Method and device for treating sewage by utilizing bacterium-algae heterotrophic bacterium compound system

Abstract

The invention provides a method and a device for treating sewage by utilizing a bacterium-algae heterotrophic bacterium compound system, and belongs to the technical field of water treatment and recycling. Aiming at recycling of soluble methane and diversified removal of various pollutants such as carbon dioxide, organic carbon and nutritive salt, a specific microalgae-methane-oxidizing bacteria-heterotrophic bacteria compound microorganism system is constructed, efficient removal efficiency parameters are limited, ternary microorganism synergistic interaction is achieved, and the synergistic interaction target of reducing pollution and carbon is achieved. The MBR membrane assembly is adopted to intercept microbial effluent, and a specific efficient microbial community is maintained; the closed reactor aims at a specific removal object, dissolved gas is prevented from escaping, and recycling of soluble methane is guaranteed. The closed membrane bioreactor is suitable for culturing a specific ternary suspended microflora and can effectively treat soluble gas.

Description

Technical Field

[0001] The present invention relates to a method and device for treating sewage by using a composite system of bacteria, algae and heterotrophic bacteria, and belongs to the technical field of water treatment and resource utilization. Background Art

[0002] In order to respond to the call of "synergistic reduction of pollution and carbon emissions", the "carbon neutral" treatment of urban sewage has become the focus of attention. The anaerobic biological fermentation process can directly capture COD from sewage and maximize energy recovery. However, the anaerobic digestion effluent contains a large amount of dissolved methane, and direct discharge will cause potential pollution and energy loss, and there is an explosion risk when mixed with air. In addition to biogas recovery and utilization, 20-50% of the methane generated during anaerobic digestion will dissolve in water, and the concentration can reach 10-30 mg / L. If not recovered or burned, it is easily released into the atmosphere, causing danger and increasing carbon emissions. Therefore, effective methods are needed for treatment to reduce energy loss and greenhouse gas emissions.

[0003] Currently, the common methods for treating dissolved methane include aeration and gas stripping, but the efficiency is low. The method of removing dissolved gas from the effluent through a degassing membrane faces problems such as membrane fouling and additional mass transfer resistance.

[0004] Chinese Patent Application CN110479079A discloses a membrane bioreaction system for treating greenhouse gases by bacteria-algae cooperation, which uses physically isolated methane-oxidizing bacteria and microalgae to treat methane and carbon dioxide. However, this system only targets gaseous methane, and its main application fields are air pollution such as coal mine gas and flue gas. For the treatment of dissolved methane in anaerobic digestion wastewater, it faces the problem of low conversion efficiency between gaseous and dissolved states. Moreover, the binary bacteria-algae system constructed in this patent cannot remove multiple pollutants and is difficult to achieve the function of synergistic reduction of pollution and carbon emissions. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a method and device for treating sewage by using a composite system of bacteria, algae and heterotrophic bacteria.

[0006] Technical Solution: The present invention provides a method for treating sewage by using a composite system of bacteria, algae and heterotrophic bacteria, comprising the following steps:

[0007] (1) Pre-culturing functional microalgae and methane-oxidizing bacteria separately to enrich them and reach the stable growth phase;

[0008] (2) Mixing the functional microalgae and methane-oxidizing bacteria pre-cultured in step (1) with a small amount of sewage to be treated for scale-up culture until reaching the stable growth phase again;

[0009] (3) Add the sewage to be treated to the mixed solution after the expansion culture in step (2), apply light, and then filter the treated sewage with an MBR membrane.

[0010] Since methane-oxidizing bacteria produce intermediate products such as organic acids during the methane metabolism process, the enrichment growth of heterotrophic bacteria is spontaneously induced. This application uses it to construct a ternary composite system of microalgae-methane-oxidizing bacteria-heterotrophic bacteria. The three microorganisms cooperate synergistically. The methane-oxidizing bacteria utilize the dissolved methane in the wastewater and release carbon dioxide. The heterotrophic bacteria treat complex organic matters such as organic carbon. The microalgae absorb carbon dioxide, degrade the metabolites of heterotrophic bacteria, and at the same time supply oxygen to the methane-oxidizing bacteria and heterotrophic bacteria. The three enhance and promote each other, and efficiently degrade various pollutants in the wastewater.

