Efficient advanced wastewater treatment process and operation system based on algae-bacteria symbiosis

Abstract

An efficient advanced wastewater treatment process and operation system based on algal-bacterial symbiosis. The process includes: (1) storing wastewater; (2) mixing the clarified liquid and pure algal liquid for reaction to form an algal-bacterial aggregate with microalgae as the main body; (3) depleting nitrogen and phosphorus nutrients during the reaction in the outdoor natural light period; (4) stirring and aerating and injecting concentrated regenerated sludge until bacteria become the main body of the algal-bacterial aggregate; (5) stopping aeration and allowing static sedimentation for separation; (6) discharging the clarified water and sludge; (7) concentrating and regenerating the sludge. Its operation system includes a water storage and regulation module, a main treatment module, a pure algal culture module, a sludge concentration and regeneration module, and an air supply module. The present invention adjusts the community structure of the algal-bacterial aggregate during the operation of the sequential batch process, forming an algal-bacterial aggregate dominated by microalgae or dominated by Zoogloea ramigera at different stages of the process, overcoming the bottleneck that traditional algal-bacterial symbiosis processes are difficult to simultaneously achieve efficient pollutant treatment and sludge-water separation.

Description

Technical Field

[0001] The present invention relates to a process for advanced treatment of wastewater, achieving efficient treatment of wastewater and efficient separation and recovery of biomass, and belongs to the field of microalgae bioengineering technology. Background Art

[0002] A large number of studies have confirmed that when photosynthetic algae coexist with heterotrophic organisms such as bacteria, a microbial community called algal-bacterial aggregates will be formed. This community has a specific community structure and ecological functions. Through complex metabolic mechanisms, nutrients and metabolites are exchanged, genes are transferred, etc. among algae and bacteria, showing a relatively high growth rate, a strong nutrient absorption capacity, an enhanced bioflocculation capacity, an excellent biochemical substance production capacity, and strong anti-pollution and anti-shock properties. Moreover, photosynthetic algae and bacteria can provide oxygen and carbon dioxide for each other, basically eliminating the dependence on aeration and greenhouse gas emissions in the process of sewage biological treatment. The algal-bacterial symbiotic wastewater treatment process using algal-bacterial aggregates as the treatment medium can obtain extremely high treatment efficiency, extremely low power consumption and temperature gas emissions, thereby simultaneously achieving the ultra-low emission of wastewater nutrients and the carbon reduction goal. Therefore, the wastewater treatment process based on algal-bacterial symbiosis, especially the advanced treatment process, has attracted increasing attention.

[0003] However, the pollutant removal capacity and precipitation separation capacity of algal-bacterial aggregates are determined by their community structure. Generally speaking, for algal-bacterial aggregates dominated by photosynthetic algae, the pollutant removal capacity is more excellent, but the formed algal-bacterial culture is not easy to precipitate and separate; while when bacteria represented by Zoogloea become the main body of algal-bacterial aggregates, good flocculation and precipitation effects will occur, but at the cost of the decline in nutrient removal capacity. This contrast greatly limits the application of the process based on algal-bacterial symbiosis in the field of advanced wastewater treatment.

[0004] Therefore, a new process that can not only exert the efficient wastewater treatment capacity of algal-bacterial symbiosis but also timely separate the algal-bacterial culture from the effluent is needed to achieve the goal of ultra-low emission of wastewater pollutants. Summary of the Invention

[0005] Aiming at the deficiencies existing in the existing advanced wastewater treatment technology, the present invention provides an efficient advanced wastewater treatment process based on algal-bacterial symbiosis, and an operating system for realizing this process. This process is a sequential batch treatment process synchronized with the 24-hour day-night cycle. At different stages of the process, pure algal liquid, concentrated and regenerated sludge, and different aeration conditions are respectively provided, so as to rapidly adjust the algal-bacterial community structure and operating environment, respectively adapt to the requirements of efficient pollutant removal and efficient separation of mud and water, thereby achieving the goal of advanced wastewater treatment and reducing energy consumption and temperature gas emissions.

[0006] The high - efficiency advanced wastewater treatment process based on algal - bacterial symbiosis of the present invention is a sequential batch process synchronized with the day - night cycle. At different stages of the process, pure algal liquid, concentrated and regenerated sludge, and different aeration conditions are provided respectively, so as to realize the rapid adjustment of the algal - bacterial community structure and the operating environment, in order to adapt to the requirements of efficient pollutant removal and efficient separation of sludge and water respectively; it includes the following steps:

[0007] (1) Water storage and regulation stage:

[0008] The continuously flowing influent is stored for 24 hours, while realizing water quality regulation, hydrolysis acidification, partial denitrification and preliminary precipitation. After precipitation, the upper clarified liquid and bottom sludge are obtained. Most of the bottom sludge is discharged, and the remaining sludge is used for the next cycle;

[0009] (2) Influent stage:

[0010] The upper clarified liquid described in step (1) and the pure algal liquid are simultaneously injected into the main reactor, and are stirred evenly with the remaining algal - bacterial mixed sludge retained in the main reactor in the previous cycle to form a mixed liquid. Ambient air is introduced into the mixed liquid for aeration until an algal - bacterial aggregate with microalgae as the main body of the community structure is formed, and then it enters the next stage;

[0011] (3) Light treatment stage:

[0012] It is placed in the outdoor natural light period within a day - night cycle (24 hours), so that pollutants are mainly removed by algal photosynthetic assimilation; the mixed liquid continuously flows under the agitation, and enriched CO₂ air is introduced into the mixed liquid for aeration to strengthen the photobiological reaction until the nitrogen and phosphorus nutrients are depleted, and then it enters the next stage;

[0013] (4) Non - light treatment stage:

[0014] The mixed liquid is placed in the non - outdoor natural light period within a day - night cycle, and pollutants are further removed through respiratory metabolism and bio - flocculation; after the mixed liquid reacts for a period of time, concentrated and regenerated sludge is injected, stirred and mixed evenly, and the material continues to flow. During the cultivation process, ambient air is introduced into the mixed liquid for aeration until bacteria represented by Zoogloea become the main body of the algal - bacterial aggregate, and then it enters the next stage;

[0015] (5) Sedimentation and separation stage:

[0016] Stop aeration, and the mixed liquid is allowed to stand for sedimentation and separation of the culture, which is divided into the upper clarified water and the lower algal - bacterial mixed sludge;

[0017] (6) Drainage and sludge discharge stage:

[0018] Drain the upper clarified water for discharge as treated effluent or reuse as makeup water for pure algal liquid culture; after draining, discharge most of the precipitated algal-bacterial mixed sludge for sludge thickening and regeneration, and use the remaining algal-bacterial mixed sludge for the next cycle;

[0019] (7) Sludge thickening and regeneration stage:

[0020] Collect the sludge (bottom sludge and algal-bacterial mixed sludge) generated in steps (1) and (6) in a thickening and regeneration pond for sludge thickening and regeneration; first, thicken the sludge by gravity thickening for 12 - 18 hours to obtain thickened sludge; discharge most of the thickened sludge for further resource recovery and utilization, aerate the remaining thickened sludge at an aeration rate of 0.2 vvm to obtain regenerated sludge, and return it to the main reactor in step (4).

