor, i.e., A-SBIAB reactor, as shown in A of FIG. 1. Figure 1

[0043] A method for treating pig farm wastewater based on algae-bacteria symbiosis: Preparation stage: The algae, activated sludge, and double-layer concentric carriers were placed in the reactor body.

[0044] Influent stage: The pretreated pig wastewater was pumped into the reactor body from the influent tank by the first peristaltic pump.

[0045] Reaction stage: Air was delivered to the annular aeration strip via the aeration pump, aeration was started, aeration was performed for 60 minutes to form an aerobic stage, and the activated sludge and algae cooperated to remove the pollutants in the pig wastewater in the aerobic stage; aeration was stopped for 40 minutes to form an anoxic stage, and denitrification and the use of NO3 - by the algae were performed in the anoxic stage; aeration was alternately started and stopped 4 times to form an alternating aerobic environment and anoxic environment in the annular area above the annular aeration strip, and an anaerobic environment in the internal area of the air-lift pipe. In the reaction stage, the two blade mixers were stirred.

[0046] Sedimentation stage: The liquid in the reactor body (4) was stationary, and the sludge and suspended solids were settled.

[0047] Drainage stage: The supernatant was discharged from the reactor body (4) to the effluent tank (14) by the second peristaltic pump (12). ​​

[0048] Sampling can be performed through the water outlet during the operation of the bioreactor.

[0049] The concentration of chlorophyll a of the algae in the bioreactor is controlled to be 800 mg / m 3 , the light intensity is 5000 lux, the light time is 8 h / d; the service life of the activated sludge is 15 d. The aeration rate is 2 L / min, and the reactor temperature is maintained at 24°C.

[0050] Example 2 The pig farm wastewater is filtered through a chemical analysis filter paper with a pore size of 50 μm to remove sand, hair and fecal impurities to obtain pretreated pig farm wastewater. The aeration is alternately turned on and off for 5 times. The concentration of chlorophyll a of the algae in the bioreactor is controlled to be 1000 mg / m 3 , the light intensity is 6000 lux, the light time is 10 h / d; the service life of the activated sludge is 20 d. The aeration rate is 2 L / min, and the reactor temperature is maintained at 26°C. The remaining steps are exactly the same as those of Example 1.

[0051] Example 3 The pig farm wastewater is filtered through a chemical analysis filter paper with a pore size of 100 μm to remove sand, hair and fecal impurities to obtain pretreated pig farm wastewater. The aeration is alternately turned on and off for 6 times. The concentration of chlorophyll a of the algae in the bioreactor is controlled to be 1200 mg / m 3 , the light intensity is 7000 lux, the light time is 12 h / d; the service life of the activated sludge is 25 d. The aeration rate is 2 L / min, and the reactor temperature is maintained at 28°C. The remaining steps are exactly the same as those of Example 1.

[0052] Experimental Example 1 To determine the optimal chlorophyll a concentration, light intensity and light time of the algae-bacteria symbiotic system. The chlorophyll a concentration (500 mg / m 3 , 1000 mg / m 3 , 1500 mg / m 3 ), light intensity (2000 lux, 4000 lux, 6000 lux) and light time (8 h / d, 10 h / d, 12 h / d) are set. According to the variable characteristics (three levels and three factors), the Box-Behnken design (BBD) in the design expert software is selected. Based on the arrangement of BBD, seventeen experimental runs are carried out, as shown in Table 2. Subsequently, the response surface method is applied to the subsequent screening of parameters. Experimental groups 8, 9, 12, 13 and 16 are respectively repeated groups. The repeated groups are automatically generated by the software as the response surface vertex.

[0053] Table 2 Experimental conditions and response results Analytical methods and results I. Analytical methods 1. Biomass collection from the bio-carriers In this experiment, ultrasonic vibration and chemical treatment were used to collect the biomass on the bio-carriers. The multi-cellular communities attached to the surface of the bio-carriers formed biofilms, which were first flushed by ultrasonic treatment to collect the non-settled biomass. Second, the bio-carriers were suspended in an alkaline solution (sodium hydroxide, 1 M) and heated in a water bath (60 °C, 30 min). Finally, the bio-carriers were treated with ultrasonic vibration (200 W, 20 min). After the above treatments, the biomass was separated from the bio-carriers and then used for the extraction of chlorophyll a.