[0011] Further, the functional microalgae in step (1) is Tetradesmus obliquus.

[0012] Further, the inoculation cell number ratio of the functional microalgae and methane-oxidizing bacteria in step (2) is 5:1.

[0013] Further, the light condition in step (3) is a light intensity of 3000 - 6000 Lux and a light ratio of 12L:12D, and the sewage residence time is 24 - 36 h.

[0014] Further, during the sewage treatment process in step (3), regularly detect the cell density of the functional microalgae. When the microalgae cell density is higher than 5.0×10 7 cells / mL, algae discharge and sludge discharge are required.

[0015] The present invention also provides a device for treating sewage using a bacteria-algae-heterotrophic bacteria composite system. The device includes a water inlet tank 1, a water outlet tank 8, a photobioreactor 10, and an LED light source 14;

[0016] The photobioreactor 10 is provided with a water inlet 3, a reserved ventilation port 4, a water outlet 5, and a microorganism sampling port 9;

[0017] The photobioreactor 10 is internally provided with an MBR membrane module 11; a stirring device is arranged at the bottom of the photobioreactor 10; an inserted dissolved oxygen probe 12 and a pH probe 13 are arranged outside the photobioreactor 10.

[0018] Among them, the LED light source provides light for the microalgae, and the MBR membrane module is used to intercept microorganisms.

[0019] Further, the stirring device includes a magnetic stirrer 15 and a magnetic stir bar 16.

[0020] Further, the inlet pipe is connected to the inlet tank 1 through the water inlet 3 on the photobioreactor 10; the outlet pipe is connected to the outlet tank 8 and the MBR membrane module 11 through the water outlet 5 on the photobioreactor 10.

[0021] Further, a feed water pump 2 is provided on the inlet pipe; a check valve 17, a pressure gauge 6 and a discharge water pump 7 are sequentially provided on the outlet pipe.

[0022] Among them, the transmembrane pressure shown by the pressure gauge is used to confirm the membrane fouling situation.

[0023] Further, the water outlet functional component in the MBR membrane module is a polyvinylidene fluoride PVDF ultrafiltration membrane.

[0024] Among them, the inserted dissolved oxygen probe and pH probe are used to detect the dissolved oxygen and pH content in the reactor to determine the water quality situation and the growth balance situation of bacteria and algae in the reactor.

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

[0026] (1) The present invention focuses on the recovery and utilization of dissolved methane in complex wastewater such as anaerobic digestate, and proposes a method for treating dissolved single-carbon greenhouse gases and nutrients in wastewater by using a microalgae-methanotrophic bacteria-heterotrophic bacteria composite system. Compared with the gaseous methane recovery process, dissolved methane faces the problems of low gas-liquid mass transfer efficiency and easy escape from the liquid phase. The present invention constructs a three-microorganism composite system of microalgae-methanotrophic bacteria-heterotrophic bacteria. Methanotrophic bacteria utilize the dissolved methane in the wastewater and release carbon dioxide. Heterotrophic bacteria treat complex organic matters such as organic carbon. Microalgae absorb carbon dioxide and degrade the metabolites of heterotrophic bacteria, and at the same time supply oxygen to methanotrophic bacteria and heterotrophic bacteria. The three work synergistically and promote each other, efficiently degrade various pollutants in the wastewater, and achieve the efficient removal of dissolved methane in the wastewater and the good removal of organic carbon and ammonia nitrogen;

[0027] (2) The closed columnar membrane bioreactor adopted in the present invention combines suspension culture with MBR, defines parameters, is suitable for culturing a specific ternary suspended microbial community, and can effectively treat the target dissolved gas. Specific HRT, inoculation ratio and light intensity ensure the efficient degradation and removal of pollutants; MBR here is not only for water outlet, but also the key to maintaining a high-concentration mixed microbial community; the closed reactor is aimed at specific removal objects, prevents the escape of dissolved gas, and ensures the recovery and utilization of dissolved methane. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic structural diagram of the device for treating sewage by using the microalgae-heterotrophic bacteria composite system of the present invention.