[0021] The water storage and regulation treatment in step (1) refers to storing the treatment water for one day and night cycle, and conducting water quality regulation, hydrolysis acidification, partial denitrification and preliminary precipitation. During the water storage process, control the dissolved oxygen concentration at 0.5 - 1 mg / L -1 by intermittent aeration, the aeration rate does not exceed 0.005 vvm, and the SS concentration of the upper clarified wastewater should not exceed 30 mg / L -1 .

[0022] The dosage of the pure microalgal liquid in step (2) is a mass ratio of 5:1 to the dry matter of the algal-bacterial mixed sludge.

[0023] The pure algal liquid in step (2) is a pure culture solution of single and multiple microalgae without miscellaneous bacteria and algae, the algal biomass concentration is not less than 5000 mg / L -1 , the nutrient salts contained should be basically depleted during the culture, the dissolved total nitrogen concentration is not higher than 5 mg / L -1 , and the dissolved total phosphorus concentration is not higher than 0.2 mg / L -1 .

[0024] The pure algal liquid culture process in step (2) is divided into two stages: the previous eutrophic culture stage and the subsequent oligotrophic culture stage. The culture process is completely sealed, and both stages are carried out for pure culture of engineering algal strains under outdoor natural light conditions. During the culture process, introduce CO2-rich air as the carbon source, and keep the aeration rate at 0.05 vvm; in the eutrophic culture stage, adopt a semi-continuous culture mode, and replace part of the algal liquid in the algal culture reactor with fresh medium rich in nutrient elements every day, with a replacement ratio of 1 / 6 to 1 / 4, and keep the algal liquid concentration at 3000 - 4000 mg / L -1; In the nutrient-deficient culture stage, a discontinuous culture mode is adopted, and no fresh culture medium is added. While maintaining the growth of microalgae, the nutrients in the culture medium are exhausted; the algal liquid replaced in the nutrient-rich culture stage is injected into the algal culture reactor in this stage for cultivation, and it is detected once a day until the required pure algal liquid requirements are met.

[0025] In the mixture in step (2), the concentration of volatile suspended solids is 1500 - 2500 mg / L -1 。

[0026] In step (3), the CO₂-rich air is prepared by mixing CO₂ with ambient air, the volume concentration of CO₂ is 5% - 20%, and the aeration rate in step (3) is not less than 0.01 vvm.

[0027] In step (4), the concentration of volatile suspended solids (MVLSS) in the mixture is 3000 - 4500 mg / L -1 ; In step (4), the aeration rate does not exceed 0.05 vvm.

[0028] The operating time of the light treatment stage in step (3) is 10 - 14 hours; the operating time of the non-light treatment stage in step (4) is: 2 - 3 hours before sludge reflux, and the operating time after reflux does not exceed 1 hour; the operating time of step (5) does not exceed 1 hour; the operating time of step (6) is 20 - 30 minutes.

[0029] In step (7), the moisture content of the concentrated sludge should be less than 96%.

[0030] To implement the operating system for the above-mentioned efficient advanced wastewater treatment process based on algal-bacterial symbiosis, the following technical solutions are adopted:

[0031] The operating system includes a water storage and regulation module, a main treatment module, a pure algae culture module, a sludge thickening and regeneration module, and a gas supply module; the upper liquid outlet of the water storage and regulation module is connected to the liquid inlet of the main treatment module, the bottom of the water storage and regulation module is connected to the sludge thickening and regeneration module through a sludge discharge pipe, the pure algae liquid outlet of the pure algae culture module is connected to the pure algae liquid inlet of the main treatment module, aeration devices (aerators) are provided in the main treatment module, the pure algae culture module, and the sludge thickening and regeneration module, the gas supply module is connected to the aeration devices in the main treatment module, the pure algae culture module, and the sludge thickening and regeneration module, the sludge thickening and regeneration module is connected to the main treatment module through a sludge reflux pipe, the main treatment module is connected to the sludge thickening and regeneration module through an algal-bacterial mixed sludge discharge pipe, and a stirrer is also provided in the main treatment module.

[0032] The water storage and regulation module includes a main reservoir and a secondary reservoir. The secondary reservoir is connected to the main reservoir through a drain pipe, and the bottom of the secondary reservoir is at least 0.5 meters higher than the bottom of the main reservoir. The operation cycle is synchronized with the main treatment module for 24 hours to store the incoming water for 24 hours for the main treatment module. In addition to storing the incoming water, this module can also achieve functions such as water quality regulation, hydrolysis acidification, partial denitrification, and preliminary precipitation, so as to provide a wastewater clarification liquid with relatively stable water quality for the main treatment module, improving the overall treatment efficiency and shock resistance of the system. The operation of the water storage and regulation module includes a water storage stage, a precipitation stage, and a drainage and sludge discharge stage: The water storage stage is the main operation stage. During the water storage stage, water is stored while achieving water quality regulation, hydrolysis acidification, and partial denitrification of the sewage; In the precipitation stage, the stored water is separated by precipitation, and after precipitation, a relatively clear clarification liquid (upper layer water) and lower layer sludge are obtained; In the drainage and sludge discharge stage, the clarification liquid is discharged into the main treatment module, and a small amount of sludge is retained for the next cycle. The amount of sludge is determined to meet the requirements of hydrolysis acidification and denitrification in the next cycle, and most of the remaining sludge is discharged into the sludge concentration and regeneration module.

