A simultaneous denitrification and defluorination method based on bacterial and algal symbiosis

Abstract

The present invention relates to a "simultaneous denitrification and fluoride removal method based on bacterial-algal symbiosis." This method utilizes a bacterial-algal symbiotic system to efficiently and simultaneously remove TN and F from wastewater. The specific mechanism is that algal assimilation removes ammonia nitrogen, while bacterial denitrification removes nitrate nitrogen. In the presence of calcium ions, the bacteria and algae further promote the formation of calcium fluoride, effectively removing fluoride ions. Furthermore, the reaction process does not require aeration, significantly reducing power consumption. Ammonia nitrogen removal does not involve the traditional nitrification and denitrification pathways, and the denitrification carbon source only needs to meet the nitrate nitrogen requirements of the raw water, thus conserving carbon sources. After 12 days of reaction, the fluoride removal rate in photovoltaic wastewater can reach over 95%, and TN removal is complete, meeting emission standards. The method of the present invention features a simple process, low equipment requirements, simple operation, easy-to-control treatment process, and low operating costs. Compared with existing processes, it is more in line with the dual carbon policy, can save energy and reduce emissions, and significantly reduce operating costs.

Description

Technical Field

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

[0002] Fluoride is a trace element essential for the human body to maintain normal physiological activities. Excessive or insufficient fluoride intake can have adverse health effects. Fluoride concentrations in drinking water below 1.0 mg / L can easily lead to dental caries. On the other hand, drinking high-fluoride water can lead to systemic chronic diseases such as dental fluorosis and skeletal fluorosis, and even damage brain nerves. To protect the human living environment, research on fluoride removal from fluoride-containing wastewater is a key task in both environmental protection and health fields, both domestically and internationally. Common sources of fluoride-containing wastewater include semiconductor manufacturing, photovoltaics, glass production, and aluminum electrolysis. Currently, scholars at home and abroad have conducted extensive research on fluoride-containing wastewater treatment technologies and methods, achieving significant progress in fluoride ion removal theory and developing novel processes. These methods include adsorption, chemical precipitation, membrane separation, coagulation and sedimentation, ion exchange, electrodialysis, electroflocculation, and reverse osmosis. Despite the availability of various methods for treating fluoride-containing wastewater, each method offers less than ideal removal results and carries significant drawbacks. For example, methods like membrane separation are costly, have short membrane lifespans, and require extensive maintenance. Chemical precipitation methods, on the other hand, require large amounts of chemicals, can cause secondary pollution, and may not completely remove fluoride. Therefore, developing a novel technology or process for treating photovoltaic wastewater that efficiently removes fluoride while conserving chemical reagents is crucial.

[0003] Excessive nitrogen is one of the important factors causing water pollution and seriously threatens the safety of water bodies. The Ministry of Ecology and Environment has revised the national environmental protection standard "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002) and issued a draft for comments. Since then, Beijing, Tianjin, Zhejiang, Taihu Basin, Chaohu Basin, Mintuojiang Basin, Dianchi Lake, Xiong'an and other places have successively issued local standards and basin standards based on quasi-Class III and quasi-Class IV standards, and put forward increasingly higher emission requirements for total nitrogen and total phosphorus. For the treatment of nitrogen-containing wastewater, the methods reported at home and abroad are mainly divided into physicochemical methods and biological denitrification methods. Physicochemical methods mainly include ion exchange resin method, stripping method, breakpoint chlorination method, chemical precipitation method and electrocatalytic oxidation method; biological denitrification method is widely used in the treatment of nitrogen-containing wastewater due to its advantages such as low cost, simple operation, convenient maintenance and stable operation.

[0004] In response to the nation's "dual carbon" policy, there is an urgent need to develop new, economical, green, and efficient denitrification and fluoride removal technologies. Given the high fluoride and nitrogen content in photovoltaic wastewater, the search for new, economical, green, and efficient denitrification technologies for deep denitrification under the stress of fluoride in wastewater is of great practical significance. Summary of the Invention

[0005] In response to the needs in the above-mentioned fields, the present invention provides a simultaneous denitrification and fluorine removal method based on bacterial and algal symbiosis, which utilizes biological treatment to efficiently and simultaneously remove TN and F from wastewater. After 12 days of reaction, the fluoride removal rate in photovoltaic wastewater can reach more than 95%, and the TN removal rate can reach more than 90%, both of which meet the emission standards.

