A municipal sewage low-carbon treatment method based on anaerobic-algal bacteria coupling

Abstract

The application discloses a kind of municipal sewage low carbon processing method based on anaerobic-algal bacteria coupling, comprising the following steps: (1) municipal sewage enters anaerobic reaction unit, and the hydraulic retention time in anaerobic reaction unit is 6~8h;After being treated by anaerobic reaction unit, the biogas generated by anaerobic reaction unit enters cogeneration unit to generate heat and generate electricity, and the low carbon nitrogen ratio anaerobic effluent enters microalgae-methane oxidizing bacteria symbiotic unit, and the carbon dioxide-containing flue gas generated after cogeneration unit generates heat and generates electricity is introduced into microalgae-methane oxidizing bacteria symbiotic unit;(2) in microalgae-methane oxidizing bacteria symbiotic unit, the inoculation concentration of microalgae is 100~1000mg / L, and the inoculation concentration of methane oxidizing bacteria is 0~250mg / L;The hydraulic retention time of sewage in microalgae-methane oxidizing bacteria symbiotic unit is 6~24h;Sludge retention time is 2~40d;Temperature is 15~35℃;Light source is artificial light source, and light-dark cycle of 12h / 12h is set, and the illumination intensity is not less than 2500lux;The treated sewage is discharged from the effluent port of microalgae-methane oxidizing bacteria symbiotic unit.

Description

Technical Field

[0001] This invention relates to a low-carbon treatment method for municipal wastewater based on anaerobic-algae-bacteria coupling. Background Technology

[0002] To achieve low-carbon (low carbon emissions) and resource recovery in wastewater treatment, technologies utilizing microalgae to fix carbon dioxide, absorb nitrogen and phosphorus, and generate recyclable biomass have attracted widespread attention. However, existing technologies struggle to simultaneously achieve efficient nitrogen recovery, biomass resource recovery, and low-carbon operation.

[0003] Chinese patent CN113800722A discloses an anaerobic-microalgae system for domestic sewage treatment. This system purifies and separates the biogas produced by an anaerobic reactor, then uses the carbon dioxide generated from methane combustion for power generation to jointly promote the production of lipids by microalgae. However, this technology neglects two main issues. First, it overlooks the issue of dissolved methane in the anaerobic effluent. This partially dissolved methane is easily released into the atmosphere during subsequent treatment or discharge, causing energy loss and increasing greenhouse gas emissions. Second, it results in a slow reactor start-up time. Furthermore, this technology requires diluting the anaerobic digestion slurry 5-10 times and necessitates prolonged aeration (15-18 hours). This process consumes significant amounts of water and energy, increasing economic costs and limiting the practical application of this technology. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a low-carbon treatment method for municipal wastewater based on anaerobic-algae-bacteria coupling. This method can achieve closed-loop carbon utilization while recovering energy; on the other hand, it can still achieve efficient nitrogen recovery and efficient removal of dissolved methane under alternating light and dark conditions, avoiding the high energy consumption caused by continuous light, and the obtained algae-bacteria biomass has a high algae-bacteria ratio.

[0005] Technical solution: The municipal wastewater low-carbon treatment method based on anaerobic-algae-bacteria coupling described in this invention includes the following steps:

[0006] (1) Municipal sewage enters the anaerobic reactor unit and is hydraulically retained in the anaerobic reactor unit for 4 to 24 hours; after treatment by the anaerobic reactor unit, the biogas produced by the anaerobic reactor unit enters the cogeneration unit to generate heat and electricity, and the low carbon-to-nitrogen ratio anaerobic effluent enters the microalgae-methane oxidizing bacteria symbiotic unit. At the same time, the carbon dioxide-containing flue gas produced by the cogeneration unit after generating heat and electricity is introduced into the microalgae-methane oxidizing bacteria symbiotic unit; further preferred, the hydraulic retention time in the anaerobic reactor unit is 6 to 8 hours.

