Sewage denitrification method and system based on algal-bacterial symbiotic system

Abstract

The invention provides a sewage denitrification method and system based on an algal-bacterial symbiotic system, and relates to the technical field of biological denitrification of sewage. The sewage denitrification method based on the algal-bacterial symbiotic system comprises the steps of sludge activation treatment, preparation of the algal-bacterial symbiotic system, sewage denitrification treatment and the like, the sludge is sludge in a secondary sedimentation tank of a sewage treatment plant, and the sludge activation treatment is aeration and sedimentation treatment. According to the method, the chlorococcus and the sludge in the secondary sedimentation tank of the sewage treatment plant are used as main raw materials to prepare the algal-bacterial symbiotic system, and through the specific chlorococcus culture and activated sludge activation process, the sewage treatment efficiency is improved, the sewage treatment cost is reduced, efficient recovery of biomass in the sewage with the low carbon nitrogen ratio and sewage treatment recycling are realized, and the method is suitable for industrial production. And a beneficial solution is provided for environmental protection and sustainable development.

Description

Technical Field

[0001] The present invention relates to the technical field of biological denitrification of sewage, and in particular to a sewage denitrification method and system based on a bacteria-algae symbiotic system. Background Art

[0002] Municipal wastewater refers to the domestic sewage of urban residents, drainage from government offices, schools, hospitals, commercial service agencies and various public facilities, as well as industrial wastewater and initial rainwater that are allowed to be discharged into the urban sewage collection system. These sewages need to be treated to remove pollutants before they can be safely discharged or reused. In urban management and environmental protection, the effective treatment and management of municipal wastewater is a very important link.

[0003] Nitrogen exists in many forms in water, including ammonia nitrogen, nitrite nitrogen and nitrate nitrogen. Ammonia nitrogen is an important pollutant that causes eutrophication of water bodies and environmental pollution. Excessive ammonia nitrogen discharge will lead to a large consumption of dissolved oxygen in water bodies, promote the reproduction of algae and microorganisms, and eventually form black and smelly water bodies, destroying the aquatic ecosystem. The other two inorganic nitrogens can also cause direct or indirect harm to water bodies. Therefore, the efficient removal of nitrogen in urban sewage is crucial. The low carbon-nitrogen ratio of urban sewage makes it difficult for the total nitrogen after water treatment to meet the discharge standards.

[0004] At present, biological treatment, physical-chemical treatment, advanced oxidation treatment and membrane separation technology are common methods for sewage treatment. Among them, biological treatment uses microorganisms in bioreactors to degrade organic matter into harmless substances and purify water quality. Common biological treatment methods include biofilters, activated sludge methods, and biofilm methods. Physical-chemical treatment is usually used to remove suspended matter, sediments, and heavy metals in sewage. Advanced oxidation treatment can oxidize and degrade organic matter into harmless substances, including ozone oxidation and ultraviolet light oxidation. Membrane separation technology uses the interception effect of membranes to remove microorganisms, colloids and particulate matter to improve water quality. These technologies can be used as pretreatment or enhanced processes to improve sewage treatment efficiency.

[0005] However, for urban sewage with a low carbon-nitrogen ratio, traditional treatment methods generally have the following shortcomings: (1) Insufficient carbon source limits the process of denitrifying bacteria reducing nitrate to nitrogen gas; (2) In order to improve the denitrification effect, a large amount of oxygen and energy are consumed, which increases the treatment cost; (3) A combination of multiple processes is required, such as short-range nitrification and denitrification, simultaneous nitrification and denitrification, anaerobic ammonia oxidation, etc., to improve the denitrification efficiency; (4) The addition of external carbon source may lead to insufficient or excessive carbon source addition, which can easily cause secondary pollution. These difficulties make denitrification of low carbon-nitrogen ratio sewage a complex and challenging process.