[0054] 2. Water quality analysis COD, TN, and TP were determined using a UV-visible intelligent parameter water quality analyzer and a digester (Beijing Lianghua Technology Co., Ltd., China).

[0055] 3. Box-Behnken design analysis The key operating conditions were optimized by BBD analysis using Design Expert software (Stat-Ease Inc., version 11). The resulting regression equation was used to predict the performance of the bioreactor, as shown in Table 3. Based on the degree of fit to the actual data, a polynomial model was used for each response, with the determination coefficient (R2) of the polynomial model as the main criterion. The quadratic model for each response and the variance analysis (ANOVA) of the regression equation are shown in Table 3. The variables (A, B, and C) in the regression equation refer to the concentration of chlorophyll a, light intensity, and light time, respectively. According to the coded factors, this equation can be used to predict the response of each factor.

[0056] In terms of statistical analysis, the significance of the model was verified by a low probability value (P-value < 0.0001). The coefficient (R²) was determined by calculating the correlation coefficient (R) and its square. In addition, the F-test for goodness-of-fit was used to test the accuracy of the model. A P-value less than 0.0500 indicates that the A, B, and A² model terms are significant, while a P-value greater than 0.1000 indicates that the model terms are not significant. If there are a large number of insignificant model terms, reducing the model can improve the quality of the model. Adeq Precision measures the signal-to-noise ratio. When this ratio is greater than 4, it is ideal. For this model, navigating in the design space is crucial. The coefficient of variation (CV) is used to demonstrate the reliability and precision of the experiment. To check the accuracy of the model, the actual and predicted values of the COD, TN, and TP removal efficiencies were obtained. The consistency of the actual and predicted values indicates that the model has high accuracy.

[0057] Table 3 ANOVA results for the quadratic model for the studied responses 4. Microbial community structure analysis During the operation, DNA was extracted from samples at different stages using a universal soil DNA extraction kit (Harbin Frog Biotechnology, China).

[0058] 5. Calculation 2.5.1. Calculation of seaweed biomass Algal accumulation and its relative content were assessed using chlorophyll a concentration. Liquid samples containing algae, activated sludge, and other microorganisms were centrifuged at 3000 rpm for 5 min. After centrifugation, the sediment was resuspended in methanol solution (10 ml, 90%) and 0.2% magnesium chloride, while the mixture was heated in the dark (70 °C, 30 min). After cooling, the extract was centrifuged again. Chlorophyll a concentration was measured using a spectrophotometer (UV1800, Shimadzu, Japan) at four wavelengths (750 nm, 665 nm, 645 nm, and 630 nm). Blank samples were prepared as 90% methanol solution and then calculated using the following formula:

[0059] (1).

[0060] Where (µg / L) is the total chlorophyll a concentration, V1 ( (ml) is the volume of the methanol extract, V (L) is the sample volume, OD is the absorbance at wavelengths of 630, 645, 665, and 750 nm, and (cm) is the optical path length of the cuvette. To eliminate the influence of photosynthetic bacteria, (µg / L) is calculated according to the following formula 2.

[0061] (2).

[0062] Where (µg / L) is the chlorophyll a concentration of photosynthetic bacteria. OD represents the absorbance at wavelengths of 772 nm and 850 nm, the same as in Formula 1. Based on Formulas 1 and 2, the algal concentration is calculated using Formula 3:

[0063] (3) 2.5.2. Calculation of Free Nitrite Nitrogen (FNA-N) The FNA-N concentration was calculated according to Equation 4, and the total NO2-N and pH were measured (Zhao et al., 2013).

[0064] (4).

[0065] Where is the FNA-N concentration (mg / L), and T is room temperature? (26℃) is NO2 - -N total concentration (mg / L).

[0066] II. Results and discussion 1. Nutrient removal by A-SBIAB (1) Removal of chemical oxygen demand The ANOVA analysis of COD is shown in Table 2. A convex quadratic model was established by programming to determine the model of COD removal efficiency. Among them, A, B and C represent the concentration of chlorophyll a (mg / m 3 ), light intensity (lux) and light time (h / d) respectively. The model includes terms such as AB, AC, BC, A, B, C, A2, B2 and C2. The factors used have a significant effect on COD removal efficiency. In terms of these factors, chlorophyll a and light intensity are more effective than light time. Therefore, the effects of chlorophyll a and light intensity on nutrient removal performance were studied, and the light time was set to 10 hours / day, as shown in A of Figure 2 .