[0029] Figure 2Treatment effects of dissolved methane and pollutants before and after treatment at different initial inoculation ratios of algae to bacteria, where (a) dissolved methane; (b) change in ammonia nitrogen content; (c) change in nitrate nitrogen content; (d) change in COD content; (e) change in total phosphorus content. Detailed implementation manners

[0030] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0031] Example 1: A method for treating dissolved single-carbon greenhouse gases and nutrients in wastewater by using a heterotrophic bacteria-algae composite system

[0032] Step 1: Enrichment and cultivation stage of bacteria and algae microorganisms: Functional microalgae and methane-oxidizing bacteria are separately pre-cultured to enrich them and reach the stable growth phase; the microalgae are enriched using BG11 medium, and the methane-oxidizing bacteria are enriched using DSMZ medium 1409. When enriching the methane-oxidizing bacteria, intermediate products such as organic acids are produced during the methane metabolism process, providing a key material basis for the enrichment and growth of induced heterotrophic bacteria. At the same time, methane-oxidizing bacteria and heterotrophic bacteria adapted to them are enriched.

[0033] Step 2: Adaptation and startup stage: The microalgae, methane-oxidizing bacteria, and other heterotrophic bacteria produced in Step 1 are introduced into the photobioreactor in the wastewater treatment device for expanded cultivation to construct a ternary composite system of microalgae-methane-oxidizing bacteria-heterotrophic bacteria. The wastewater to be treated is gradually introduced to make it adapt and reach the stable growth phase again.

[0034] Step 3: Carbon fixation and nutrient removal stage: The treated wastewater is introduced into the photobioreactor obtained in Step 2 for treatment. The ternary composite system cooperates synergistically. The methane-oxidizing bacteria utilize the dissolved methane in the wastewater and release carbon dioxide. The heterotrophic bacteria treat complex organic substances such as organic carbon. The microalgae absorb carbon dioxide and degrade the metabolites of the heterotrophic bacteria. At the same time, they also supply oxygen to the methane-oxidizing bacteria and heterotrophic bacteria. The three work together synergistically to efficiently remove the dissolved methane, carbon dioxide greenhouse gas, organic matter, and nutrients in the wastewater in a targeted manner.

[0035] Treat the wastewater under the illumination conditions of a light intensity of 3000 - 6000 Lux, a light-dark ratio of 12L:12D, and a hydraulic retention time of 24 - 36 h. The parameter limitations ensure the high activity of the microorganisms and the efficient degradation and removal of pollutants. When the microalgae cell density is detected to be higher than 5.0×10 7 cells / mL, algae and sludge are discharged through the microbial sampling port to achieve wastewater treatment and biomass product recovery.

[0036] This embodiment adopts a device for treating dissolved one-carbon greenhouse gases and nutrients in wastewater by using a heterotrophic bacteria-algae composite system. In step two, the wastewater treatment device includes a water inlet tank 1, a water outlet tank 8, a photobioreactor 10, and an LED light source 14. The photobioreactor 10 is provided with a water inlet 3, a reserved ventilation port 4, a water outlet 5, and a microbial sampling port 9; an MBR membrane module 11 is arranged inside the photobioreactor 10; a magnetic stirrer 15 and a magnetic stir bar 16 are arranged at the bottom of the photobioreactor 10; an inserted dissolved oxygen probe 12 and a pH probe 13 are arranged outside the photobioreactor 10. The water inlet pipe is connected to the water inlet tank 1 through the water inlet 3 on the photobioreactor 10, and a water inlet pump 2 is provided on the water inlet pipe; the water outlet pipe is connected to the water outlet tank 8 and the MBR membrane module 11 through the water outlet 5 on the photobioreactor 10, and a one-way valve 17, a pressure gauge 6, and a water outlet pump 7 are arranged in sequence on the water outlet pipe. The LED light source 14 is arranged on one side of the photobioreactor 10.