[0007] (2) In the microalgae-methanogenic bacteria symbiotic unit, the microalgae inoculation concentration is 100~1000mg / L, and the methanogenic bacteria inoculation concentration is 0~250mg / L; the hydraulic retention time of wastewater in the microalgae-methanogenic bacteria symbiotic unit is 6~24h; the sludge retention time is 2~40d; the temperature is 15~35℃; the light source is an artificial light source, and a 12h / 12h light-dark cycle is set, with a light intensity of not less than 2500lux; the treated wastewater is discharged from the outlet of the microalgae-methanogenic bacteria symbiotic unit; further preferably, the microalgae inoculation concentration is 150~300mg / L, the methanogenic bacteria inoculation concentration is 50~150mg / L; the hydraulic retention time of wastewater in the microalgae-methanogenic bacteria symbiotic unit is 22~24h; and the sludge retention time is 40~60d;

[0008] In step (1), the anaerobic reaction unit is an upflow anaerobic sludge blanket (UASB), an anaerobic membrane bioreactor (AnMBR), or an anaerobic fixed bed reactor (AFBR), and the anaerobic reaction unit is equipped with a biogas collection device.

[0009] The cogeneration unit used in this invention is the biogas cogeneration cycle high-efficiency system disclosed in patent CN207210353U, wherein the biogas outlet of the anaerobic reaction unit is connected to the air inlet of the biogas cogeneration cycle high-efficiency system, and the air outlet of the biogas cogeneration cycle high-efficiency system is connected to the flue gas inlet of the microalgae-methane oxidizing bacteria symbiotic unit.

[0010] A sedimentation tank can also be set up between the anaerobic reaction unit and the microalgae-methane oxidizing bacteria symbiotic unit. When the anaerobic treatment unit is not equipped with a membrane separation system, its outlet is connected to the inlet of the sedimentation tank, and the outlet of the sedimentation tank is connected to the inlet of the microalgae-methane oxidizing bacteria symbiotic unit. When the anaerobic treatment unit is equipped with a membrane separation system, its outlet is directly connected to the inlet of the microalgae-methane oxidizing bacteria symbiotic unit.

[0011] The microalgae in the microalgae-methanogenic bacteria symbiotic unit are microalgae widely used in the field of wastewater treatment, and can be one or more of Chlorella, Scenedesmus, or Chlamydomonas. The bacteria in the microalgae-methanogenic bacteria symbiotic unit are methanogenic bacteria, which can be pure cultured methanogenic bacteria, or a complex bacterial community containing methanogenic bacteria, or can be enriched from environmental samples including activated sludge, anaerobic sludge, natural water sediments, or other environmental samples containing methanogenic bacteria; or, the methanogenic bacteria in the microalgae-methanogenic bacteria symbiotic unit are naturally enriched from bacterial communities carried in anaerobic effluent.

[0012] The microalgae-methane-oxidizing bacteria symbiotic unit is a membrane photobioreactor (MPBR). The influent and effluent of the MPBR are controlled by influent pumps and effluent pumps, respectively. An external LED light source is installed, and the internal liquid is mixed by a magnetic stirrer. The MPBR is equipped with an inlet, an outlet, a sampling port, an air outlet, and an air inlet. The MPBR is equipped with a membrane module to achieve solid-liquid separation, and the membrane fouling is monitored by a pressure gauge. A gas collection bag is connected to the top of the MPBR, and a peristaltic pump is used to achieve external circulation aeration of gas. The flue gas generated by the cogeneration unit is directly introduced into the closed microalgae-methane-oxidizing bacteria symbiotic unit, and external circulation aeration is set, so as to provide inorganic carbon source for microalgae while mitigating membrane fouling.

[0013] The membrane module in the membrane photobioreactor (MPBR) operates in an intermittent suction mode, with a suction time of 2–15 min and a stop time of 2–5 min, and a membrane flux of 5–30 L / (m²). 2 The transmembrane pressure difference is 0~50 kPa; further preferably, the pumping time is 8~15 min, the stopping time is 2~5 min, and the membrane flux is 10~20 L / (m²). 2 The transmembrane pressure difference is 30-40 kPa. The microalgae-methanogenic bacteria symbiotic unit of this invention operates the membrane module in the above manner, achieving long-term stable operation of the reactor.