[0006] Therefore, how to overcome these problems, provide a treatment method for low carbon-nitrogen ratio urban sewage, improve the treatment efficiency of low carbon-nitrogen ratio urban sewage, reduce treatment costs, and achieve efficient recovery of biomass in sewage and resource utilization of sewage treatment is one of the technical problems that need to be solved at present. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a sewage denitrification method and system based on a bacteria-algae symbiotic system. The present invention uses Chlorella and sludge from the secondary sedimentation tank of a sewage treatment plant as the main raw materials to prepare a bacteria-algae symbiotic system. Through a specific Chlorella cultivation and activated sludge activation process, the treatment efficiency of urban sewage with a low carbon-nitrogen ratio is improved, and the efficient recovery of biomass in urban sewage with a low carbon-nitrogen ratio and the resource utilization of sewage treatment are achieved, providing a beneficial solution for environmental protection and sustainable development.

[0008] The sewage denitrification method based on the bacteria-algae symbiotic system of the present invention comprises the following steps: S1, inoculating the sludge into sewage after natural sedimentation to form a sludge mixed liquid, and activating the sludge mixed liquid to obtain aerobic sludge; S2, centrifuging the Chlorella in the logarithmic growth phase and the aerobic sludge respectively and mixing them according to a certain proportion to obtain a bacteria-algae symbiotic system; S3. Adding the bacteria-algae symbiotic system into sewage to achieve sewage denitrification treatment.

[0009] Furthermore, the sludge is sludge from a secondary sedimentation tank of a sewage treatment plant.

[0010] Furthermore, the natural sedimentation time of the sludge is 30 min, and the volume ratio of the sludge to sewage is 1:2.

[0011] Furthermore, the activation treatment is aeration for 6 to 24 hours and sedimentation for 15 to 45 minutes. Preferably, the activation treatment is aeration for 12 hours and sedimentation for 30 minutes.

[0012] Furthermore, the Chlorella is deposited in the General Microbiology Center of China Microorganism Culture Collection Administration, with the deposit number CGMCC No.41189, the deposit address is No. 3, Yard No. 1, Beichen West Road, Chaoyang District, Beijing, the deposit date is April 3, 2024, and the classification name is Cladophora aegagrophila.

[0013] Furthermore, the cultivation method of the green algae is as follows: The Chlorella culture medium was sterilized at high temperature, inoculated with Chlorella, and cultured until the Chlorella growth logarithmic phase.

[0014] Furthermore, the Chlorella culture medium is BG11 culture medium.

[0015] Furthermore, the high temperature sterilization temperature is 120°C and the high temperature sterilization time is 20 min.

[0016] Further, the culture temperature is 25°C to 30°C, the culture time is 15 to 20 days, the light intensity is 5000 to 8000 lux, and the light-dark ratio is 12 h:12 h. Preferably, the culture temperature is 25°C, the culture time is 15 days, and the light intensity is 5000 lux.

[0017] Furthermore, the centrifugal speed is 5000-8000 r / min, the centrifugal time is 5-15 min, and the number of centrifugal times is 1-3 times. Preferably, the centrifugal speed is 6000 r / min, the centrifugal time is 10 min, and the number of centrifugal times is 2 times.

[0018] Further, based on dry weight, the weight ratio of the Chlorella to the activated sludge is 1:(1-10). Preferably, based on dry weight, the weight ratio of the Chlorella to the activated sludge is 1:(1-3). More preferably, based on dry weight, the weight ratio of the Chlorella to the activated sludge is 1:1.

[0019] Furthermore, the carbon-nitrogen ratio of the sewage is 1-5.

[0020] Furthermore, based on dry weight, the weight volume ratio of the Chlorella and activated sludge to sewage is 2 g / L.

[0021] Further, the wastewater denitrification treatment is carried out at a temperature of 25°C to 30°C, a light intensity of 5000 to 8000 lux, a light-to-dark ratio of 12 h:12 h, and a treatment time of 3 to 8 days. Preferably, the wastewater denitrification treatment is carried out at a temperature of 25°C, a light intensity of 5000 lux, a light-to-dark ratio of 12 h:12 h, and a treatment time of 5 days.