[0037] The usage method of the above device is as follows: The wastewater to be treated in the water inlet tank 1 enters through the water inlet 3 below the photobioreactor 10 by the water inlet pump 2, is treated in the photobioreactor 10, and after the microorganisms are intercepted by the MBR membrane module 11, it then enters the water outlet pipe, and the treated sewage is pumped to the water outlet tank 8 by the water outlet pump 7.

[0038] Example 2: Test on the initial inoculation ratio of algae and bacteria

[0039] This embodiment adopts the following method for testing to explore the treatment effects of the device on dissolved methane, ammonia nitrogen, nitrate nitrogen, COD, and total phosphorus when the initial inoculation cell number ratio of algae and bacteria is 1:0, 1:1, 1:5, 5:1, and 0:1.

[0040] (1) Place the microalgae Tetradesmus obliquus (FACHB - 416) and the methane-oxidizing model strain Methylocystis bryophila (DSM - 21852) in a constant-temperature light incubator and a constant-temperature incubator for cultivation respectively. The medium used for cultivating the microalgae Tetradesmus obliquus is BG11 liquid medium, set the stirring rate at 200 rpm, the light condition is a light intensity of 3000 Lux, a light-dark ratio of 12L:12D, and the temperature is set at 26°C, and cultivate for 5 - 7 days; the medium used for cultivating the methane-oxidizing model strain is 1409 liquid medium, set the stirring rate at 200 rpm, and the temperature is set at 26°C, and cultivate for 5 - 7 days.

[0041] (2) Configure artificial anaerobic digestion wastewater, where COD = 200 mg / L, NH4 + -N = 150 mg / L, NO3 -- N = 30 mg / L, TP = 50 mg / L. Add NaOH to adjust the pH to 7.2. Pour 200 mL of artificial anaerobic digestion wastewater into a 500 mL transparent serum bottle and seal it with an aluminum-plastic composite cap. Use a vacuum pump to extract the headspace gas and replace it with a 70% CH4 + 30% CO2 mixed gas. Subsequently, autoclave the serum bottle at 121 °C for 30 min and then cool it to room temperature.

[0042] (3) Conduct tests at 5 initial ratios of algal and bacterial cell numbers, which are 1:0, 1:1, 1:5, 5:1, and 0:1 respectively. Use a sterile syringe to inoculate the bacterial microorganisms into the serum bottles according to the ratios inside a laminar flow hood. Place each group in an illumination incubator for cultivation, and set the conditions as follows: 25 °C, continuous stirring at 200 rpm, light intensity of 4000 Lux, and light ratio of 12L:12D.

[0043] Take samples of the headspace gas every 24 h and determine the changes in the composition of the headspace gas through a gas chromatograph; at the same time, take water samples every 24 h to determine the changes in microbial biomass, and then filter the water samples through a 0.45 μm filter membrane to determine the changes in the concentrations of pollutants such as dissolved methane, ammonia nitrogen, nitrate nitrogen, COD, and total phosphorus. Process and plot the experimental data using Origin9.0. The specific results are shown in Figure 2 as follows.