[0067] In the design space, the COD removal efficiency of A-SBIAB can be as high as 83.09%-93.91%, and the highest can reach 93.91% when the concentration of chlorophyll a is 1500 mg / m 3 , the light intensity is 6000 lux and the light time is 12 hours. It is found that the concentration of chlorophyll a and the light time have a positive effect on COD removal, while higher light intensity is not conducive to COD removal. Initially, as the light intensity increases from 4000 lux to 6000 lux, the COD removal efficiency improves, but when the light intensity increases to 8000 lux, the efficiency drops sharply. Algal growth mainly depends on photosynthesis and respiration, which are mainly affected by important variables such as CO2 and O2 concentrations, temperature and light intensity. Respiration includes photorespiration and dark respiration. Photorespiration is a biochemical process that occurs in all photosynthetic cells under high oxygen, low carbon dioxide and light conditions, and is a byproduct of energy loss in the process of photosynthesis. Although the substrate is also released during decomposition and transformation, it cannot be converted into adenosine triphosphate (ATP), so the photosynthetic product is wasted. Photorespiration is considered a self-protection mechanism for algae when they face environmental stress. Dark respiration occurs in the dark and can continuously produce ATP and release free energy to meet the needs of root absorption function, organic matter synthesis and transformation, and various material metabolism reactions, thereby promoting the continuous progress of life activities. Based on the above light conditions, it is concluded that the rate of photosynthesis will be limited by stronger light intensity. In addition, when the light intensity exceeds 800 ft-c (1 lux = 0.0929 ft-c), the growth rate of the unsynchronized algal suspension begins to decline. In this invention, 8000 lux is equivalent to 743.2 ft-c, which is close to 800 ft-c.Figure 4 As shown, the SOUR of the mixed solution decreased significantly as the light intensity increased from 6000 lux to 8000 lux. Therefore, at a light intensity of 8000 lux, limited photosynthesis inhibited algal growth, negatively impacting the algae-bacteria symbiotic system and reducing COD removal efficiency. Furthermore, as the chlorophyll a concentration increased from 1000 mg / m³, the SOUR of the mixed solution decreased significantly. 3 Increase to 1500 mg / m 3 The COD removal efficiency did not show a linear increase. As the algae concentration increased from 1000 mg / m³... 3 Up to 1500mg / m 3 With the increase, the MLSS concentration in the effluent suddenly rose. Furthermore, when the algal concentration increased from 1000 mg / m³... 3 Up to 1500mg / m 3 When the concentration of algae increased, the solubility (SOUR) did not rise significantly. It was also found that photosynthetic efficiency gradually decreased due to enhanced photorespiration at high algal concentrations. Therefore, high light intensity and algal concentrations are unfavorable for the formation of algal-bacterial symbionts. Considering algal biomass production and high-quality effluent, the A-SBIAB system is expected to be suitable for algal concentrations of 1000 mg / m³. 3 It operates under the conditions of a light intensity of 6000 lux and a light duration of 10 hours / day.

[0068] (2) Removal of total nitrogen Total nitrogen is abbreviated as TN. The total nitrogen removal performance of A-SBIAB is evaluated by observing the total nitrogen removal efficiency. In Table 2, the terms A2, B2, C2, A, B, C, AB, AC, and BC in the model were estimated and recommended in the fitting summary calculation.

[0069] Figure 2 Figure B shows the effects of chlorophyll a concentration, light duration, and light intensity on total nitrogen removal efficiency, presented in a three-dimensional plot. The results indicate that the total nitrogen removal efficiency is highest within the range of 59.61%–86.03% when the chlorophyll a concentration is 1000 mg / m³. 3 The total nitrogen removal rate reached its highest level of 86.03% when the light intensity was 6000 lux and the light duration was 10 hours. As the algae concentration increased from 500 mg / m³ to 1000 mg / m³, the removal rate decreased. 3 The total nitrogen removal efficiency improved, but further increased to 1500 mg / m³. 3 Subsequently, regardless of light intensity and duration, the total nitrogen removal efficiency decreased. The results indicate that higher algal concentrations are detrimental to total nitrogen removal.