[0022] The present invention also provides a sewage denitrification system based on the bacteria-algae symbiotic system, comprising a real-time control system, a water inlet system, an aeration, illumination, and sedimentation system, and a water outlet system.

[0023] The operation method of the sewage denitrification system is as follows: The real-time control system starts the water inlet pump to transport the untreated sewage in the water inlet tank to the water inlet of the reactor through the water inlet pipe. When the water inflow of the reactor reaches the working volume, the real-time control system turns off the water inlet pump, and the water inflow stage ends; The real-time control system controls the opening of the aeration device and the lamp tube, and after all the ammonia nitrogen is removed during the aerobic and photosynthetic stages in the reactor, the real-time control system closes the aeration device and the lamp tube, and ends the aerobic-photosynthetic process and post-precipitation in the reactor; The real-time control system turns on the outlet pump, and the treated water is transported to the outlet tank through the outlet pipe. When the water discharge reaches 50% of the working volume of the reactor, the real-time control system turns off the outlet pump, and the water discharge stage ends. According to actual needs, the system automatically enters the next cycle, repeating water inlet, aeration and lighting, sedimentation, water outlet or stopping operation.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are: The present invention utilizes the synergistic effect of Chlorella and activated sludge, avoids the investment and use of a large amount of aeration equipment, saves energy consumption, improves the removal efficiency of nitrogen in low carbon-nitrogen ratio urban sewage and reduces the removal cost.

[0025] The present invention finds a highly efficient denitrification microbial system by controlling the ratio of Chlorella and activated sludge, which improves the treatment efficiency of low-carbon-nitrogen ratio urban sewage and promotes the enrichment of Chlorella, thereby achieving efficient recovery of biomass in low-carbon-nitrogen ratio urban sewage and resource utilization of sewage treatment, providing a beneficial solution for environmental protection and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below in conjunction with the accompanying drawings.

[0027] Figure 1 It is a schematic diagram of the structure of the sewage denitrification system of the present invention; Figure 2 The graph of chlorophyll a concentration changes in microalgae in the bacteria-algae symbiotic system with different bacteria-algae ratios; Figure 3 This is a graph showing the changes in ammonia nitrogen over time in the bacteria-algae symbiotic system with different bacteria-algae ratios during the stable period; Figure 4 This is a bar chart of the total inorganic nitrogen concentration in the effluent of sewage treated by the bacteria-algae symbiotic system with different bacteria-algae ratios. DETAILED DESCRIPTION

[0028] The present invention provides a sewage denitrification method based on a bacteria-algae symbiotic system, comprising the following steps: S1, inoculating the sludge into sewage after natural sedimentation to form a sludge mixed liquid, and activating the sludge mixed liquid to obtain aerobic sludge; S2, centrifuging the Chlorella in the logarithmic growth phase and the aerobic sludge respectively, mixing them in proportion, and then adding water to obtain a bacteria-algae symbiotic system; S3. Adding the bacteria-algae symbiotic system into sewage to achieve sewage denitrification treatment.

[0029] In one embodiment, the sludge is sludge from a secondary sedimentation tank of a sewage treatment plant.

[0030] Generally, in sewage treatment, the sludge in the primary sedimentation tank adopts the principle of free sedimentation to remove the settleable and floating objects, thus reducing the load of the subsequent treatment facilities. However, unlike the primary sedimentation tank, the secondary sedimentation tank uses the principle of layered sedimentation and compression sedimentation. The flocculated suspended matter forms a layered object, which is precipitated as a whole, forming a more obvious solid-liquid interface to clarify the mixed liquid and recover and concentrate the activated sludge to ensure the effluent water quality and the concentration of the return sludge. The activated sludge finally obtained has the characteristics of high concentration (2000~4000 mg / L), flocculability, light weight, and slow sedimentation rate.