[0014] The methanotrophic bacteria in the microalgae-methanogenic bacteria symbiotic unit can utilize oxygen produced by microalgae photosynthesis to oxidize dissolved methane in anaerobic effluent, thus solving the dissolved methane problem. In this unit, inorganic carbon in the flue gas promotes the growth and metabolism of microalgae during the light phase, enhancing their nitrogen assimilation, promoting the accumulation of carbon and nitrogen in the form of intracellular organic matter, and increasing the dissolved oxygen concentration within the system. Furthermore, the accumulated intracellular organic matter and dissolved oxygen provide a more sufficient material and energy basis for microalgae metabolism during the dark phase, allowing more nitrogen to be absorbed through assimilation during this phase, thereby improving the nitrogen assimilation and removal capacity and the quality of the resulting algal and bacterial biomass. The efficient nitrogen assimilation of the microalgae-methanogenic bacteria symbiotic unit of this invention does not depend on continuous light; it can maintain a nitrogen removal pathway dominated by assimilation even under alternating light and dark conditions, and maintain a high nitrogen assimilation and removal capacity during the dark phase. After the anaerobic treatment unit generates carbon capture capacity, the resulting carbon dioxide can enter the microalgae-methane-oxidizing bacteria symbiotic unit and be fixed within the microalgae, achieving closed-loop carbon utilization. The algae-bacteria biomass obtained by the method of this invention has a high algae-bacteria ratio, which is beneficial for subsequent resource utilization, including the preparation of biodiesel, proteins, polysaccharides, pigments, organic fertilizers, or bio-based materials.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The method of the present invention realizes a closed-loop carbon utilization path based on anaerobic-cogeneration-algae-bacteria, introduces the biogas generated by the anaerobic treatment unit into the cogeneration unit's production capacity, and uses the flue gas generated by combustion as an inorganic carbon source for the microalgae-methane-oxidizing bacteria symbiotic unit. The microalgae, as a biological carbon sink, fixes the carbon dioxide in the flue gas and converts it into biomass, which not only reduces carbon dioxide emissions but also realizes closed-loop carbon utilization. (2) The introduction of flue gas in the present invention can promote nitrogen assimilation of microalgae and accumulation of intracellular organic matter under light conditions, providing sufficient material and energy basis for nitrogen assimilation in the dark stage; therefore, the present invention can obtain a high nitrogen removal rate under alternating light and dark conditions, and nitrogen is mainly removed through microalgae assimilation, which can not only achieve efficient nitrogen recovery but also avoid the high energy consumption caused by continuous light. (3) This invention can also achieve efficient removal of dissolved methane in anaerobic effluent. The methane-oxidizing bacteria can oxidize the dissolved methane and convert it into substances and energy required for their own growth. At the same time, the microalgae release oxygen through photosynthesis, providing oxygen for the metabolism of the methane-oxidizing bacteria, thereby enhancing the system's ability to remove dissolved methane. (4) The algae-bacterial biomass produced by this invention has a high algae-bacterial ratio, which is beneficial for subsequent resource utilization. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the method of the present invention;

[0017] Figure 2 A schematic diagram showing the total organic carbon level and methane content of an anaerobic reactor after 300 days of operation;

[0018] Figure 3 This is a schematic diagram of the structure of a microalgae-methanogenic bacteria symbiotic unit;

[0019] Figure 4 A schematic diagram illustrating the removal rate of dissolved methane in the microalgae-methane-oxidizing bacteria symbiotic unit after inoculation with enriched methane-oxidizing bacteria;

[0020] Figure 5 Schematic diagram of nitrogen concentration in the effluent of a microalgae-methane-oxidizing bacteria symbiotic unit;

[0021] Figure 6 This is a schematic diagram illustrating the nitrogen removal pathway in a microalgae-methane-oxidizing bacteria symbiotic unit, with and without CO2 supply. Detailed Implementation

[0022] like Figure 1As shown, the method of this invention is as follows: municipal sewage enters the anaerobic reactor unit through an inlet pipe. After suspended solids are removed in a sedimentation tank, the effluent from the anaerobic reactor unit enters the microalgae-methane-oxidizing bacteria symbiotic unit for denitrification and removal of dissolved methane. The biogas produced by the anaerobic reactor unit is used to generate electricity through a cogeneration unit. The resulting flue gas containing carbon dioxide is then introduced into the microalgae-methane-oxidizing bacteria symbiotic unit to provide an inorganic carbon source for the growth of microalgae. The algae and bacteria biomass produced by the microalgae-methane-oxidizing bacteria symbiotic unit is used to synthesize biodiesel, thus realizing resource recycling. The cogeneration unit used in this invention is the biogas cogeneration cycle high-efficiency system disclosed in patent CN207210353U. The biogas outlet of the anaerobic reactor unit is connected to the inlet of the biogas cogeneration cycle high-efficiency system, and the outlet of the biogas cogeneration cycle high-efficiency system is connected to the flue gas inlet of the microalgae-methane-oxidizing bacteria symbiotic unit.