[0044] At the initial inoculation ratio of algal and bacterial cells A:B = 5:1, methane is utilized maximally, maintaining the highest methane removal efficiency throughout the entire cultivation process, achieving a methane removal amount of 52.03 ± 6.78 mL. Nitrate nitrogen has the highest nitrogen removal rate at the algal-bacterial ratio A:B = 5:1, especially the removal amount of nitrate nitrogen is twice that of the single-algae group, and the degradation rates of ammonia nitrogen and nitrate nitrogen reach 47.38% and 76.53% respectively; COD also has the highest utilization rate, and the corresponding COD degradation rate and degradation amount are 77.50% and 155 mg / L respectively; in the part of total phosphorus removal, although the group with the algal-bacterial ratio A:B = 1:1 shows an advantage in the total phosphorus treatment in the first 6 days, after 12 days, the highest TP utilization rate of 63.60% is obtained at the algal-bacterial ratio A:B = 5:1. It can be seen that when the initial inoculation ratio of Scenedesmus microalgae and methanotrophic bacteria A:B = 5:1, the system has the best removal efficiency.

[0045] Example 3: Tests of different hydraulic retention times

[0046] In this embodiment, the method and device in Example 1 are used for testing. At two different hydraulic retention times (HRTs) of 24 h and 36 h, explore the treatment effects of the device on dissolved methane, COD, ammonia nitrogen, and nitrate nitrogen.

[0047] (1) The microalgae Tetradesmus obliquus (FACHB - 416) and the methane - oxidizing model strain Methylocystis bryophila (DSM - 21852) were respectively cultured in a constant - temperature light incubator and a constant - temperature incubator. The medium used for culturing Tetradesmus obliquus was BG11 medium, with the stirring rate set at 200 rpm, the light intensity at 3000 Lux, the light - dark ratio at 12L:12D, the temperature at 26 °C, and cultured for 5 - 7 days; the medium used for culturing the methane - oxidizing model strain was 1409 medium, with the stirring rate set at 200 rpm, the temperature at 26 °C, and cultured for 5 - 7 days.

[0048] (2) Artificial simulated biogas slurry (i.e., the wastewater to be treated) was prepared and introduced into the photobioreactor. Simulated biogas (70% CH4 + 30% CO2) was aerated into the reactor to saturate methane in the water body, and the D - CH4 concentration was about 21 g / m 3 . The device was started, and microalgae and methane - oxidizing bacteria (including other heterotrophic bacteria generated during the process) were introduced into the photobioreactor for enlarged cultivation. The inoculation ratio of the number of algal and bacterial cells was 5:1. The light time was set at 12L:12D, the light intensity was set at 3000 Lux, and the stirring speed of the magnetic stirrer was set at 150 rpm to keep the algal and bacterial cells in suspension in the photobioreactor. During this period, the wastewater to be treated was regularly introduced and discharged to fully mix and contact the algal and bacterial microorganisms with the wastewater to adapt to the quality of the wastewater to be treated, and cultured for 2 - 3 days. Wait for the algae and bacteria to adapt and gradually increase the COD, NH4 + -N, and D - CH4 content of the wastewater to be treated until the COD, NH4 + -N, and D - CH4 content reached 100 mg / L, 150 mg / L, and 20 g / m 3 respectively.

[0049] (3) The device was officially operated, and artificial simulated biogas slurry was introduced; two different hydraulic retention times HRT (treatment time of the wastewater to be treated) were tested, which were 36 h and 24 h respectively. The light intensity was set at 3000 Lux, and the light - dark ratio was set at 12L:12D. 30 replicates were made for each group of hydraulic retention times. During this period, samples were taken every 2 days to detect the microalgae cell density. When the microalgae cell density was higher than 5.0×10 7 cells / mL, about 20% of the algal - bacterial mixture needed to be discharged through the microbial sampling port to remove algae and sludge.

[0050] After the treated water sample was discharged, it was passed through a 0.45 - μm filter membrane and then the COD, ammonia nitrogen (NH4 + -N), and nitrate nitrogen (NO3 -The concentration of (-N) was measured by referring to the national standard method. The test data were processed and plotted using Origin 9.0, and the specific results are shown in Table 1.