[0006] A method for simultaneous denitrification and defluorination based on bacterial and algal symbiosis, comprising the following steps:

[0007] Step a) obtaining biological materials: the microalgae is a green algae species, Chlamydopodium, and the activated sludge is return sludge from a sewage treatment plant;

[0008] Step b) Pretreatment of fluorine-containing photovoltaic wastewater by coagulation and sedimentation: The wastewater is coagulated and precipitated using a flocculant to remove SS and part of F from the wastewater;

[0009] Step c) Wastewater conditioning after coagulation and sedimentation: adding the carbon source required for complete denitrification of the original NO3-N in the wastewater,

[0010] Step d) domestication and screening of microalgae to improve their adaptability to wastewater;

[0011] Step e) algae-bacteria treatment of fluorine- and nitrogen-containing wastewater: activated sludge and domesticated and screened microalgae are added to the conditioned wastewater in a dry weight ratio of (1-6):1, with an initial biomass of 1-5 g / L, and allowed to grow and multiply to remove nitrogen and fluoride from the wastewater. The growth and multiplication time is 6-12 days; the bacteria-algae mixture is filtered and collected using a filter membrane, and the wastewater enters the next treatment unit.

[0012] The microalgae acclimation and screening method in step f) is as follows: the wastewater after coagulation and sedimentation in step b) or the wastewater adjusted in step c) is diluted in a gradient manner, the microalgae are added to the low-concentration coagulation and sedimentation wastewater, and the microalgae are allowed to grow under natural light conditions. A new microalgae sample is taken from the wastewater, and a higher-concentration coagulation and sedimentation wastewater is added to allow the microalgae to grow. The above operation is repeated to continuously improve the tolerance of the microalgae until the microalgae can grow well in the wastewater. The microalgae are collected, their concentration is measured, and they are stored in BG11 medium or refrigerated.

[0013] The activated sludge in step e) needs to be activated before use. The activation method is as follows: placing the activated sludge in a beaker, allowing it to settle, removing the supernatant, adding synthetic wastewater with a C:N ratio of 5 for activation, wherein the synthetic wastewater has a COD of 2000 mg / L, a TN of 400 mg / L, a TP of 40 mg / L, and a pH of 7.0; maintaining continuous aeration during the activation process; stopping the aeration after 8 hours, removing the supernatant, taking the sludge at the bottom of the beaker, measuring its concentration, and storing it in a refrigerator;

[0014] The carbon source of the artificial synthetic wastewater is glucose, and the nitrogen source is composed of ammonium chloride: sodium nitrate = 1:1, and potassium dihydrogen phosphate and trace elements are supplemented.

[0015] The composition of the artificial synthetic wastewater is shown in the following table:

[0016] Water quality of synthetic wastewater

[0017] index COD TN TP pH trace elements Concentration (mg / L) 2000 400 40 7.0 See the table below

[0018] Trace element addition

[0019]

[0020]

[0021] The added amounts of the flocculants were 1500 mg / L CaCl2 and 600 mg / L PAC.

[0022] In step c), one or more of glucose, methanol, sodium acetate and acetic acid are added as carbon sources.

[0023] The carbon source is glucose, and its dosage is 2.86 times the concentration of NO3-N.

[0024] The activated sludge and the domesticated and screened microalgae are mixed in a dry weight ratio of (3-4):2, and the initial biomass is 3-5 g / L.

[0025] Application of the above method in photovoltaic wastewater treatment.

[0026] The present invention is achieved through the following technical solutions:

[0027] A new biological synchronous denitrification and defluorination technology: including the following steps:

[0028] Step a) Microalgae and Sludge Source: The microalgae used were obtained from a laboratory-existing green algae species, Chlamydopodium, screened and domesticated from actual wastewater and exhibited a certain degree of tolerance to poor water quality. Activated sludge was obtained from the Qingshan Lake Wastewater Treatment Plant in Nanchang.

[0029] Step b) Coagulation and Sedimentation of Fluorine-Containing Photovoltaic Wastewater: The wastewater was coagulated and precipitated using a flocculant (1500mg / L CaCl2 and 600mg / L PAC) to remove SS and some F from the wastewater. The purpose of coagulation was to remove the high concentration of fluoride ions in the raw water through chemical precipitation. Fluoride levels were reduced from approximately 700mg / L to approximately 15mg / L, but still exceeded the standard. The most relaxed emission standard is 10mg / L, necessitating the subsequent bacterial and algal system.