[0070] like Figure 3 As shown, at a chlorophyll a concentration of 1500 mg / m³ 3 In the case of NO2 in the effluent- -NO2-N concentration range was 7.9 to 78.7 mg / L. In the case of 1500 mg / m 3 of chlorophyll-a concentration, NO2 - -N concentration was higher and total nitrogen removal efficiency was lower. In addition, the high concentration of algae enhanced the light respiration, which also led to the decrease of photosynthetic efficiency of algae. Therefore, the high concentration of algae inhibited the photosynthesis of algae and nitrifying bacteria, which reduced the TN removal efficiency. Moreover, the TN removal efficiency also decreased at higher light intensity (8000 lux). It was found that the growth of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was inhibited at 75 pmol / m2 / s light intensity. For fluorescent light, 1000 lux is equivalent to 12.5 pmol / m2 / s. Therefore, 8000 lux is equivalent to 100 pmol / m2 / s, which is significantly higher than 75 pmol / m2 / s, indicating that AOB and NOB will be inhibited at 8000 lux light intensity. In addition, at 8000 lux light intensity, the SOUR of mixed liquor was significantly reduced, as shown in Figure 4 , which was due to the limitation of photosynthesis. Therefore, higher light intensity and algae concentration were not conducive to TN removal.

[0071] (3) Removal of total phosphorus Total phosphorus is referred to as TP. The TP removal efficiency of A-SBIAB under different conditions is shown in Table 2. The model includes terms such as AB, AC, BC, A, B, C, A2, B2, and C2. According to the variable conditions, the response of TP removal efficiency is shown in Figure 2 C. Among these variables, the chlorophyll-a concentration and light intensity had the greatest impact on the TP removal performance. With the increase of chlorophyll-a concentration from 500 mg / m 3 to 1000 mg / m 3 , the TP removal response improved; while when the chlorophyll-a concentration further increased to 1500 mg / m 3 , the TP removal response decreased. In addition, the TP removal effect was also inhibited at 8000 lux light intensity. Higher chlorophyll-a concentration and light intensity had a negative impact on TP removal. As mentioned earlier, at 1500 mg / m 3 of chlorophyll-a concentration and 8000 lux light intensity, the accumulation of NO2 - -N was observed due to the inhibition of NOB activity. At 1500 mg / m 3 of chlorophyll-a concentration and 8000 lux light intensity, the NO2 - -N concentration in the supernatant ranged from 7.9 to 78.7 mg / L. According to the formula, the FNA concentration ranged from 0.56 x 10 -3to 5.6 x 10 -3 mg HNO2-N / L. Previous studies showed that PAO growth, glycogen production and phosphate uptake were inhibited by 50% at FNA concentration of about 0.5 x 10 -3 mg HNO2-N / L, while these processes were completely inhibited at FNA concentration of about 6 x 10 -3 mg HNO2-N / L. In this work, the average concentration of FNA was 3.08 x 10 -3 mg HNO2-N / L, which might be due to limited nitrification process. This process was inhibited by high algal concentration and high light intensity, resulting in NO2-N accumulation. Therefore, the total phosphorus removal efficiency suddenly decreased at chlorophyll-a concentration of 1500 mg / m 3 and light intensity of 8000 lux, which might be attributed to the inhibition of FNA on PAOs activity.

[0072] (4) Verification of screening conditions Figure 5 The results in Table 3 showed that the yellow region met the criteria (COD, TN and TP removal efficiencies were more than 90%, 80% and 80%, respectively). The yellow region was considered as the ideal operating conditions at chlorophyll-a concentration of 1000 mg / m 3 , light intensity of 6000 lux and light duration of 10 hours. Subsequently, the A-SBIAB system was operated under the ideal conditions to evaluate the model accuracy. The COD, TN and TP responses under the ideal conditions were analyzed. The actual and predicted data were listed in Table 4 and Figure 6 , respectively. The actual data agreed well with the predicted data, as shown in Figure 6 , indicating that the model was designed reasonably.

[0073] Table 4 Verification test under the optimal conditions According to the above experimental results, the nutrient removal performance of the A-SBIAB was observed under the optimal conditions (chlorophyll-a concentration of 1000 mg / m 3 , light intensity of 6000 lux and light duration of 10 hours) during long-term operation. The nutrient removal efficiencies were monitored. The COD, TN and TP removal efficiencies of the A-SBIAB were as high as 92.0%, 81.7% and 89.3%, respectively, as shown in Table 4. Its nutrient removal performance was superior to that of the conventional UASB without algae. In particular, the TN and TP removal efficiencies of the A-SBIAB were 20.6% and 39.3%, respectively, which were higher than the results of previous studies. Therefore, the algal assistance had a significant positive impact on the nitrogen and phosphorus removal performance of the A-SBIAB.