[0023] The microalgae-methanogenic bacteria symbiotic unit of this invention is a membrane photobioreactor (MPBR), the structure of which is as follows: Figure 3 As shown, the membrane photobioreactor includes a reaction chamber 14, whose inlet and outlet water are controlled by an inlet pump 1 and an outlet pump 8, respectively. An LED light source 3 is installed outside the reaction chamber 14, and the liquid inside is mixed by a magnetic stirrer 4. The reaction chamber 14 is equipped with an inlet 2, an outlet 6, a sampling port 13, an outlet 9, and an air inlet 12. The reaction chamber 14 is equipped with a membrane module 5 to achieve solid-liquid separation, and the membrane fouling is monitored by a pressure gauge 7. A gas collection bag 10 is connected to the top of the reaction chamber 14, and the gas is aerated by a peristaltic pump 11.

[0024] Example 1

[0025] This invention relates to a low-carbon treatment method for municipal wastewater based on anaerobic-algae-bacteria coupling, comprising the following steps:

[0026] (1) In this embodiment, the anaerobic reactor is selected as the AFBR reactor. The influent TOC of a certain municipal sewage is 100 mg C / L and the ammonia nitrogen is 27 mg / L. The municipal sewage enters the anaerobic reactor at a flow rate of 25 L / d. The temperature of the anaerobic reactor is ambient temperature (15~35℃). The sewage has a hydraulic retention time of 6 hours in the anaerobic reactor (stable operation for 300 days at a hydraulic retention time of 6 hours and a temperature of 15~35℃). After treatment by the anaerobic reactor, the biogas produced by the anaerobic reactor enters the cogeneration unit to generate heat and electricity. The low C / N ratio anaerobic effluent enters the microalgae-methane oxidizing bacteria symbiotic unit. At the same time, the carbon dioxide-containing flue gas produced by the cogeneration unit after generating heat and electricity is introduced into the microalgae-methane oxidizing bacteria symbiotic unit. After the reaction, the TOC removal rate of the anaerobic reactor is 96% (the TOC concentration in the effluent is 4 mg / L, the ammonia nitrogen concentration is 26 mg / L, and the methane concentration is 17 mg / L). The biogas produced contained 60% methane by volume (CH4 / L), with a methane yield of 252 mL CH4 / g COD, indicating that the anaerobic reactor had high carbon capture efficiency.

[0027] (2) Low C / N ratio anaerobic effluent enters the microalgae-methanogenic bacteria symbiotic unit (MPBR) through the inlet, while carbon dioxide-containing flue gas generated by the cogeneration unit after heat generation is introduced into the microalgae-methanogenic bacteria symbiotic unit through the air inlet; the flow rate of anaerobic effluent entering the microalgae-methanogenic bacteria symbiotic unit is 2 L / d, and the flow rate of flue gas is 60 mL / min (CO2 accounts for about 10% vol in the flue gas); in the microalgae-methanogenic bacteria symbiotic unit, the initial inoculation concentration of microalgae (Chlorella) is 250 mg / L, and the initial inoculation concentration of methanogenic bacteria is 9 mg / L. 0 mg / L; the hydraulic retention time of wastewater in the microalgae-methane-oxidizing bacteria symbiotic unit is 24 h; the sludge (algae and bacteria biomass) retention time is 40 d; the temperature is 15~35℃; the light source is artificial light source with a 12 h / 12 ​​h light-dark cycle and a light intensity of not less than 2500 lux; the treated water is discharged from the outlet of the microalgae-methane-oxidizing bacteria symbiotic unit; after 80 days of continuous and stable operation, the TOC concentration in the effluent is 2 mg / L, the ammonia nitrogen concentration is 3 mg / L, and the nitrate nitrogen concentration is 4 mg / L; the methane concentrations detected in the MPBR influent and effluent are 17 mg CH4 / L and 1.4 mg CH4 / L, respectively, and the total nitrogen removal rate is 74%.

[0028] The membrane module in the membrane photobioreactor (MPBR) of this invention operates in an intermittent suction mode, with a suction time of 8 minutes and a stop time of 2 minutes, and a membrane flux of 14 L / (m²). 2 With a transmembrane pressure difference of 30 kPa, the microalgae-methane-oxidizing bacteria symbiotic unit of this invention operates the membrane module in the above manner, achieving long-term stable operation of the reactor.

[0029] In this study, the final algae-to-bacterial biomass ratio was 3:1, indicating that microalgae were the dominant community and that most of the nitrogen was assimilated and absorbed by microalgae. Furthermore, the intracellular lipid content of the biomass accounted for 43% of the dry weight, indicating that it has good oil production potential, which is conducive to its subsequent high-value utilization.