[0031] In the present invention, the secondary sedimentation tank sludge contains a large number of active microorganisms, which have been activated in the sewage treatment process and can efficiently decompose organic matter and convert nitrogen. Secondly, the secondary sedimentation tank sludge contains rich nutrients, which can promote the growth of algae and microorganisms in the bacteria-algae symbiotic system, thereby improving the denitrification efficiency. In addition, the microorganisms in the secondary sedimentation tank sludge have adapted to various pollutants and operating conditions in the sewage treatment environment, have strong environmental adaptability, and can quickly play a role in the denitrification treatment. Furthermore, as a by-product of the sewage treatment process, the secondary sedimentation tank sludge has a wide source and is easy to obtain, which can reduce costs and operational difficulties. Finally, using the secondary sedimentation tank sludge for denitrification treatment helps to reuse resources, reduce the pressure of sludge treatment and disposal, and has environmental protection and economic benefits. Therefore, the present invention adopts the rich microbial resources and nutrients of the secondary sedimentation tank sludge to improve the efficiency and effect of denitrification treatment, and is also an environmental protection measure for resource recycling.

[0032] In one embodiment, the natural sedimentation time of the sludge is 30 min, and the volume ratio of the sludge to sewage is 1:2.

[0033] In one embodiment, the activation treatment is aeration for 6 to 24 hours and sedimentation for 15 to 45 minutes.

[0034] In one embodiment, the activation treatment is aeration for 12 h and sedimentation for 30 min.

[0035] In one embodiment, the Chlorococcus aureus is deposited in the General Microbiological Center of China Microorganism Culture Collection Administration, with the deposit number being CGMCC No.41189.

[0036] Chlorella Cladophora aegagrophila ) and Chlorella ( Chlorella) Although they are both green algae, they have significant differences in morphology, ecological habits and applications. Both live in freshwater environments and produce organic matter through photosynthesis. The single cells of Chlorella are spherical, subspherical, ellipsoidal and heart-shaped. They are commonly found in flowing water and attached to rocks. Chlorella belongs to the Chlorella phylum, which is a single-cell algae with spherical or ellipsoidal cells suspended in water and growing at a faster rate. Chlorella grows relatively slowly and adapts to colder water bodies, while Chlorella is highly adaptable and grows rapidly in warm conditions.

[0037] At present, Chlorella and activated sludge are often used for sewage treatment because the bacteria-algae system prepared by Chlorella and activated sludge can be started quickly. However, Chlorella is not as tolerant and stable as Chlorella, and is not suitable for projects that require long-term stable operation. Therefore, Chlorella is more suitable for preparing bacteria-algae systems when long-term stable operation is required.

[0038] In one embodiment, the method for culturing Chlorella is as follows: The Chlorella culture medium was sterilized at high temperature, inoculated with Chlorella, and cultured until the Chlorella growth logarithmic phase.

[0039] In one embodiment, the Chlorella culture medium is BG11 culture medium.

[0040] In one embodiment, the high temperature sterilization temperature is 120° C. and the high temperature sterilization time is 20 min.

[0041] In one embodiment, the culture temperature is 25°C-30°C, the culture time is 15-20 days, the light intensity is 5000-8000 lux, and the light-dark ratio is 12 h:12 h.

[0042] In one embodiment, the culture temperature is 25° C., the culture time is 15 d, and the light intensity is 5000 lux.

[0043] In one embodiment, the centrifugal speed is 5000-8000 r / min, the centrifugal time is 5-15 min, and the number of centrifugation times is 1-3 times.

[0044] In one embodiment, the centrifugal speed is 6000 r / min, the centrifugal time is 10 min, and the number of centrifugation is 2 times.

[0045] In one embodiment, based on dry weight, the weight ratio of the Chlorella vulgaris to the activated sludge is 1:(1-10).

[0046] In one embodiment, based on dry weight, the weight ratio of the Chlorella vulgaris to the activated sludge is 1:(1-3).

[0047] In one embodiment, the weight ratio of the Chlorella vulgaris to the activated sludge is 1:1 based on dry weight.

[0048] In one embodiment, the carbon-nitrogen ratio of the sewage is 1-5.