[0074] Experimental Example 2 Relationship of A-SBIAB operation with functional microorganisms (1) Bacterial community structure Table 5 lists the sequence details of microorganisms in the mixed liquor sample (algae + sludge) at the start-up phase (1st day) of the reactor and the mixed liquor sample at the 100th day of the reactor operation. The dilution curve has a sequence similarity of 97%, as shown in A of Figure 7 , and the two curves almost reach a gentle slope, indicating that the sequencing number of the two samples is reasonable. Most of the bacterial community has been detected by Miseq sequencing. In addition, the bacterial composition at the genus level was evaluated using hierarchical clustering analysis, as shown in B of Figure 7 and a Venn diagram, as shown in C of Figure 7 . The results show that in the sample at the 1st day, there are Azospira, Vibrionaceae, Desulfovibrio, Pseudovibrio, Sulfurspirillum, Sulfuricella, Sulfomonas, etc., while in the sample at the 100th day, there are Vibrionaceae, Desulfovibrio, Sulfurspirillum, Sulfomonas, etc. After 100 days, the microorganisms at the genus level are mainly dominated by Vibrionaceae, Desulfovibrio, Sulfurspirillum and Sulfomonas. At the genus level, each of the two samples has 192 members, and there are 16 unique members in the sample at the 100th day. After a period of operation, 44 members were eluted from the A-SBIAB due to the adaptation of the reactor operation.

[0075] Table 5 Classification of main bacterial community at genus, class, and phylum levels In order to better understand the changes in the microbial community structure, the microbial abundance at different classification levels of each sample was analyzed, as shown in Figure 8 . During the entire operation, there were 13 members of this group in the A-SBIAB. At the end of the operation, Campylobacter (72.05%) was the most abundant member in the A-SBIAB. Other members are arranged in descending order, such as Desulfovibrio (11.16%), Sulfurspirillum (3.10%), Gamma-proteobacteria (2.46%), Bacteroides (1.73%), Desulfosphaera (1.59%), Clostridia (0.96%), Syntrophus (0.51%), Alpha-proteobacteria (0.38%), Desulfovibrio (0.32%), Bacillus (0.11%), and Blautia (0.01%), as shown in Figure 8A shown in FIG. 1. During the period of operation, the abundance of Campylobacter, Desulfovibrio, Spirochetes, and Bacteroidetes increased by 40.15%, 9.69%, 2.2%, and 0.04%, respectively. The growth of Campylobacter was enhanced under microaerobic conditions compared to aerobic conditions. In previous studies, aerobic-anaerobic-anoxic conditions were created in an upflowing air bioreactor by intermittent aeration and controlling air flow rate. In this work, the algae-assisted enhanced the oxygen transfer process and extended the microaerobic environment, which benefited from the algal-bacterial symbiotic system. Therefore, the abundance of Campylobacter was significantly improved. In addition, Campylobacter has a strong ability of cohesive interaction, which has been confirmed by electron microscopy. Its enrichment helps to consolidate the algal-bacterial symbiotic system. Desulfovibrio was found to reduce oxidized forms of nitrogen. The increase in Desulfovibrio abundance is crucial for the removal of nitrate- and nitrous dioxide- According to the study of, the order Campylobacter, class Spirochetes, and Desulfovibrio are the main bacterial members, which play an important role in nitrogen cycle, such as nitrate ammonification (order Campylobacter), nitrogen fixation (class Spirochetes), and nitrate reduction (Desulfovibrio). Their enrichment plays a significant role in TN removal. Bacteroidetes are important and common microorganisms for the degradation of organic pollutants, most of which are anaerobic, some are facultative anaerobic, and a few are aerobic. The slight increase in the abundance of Bacteroidetes during the operation period can be attributed to its ability to adapt to the integrated oxygen environment, and it plays a key role in the removal of organic matter in wastewater.