[0030] Step c) Microalgae Acclimation and Screening: Add algae seeds to low-concentration wastewater after coagulation and sedimentation and allow them to grow under natural light. New microalgae samples are then removed and added to higher-concentration wastewater after coagulation and sedimentation and allowed to grow. Repeat this process to continuously improve the microalgae's tolerance until they can grow well in the wastewater. Microalgae acclimation and screening are standard procedures.

[0031] Step d) Activation of Activated Sludge: Before use, activated sludge should ideally be activated to maintain optimal physical and chemical properties. Place the activated sludge in a beaker, allow it to settle, remove the supernatant, and add synthetic wastewater with a C:N ratio of 5 for activation. This is a conventional method. The specific water quality and concentration of commonly used synthetic wastewater are shown in the table above. The carbon source is glucose, and the nitrogen source is a 1:1 ratio of ammonium chloride to sodium nitrate. A small amount of potassium dihydrogen phosphate and trace elements are also added. Continuous aeration is maintained during the activation process.

[0032] Step e) Algae-bacteria treatment of fluoride-containing wastewater: Activated sludge and microalgae are added to the wastewater after coagulation and sedimentation in a ratio of (1-6):1 (dry weight ratio), with an initial biomass of 1-5 g / L. A carbon source is added to completely denitrify the NO₃-N present in the wastewater, and the microalgae are allowed to grow and reproduce, removing nitrogen and fluoride from the wastewater. The growth period is 12 days. The microalgae are filtered using a membrane and collected, and the wastewater enters the next treatment unit.

[0033] Carbon source addition: PV wastewater lacks sufficient carbon to sustain normal microbial growth and the carbon required for denitrification. Using glucose as a carbon source, by leveraging the circulation of intercellular substances, the addition of additional energy is reduced, and only the carbon source required to completely denitrify the existing NO₃-N in the wastewater is added. The glucose dosage is controlled to 2.86 times the NO₃-N concentration (theoretical calculation: denitrification requires 2.86g of carbon source, calculated as COD, to remove 1g of nitrate nitrogen).

[0034] The beneficial effects of the present invention are as follows: The present invention utilizes the bacteria-algae symbiotic system for the first time, and utilizes biological treatment to efficiently and simultaneously remove TN and F from wastewater. After 12 days of reaction, the fluoride removal rate in photovoltaic wastewater can reach more than 95%, and the TN removal rate can reach more than 90%, both of which meet the emission standards. In summary, the present invention first uses flocculants to remove a large amount of F ions in the wastewater, and then forms such a bacteria-algae system. The algae assimilates and removes ammonia nitrogen, and the bacteria denitrifies and removes nitrate nitrogen. The bacteria and algae further promote the formation of calcium fluoride in the presence of calcium ions, and efficiently remove fluoride ions. The principle is mainly that the addition of bacteria and algae promotes the aggregation and sedimentation of fluoride-containing precipitates in water. This process is related to the metabolites (CO3 2- ) is similar to the formation of calcium carbonate precipitation induced by microorganisms. As nucleation centers, they can accelerate the induction and precipitation speed and remove fluoride ions more thoroughly. At the same time, the reaction process does not require aeration and oxygen supply, which significantly reduces power consumption. Ammonia nitrogen removal does not go through the traditional nitrification and denitrification pathway. The denitrification carbon source only needs to meet the nitrate nitrogen requirements in the raw water, which saves carbon source. That is, in the absence of a carbon source in photovoltaic wastewater, by utilizing the advantages of the circulation of intercellular substances, the consumption of additional energy is reduced. Only the carbon source required for complete denitrification of the existing NO3-N in the wastewater is added, and the amount of glucose added is controlled to 2.86 times the NO3-N concentration. Compared with traditional nitrification and denitrification, the addition of carbon source is significantly reduced, reducing energy consumption.

[0035] The method of the present invention has the characteristics of simple raw materials, low equipment requirements, simple operation, easy control of the treatment process, simple treatment process flow, and low operating costs. Compared with the existing process, it is more in line with the dual carbon policy, can save energy and reduce emissions, and greatly reduce operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The changes of N and F concentrations in photovoltaic wastewater treated with different bacterial and algal biomasses (2:1) over time are shown.