[0033] The pure algal culture module provides a pure culture solution of high-concentration engineering algal strains for the main treatment module, adjusts the community structure in the main treatment module to be mainly microalgae, and is a sealed photobioreactor. The pure algal solution provided to the main treatment module not only requires a high algal concentration but also requires minimizing the return of nitrogen and phosphorus to the main treatment reactor. Therefore, the pure algal culture module is divided into two stages: eutrophic culture and oligotrophic culture. Generally, the same algal culture reactor is used in both stages for the pure culture of engineering algal strains under outdoor natural light conditions. During the culture process, air enriched with CO2 is aerated to serve as a carbon source and for agitation. The difference between the two stages is that the eutrophic culture stage comes first and is a semi-continuous culture mode. Fresh medium rich in nitrogen and phosphorus nutrients is added every day to promote the growth of microalgae and maintain a high algal solution concentration; The oligotrophic culture stage is a discontinuous culture mode. No fresh medium is added, and while maintaining the growth of microalgae, the nitrogen and phosphorus nutrients in the medium are depleted.

[0034] The main equipment of the sludge thickening and regeneration module is the thickening and regeneration pond, which is used to thicken the sludge discharged from the main treatment module and the water storage and regulation module, and regenerate and reuse part of the sludge. The thickening and regeneration pond is a construction unit for sludge thickening and regeneration, and its designed volume and surface load can be analogized with those of the sludge thickening pond for municipal wastewater treatment. The volume of the thickened sludge is reduced, which is conducive to transportation and utilization. For the sludge regenerated by activation, the algal cells are basically destroyed, and the algal biomass and adsorbed organic matter are stably transformed. During the endogenous respiration stage of bacteria, the adsorption and precipitation separation ability is better than that of general activated sludge. Adding it to the main treatment reactor can quickly adjust the algal-bacterial community structure and strengthen the sludge-water separation ability. The operation of the sludge thickening and regeneration module includes the sludge inlet stage, the drainage and sludge discharge stage, the thickening stage, the regeneration stage, the reflux stage and the idle stage. In these six stages, the sludge discharged from the water storage and regulation module and the algal-bacterial mixed sludge discharged from the main treatment module are received respectively, the sludge is thickened by gravity, the supernatant is refluxed to the main treatment module, most of the sludge is discharged for utilization, the reactivation of the retained thickened sludge is carried out, the regenerated activated sludge is refluxed to the main treatment module, and it waits idle for the next cycle and so on.

[0035] The air supply module provides the air source required for aeration to the other four modules. This module consists of a blower, a gas supply pipeline, an aeration device and a gas source, and provides two gas sources including CO2-rich air and ambient air.

[0036] Compared with the existing wastewater treatment process, the present invention has the following characteristics:

[0037] (1) In order to overcome the disadvantage that general algal-bacterial symbiotic cultivation cannot have both high treatment efficiency and high separation efficiency at the same time, by adjusting the community structure of algal-bacterial aggregates during the batch operation process, a microalgae-dominated aggregate is formed in different stages of the process for efficient pollutant treatment, and a bacterium-dominated aggregate is formed for efficient precipitation separation of the algal-bacterial mixed culture.

[0038] (2) The ultra-low emissions of nitrogen and phosphorus can be achieved in the effluent, and the discharge concentration can meet the water quality requirements of Class IV water bodies in the Environmental Quality Standards for Surface Water (GB3838-2002).

[0039] (3) During the wastewater treatment process, the aeration volume and the reflux volume of sewage sludge are reduced, thus reducing the operation cost, and CO2 can be fixed to achieve carbon neutrality in the process stage.

[0040] (4) The biorefining potential of the algal-bacterial mixed sludge produced is far greater than that of general activated sludge, and it has higher economic benefits.

[0041] (5) Due to the characteristics of excessive phosphorus absorption by microalgae and non-release of phosphorus under anaerobic conditions, the concentration time of the algal-bacterial mixed sludge can be extended, and the thickening effect can be improved.

[0042] (6) Adopt modular design, where different modules perform their respective functions, and the substances between modules are all transported through pipe fittings, greatly reducing the difficulty of design, construction, maintenance and management. Moreover, the treatment capacity of each unit can be adjusted according to the working conditions at any time to maintain production under the optimal working conditions. Description of the Drawings

[0043] Figure 1 It is a schematic diagram of the operation process of the efficient advanced wastewater treatment process based on algal-bacterial symbiosis of the present invention.

[0044] Figure 2 It is a schematic diagram of the structural principle of the water storage and regulation module in the present invention.

[0045] Figure 3 It is a schematic diagram of the structural principle of the main treatment module in the present invention.

[0046] Figure 4 It is a schematic diagram of the structural principle of the pure algae cultivation module in the present invention.

[0047] Figure 5 It is a schematic diagram of the structural principle of the sludge thickening and regeneration module in the present invention.

[0048] Figure 6 It is a schematic diagram of the structural principle of the air supply module in the present invention.

[0049] Figure 7 It is a schematic diagram of the coordination of the operation cycles between different stages in the efficient advanced wastewater treatment process based on algal-bacterial symbiosis of the present invention. Detailed Embodiments

[0050] The present invention will be described in detail below in conjunction with the drawings and two non-limiting embodiments, which can enable those of ordinary skill in the art to understand the present invention more comprehensively, but the protection scope of the present invention is not limited by the embodiments.

[0051] The present invention is mainly used for the advanced treatment of the effluent from secondary biological treatment or wastewater and surface water with similar water quality, and the water quality is shown in Table 1. The treatment goal is that the effluent discharge concentration can meet the water quality requirements of Class IV water bodies in the Environmental Quality Standards for Surface Water (GB3838 - 2002). The process of the present invention is a sequential batch treatment process synchronized with the 24-hour day-night cycle. At different stages of the process, pure algal liquid, concentrated and regenerated sludge, and different aeration conditions are provided respectively, so as to quickly adjust the algal-bacterial community structure and operating environment to adapt to the requirements of efficient pollutant removal and efficient separation of mud and water respectively, thereby achieving the goal of advanced wastewater treatment and reducing energy consumption and greenhouse gas emissions.