[0076] As Figure 8B, the microorganisms at the genus level were further analyzed. After a period of operation, Pseudoalteromonas, Azospira, and Marinobacter, which are responsible for efficient removal of NOx and COD, were enriched as denitrifying bacteria. Thioalkalivibrio, unclassified Vibrionaceae, and unclassified Rhodobacteraceae, which are capable of secreting extracellular polymeric substances (EPS) to form biofilm and sludge flocs, especially unclassified Vibrionaceae, prefer microaerobic environment. Overall, microorganisms will secrete more EPS to resist environmental changes. Therefore, under the intervention of algae, Thioalkalivibrio, unclassified Vibrionaceae, and unclassified Rhodobacteraceae were enriched. A large amount of EPS will further strengthen the algae-bacteria symbiotic system. In A-SBIAB, the enrichment of Thioalkalivibrio and unclassified Vibrionaceae plays an important role in forming sludge flocs and improving sludge settling performance. After a period of operation, the increase of Lentimicrobium indicates its adaptability to the high-salinity environment of A-SBIAB. Its enrichment plays a key role in the degradation of refractory organic matter. It is found that Dechlorobacter can well degrade chlorinated organic compounds. Acholeplasma appears only in anaerobic sludge and can degrade sludge pollutants. It is reported that Halothiobacillaceae may contribute to low sulfide production and efficient COD removal. Studies on extracellular DNA show that Izemoplasmataceae can actively participate in the degradation of extracellular DNA multimers under anaerobic conditions. Therefore, the increase of Izemoplasmataceae may be the result of the system's own adjustment to control the ideal EPS level. It is observed that some members of Desulfovibrio can utilize nitrate instead of sulfate as the final electron acceptor, thereby reducing nitrate to nitrite and molecular nitrogen, and then further reducing it. It can also be concluded that Desulfovibrio, as a carbohydrate-degrading bacterium, is sensitive to nutrient deficiency. In A-SBIAB, the increase in Desulfovibrio abundance is attractive for TN and COD removal. As mentioned above, the enrichment of these species, such as Pseudoalteromonas, Azospira, Marinobacter, Thioalkalivibrio, unclassified Vibrionaceae, unclassified Rhodobacteraceae, Lentimicrobium, Dechlorobacter, Acholeplasma, Halothiobacillaceae, Izemoplasmataceae, and Desulfovibrio, plays a major role in consolidating the algae-bacteria symbiotic system and improving wastewater treatment performance.

[0077] (2) Algal community structure The present application further analyzes the algal community structure, as shown in Table 6. The dilution curve shows that the sequence similarity exceeds 90%, reaching a moderate level, as shown in Figure 9The results showed that the sequencing quantity was reasonable. In addition, hierarchical clustering analysis showed that the community distribution of sample 1 was different from that of sample 2. Venn diagram analysis also showed that the community mainly composed of Chlorella sp., Streptomyces sp., Saccharomycetales sp., Debaryomyces sp., etc. existed in A-SBIAB all the time. At the end of operation, the abundance of Chlorella sp. was as high as 99.74%, while the initial communities such as uncultured eukaryote, Microsporidium sp., Mucor sp., Mucorales sp., uncultured fungus, Aspergillus sp., nematode, lichen, Bannetomyces sp., Leucosporidium sp., Malassezia sp., etc. were washed away. It is reported that Debaryomyces sp. has high salt-tolerant potential. It shows some beneficial properties - it can metabolize a variety of sugars. Overall, pig farm wastewater is rich in organic components and salt concentration. The stable presence of Debaryomyces sp. indicates that it has high salt-tolerant potential in the treatment of pig farm wastewater. In addition, it helps to degrade organic matter in pig farm wastewater. In addition, it was found that Chlorella sp. as a microalgae showed high growth rate, nutrient removal and carbon dioxide consumption potential. Therefore, the establishment of Saccharum sp. in A-SBIAB played an important role in the treatment of pig farm wastewater. Methyl blue algae can quickly degrade chlorpyrifos by co-metabolizing carbon and nitrogen sources. At present, chlorpyrifos is one of the five most commonly used pesticides in agricultural planting, which may enter pig farms along the food chain. In addition, microalgae can remove 50% of chlorpyrifos. In A-SBIAB, microalgae and methyl blue algae remained relatively stable throughout the operation, thereby promoting the removal of chlorpyrifos. A-SBIAB was operated with fluctuating influent load and achieved the integration of aerobic, anoxic and anaerobic conditions through a special operation mode. At the end of operation, the abundance of Chlorella sp. was as high as 99.74%, indicating that it adapted to the environment of A-SBIAB. It is reported that Chlorella sp. as a biological system has great potential in the recovery of nitrogen and phosphorus from wastewater. With the progress of operation, the enrichment of Chlorella sp. played a decisive role in the removal of organic matter and nitrogen.