[0049] In one embodiment, the weight volume ratio of the Chlorella and activated sludge to sewage is 2 g / L on a dry weight basis.

[0050] Compared with Chlorella, the use of Chlorella and activated sludge to prepare the bacteria-algae system needs to overcome many difficulties, such as: Chlorella grows slowly, has a thicker cell structure, has high requirements for environmental conditions, and the stability of the system is difficult to ensure. Therefore, the present invention strictly controls the weight ratio of Chlorella to activated sludge. At the same time, the cultivation method of Chlorella is strictly controlled. Combined with the activation of activated sludge, the problems existing in the preparation of bacteria-algae systems using Chlorella can be overcome, and ultimately the effective application of Chlorella and activated sludge systems in the fields of sewage treatment and ecological restoration can be achieved.

[0051] In one embodiment, the wastewater denitrification treatment is carried out at a temperature of 25°C to 30°C, a light intensity of 5000 to 8000 lux, a light-to-dark ratio of 12 h:12 h, and a treatment time of 3 to 8 d.

[0052] In one embodiment, the wastewater denitrification treatment is carried out at a temperature of 25°C, a light intensity of 5000 lux, a light-dark ratio of 12 h:12 h, and a treatment time of 5 days. The present invention also provides a sewage denitrification system based on the bacteria-algae symbiotic system, comprising a real-time control system, a water inlet system, an aeration, illumination, and sedimentation system, and a water outlet system.

[0053] The operation method of the sewage denitrification system is as follows: The real-time control system starts the water inlet pump to transport the untreated sewage in the water inlet tank to the water inlet of the reactor through the water inlet pipe. When the water inflow of the reactor reaches the working volume, the real-time control system turns off the water inlet pump, and the water inflow stage ends; The real-time control system controls the opening of the aeration device and the lamp tube, and after all the ammonia nitrogen is removed during the aerobic and photosynthetic stages in the reactor, the real-time control system closes the aeration device and the lamp tube, and ends the aerobic-photosynthetic process and post-precipitation in the reactor; The real-time control system turns on the outlet pump, and the treated water is transported to the outlet tank through the outlet pipe. When the water discharge reaches 50% of the working volume of the reactor, the real-time control system turns off the outlet pump, and the water discharge stage ends. According to actual needs, the system automatically enters the next cycle, repeating water inlet, aeration and lighting, sedimentation, water outlet or stopping operation.

[0054] The technical solution provided by the present invention is further described below in conjunction with embodiments.

[0055] Example 1 Wastewater denitrification method based on bacteria-algae symbiotic system: (1) Cultivation of Chlorella: The Chlorella was centrifuged and washed three times with deionized water at a speed of 6000 r / min and a single washing time of 15 min. After the washing was completed, the supernatant was poured out to obtain enriched Chlorella. Prepare BG11 medium with a concentration of 1.7 g / L, sterilize it at 120℃ for 20 min, and then cool it for use. Inoculate it in a clean bench, and the inoculation amount of enriched Chlorella is 6.67 g / L. After inoculation, the logarithmic phase Chlorella was obtained after culturing for 15 days at a temperature of 25°C, a light intensity of 5000 lux, and a light-dark ratio of 12 h:12 h, and used to prepare the bacterial-algal symbiotic system; (2) Activated sludge activation: The sludge from the secondary sedimentation tank of the sewage treatment plant was collected and naturally settled for 30 minutes. Then, the sludge was inoculated into the sewage at a volume ratio of 1:2 to form a sludge mixture. The sludge mixture was aerated for 12 hours and settled for 30 minutes under light-proof conditions to complete the activation. Preparation of bacteria-algae symbiotic system: The logarithmic phase Chlorella and activated sludge were mixed at dry weight ratios of 1:1, 1:3, 1:5 and 1:10, respectively, to obtain a bacteria-algae symbiotic system; The dry weight determination method is as follows: weigh the dried filter paper, drop the centrifuged Chlorella and activated sludge onto the dried filter paper, dry in an oven at 105° C. for 24 h, take out and weigh, and use the difference method to obtain the dry weight of Chlorella and activated sludge; The mixed bacteria-algae symbiotic system with different bacteria-algae ratios (i.e., the dry weight ratio of activated sludge and Chlorella) was mixed with the sewage to be treated at an initial dry weight to water volume ratio of 2 g / L. The sewage was treated at a temperature of 25°C, a light intensity of 5000 lux, and a light-dark ratio of 12 h:12 h for 5 days, and samples were taken every 12 hours for measurement.