[0052] Table 1

[0053] Water quality indicators Raw water data COD <![CDATA[≤150mg L -1 > Suspended solids <![CDATA[≤100mg L -1 > Total nitrogen (calculated as N) <![CDATA[≤75mg L -1 > Ammonia nitrogen (calculated as N) <![CDATA[≤30mg L -1 > Total phosphorus (calculated as P) <![CDATA[≤5mg L -1 > pH 6-9

[0054] The operating system of the present invention has five relatively independent functional modules, and an efficient advanced wastewater treatment process based on algal-bacterial symbiosis is realized through these five modules. As Figure 1 shown, the operating system includes a water storage and regulation module, a pure algae culture module, a main treatment module, a sludge thickening and regeneration module, and an air supply module. Each module is interconnected through pipe fittings to achieve the mutual supply of gas and liquid. The raw water directly enters the water storage and regulation module. The upper liquid outlet of the water storage and regulation module is connected to the liquid inlet of the main treatment module, and the bottom of the water storage and regulation module is connected to the sludge thickening and regeneration module through a sludge discharge pipe. The pure algae liquid outlet of the pure algae culture module is connected to the pure algae liquid inlet of the main treatment module. Aeration devices (aerators) are provided in the main treatment module, the pure algae culture module, and the sludge thickening and regeneration module, and the air supply module is connected to the aeration devices in the main treatment module, the pure algae culture module, and the sludge thickening and regeneration module. The sludge thickening and regeneration module is connected to the main treatment module through a sludge return pipe, and a stirrer is also provided in the main treatment module. The main treatment module is connected to the sludge thickening and regeneration module through an algal-bacterial mixed sludge discharge pipe.

[0055] The structure and operation process of each module are described in detail below

[0056] I. Water storage and regulation module, see Figure 2

[0057] The water storage and regulation module is set up to store and regulate the wastewater (raw water) to be advanced treated to adapt to the intermittent water inlet mode of the process batch treatment, and it also has the function of improving the shock resistance of the system. In addition to storing the water volume for one cycle (24 hours) for the main treatment module, the water storage and regulation module also needs to achieve water quality regulation, hydrolysis acidification, partial denitrification, and preliminary precipitation. The water quality provided for the main treatment module should be relatively clear, and the SS concentration should not exceed 30 mg / L -1 . This module includes a main reservoir and a secondary reservoir, and the secondary reservoir is connected to the main reservoir through a drain pipe. The main reservoir is the main structure for water volume regulation, and it is equipped with a stirrer and aeration facilities for promoting the circulation of wastewater in the reservoir and intermittent aeration. The volume of the pool is determined by multiplying the average daily water inflow by the variation coefficient (optional 1.2). The secondary reservoir is a structure for temporarily storing water when the main reservoir is precipitating and draining sludge, and it is not equipped with stirrers, aeration and other facilities. Its volume is determined according to 1 / 20 - 1 / 40 of the main reservoir. The bottom of the secondary reservoir is at least 0.5 meters higher than the bottom of the main reservoir. The upper layer of water after precipitation in the main reservoir is discharged into the main treatment module, and part of the sludge is discharged into the sludge thickening and regeneration module after drainage.

[0058] The specific treatment process of this module can be subdivided into three different stages:

[0059] (1) Water storage stage

[0060] This stage is the start stage of a cycle. It is initiated after the drainage and sludge discharge in the previous cycle. The raw water stored in the secondary reservoir is emptied into the main reservoir and no longer receives raw water. Instead, the raw water is injected into the main reservoir. The injection method is submerged injection, and stirring is carried out in the main reservoir. The water storage time is 23 hours, and the dissolved oxygen concentration is controlled at 0.5 - 1 mg / L through intermittent aeration. -1 .

[0061] (2) Sedimentation stage

[0062] In this stage, the main reservoir stops storing water and the secondary reservoir starts to store water instead. Stirring and aeration in the main reservoir stop, and sedimentation separation is carried out. The operation time is 30 - 40 minutes.

[0063] (3) Drainage and sludge discharge stage

[0064] In this stage, the upper layer of water after sedimentation in the main reservoir is discharged into the main treatment reactor. After drainage, part of the sludge is discharged into the concentration and regeneration pool of the sludge concentration and regeneration module, and the remaining sludge volume is determined to meet the requirements of hydrolysis acidification and denitrification in the next cycle. This stage still stores water in the secondary reservoir, and the operation time is 20 - 30 minutes.

[0065] II. Main treatment module, see Figure 3

[0066] The main treatment module is the core module of the entire wastewater treatment of the present invention. The main body of the main treatment module is the main treatment reactor, and a raceway pond reactor commonly used in microalgae cultivation is preferably used. This type of reactor is in the shape of a circular raceway, with semicircular arcs at both ends of the bend. The baffle wall divides the pool into two parts. There is a stirrer to drive the flow of the mixed liquid and an aeration device. The operation mode of this module is batchwise, and each operation cycle is 24 hours, synchronized with the day-night cycle. The specific treatment process of the main treatment module can be further divided into five different stages.

[0067] (1) Inlet stage

[0068] At the beginning of this stage, the clarified liquid discharged from the water storage and regulation module and the pure algae liquid cultured in the pure algae cultivation module are simultaneously injected into the main treatment module (main treatment reactor), and are mixed evenly with the remaining algal and bacterial mixed sludge retained in the previous cycle under the push of the stirrer, and a new algal and bacterial composite community is formed through adaptation. Air aeration is adopted in this stage, and the aeration rate does not exceed 0.005 vvm. The unit vvm of the aeration speed refers to the ratio of the aeration volume per minute to the working volume of the culture solution. The dosage of the pure microalgae liquid can be adjusted according to water quality, working conditions, etc., and it is advisable that the mass ratio of the pure microalgae liquid to the dry matter of the algal and bacterial mixed sludge is 5:1. The concentration of volatile suspended solids (MVLSS) in the mixed liquid is 1500 - 2500 mg / L -1 . The operation time is determined by the time occupied by other stages to make up a full cycle of 24 hours.

[0069] The purpose of this stage is to enable the remaining algal-bacterial mixed sludge and engineered algal strains to adapt to the clarified wastewater to be treated and mix well with it, forming a new algal-bacterial composite aggregate with engineered pure algae as the dominant population, thereby preparing for enhanced wastewater treatment.

[0070] (2) Illumination treatment stage

[0071] This stage needs to be placed in an outdoor natural light period in a day-night cycle. The mixed liquor continuously flows under the push of a stirrer, and during the cultivation process, air rich in CO2 is introduced into the mixed liquor. The aeration rate is not less than 0.01 vvm, and the operation time is determined by the duration of the light in the day-night cycle, generally 10 - 14 hours.

[0072] This stage is the key stage of advanced wastewater treatment. The algal biomass is higher than the bacterial biomass, and the engineered algal strains are the dominant population. Moreover, being under the conditions of light and introducing air rich in CO2 is more conducive to the growth of microalgae. Therefore, microalgae, especially the engineered algal strains as the dominant species of the community, have a better nitrogen and phosphorus removal effect than the activated sludge method, and the organic matter removal effect is also enhanced.