[0078] Table 6 Classification of main algae at genus, class and phylum levels Figure 10 In addition, the change of classification level of algal community in A was also analyzed. With the operation of A-SBIAB, the abundance of Chlorophyta increased from 0.47% to 98.21%. In the present invention, algae were fed with pig farm wastewater. In A-SBIAB, with the stable concentration of algae at 1000 mg / m 3, forming an algae-bacteria symbiotic system. SBIAB was operated in a special mode of aerobic / anoxic / anaerobic cycles. The algae-bacteria symbiotic system in A-SBIAB enhanced the change of DO environment. Therefore, 98.21% of Chlorophyta at the end of operation indicated that it adapted to the special conditions of the reactor. Overall, Chlorophyta members exist in wastewater treatment, with great potential for producing biodiesel feedstock and biological treatment of wastewater. The maximum enrichment of Chlorophyta is crucial for the treatment of pig farm wastewater.

[0079] Figure 10 The genus level changes of algal community were also analyzed in B. The microbial community structure on the first day was more abundant than on the 100th day. As the operation proceeded, a large number of species decreased and were washed away, while some species, such as Chlorella, Cryptosporidium, Chlorella, and Chlorella, were enriched at the end of the operation. In recent years, Chlorella strains have been widely used to remove nutrients in wastewater, i.e., municipal sewage, salt water, furfural, and high-ammonia wastewater, with excellent wastewater treatment effect. In the present invention, algae came from a pond near the pig farm. As the operation proceeded, Chlorella became the dominant algal community and played a core role in nutrient removal. Cryptosporidium is most common in pig farms and can cause cryptosporidiosis. In the present invention, pig farm wastewater was fed into A-SBIAB, and Cryptosporidium remained stable throughout the experiment. It is important to note the risk of cryptosporidiosis in pig farms. Chlorella is another enriched algal community in A-SBIAB. It is known to grow well under high nitrogen-phosphorus ratios and exhibit excellent nitrogen-phosphorus removal performance. In nutrient-rich wastewater, Chlorella can improve wastewater quality in an environmentally sustainable manner. It also regulates lipid and carbohydrate metabolism, thereby increasing biomass production. Therefore, the enrichment of Chlorella has a positive impact on the removal of organic matter and nutrients. During the operation, A-SBIAB was also enriched with Chlorella. Chlorella is usually a member of the microalgal community in wastewater treatment. However, it rarely becomes a dominant member, and therefore is considered to have a poorer growth potential than other competing members, especially when its survival conditions change dramatically. In this study, the A-SBIAB system was operated under integrated aerobic, anoxic, and anaerobic conditions. However, the abundance of Coelastrum still increased at the end of the operation. This indicates that Coelastrum can adapt to the integrated conditions during the operation process. To develop its functions in subsequent experiments, this strain of Coelastrum should be further screened and identified. Recently, more and more researchers have begun to study Coelastrum species because of their ability to accumulate lipids and pigments in wastewater treatment. Therefore, the enrichment of Coelastrum may play a role in the decolorization and nutrient removal of pig farm wastewater.

[0080] (3) Relationship between nutrient removal and functional microorganisms Compared with the previous up-flow air reactor, the COD, TN and TP removal efficiencies of A-SBIAB were increased by 2.5%, 20.6% and 39.3%, respectively. Algal assistance had a significant effect on nutrient removal in swine wastewater. With the operation of A-SBIAB, the phyla of Flexibacteriia, Desulfosporomonadia, Spirochaetes and Bacteroidetes became the main bacterial members, which played a role in nitrogen cycling and organic matter removal, including nitrate ammonification (Flexibacteriia), nitrogen fixation (Spirochaetes), nitrate reduction (Desulfosporomonadia) and organic matter degradation (Bacteroidetes). At the same time, algae such as Chlorophyta (98.21%) became the dominant community. As mentioned above, the enrichment of these functional communities was closely related to the operating conditions of A-SBIAB, thereby improving the nutrient removal effect in swine wastewater.