[0037] Where A is NO3 - -N concentration changes, B is NH4 + -N concentration changes, C is the removal rate of fluoride,

[0038] Figure 2 SEM images of activated sludge, microalgae, and algae-bacteria symbiosis systems before and after wastewater treatment. (A) and (B) are images of activated sludge before and after wastewater treatment, (C) and (D) are images of microalgae before and after wastewater treatment, (E) is the wastewater after algae-bacteria symbiosis treatment, and (F) is calcium fluoride crystals on the cell surface.

[0039] Figure 3The effects of pure bacteria (AS), bacteria-algae (SA), and pure algae (MA) systems on the concentration changes of pollutants in photovoltaic wastewater, including (A) NO3-N, (B) NH4+-N, (C) NO2-N, (D) TOC, (E) TN, and (F) fluoride. DETAILED DESCRIPTION

[0040] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with actual examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0041] Example 1

[0042] The wastewater comes from the photovoltaic enterprise comprehensive regulating pool. The water quality indicators after filtration are shown in the following table. The water pH is neutral, the COD content is 90.8mg / L, but its available organic carbon content (TOC) is only 17.3mg / L, and the total nitrogen is mainly composed of NH4 + -N and NO3-N, with concentrations reaching up to 420 mg / L and a C / N ratio of only 0.21. Fluoride concentrations were essentially unchanged before and after filtration, indicating that fluoride in the wastewater exists primarily as fluoride ions, with concentrations reaching up to 711.1 mg / L. The water is clear and essentially phosphate-free, though small amounts of calcium ions are present.

[0043] Water quality indicators of a photovoltaic enterprise's wastewater after filtration

[0044]

[0045] The wastewater was first coagulated and precipitated with flocculants to remove SS and part of the fluorine in the water. The flocculants were 1500mg / L CaCl2 and 600mg / L PAC.

[0046] Water quality parameters after coagulation and sedimentation with addition of carbon source

[0047]

[0048] In order to explore the treatment effect of the bacteria-algae symbiotic system on wastewater, three comparative experiments were designed (initial biomass 3g / L), namely pure bacteria (activated sludge AS), bacteria-algae (2:1) (SA), and pure algae (MA) systems, to investigate their effects on various water quality indicators in wastewater. Figure 2 These are SEM images of the activated sludge, microalgae, and bacteria-algae symbiotic system before and after wastewater treatment.

[0049] All three systems have good removal effects on NO3-N in wastewater. Figure 3However, the treatment effect of the bacteria-algae symbiotic system was the best due to the presence of microalgae. The trends of the pure bacteria and bacteria-algae systems were similar in the initial stage of the reaction (1-4 days). NO3-N was quickly utilized and reduced to the lowest level, with removal rates of 90.0% and 98.9% respectively. However, NO3-N in the pure algae system was not completely removed until the 12th day (e.g. Figure 3 (A). NH4 + -N concentration changes as Figure 3 In B, in both pure bacteria and algae systems, rapid consumption of NO3-N occurred in a short period of time, leading to NH4 + -N removal delay phenomenon, after the 3rd day NH4 + -N began to decline, and the rate of decline in the bacteria-algae system was faster than that in the pure bacteria. On the 12th day, NH4 + -N was almost completely consumed, with a removal rate of 100%, while the removal rate in pure bacteria was only 58.9% and that in pure algae was only 22.7%. In wastewater with insufficient carbon source, the TN residue in the pure bacteria system was 155.1 mg / L, with a removal rate of 66.4%. In the pure algae system, TN was reduced from 461.0 mg / L to 146.2 mg / L, with a removal rate of 68.3%. In the bacteria-algae symbiotic system, TN was reduced to 39.3 mg / L, with a removal rate of up to 91.5%. Figure 3 Middle E).

[0050] The fluoride concentration in the effluent of the three systems dropped from 15.6 mg / L to 0.4 mg / L, 0.5 mg / L and 3.8 mg / L respectively. The removal rate of the activated sludge group could reach as high as 97%, while that of the pure algae system was only 75.6%, but all met the emission standards.

[0051] The results indicate that the algae-microbe symbiotic system effectively treats a wide range of pollutants. Even in wastewater with insufficient carbon sources, the synergistic interaction between microalgae and bacteria significantly removes pollutants, achieving effluent quality that meets the "Battery Industry Pollutant Emission Standard" (GB 30484-2013).