[0073] (3) Non-illumination treatment stage

[0074] At the beginning of this stage, the mixed liquor continues to react in the main treatment reactor for a period of time. The concentrated regenerated sludge in the sludge concentration and regeneration module is refluxed into the main treatment reactor through the sludge reflux pipe and mixed evenly with the mixed liquor under the push of a stirrer. The mixed liquor's volatile suspended solid concentration (MVLSS) is increased to 3000 - 4500 mg / L -1 . The mixed liquor continuously flows under the push of a stirrer, and during the cultivation process, air is introduced into the mixed liquor. The aeration rate does not exceed 0.05 vvm. The operation time before sludge reflux is 2 - 3 hours, and the operation time after reflux does not exceed 1 hour. The specific duration is determined by process optimization.

[0075] The refluxed concentrated regenerated sludge injected in this stage refers to the sludge treated by the sludge concentration and regeneration module. Its water content is greatly reduced, the algal cells are basically destroyed, the algal biomass and adsorbed organic matter are stably transformed, and the bacteria grow to the endogenous respiration stage. Due to the introduction of concentrated regenerated sludge, while further removing organic matter, nitrogen and phosphorus, bacteria represented by Zoogloea in the community of the newly formed algal-bacterial aggregate are dominant, thus preparing for sedimentation separation.

[0076] (4) Sedimentation separation stage

[0077] In this stage, the main treatment reactor stops aeration, and the mixed liquor is left standing for sedimentation separation. The operation time does not exceed 1 hour, and the specific duration is determined by process optimization.

[0078] During the non-illumination treatment stage, bacteria represented by Zoogloea have become dominant in the algal-bacterial aggregate community, and the bacteria are in the endogenous respiration stage, making it easy to form a large amount of biological flocs. Therefore, the biological flocculation ability is greatly enhanced during this stage, the separation effect of the algal-bacterial mixed culture is strengthened, and the removal and precipitation abilities of organic matter and phosphorus are also enhanced, improving the water quality of the upper clarified water.

[0079] (5) Drainage and sludge discharge stage

[0080] The upper clarified water is discharged through a decanter. Most of it is discharged as treated effluent, and a small part is reused as the water for preparing the culture medium in the pure algae culture module. After drainage, the sludge volume that meets the dry matter mass ratio of the algal sludge mixture and the volatile suspended solid concentration of pure microalgae required for the next cycle's influent stage is retained, and most of the remaining algal-bacterial mixed sludge is discharged into the sludge thickening and regeneration module. The operation time is 20 - 30 minutes, and the specific duration is determined by process optimization.

[0081] This stage is the final link of wastewater treatment, and the effluent discharge concentration can meet the water quality requirements of Class IV water bodies in the Environmental Quality Standards for Surface Water (GB3838 - 2002).

[0082] III. Pure algae culture module, see Figure 4

[0083] The pure algae culture module is an auxiliary module set up to provide a pure culture solution of high-concentration engineering algal strains for the main treatment reactor. The required algal biomass concentration of the pure algal solution it provides should not be lower than 5000 mg / L -1 , and the nutrient salts contained should be basically depleted during the culture, and the dissolved total nitrogen concentration should not be higher than 5 mg / L -1 , and the dissolved total phosphorus concentration should not be higher than 0.2 mg / L -1 . Moreover, to ensure pure algae culture, no miscellaneous bacteria or algae should be mixed in during the culture process.

[0084] To meet the above requirements, the microalgae culture process is divided into two operating stages: the eutrophic culture stage and the oligotrophic culture stage. Generally, the same algal culture reactor is used in both stages, usually a columnar, tubular, or flat-plate photobioreactor commonly used in the microalgae culture process. In addition to strict sealing, there are other measures to prevent the mixing of miscellaneous bacteria and algae. Both stages are for the pure culture of engineering algal strains under outdoor natural light conditions. During the culture process, air rich in CO2 is introduced as the carbon source, and the aeration rate is maintained at 0.05 vvm. The difference between the two stages is as follows:

[0085] (1) Eutrophic culture stage

[0086] This stage comes first and adopts a semi - continuous cultivation mode with the aim of maximizing microalgae growth. Every day, a part of the algal liquid is replaced from the algal cultivation reactor with fresh culture medium rich in nutrient elements. The replacement ratio is determined by the process optimization results, generally ranging from 1 / 6 to 1 / 4, and the algal liquid concentration is maintained at 3000 - 4000 mg / L. -1 .

[0087] The culture medium is prepared by adding nutrient salts to the treated effluent from the main treatment stage and then sterilizing it. It can refer to the common BG11, SE and other microalgae culture medium components in this field, and the nutrient salt ratio is appropriately adjusted for preparation. The nitrogen - phosphorus ratio is preferably maintained at 8:1.

[0088] The replacement ratio is the ratio of the volume of the algal liquid replaced or the fresh culture medium added from the algal cultivation reactor every day to the working volume of the reactor.

[0089] (2) Nutrient - deficient cultivation stage

[0090] This stage comes later and adopts a discontinuous cultivation mode. No fresh culture medium is added. While maintaining microalgae growth, the nutrients in the culture medium are exhausted. The algal liquid replaced in the eutrophic cultivation stage is injected into the algal cultivation reactor of this stage for cultivation, and it is detected once a day. When the algal liquid meets the requirements of the pure algal liquid needed by the main treatment reactor, the cultivation ends when the water inlet stage of the main treatment stage is started, and it is transported to the main processor.

[0091] IV. Sludge thickening and regeneration module, see Figure 5

[0092] The sludge thickening and regeneration module is set up to thicken the sludge discharged from the main treatment module and the water storage and regulation module, and to recycle and reuse part of the sludge after re - activation. The water content of the thickened sludge is < 96%; there are basically no intact algal cells in the re - activated sludge, the algal biomass and adsorbed organic matter are stably transformed, the organic matter content accounts for < 20% of the dry matter content, and the bacteria are in the endogenous respiration stage, making the adsorption and flocculation ability of the sludge higher than that of ordinary activated sludge. The main facility of this module is a thickening and regeneration pond, and its designed volume and surface load can be analogized by referring to the sludge thickening pond for municipal wastewater treatment.