[0056] The carbon-nitrogen ratio of the sewage to be treated is 5, the COD concentration is 275 mg / L, and the ammonia nitrogen concentration is 55 mg / L; it includes 352.56 mg / L NaAc, 90 mg / L MgSO4, 14 mg / L CaCl2, 211.54 mg / L NH4Cl, 46 mg / L Na2HPO4, 10 mg / L yeast extract and 1 mL / L trace elements; the trace elements include 120 mg / L ZnSO4·7H2O, 150 mg / LH3BO3, 30 mg / L CuSO4·5H2O, 120 mg / L MnCl2·4H2O, 180 mg / L KI, 60 mg / L Na2MoO4, 10000mg / L EDTA, 1540 mg / L FeSO4·7H2O, and 150 mg / L CoCl2·6H2O.

[0057] The present invention uses the change of chlorophyll a to represent the change of Chlorella. Figure 2 The figure shows the changes in chlorophyll a concentration in microalgae in the bacteria-algae symbiotic system with different bacteria-algae ratios. It can be seen that the system with a bacteria-algae ratio of 1:1 has the highest microalgae enrichment. The system entered a stable period after 20 days of operation. The average concentration of chlorophyll a during the stable period (20-60 days) was 11 mg / L.

[0058] Figure 3 The graph of the change of ammonia nitrogen over time in the bacterial-algal symbiotic system with different bacterial-algal ratios during the stable period. Figure 3 It can be observed that the system with a bacteria-algae ratio of 1:1 has the highest ammonia nitrogen removal efficiency compared with the other three groups, achieving 100% ammonia nitrogen removal rate.

[0059] Figure 4 This is a bar chart of the total inorganic nitrogen concentration in the effluent of the bacteria-algae symbiotic system treating sewage with different bacteria-algae ratios. Figure 4 It can be seen that the treated water meets the Class A sewage discharge standard in the Pollutant Discharge Standard for Urban Sewage Treatment Plants (GB 18918-2002).

[0060] Example 2 Sewage denitrification system based on bacteria-algae symbiotic system: (1) The bacteria-algae symbiotic system with a bacteria-algae ratio of 1:1 in Example 1 was added into the reactor, and the initial dosage was 2 g / L in terms of the ratio of the initial dry weight to the water volume; (2) The real-time control system starts the water inlet pump to transport the synthetic sewage in the water inlet tank to the reactor. When the water inflow into the reactor reaches 100% of the reactor working volume, the water inlet control system is shut down and the water inflow ends. (3) After the water inflow is completed, the anaerobic stage reaction ends after 4 hours (including the water inflow time), and the aeration device and the lamp are turned on synchronously by the real-time control system. The aerobic-photosynthetic stage reaction ends after 12 hours, and the aeration device and the lamp are turned off synchronously by the real-time control system, and the sedimentation is continued for 4 hours; (4) After sedimentation is completed, the real-time control system starts the outlet pump to transport the treated sewage in the reactor from the outlet through the outlet pipe to the outlet tank. When the drainage volume reaches 50% of the working volume of the reactor, the outlet pump automatically shuts down, and the drainage stage ends. Samples are taken for measurement during the drainage stage. (5) The system automatically enters the next cycle and repeats steps (2) to (4).