[0052] (1) Acclimation and screening of microalgae: Add algae seeds to wastewater after coagulation and sedimentation at a lower concentration and allow them to grow under natural light conditions. Take out new microalgae samples from them and add them to wastewater after coagulation and sedimentation at a higher concentration and allow them to grow. Repeat the above steps to continuously improve the tolerance of microalgae until the microalgae can grow well in the wastewater. Collect the microalgae for later use.

[0053] Activation of activated sludge: The activated sludge just produced can be used directly, but the stored activated sludge needs to be activated before use so that the activated sludge maintains good physical and chemical properties. Place the activated sludge in a beaker, let it settle and remove the supernatant, add artificial synthetic wastewater with a C:N ratio of 5 for activation. The specific water quality composition and concentration are shown in the table below. Among them, the carbon source is glucose, and the nitrogen source is composed of ammonium chloride: sodium nitrate = 1:1, and a small amount of potassium dihydrogen phosphate and trace elements are added. Continuous aeration is maintained during the activation process. Remove the supernatant and take the activated sludge at the bottom of the beaker for later use;

[0054] Water quality of synthetic wastewater

[0055] index COD TN TP pH trace elements Concentration (mg / L) 2000 400 40 7.0 See the table below

[0056] Trace element addition

[0057]

[0058] (2) Wastewater conditioning after coagulation and sedimentation: Carbon source addition: Since the carbon source in photovoltaic wastewater is insufficient to maintain the normal growth of microorganisms and the carbon required for the denitrification process, a carbon source needs to be added. Glucose is used as a carbon source. By taking advantage of the circulation of intercellular substances, the addition of additional energy is reduced. Only the carbon source required for complete denitrification of the existing NO3-N in the wastewater is added. The glucose dosage is controlled to be 2.86 times the NO3-N concentration.

[0059] (3) Nitrogen and Fertilizer Removal by Bacteria and Algae: Microalgae and activated sludge were added to the conditioned wastewater after coagulation and sedimentation for biological treatment. The ratio of activated sludge to Clemenia in the bacteria-algae symbiotic system was controlled to be 2:1 by dry weight. The initial biomass (dry weight ratio) of the bacteria-algae symbiotic system was set to 1 g / L, 2 g / L, and 3 g / L. After 2 days of treatment with bacteria and algae, the biomass of 1 g / L, 2 g / L, and 3 g / L corresponded to NO3-N reduced from 257.0 mg / L to 102.3 mg / L, 79.9 mg / L, and 55.3 mg / L, respectively. The removal rate slowed down in the later period. At a biomass of 3 g / L, it only took 6 days to reduce NO3-N to a minimum of 1.7 mg / L. However, at the 1 g / L and 2 g / L bacteria and algae, NO3-N was reduced to 44.7 mg / L and 8 mg / L, respectively, on the 12th day. In the 3g / L bacteria and algae group, NH4+-N decreased slowly in the first 4 days, and then was quickly removed and completely. The removal rate reached 100% on the 12th day. In the other 1g / L and 2g / L biomass groups, the removal of NH4+-N was slightly inhibited in the first 2 days, and then kept decreasing at a constant rate. On the 12th day, NH4 +-N decreased from 188.7 mg / L to 100.7 mg / L and 61.5 mg / L, respectively, with removal rates of 67.1% and 46.6%. Among them, the TN removal rate of the 3 g / L bacteria and algae group can reach more than 90%, and the other two groups can also reach more than 80%. Bacteria and algae with different biomasses have good removal effects on fluoride in wastewater. After 12 days of reaction, the fluoride concentration in the wastewater dropped from 15.6 mg / L to below 0.7 mg / L, and the removal rate reached more than 95%. The larger the biomass, the higher the removal rate. Figure 1 .

[0060] Implementation Case 2

[0061] The water quality of photovoltaic wastewater generated by a photovoltaic enterprise after filtration

[0062]

[0063] The wastewater was first coagulated and precipitated with flocculants to remove SS and part of the fluorine in the water. The flocculants were 1500mg / L CaCl2 and 600mg / L PAC.

[0064] Wastewater regulation after coagulation and sedimentation: Carbon source addition: Sodium acetate is used as the carbon source. By taking advantage of the circulation of intercellular substances, the addition of additional energy is reduced. Only the carbon source required for complete denitrification of the existing NO3-N in the wastewater is added. The addition amount of sodium acetate is controlled to 3.7 times the amount of NO3-N removed (mass ratio).