[0093] The specific treatment process of this module can be subdivided into six different stages:

[0094] (1) Sludge inlet stage

[0095] The thickening and regeneration pond successively receives the algal - bacteria mixed sludge discharged from the main treatment reactor and the sludge discharged from the water storage and regulation system. The sludge inlet time is consistent with the sludge discharge time of the main treatment reactor and the sludge discharge time of the water storage and regulation system, lasting for 40 - 60 minutes.

[0096] (2) Thickening stage

[0097] The algal-bacterial mixed sludge discharged from the main treatment reactor and the sludge discharged from the water storage and regulation module are injected into the thickening and regeneration pond for gravity thickening, and the operation time is 12 - 18 hours.

[0098] (3) Drainage and sludge discharge stage

[0099] After thickening, the supernatant is refluxed to the main reservoir. Most of the thickened algal-bacterial biomass is discharged in the form of sludge for further biorefining and utilization. The remaining part of the sludge remains in the thickening and regeneration pond for 20 - 30 minutes. The amount of retained sludge should meet the required amount of refluxed and regenerated sludge for the main treatment system, generally accounting for 10% - 25% of the total thickened sludge.

[0100] (4) Regeneration stage

[0101] The retained thickened sludge is aerated with air, and the aeration rate is maintained at 0.2 vvm. The end time of this stage is determined by the end time of the light treatment stage of the main treatment module, and the operation time is generally 3 - 6 hours. After this stage, the algal cells in the thickened sludge are basically dissolved and destroyed, the algal biomass and adsorbed organic matter are stably transformed, the bacteria in the sludge grow and develop to the endogenous respiration stage, and the external manifestation is that the total amount of dry matter in the sludge decreases, and the adsorption capacity and sedimentation performance are greatly enhanced.

[0102] (5) Reflux stage

[0103] The regenerated sludge is refluxed to the main treatment reactor during the non-light treatment stage of the main treatment module to adjust the algal-bacterial community structure in the main treatment reactor, strengthen the bioflocculation ability, and promote the separation of mud and water. This stage lasts for 10 - 15 minutes.

[0104] (6) Idle stage

[0105] The thickening and regeneration pond is in the idle stage between the discharge of the regenerated sludge and the reception of the sludge in the next cycle.

[0106] V. Air supply module, see Figure 6

[0107] The air supply module is to provide the gas required for aeration to the other four modules. The air supply module consists of a blower, an air supply pipeline, an aeration device and an air source, providing two air sources, namely CO₂-rich air and air required for forced aeration. The air is the ambient air provided by the blower. The CO₂-rich air can be prepared by mixing CO₂ with ambient air, and the volume concentration of CO₂ is 5% - 20%. Industrial waste gas containing CO₂ should be preferentially used as the CO₂ air source.

[0108] In the present invention, the operation cycle between each stage can be carried out according to Figure 7Coordinate as shown. It should be particularly emphasized that the operation cycle of the main processing module is set based on the strongest outdoor natural light period in a day-night cycle during the light treatment stage; the operation cycles of other modules are set to meet the operation requirements of the main processing module.

[0109] The following gives specific embodiments

[0110] Embodiment 1

[0111] This embodiment is a small-scale indoor simulation verification experiment carried out in the laboratory, with a treatment capacity of 120 L / d -1 , and is implemented according to the technical solution described in the specific implementation manner. The methods and materials used include:

[0112] The raw water used is artificial simulated wastewater prepared in the laboratory, and the water quality is shown in Table 2.

[0113] Table 2

[0114] Water quality indicators Raw water data COD <![CDATA[95mg L -1 > Suspended solids <![CDATA[85mg L -1 > Total nitrogen (calculated as N) <![CDATA[70mg L -1 > Ammonia nitrogen (calculated as N) <![CDATA[15mg L -1 > Total phosphorus (calculated as P) <![CDATA[4.5mg L -1 > pH 6.9

[0115] The indoor environment is: temperature 25°C; light cycle is 12 h:12 h for day:night; daytime light intensity is maintained at 10000 Lux.

[0116] The main treatment reactor, main reservoir, algae culture reactor, and sludge thickening and regeneration tank used are all unified columnar photobioreactors. The secondary reservoir uses a beaker, and the CO2 gas source is provided by an industrial CO2 gas cylinder.

[0117] The operation times of the water inlet stage, light treatment stage, non-light treatment stage, sedimentation separation stage, and drainage and sludge discharge stage of the main processing module are set to 8 hours, 12 hours, 3 hours, 0.5 hours, and 0.5 hours respectively. The air aeration rate during the water inlet stage is 0.002 vvm, the dry matter mass ratio of the added pure micro-liquid to the algae-bacteria mixed sludge is 5:1, and the concentration of volatile suspended solids in the mixed liquid is maintained at about 2000 mg / L -1 around. The CO2-rich air aeration rate during the light treatment stage is 0.01 vvm. The air aeration rate during the non-light treatment stage is 0.05 vvm, and the concentration of volatile suspended solids in the mixed liquid is maintained at about 3000 mg / L -1 around.

[0118] The operation times of the water storage stage, sedimentation stage, and drainage and sludge discharge stage of the water storage and regulation module are set to 23 hours, 35 minutes, and 25 minutes respectively. The aeration rate during intermittent aeration in the water storage stage is 0.01 vvm.

[0119] The algal biomass concentration of the pure algal liquid provided by the pure algae culture module can reach 6500 mg / L -1 , and the total dissolved nitrogen concentration is less than 4 mg / L -1, the total dissolved phosphorus concentration is less than 0.2 mg / L -1 . The enhanced engineered algal strain used is Chlorella SDJZ-A14. This is a denitrification and phosphorus removal enhanced mutant strain obtained by directional screening from a wild strain of Chlorella SDJZ-A with high growth rate and high CO2 tolerance after atmospheric and room temperature plasma mutagenesis. It can develop into a stable algal-bacterial aggregate with bacteria in the activated sludge. The aeration rate of CO2-rich air is 0.05 vvm. The medium used is the improved SE medium with adjusted nitrogen and phosphorus contents. The components of 1 L of this medium are shown in Table 3:

[0120] Table 3

[0121]

[0122]

[0123] The A5 solution used in the improved SE medium is characterized in that the components of 1 L of the medium are shown in Table 4:

[0124] Table 4

[0125]

[0126] The soil filtrate used in the improved SE medium is obtained by taking 200 g of unfertilized garden soil and placing it in a beaker or Erlenmeyer flask, adding 1000 ml of distilled water, sealing the bottle mouth with a breathable plug, boiling in a water bath for 3 hours, cooling, and precipitating for 24 hours. This process is carried out continuously 3 times, and then filtered. The supernatant is taken and sterilized in an autoclave for later use.