[0051] Table 1 Treatment effects of dissolved methane and pollutants before and after treatment at different hydraulic retention times

[0052]

[0053] Methanotrophs showed good methane oxidation efficiency at two HRTs of 24 h and 36 h, and the removal efficiency of dissolved methane was always higher than 96.97%. The average COD removal efficiencies were 63.30% and 71.50% respectively. Although some previous reports have pointed out that microalgae have low efficiency in removing organic matter under mixotrophic conditions, due to the construction of a ternary microbial composite system in the present invention, in addition to the contribution of microalgae heterotrophy, heterotrophic bacteria such as nitrifying bacteria in the system also make a great contribution. Therefore, a high COD removal efficiency can be continuously achieved at both HRTs. The average removal efficiencies of NH4 + -N were 12.52% and 17.15% respectively, and the removal amounts were 18.79 and 25.73 mg / (L·d) respectively. The average removal efficiencies of NO3 - -N were 39.72% and 49.28% respectively, and the removal amounts were 11.92 and 14.78 mg / (L·d) respectively. Considering the relatively high nitrogen source concentration in the anaerobic digestion wastewater, the nitrogen removal rate is not high. However, compared with other literature reports using PBR reactors to treat nitrogen-containing sewage (13 - 30 mg NH4 + -N / (L·d)), the single-day nitrogen removal amount of this implementation method is relatively high.

[0054] Example 4: Testing of sewage with different initial COD concentrations

[0055] In this implementation manner, the method and device in Example 1 were used for testing. Under different initial COD concentrations of artificially simulated biogas slurry, the treatment effects of the device on dissolved methane, COD, ammonia nitrogen, and nitrate nitrogen were explored.

[0056] (1) Tetradesmus obliquus (FACHB - 416) and the methanotrophic model strain Methylocystis bryophila (DSM - 21852) were respectively cultured in a constant - temperature light incubator and a constant - temperature incubator. The medium used for culturing the microalgae Tetradesmus obliquus was BG11 medium, with a stirring rate set at 200 rpm, a light intensity of 3000 Lux, a light - dark ratio of 12L:12D, and a temperature set at 26°C for 5 - 7 days. The medium used for culturing the methanotrophic model strain was 1409 medium, with a stirring rate set at 200 rpm and a temperature set at 26°C for 5 - 7 days.

[0057] (2) Artificial simulated biogas slurry (i.e., the wastewater to be treated) was prepared and introduced into the photobioreactor. Simulated biogas (70% CH4 + 30% CO2) was aerated into the reactor to saturate methane in the water body, and the D - CH4 concentration was approximately 21 g / m 3 . The device was started, and microalgae and methanotrophic bacteria (along with other heterotrophic bacteria generated during the process) were inoculated into the photobioreactor for enlarged cultivation. The inoculation ratio of algal and bacterial cell numbers was 5:1. The light time was set at 12L:12D, the light intensity was set at 4000 Lux, and the stirring speed of the magnetic stirrer was set at 150 rpm to keep the algal and bacterial cells in suspension in the photobioreactor. During this period, the wastewater to be treated was regularly introduced and discharged to fully mix and contact the algal - bacterial microorganisms with the wastewater to adapt to the quality of the wastewater to be treated for 2 - 3 days. Wait for the algae and bacteria to adapt and gradually increase the COD, NH4+-N, and D - CH4 contents of the wastewater to be treated until the COD, NH4+-N, and D - CH4 contents reach 100 mg / L, 150 mg / L, and 20 g / m 3 .

[0058] (3) The device was officially operated, and artificial simulated biogas slurry was introduced. Two different initial COD concentrations were tested, namely 87 - 103 and 148 - 196 mg / L in two concentration gradients. Each initial COD concentration treatment was repeated 30 times. The light intensity was set at 4000 Lux, the light - dark ratio was set at 12L:12D, and the hydraulic retention time was set at 36 h. During the reaction process, samples were taken every 2 days to detect the microalgal cell density. When the microalgal cell density was higher than 5.0×10 7 cells / mL, it was necessary to discharge algae and sludge through the microbial sampling port, discharging approximately 20% of the algal - bacterial mixture.