[0065] The water quality of photovoltaic wastewater generated by a photovoltaic enterprise after adjustment

[0066]

[0067]

[0068] Nitrogen and fluorine removal by bacteria and algae: add microalgae and activated sludge to the conditioned wastewater after coagulation and sedimentation for biological treatment. Control the ratio of activated sludge to Clemenia in the bacteria-algae symbiotic system to be 3:2 by dry weight. Set the initial biomass (dry weight ratio) of the bacteria-algae symbiotic system to 5g / L. After 7 days of reaction, the fluoride concentration in the wastewater can meet the emission standards.

[0069] The water quality of photovoltaic wastewater generated by a photovoltaic enterprise after bacterial and algal treatment

[0070]

Claims

1. A method for simultaneous denitrification and defluorination based on bacterial and algal symbiosis, comprising the following steps: Step a) obtaining biological materials: the microalgae is the green algae species Chlamydopodium, and the activated sludge is the return sludge from a sewage treatment plant; Step b) Pretreatment of fluorine-containing photovoltaic wastewater by coagulation and sedimentation: The wastewater is coagulated and precipitated using a flocculant to remove SS and some fluorine from the wastewater; Step c) Wastewater conditioning after coagulation and sedimentation: Add the carbon source required for complete denitrification of the original NO3-N in the wastewater, Step d) domestication and screening of microalgae to improve their adaptability to wastewater; Step e) Algae-bacteria treatment of fluorine- and nitrogen-containing wastewater: activated sludge and domesticated and screened microalgae are added to the conditioned wastewater at a dry weight ratio of (1-6):1, with an initial biomass of 1-5 g / L. The microalgae are allowed to grow and multiply to remove nitrogen and fluoride from the wastewater. The growth and multiplication time is 6-12 days. The microalgae mixture is filtered and collected using a membrane filter, and the wastewater enters the next treatment unit. The added amounts of the flocculants were 1500 mg / L CaCl2 and 600 mg / L PAC.

2. The method according to claim 1, wherein the microalgae acclimation and screening method in step d) comprises: gradiently diluting the wastewater after coagulation and sedimentation in step b) or the conditioned wastewater in step c), adding the microalgae to the low-concentration coagulation and sedimentation wastewater, and allowing the microalgae to grow under natural light conditions; removing a new microalgae sample from the wastewater, adding the higher-concentration coagulation and sedimentation wastewater, and allowing the microalgae to grow; repeating the above steps to continuously improve the tolerance of the microalgae until the microalgae can grow well in the wastewater; collecting the microalgae, measuring their concentration, and storing them in BG11 medium or refrigerated.

3. The method according to claim 1, wherein the activated sludge in step e) needs to be activated before use. The activation method comprises placing the activated sludge in a beaker, allowing it to settle, removing the supernatant, and adding synthetic wastewater with a C:N ratio of 5 for activation, wherein the synthetic wastewater has a COD of 2000 mg / L, a TN of 400 mg / L, a TP of 40 mg / L, and a pH of 7.0; maintaining continuous aeration during the activation process; stopping aeration after 8 hours, removing the supernatant, collecting the sludge at the bottom of the beaker, measuring its concentration, and storing it in a refrigerator.

4. The method according to claim 3, wherein the carbon source of the artificial synthetic wastewater is glucose, the nitrogen source is composed of ammonium chloride: sodium nitrate = 1:1, and potassium dihydrogen phosphate and trace elements are supplemented.

5. The method according to claim 4, wherein the artificial synthetic wastewater consists of: COD is 2000 mg / L, TN is 400 mg / L, TP is 40 mg / L, pH is 7.0, boric acid is 2.86 mg / L, manganese chloride tetrahydrate is 1.86 mg / L, zinc sulfate heptahydrate is 0.222 mg / L, copper sulfate pentahydrate is 0.079 mg / L, sodium molybdate dihydrate is 0.39 mg / L, and cobalt nitrate hexahydrate is 0.049 mg / L.

6. The method according to claim 1, wherein the carbon source added in step c) is one or more of glucose, methanol, sodium acetate, and acetic acid.

7. The method according to claim 6, wherein the carbon source added in step c) is glucose, and the amount added is 2.86 times the concentration of NO3-N.

8. The method according to claim 1, wherein the dry weight ratio of the activated sludge to the acclimated and screened microalgae is (3-4):2, and the initial biomass is 3-5 g / L.

9. Application of the method according to any one of claims 1 to 8 in photovoltaic wastewater treatment.

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