[0127] The operating times of the sludge concentration and regeneration module in the sludge inlet stage, concentration stage, drainage and sludge discharge stage, regeneration stage, reflux stage, and idle stage are set to 1 hour, 15.5 hours, 0.5 hour, 5 hours, 0.5 hour, and 1.5 hours respectively. The sludge retained for regeneration accounts for 18% of the total concentrated sludge volume.

[0128] Other methods and materials are conventional methods and conventional materials in this field without special instructions.

[0129] After the implementation of this example, the following results are obtained:

[0130] (1) The main water quality indicators of the effluent are shown in Table 6, which can meet the water quality requirements of Class IV water bodies in the "Surface Water Environment Quality Standard" (GB3838 - 2002).

[0131] Table 6

[0132] Water quality indicators Effluent data COD <![CDATA[14.5mg L -1 > Suspended solids <![CDATA[11.1mg L -1 > Total nitrogen (calculated as N) <![CDATA[1.4mg L -1 > Ammonia nitrogen (calculated as N) <![CDATA[0.2mg L -1 <!-- 10 -->]]> Total phosphorus (calculated as P) <![CDATA[0.27mg L -1 > pH 7.2

[0133] (2) The unit power consumption of the treatment process is 0.08 kW·h / m of sewage 3 .

[0134] (3) The net greenhouse gas emission equivalent is negative, which is a carbon-negative process.

[0135] Example 2

[0136] This example is a demonstration project for improving the environmental quality of surface water bodies. The implementation location is a small surface river, and the treatment capacity is 1000 - 1500 m 3 d -1 , and it is implemented according to the technical solutions described in the specific implementation manner. The methods and materials used include:

[0137] The raw water used is surface river water of inferior Class V, and the water quality is shown in Table 7.

[0138] Table 7

[0139]

[0140]

[0141] The outdoor environment is as follows: temperature 18 - 26°C; light cycle is 13h:11h for day:night; the highest daytime light intensity is 22000 Lux.

[0142] The main treatment reactor, main reservoir, and secondary reservoir used are formed by segmentally intercepting the river course of the implementation river. One more section is intercepted downstream to add an effluent tank to maintain a stable water volume in the downstream river course. A sludge thickening and regeneration pond is constructed beside the river course. The algae cultivation reactor used is a flat-panel photobioreactor with an algae species rapid proliferation device (patent number ZL201610991205X). The CO2-rich air used is the waste gas after desulfurization and denitrification from a nearby gas boiler, and there is no need to mix it with air. The CO2 volume concentration is 9% - 12%. The water flow power mainly relies on the natural slope of the river, and the power consumption is mainly used for aeration and stirring.

[0143] The operating times of the main treatment module's water inlet stage, light treatment stage, non-light treatment stage, sedimentation and separation stage, and drainage and sludge discharge stage are set to 6 hours, 13 hours, 4 hours, 0.5 hours, and 0.5 hours respectively. The air aeration rate in the water inlet stage is 0.001 vvm, the dry matter mass ratio of the added pure micro-liquid to the algae-bacteria mixed sludge is 3:1, and the concentration of volatile suspended solids in the mixed liquid is maintained at about 1800 mg L -1 . The CO2-rich air aeration rate in the light treatment stage is 0.005 vvm. The air aeration rate in the non-light treatment stage is 0.03 vvm, and the concentration of volatile suspended solids in the mixed liquid is maintained at about 2500 mg L -1 .

[0144] The operating times of the water storage and regulation module during the water storage stage, sedimentation stage, and drainage and sludge discharge stage are set at 23 hours, 40 minutes, and 20 minutes respectively. During the intermittent aeration in the water storage stage, the aeration rate is 0.01 vvm.

[0145] The algal biomass concentration of the pure algal solution provided by the pure algal culture module can reach 7000 mg / L -1 , and the dissolved total nitrogen concentration is less than 3.5 mg / L -1 , and the dissolved total phosphorus concentration is less than 0.2 mg / L -1 . The enhanced engineering algal strains used are Chlorella SDJZ-A14 and Scenedesmus SDJZ-B21. The two algal strains are co-cultured, accounting for 60 - 65% and 35% - 40% of the biomass of the pure algal solution respectively. Chlorella SDJZ-A14 is the same as in Example 1. Scenedesmus SDJZ-B21 is a nitrogen and phosphorus removal enhanced mutant strain obtained by directional screening after atmospheric room temperature plasma mutagenesis of a Scenedesmus SDJZ-B wild strain with high growth rate and high CO2 tolerance. It can develop into a stable algal-bacterial aggregate with bacteria in the activated sludge. The aeration rate of the CO2-rich air is 0.05 vvm. The culture medium used is the improved SE medium with adjusted nitrogen and phosphorus contents, the same as in Example 1.

[0146] The operating times of the sludge thickening and regeneration module during the sludge inlet stage, thickening stage, drainage and sludge discharge stage, regeneration stage, reflux stage, and idle stage are set at 1 hour, 15 hours, 0.5 hour, 6 hours, 0.5 hour, and 1 hour respectively. The sludge retained for regeneration accounts for 14% of the total thickened sludge volume.

[0147] Other methods and materials are conventional methods and conventional materials in the art unless otherwise specified.

[0148] After implementing this example, the following results are obtained:

[0149] (1) The main water quality indicators of the effluent are shown in Table 8, which can meet the water quality requirements of Class IV water bodies in the Environmental Quality Standards for Surface Water (GB3838 - 2002) and can be directly returned.

[0150] Table 8

[0151]

[0152]

[0153] (2) The unit power consumption during the treatment process is less than 0.03 kW·h / m³ of sewage 3 .

[0154] (3) The net greenhouse gas emission equivalent is negative, and it is a carbon-negative process.