[0061] After the system was operated for 15 days, the ammonia nitrogen concentration in the reactor effluent tended to be stable, with an average effluent concentration of 5 mg / L; then, within 55 days of continuous operation, the ammonia nitrogen concentration in the reactor effluent was 0 mg / L (below the detection limit, not detected), the average ammonia nitrogen removal rate was 100%, and the average total nitrogen removal rate was 87.96%. The treated effluent water quality met the Class A sewage discharge standard in the Pollutant Discharge Standard for Urban Wastewater Treatment Plants (GB 18918-2002). The system entered a stable period after 15 days of operation, which lasted for 55 days (15-70 days).

[0062] Comparative Example 1 Same as Example 2, except that the Chlorella in the bacteria-algae symbiotic system is replaced by an equal amount of Chlorella.

[0063] After the system had been running stably for 55 days, the average removal efficiency of ammonia nitrogen was 97% and the average removal efficiency of total nitrogen was 87.6%.

[0064] Comparative Example 2 Same as Example 2, except that: the activated sludge is not subjected to activation treatment.

[0065] The startup time was long, and the system entered the stable period on the 24th day. The time to enter the stable period was 160% of that in Example 2. After the system had been running stably for 55 days, the average removal rate of ammonia nitrogen was 78.27%, and the average removal rate of total nitrogen was 72.68%.

[0066] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for denitrification of sewage based on a bacterial-algal symbiotic system, characterized in that: The following steps are involved: S1, inoculating the sludge into sewage after natural sedimentation to form a sludge mixed liquid, and activating the sludge mixed liquid to obtain aerobic sludge; S2, centrifuging the Chlorella in the logarithmic growth phase and the aerobic sludge respectively and mixing them according to a certain proportion to obtain a bacteria-algae symbiotic system; S3, adding the bacteria-algae symbiotic system into sewage to achieve sewage denitrification treatment; The sludge is the sludge from the secondary sedimentation tank of a sewage treatment plant; The activation treatment comprises aeration for 6 to 24 hours and sedimentation for 15 to 45 minutes.

2. The method for denitrifying sewage based on a bacteria-algae symbiotic system according to claim 1, characterized in that: The activation treatment includes aeration for 12 hours and sedimentation for 30 minutes.

3. The method for denitrifying sewage based on a bacteria-algae symbiotic system according to claim 1, characterized in that: The Chlorococcus aureus is deposited in the General Microbiological Center of China Microbiological Culture Collection Administration, with the deposit number being CGMCC No.41189.

4. The method for denitrifying sewage based on a bacteria-algae symbiotic system according to claim 1, characterized in that: The cultivation method of the green algae is as follows: The Chlorella culture medium was sterilized at high temperature, inoculated with Chlorella, and cultured until the Chlorella growth logarithmic phase.

5. The method for denitrifying sewage based on a bacteria-algae symbiotic system according to claim 1, characterized in that: The culture temperature is 25° C. to 30° C., the culture time is 15 to 20 days, the light intensity is 5000 to 8000 lux, and the light-dark ratio is 12h:12h.

6. The method for denitrifying sewage based on a bacteria-algae symbiotic system according to claim 1, characterized in that: Based on dry weight, the weight ratio of the green algae to the activated sludge is 1:(1-10).

7. The method for denitrifying sewage based on a bacteria-algae symbiotic system according to claim 1, characterized in that: The carbon-nitrogen ratio of the sewage is 1-5.

8. The method for denitrifying sewage based on a bacteria-algae symbiotic system according to claim 1, characterized in that: The ratio of the total weight of the Chlorella and the activated sludge to the volume of the sewage is 2 g / L on a dry weight basis.

9. The method for denitrifying sewage based on the bacteria-algae symbiotic system according to claim 1, characterized in that: The wastewater denitrification treatment is carried out under the conditions of a temperature of 25°C to 30°C, a light intensity of 5000 to 8000 lux, a light-dark ratio of 12h:12h, and a treatment time of 3 to 8d.

10. A sewage denitrification system based on a bacteria-algae symbiotic system, comprising a real-time control system, a water inlet system, an aeration, lighting, and sedimentation system, and a water outlet system.

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