[0030] Figure 2 The effluent from the anaerobic reactor (AFBR) of the present invention under 300°C operation showed that the TOC removal rate remained at around 96%, the methane content in the biogas was 60% vol, and the methane yield was 252 mL CH4 / g COD, indicating that the anaerobic reactor has high carbon capture efficiency.

[0031] Comparative Example 1

[0032] A low-carbon treatment method for municipal wastewater includes the following steps:

[0033] (1) An AFBR reactor was selected as the anaerobic reaction unit. The influent TOC of a certain municipal sewage was 100 mg C / L and the ammonia nitrogen was 27 mg / L. The municipal sewage entered the anaerobic reaction unit at a flow rate of 25 L / d. The temperature of the anaerobic reaction unit was ambient (15~35℃). The sewage was hydraulically retained in the anaerobic reaction unit for 6 hours. After treatment by the anaerobic reaction unit, the biogas produced by the anaerobic reaction unit was fed into the cogeneration unit to generate heat and electricity. The low carbon-to-nitrogen ratio anaerobic effluent was fed into the microalgae-methane-oxidizing bacteria symbiotic unit. At the same time, the carbon dioxide-containing flue gas produced by the cogeneration unit was fed into the microalgae-methane-oxidizing bacteria symbiotic unit. After the reaction, the TOC concentration in the anaerobic effluent was 4 mg / L, the ammonia nitrogen concentration was 26 mg / L, and the methane concentration was 17 mg CH4 / L.

[0034] (2) Low C / N ratio anaerobic effluent enters the MPBR from the inlet, while carbon dioxide-containing flue gas generated by the cogeneration unit after heat generation is introduced into the MPBR from the air inlet; the flow rate of anaerobic effluent entering the MPBR is 2 L / d, and the flow rate of flue gas is 60 mL / min (CO2 accounts for about 10% vol in the flue gas); in the MPBR, the initial inoculum concentration of microalgae (Chlorella) is 250 mg / L, and the initial inoculum concentration of methanogenic bacteria is 0 mg / L. g / L; the hydraulic retention time of wastewater in the MPBR is 24h; the sludge (algae and bacteria biomass) retention time is 40d; the temperature is 15~35℃; the light source is artificial light source with a 12h / 12h light-dark cycle and a light intensity of not less than 2500 lux; the treated water is discharged from the MPBR outlet; after 80 days of continuous and stable operation, the effluent concentration is 3mg / L TOC, 6mg / L ammonia nitrogen, 3mg / L nitrate nitrogen, 3mg / L methane, 3mg CH4 / L, and the total nitrogen removal rate is 67%.

[0035] like Figure 4 As shown, in the MPBR without exogenous inoculation of methanogenic bacteria, the methanogenic bacteria can gradually and naturally accumulate from the original functional bacteria in the anaerobic effluent during system operation, thus achieving the removal of dissolved methane. In contrast, the MPBR inoculated with enriched methanogenic bacteria starts up faster, approximately 30 days earlier than the uninoculated group. A comparison of Example 1 and Comparative Example 1 shows that inoculating the MPBR with enriched methanogenic bacteria not only improves the removal of dissolved methane but also significantly enhances the denitrification effect.

[0036] Comparative Example 2

[0037] The only difference between Comparative Example 2 and Example 1 is that CO2 is not introduced into the microalgae-methane oxidizing bacteria symbiotic unit (MPBR). That is, the biogas outlet of the anaerobic reaction unit is connected to the air inlet of the cogeneration unit, but the air outlet of the cogeneration unit is not connected to the flue gas inlet of the microalgae-methane oxidizing bacteria symbiotic unit.