Claims

1. An efficient advanced wastewater treatment process based on algae-bacteria symbiosis, characterized in that This process is a sequential batch process synchronized with the day-night cycle. At different stages of the process, pure algal solution, concentrated regenerated sludge, and different aeration conditions are provided respectively, so as to rapidly adjust the algal-bacterial community structure and operating environment to meet the requirements of efficient pollutant removal and efficient separation of mud and water respectively; Specifically, it includes the following steps: (1) Water storage and regulation stage: The continuously incoming influent is stored for 24 hours, while achieving water quality regulation, hydrolysis acidification, partial denitrification, and preliminary precipitation. After precipitation, the upper clarified liquid and bottom sludge are obtained. Most of the bottom sludge is discharged, and the remaining sludge is used for the next cycle; (2) Influent stage: The upper clarified liquid described in step (1) and the pure algal solution are simultaneously injected into the main reactor, and stirred evenly with the remaining algal-bacterial mixed sludge retained in the main reactor in the previous cycle to form a mixed liquid. Ambient air is introduced into the mixed liquid for aeration until an algal-bacterial aggregate with microalgae as the main body of the community structure is formed, and then it enters the next stage; (3) Light treatment stage: It is placed in an outdoor natural light period within a day-night cycle, so that pollutants are mainly removed by algal photosynthetic assimilation; the mixed liquid continuously flows under the agitation, and rich CO2 air is introduced into the mixed liquid for aeration to strengthen the photobiological reaction until the nitrogen and phosphorus nutrients are completely depleted, and then it enters the next stage; (4) Non-light treatment stage: After the mixed liquid continues to react for a period of time, concentrated regenerated sludge is injected, stirred and mixed evenly, and the material continues to flow. During the cultivation process, ambient air is introduced into the mixed liquid for aeration until bacteria represented by Zoogloea become the main body of the algal-bacterial aggregate, and then it enters the next stage; (5) Sedimentation and separation stage: Stop aeration, and let the mixed liquid stand for sedimentation and separation of the culture, which is divided into the upper clarified water and the lower algal-bacterial mixed sludge; (6) Drainage and sludge discharge stage: Discharge the upper clarified water as treated effluent for discharge or reuse as the preparation water for pure algal liquid cultivation; after drainage, most of the precipitated algal-bacterial mixed sludge is discharged for sludge concentration and regeneration, and the remaining algal-bacterial mixed sludge is used for the next cycle; (7) Sludge concentration and regeneration stage: The bottom sludge generated in step (1) and the algal-bacterial mixed sludge generated in step (6) are concentrated in a concentrated regeneration pool for sludge concentration and regeneration; first, the sludge is concentrated by gravity concentration for 12 - 18 hours to obtain concentrated sludge; most of the concentrated sludge is discharged for further resource recovery and utilization, and the remaining concentrated sludge is aerated and regenerated. The aeration rate is maintained at 0.2 vvm to obtain regenerated sludge, which is refluxed to the main reactor in step (4); In step (2), the pure algal solution is a pure culture solution of single or multiple microalgae without miscellaneous bacteria and algae, and the algal biomass concentration is not less than 5000 mg﹒L -1 , and the nutrient salts contained should be basically exhausted during cultivation, and the dissolved total nitrogen concentration is not higher than 5 mg﹒L -1 , and the dissolved total phosphorus concentration is not higher than 0.2 mg﹒L -1 ; In the pure algal liquid culture process in step (2), it is divided into two stages: the previous eutrophic culture stage and the subsequent oligotrophic culture stage. The culture process is completely sealed. The pure culture of the engineered algal strain is carried out under natural outdoor light conditions in both stages. During the culture process, CO₂-rich air is introduced as a carbon source, and the aeration rate is maintained at 0.05 vvm. In the eutrophic culture stage, a semi-continuous culture mode is adopted. Every day, a part of the algal liquid is replaced from the algal culture reactor with fresh medium rich in nutrient elements, and the replacement ratio is 1 / 6 to 1 / 4, and the algal liquid concentration is maintained at 3000-4000 mg﹒L -1 ; In the oligotrophic culture stage, a discontinuous culture mode is adopted. No fresh medium is added. While maintaining the growth of microalgae, the nutrients in the medium are exhausted. The algal liquid replaced in the eutrophic culture stage is injected into the algal culture reactor in this stage to start the culture, and it is detected once a day until the required pure algal liquid requirements are met.

2. The high-efficiency advanced wastewater treatment process based on algal-bacterial symbiosis according to claim 1, characterized in that, During the water storage process in step (1), the dissolved oxygen concentration is controlled at 0.5-1 mg·L -1 by intermittent aeration, the aeration rate does not exceed 0.005 vvm, and the SS concentration of the upper clarified wastewater should not exceed 30 mg·L -1 .

3. The high-efficiency advanced wastewater treatment process based on algal-bacterial symbiosis according to claim 1, characterized in that, The concentration of volatile suspended solids in the mixed solution in step (2) is 1500 - 2500 mg﹒L -1 .

4. The high-efficiency advanced wastewater treatment process based on algal-bacterial symbiosis according to claim 1, characterized in that, The rich CO2 air in step (3) is prepared by mixing CO2 with ambient air, and the volume concentration of CO2 is 5% - 20%. The aeration rate in step (3) is not less than 0.01 vvm.

5. The high-efficiency advanced wastewater treatment process based on algae-bacteria symbiosis according to claim 1 is characterized in that, The volatile suspended solid concentration of the mixed liquid in step (4) is 3000-4500 mg﹒L -1 ; The aeration rate in step (4) does not exceed 0.05 vvm.

6. The high-efficiency advanced wastewater treatment process based on algal-bacterial symbiosis according to claim 1, characterized in that, The operating time of the light treatment stage in step (3) is 10 - 14 hours; the operating time of the non-light treatment stage in step (4) is: 2 - 3 hours before sludge reflux, and no more than 1 hour after reflux; the operating time of step (5) is no more than 1 hour; the operating time of step (6) is 20 - 30 minutes.

7. A system for implementing the high-efficiency advanced wastewater treatment process based on algal-bacterial symbiosis according to claim 1, characterized in that, Adopting a modular assembly design, each module operates relatively independently, including a water storage and regulation module, a main treatment module, a pure algae cultivation module, a sludge thickening and regeneration module, and an air supply module; the upper liquid outlet of the water storage and regulation module is connected to the liquid inlet of the main treatment module, the bottom of the water storage and regulation module is connected to the sludge thickening and regeneration module through a sludge discharge pipe, the pure algae liquid outlet of the pure algae cultivation module is connected to the pure algae liquid inlet of the main treatment module, aeration devices are provided in the main treatment module, the pure algae cultivation module, and the sludge thickening and regeneration module, the air supply module is connected to the aeration devices in the main treatment module, the pure algae cultivation module, and the sludge thickening and regeneration module, the sludge thickening and regeneration module is connected to the main treatment module through a sludge return pipe, the main treatment module is connected to the sludge thickening and regeneration module through an algae-bacteria mixed sludge discharge pipe, and a stirrer is also provided in the main treatment module.

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