[0059] Table 2 Treatment effects of dissolved methane and pollutants before and after treatment at different initial COD concentrations

[0060]

[0061] The operation effect of the device shows that the treatment effect of dissolved methane in wastewater is good, the treatment rate of dissolved methane > 99%, and the average concentration of dissolved methane after treatment is lower than 0.05 g / m 3 , and there is also a certain removal effect on COD, ammonia nitrogen, and nitrate nitrogen. The treatment effect of COD, ammonia nitrogen, and nitrate nitrogen can be optimized by changing the hydraulic retention time and enhancing the role of heterotrophic bacteria by changing the COD concentration.

[0062] It can be seen from the above test results that the method and device for treating dissolved single-carbon greenhouse gases and nutrients in wastewater using a composite system of microalgae and heterotrophic bacteria in Example 1 can achieve the co-treatment of dissolved methane, organic carbon, and nutrients in artificial simulated biogas slurry. At the same time, microalgae biomass has been effectively enriched and accumulated, and biomass energy has been accumulated while pollutants are removed.

Claims

1. A method for treating sewage using a bacterial-algal heterotrophic bacteria composite system, characterized in that: The following steps are involved: (1) Pre-culturing the functional microalgae and methanotrophic bacteria separately to enrich them and reach a stable growth period; (2) mixing the functional microalgae and methanotrophic bacteria pre-cultured in step (1) with a small amount of wastewater to be treated, and performing expansion culture until a stable growth period is reached again; (3) Add the wastewater to be treated to the mixed solution after the expanded culture in step (2), expose it to light, and filter the treated wastewater using an MBR membrane.

2. The method for treating sewage using a bacterial-algal heterotrophic bacteria complex system according to claim 1, characterized in that: The functional microalgae in step (1) is Tetradesmus obliquus.

3. The method for treating sewage using a bacterial-algal heterotrophic bacteria complex system according to claim 1, characterized in that: The cell number ratio of the functional microalgae and the methanotrophic bacteria in step (2) is 5:

1.

4. The method for treating sewage using a bacterial-algal heterotrophic bacteria complex system according to claim 1, characterized in that: The illumination conditions described in step (3) are 3000-6000 Lux light intensity, 12L:12D illumination ratio, and sewage retention time of 24-36 hours.

5. The method for treating sewage using a bacterial-algal heterotrophic bacteria complex system according to claim 1, characterized in that: In step (3), the cell density of functional microalgae is regularly detected during the sewage treatment process. When the cell density of microalgae is higher than 5.0×10 7 cells / mL, algae and sludge removal is required.

6. A device for treating sewage using a bacterial-algal heterotrophic bacteria composite system, characterized in that: The device comprises a water inlet tank (1), a water outlet tank (8), a photobioreactor (10) and an LED light source (14); The photobioreactor (10) is provided with a water inlet (3), a reserved vent (4), a water outlet (5) and a microorganism sampling port (9); An MBR membrane assembly (11) is arranged inside the photobioreactor (10); a stirring device is arranged at the bottom of the photobioreactor (10); and an inserted dissolved oxygen probe (12) and a pH probe (13) are arranged outside the photobioreactor (10).

7. The device according to claim 6, characterized in that The stirring device comprises a magnetic stirrer (15) and a magnetic stirring bar (16).

8. The device according to claim 6, characterized in that The water inlet pipe is connected to the water inlet tank (1) through the water inlet (3) on the photobioreactor (10); and the water outlet pipe is connected to the water outlet tank (8) and the MBR membrane assembly (11) through the water outlet (5) on the photobioreactor (10).

9. The device according to claim 8, characterized in that The water inlet pipe is provided with a water inlet pump (2); the water outlet pipe is provided with a one-way valve (17), a pressure gauge (6) and a water outlet pump (7) in sequence.

10. The device according to claim 6, characterized in that The water outlet functional component in the MBR membrane component is a polyvinylidene fluoride PVDF ultrafiltration membrane.

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