[0038] pass Figure 5 It can be seen that, compared to Comparative Example 2 (where no CO2 was introduced into the microalgae-methanogenic bacteria symbiotic unit), the introduction of CO2 into the microalgae-methanogenic bacteria symbiotic unit in Example 1 significantly enhanced the nitrogen removal efficiency of the MPBR. The effluent ammonia nitrogen concentration in Comparative Example 2 was 21 mg / L, and no nitrate nitrogen was detected; its total nitrogen removal rate was 22%. In the reactor, ammonia nitrogen is removed through nitrification and assimilation, while total nitrogen is removed through denitrification and assimilation, with assimilation playing a dominant role. Figure 6 As shown, under light conditions, the total nitrogen removal rate increased from 33% to 78%. Since higher dissolved oxygen concentrations inhibit the activity of denitrifying bacteria, almost all nitrogen was removed through assimilation. In the dark phase, the total nitrogen removal rate increased from 19% to 71%. Without CO2, since no nitrite or nitrate nitrogen was detected in the system, nitrogen removal was primarily through assimilation. However, after CO2 was introduced, analysis of nitrogen transformation pathways showed that assimilation contributed 43% to total nitrogen removal, while denitrification accounted for 28%, indicating that assimilation remained the main pathway for nitrogen removal. Therefore, whether under light or dark conditions, assimilation is the primary pathway for nitrogen removal, and CO2 introduction promotes nitrogen assimilation, facilitating nitrogen recovery. Furthermore, CO2 introduction significantly enhances the dissolved methane removal efficiency of the MPBR. Methanogenic bacteria utilize oxygen produced by microalgal photosynthesis to oxidize dissolved methane, and CO2 introduction promotes microalgal photosynthesis, resulting in almost complete removal of dissolved methane from the anaerobic effluent.

Claims

1. A low-carbon treatment method for municipal wastewater based on anaerobic-algae-bacteria coupling, characterized in that, Includes the following steps: (1) Municipal sewage enters the anaerobic reaction unit and is hydraulically retained in the anaerobic reaction unit for 4 to 24 hours. After treatment by the anaerobic reaction unit, the biogas produced by the anaerobic reaction unit enters the cogeneration unit to generate heat and electricity. The low carbon-nitrogen ratio anaerobic effluent enters the microalgae-methane oxidizing bacteria symbiotic unit. At the same time, the carbon dioxide-containing flue gas produced by the cogeneration unit after generating heat and electricity is introduced into the microalgae-methane oxidizing bacteria symbiotic unit. (2) In the microalgae-methanogenic bacteria symbiotic unit, the microalgae inoculation concentration is 100~1000mg / L, and the methanogenic bacteria inoculation concentration is 0~250mg / L; the hydraulic retention time of wastewater in the microalgae-methanogenic bacteria symbiotic unit is 6~24h; The sludge retention time is 2~40 days; the temperature is 15~35℃; the light source is artificial light source with a 12h / 12h light-dark cycle and a light intensity of not less than 2500 lux; the treated wastewater is discharged from the outlet of the microalgae-methane oxidizing bacteria symbiotic unit.

2. The municipal wastewater low-carbon treatment method based on anaerobic-algae-bacteria coupling according to claim 1, characterized in that: In step (1), the flow rate of municipal sewage entering the anaerobic reaction unit is 25~28L / d.

3. The municipal wastewater low-carbon treatment method based on anaerobic-algae-bacteria coupling according to claim 1, characterized in that: In step (1), the anaerobic reaction unit is an upflow anaerobic sludge bed, an anaerobic membrane bioreactor, or an anaerobic fixed bed reactor.

4. The municipal wastewater low-carbon treatment method based on anaerobic-algae-bacteria coupling according to claim 1, characterized in that: In step (1), a sedimentation tank is also provided between the anaerobic reaction unit and the microalgae-methane oxidizing bacteria symbiotic unit. The outlet of the anaerobic treatment unit is connected to the inlet of the sedimentation tank, and the outlet of the sedimentation tank is connected to the inlet of the microalgae-methane oxidizing bacteria symbiotic unit.

5. The municipal wastewater low-carbon treatment method based on anaerobic-algae-bacteria coupling according to claim 1, characterized in that: In step (2), the flow rate of anaerobic effluent is 2~3L / d, and the flow rate of flue gas is 60~80mL / min; wherein, CO2 accounts for 10~12% vol in the flue gas.

6. The low-carbon treatment method for municipal wastewater based on anaerobic-algae-bacteria coupling according to claim 1, characterized in that: In step (2), the microalgae in the microalgae-methane-oxidizing bacteria symbiotic unit are one or more of Chlorella, Scenedesmus, or Chlamydomonas.

7. The municipal wastewater low-carbon treatment method based on anaerobic-algae-bacteria coupling according to claim 1, characterized in that: In step (2), the microalgae-methane-oxidizing bacteria symbiotic unit is a membrane photobioreactor.

8. The municipal wastewater low-carbon treatment method based on anaerobic-algae-bacteria coupling according to claim 7, characterized in that: The membrane module in the membrane photobioreactor operates in an intermittent suction mode, with a suction time of 2-15 minutes and a stop time of 2-5 minutes, and a membrane flux of 5-30 L / (m²). 2 ·h), the transmembrane pressure difference is 0~50kPa.

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