[0081] Each technical feature of the above-described embodiments can be combined arbitrarily. To make the description concise, each technical feature of the above-described embodiments has not been described all possible combinations, however, as long as the combinations of technical features do not exist contradictions, it should be considered as the scope of the present disclosure.

[0082] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. For ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent protection of the present application should be subject to the appended claims.

Claims

1. A biological reactor for treating wastewater based on algal-bacterial symbiosis, characterized in that, It comprises: The reactor body (4) is internally provided with a gas-lifting pipe (7), the inner side of the gas-lifting pipe (7) is provided with a vane mixer (8), a double-layer concentric carrier (5) is arranged in the reactor body (4), the double-layer concentric carrier (5) is located above the vane mixer (8), an annular aeration strip (9) is arranged in the annular area outside the gas-lifting pipe (7) at the bottom of the reactor body (4), an aeration pump (15) is arranged on the side of the reactor body (4), the aeration pump (14) is communicated with the annular aeration strip (9); the double-layer concentric carrier (5) comprises an inner ring (1-1), a middle ring (2-1) and an outer ring (3-1) from inside to outside, the inner ring (1-1), the middle ring (2-1) and the outer ring (3-1) are fixed on snowflake-shaped plastic branches (5-1), polyester fiber filaments (4-1) are fixed on the outer ring (3-1) and radiate outward from the outer ring (3-1); The water inlet pool (1) is connected with the bottom of the reactor body (4) in a penetrating manner, and a first peristaltic pump (3) is arranged between the water inlet pool (1) and the reactor body (4); The water outlet pool (14) is connected with the reactor body (4) in a penetrating manner, and a second peristaltic pump (12) is arranged between the water outlet pool (14) and the reactor body (4).

2. The bioreactor of claim 1, wherein, The first peristaltic pump (3) is connected with a first timer (2); the aeration pump (15) is connected with a second timer (10); the second peristaltic pump (12) is connected with a third timer (13); the side of the reactor body (4) is connected with a water outlet (11); the inner ring (1-1), the middle ring (2) and the outer ring (3) are circular.

3. A method for treating swine waste water using the bioreactor of claim 1, characterized by, It comprises the following steps: Preparation stage: algae, activated sludge and double-layer concentric carrier (5) are placed in the reactor body (4); Water inlet stage: pretreated pig farm wastewater is pumped into the reactor body (4) from the water inlet pool (1) through the first peristaltic pump (3); Reaction stage: air is delivered to the annular aeration strip (9) through the aeration pump (15), aeration is started, an aerobic stage is formed, and pollutants in the pig wastewater are removed by activated sludge and algae in the aerobic stage; stop aeration, form an anoxic stage, and carry out denitrification and algae use NO3 - ; by controlling the opening and closing of the aeration pump (15), an alternating aerobic environment and anoxic environment is formed in the annular area above the annular aeration strip (9), and an anaerobic environment is formed in the internal area of the gas lift pipe (7); Precipitation stage: the liquid in the reactor body (4) is static, so that the sludge and suspended solids are settled; Drainage stage: the supernatant is discharged from the reactor body (4) to the water outlet pool (14) through the second peristaltic pump (12).

4. The method of claim 3, wherein, The time of starting aeration is 60 minutes; the time of stopping aeration is 40 minutes; the aeration is started and stopped alternately for 4-6 times.

5. The method of claim 3, wherein, The microbial community in the activated sludge comprises at least one of the following phylum-level classification units: (1) Campilobacterota; (2) Desulfobacterota; (3) Spirochaetota; (4) Bacteroidota.

6. The method of claim 3, wherein, The concentration of chlorophyll a of said algae is 800 mg / m 3 1200 mg / m 3 is a green algae; said algae is a green algae.

7. The method of claim 3, wherein, The mass of activated sludge corresponding to each liter of pig farm wastewater is 2500mg-3500mg.

8. The method of claim 3, wherein, The biological reactor is controlled to operate under the condition that the light intensity is 5000lux-7000lux and the light time is 8h / d-12h / d; the service life of the activated sludge is 15d-25d.

9. The method of claim 3, wherein, The aeration rate is 2L / min, and the reactor temperature is maintained at 24℃-28℃.

10. The method of claim 3, wherein, The method for pretreating the pig farm wastewater is to filter the pig farm wastewater through a chemical analysis filter paper with a pore size of 20-100 mu m to remove sand, hair and fecal impurities.

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