Sewage treatment method for fully stirring and degrading organic matters based on activated sludge

Abstract

The invention relates to the technical field of sewage treatment, in particular to a sewage treatment method for fully stirring and degrading organic matters based on activated sludge, which comprises the following steps: sequentially introducing to-be-treated sewage into a grating tank and a grit chamber, respectively removing large floating matters, suspended matters and inorganic sand grains, introducing the pretreated sewage into an improved activated sludge reaction tank, adding a compound microbial agent and a modified adsorption carrier into the reaction tank, and treating by adopting a sectional stirring and aeration cooperative control mode; the interior of the single improved activated sludge reaction tank is divided into the anaerobic stirring area, the anoxic stirring area and the aerobic stirring area through the partition plates, independent tank bodies such as an anaerobic tank and an anoxic tank do not need to be additionally arranged, the engineering investment cost is greatly reduced, meanwhile, the technological process is simplified, and the operation complexity is reduced; the sewage naturally flows through the water through holes in the bottoms of the partition plates in all the areas, sewage lifting equipment does not need to be additionally arranged, and energy consumption and operation and maintenance cost are further reduced.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and specifically to a wastewater treatment method based on the thorough agitation and degradation of organic matter by activated sludge. Background Technology

[0002] With the rapid development of society and economy, the discharge of urban domestic sewage and industrial wastewater is increasing day by day, and the problem of eutrophication of water bodies is becoming more and more serious. Countries are also constantly raising the standards for nitrogen and phosphorus discharge of sewage treatment plant effluent. Traditional sewage treatment methods based on the full mixing and degradation of organic matter by activated sludge are one of the most widely used sewage treatment technologies. Their core design goal is to remove carbon source pollutants (characterized by BOD / COD) and suspended solids (SS) from sewage. In the actual application of this technology, by fully mixing activated sludge and sewage in the aeration tank, the metabolic action of microorganisms in the activated sludge can effectively decompose organic pollutants in sewage into harmless carbon dioxide and water, and achieve the separation and removal of suspended solids through sedimentation. However, the traditional activated sludge process has significant technical drawbacks: its ability to remove nutrients such as nitrogen and phosphorus from wastewater is extremely limited. This is because the process environment of the traditional activated sludge process is mainly aerobic, while nitrogen removal requires two processes: nitrification (converting ammonia nitrogen into nitrate nitrogen under aerobic conditions) and denitrification (converting nitrate nitrogen into nitrogen gas under anoxic conditions). Phosphorus removal requires polyphosphate-accumulating bacteria to release phosphorus under anaerobic conditions and to absorb excess phosphorus under aerobic conditions. The single aerobic stirring environment of the traditional activated sludge process cannot meet the process requirements for nitrogen and phosphorus removal.

[0003] To meet increasingly stringent nitrogen and phosphorus emission standards, existing technologies typically require the addition of anaerobic and anoxic tanks, along with corresponding mixing, aeration, and reflux facilities, to the traditional activated sludge process, creating complex processes such as A / O (anaerobic-aerobic) and A² / O (anaerobic-anoxic-aerobic). This modification not only significantly increases the initial investment cost of wastewater treatment projects (including tank construction, equipment procurement and installation), but also increases the complexity of process operation. For example, it requires precise control of multiple process parameters, such as the hydraulic retention time ratio, dissolved oxygen concentration, and sludge recirculation ratio between the anaerobic, anoxic, and aerobic tanks. Process control is extremely difficult, and fluctuations in any parameter can lead to unstable nitrogen and phosphorus removal, or even failure to meet emission standards. Furthermore, the additional tanks and equipment increase the energy consumption and maintenance costs of the wastewater treatment plant. Therefore, developing a wastewater treatment method that can simultaneously achieve efficient nitrogen and phosphorus removal without the need for additional large tanks and supporting facilities, based on the thorough agitation and degradation of organic matter by activated sludge, has become a key issue that urgently needs to be addressed in the current wastewater treatment technology field. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a wastewater treatment method based on the thorough agitation and degradation of organic matter by activated sludge, which can effectively solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a wastewater treatment method based on the thorough agitation and degradation of organic matter by activated sludge, comprising the following steps: (1) Pretreatment stage: The wastewater to be treated is introduced into the grit chamber and the grit chamber in sequence to remove large floating objects, suspended solids and inorganic sand particles respectively; (2) Modified activated sludge reaction stage: The pretreated wastewater is introduced into the modified activated sludge reaction tank, and compound microbial agents and modified adsorption carriers are added to the reaction tank. The treatment is carried out by segmented stirring and aeration synergistic control. The modified activated sludge reaction tank is a single tank. The tank is divided into anaerobic stirring zone, anoxic stirring zone and aerobic stirring zone by partitions. Water passage holes are provided at the bottom of the partitions. Anaerobic mixing zone: Dissolved oxygen concentration ≤0.2mg / L, mixing rate 30-50r / min, hydraulic retention time 1.5-2.5h; Anoxic mixing zone: control dissolved oxygen concentration at 0.2-0.5 mg / L, stirring rate at 40-60 r / min, hydraulic retention time at 2-3 h, and return the mixture from the aerobic mixing zone to this zone at a reflux ratio of 100%-200%. Aerobic mixing zone: Dissolved oxygen concentration controlled at 2-4 mg / L, aeration intensity at 1.5-2.5 m / s. 3 / (m 2 h), stirring rate 50-70 r / min, hydraulic retention time 4-6 h; (3) Sedimentation and separation stage: The effluent from the modified activated sludge reactor is introduced into the secondary sedimentation tank and allowed to settle for 2-3 hours to achieve solid-liquid separation. The supernatant is the effluent that meets the standards. (4) Sludge treatment and resource recovery stage: A portion of the sludge settled at the bottom of the secondary sedimentation tank is returned to the anaerobic mixing zone at a return ratio of 50%-100%. The remaining sludge is concentrated and dewatered, and the sludge filtrate produced by dewatering is returned to the anaerobic mixing zone. Furthermore, the composite microbial agent is prepared by mixing polyphosphate-accumulating bacteria, denitrifying bacteria, nitrifying bacteria, and aerobic heterotrophic bacteria in a mass ratio of 1:(1.2-1.5):(0.8-1.0):(2.0-2.5); wherein the polyphosphate-accumulating bacteria are Pseudomonas strains, the denitrifying bacteria are Alcaligenes strains, the nitrifying bacteria are a mixture of Nitrosomonas and Nitrobacter strains in a mass ratio of 1:1, and the aerobic heterotrophic bacteria are Bacillus strains. Furthermore, the modified adsorbent carrier is modified diatomaceous earth, and its preparation method includes: ① Pulverize diatomaceous earth to 100-200 mesh, add 5%-10% hydrochloric acid solution, stir and react at 80-90℃ for 2-3 hours, wash with deionized water until neutral, and dry at 105-110℃. ② Add a 3%-5% ferric chloride solution to the dried diatomaceous earth. The mass-volume ratio of diatomaceous earth to ferric chloride solution is 1g:(10-15)mL. Stir and react at 60-70℃ for 1.5-2h, then calcine at 500-600℃ for 2-3h. After cooling, the modified diatomaceous earth is obtained. Furthermore, the dosage of the compound microbial agent is 0.1-0.3g per liter of pretreated wastewater. Furthermore, the modified adsorption carrier is added at a rate of 0.5-1.0 g per liter of pretreated wastewater. Furthermore, during the operation of the modified activated sludge reactor, the concentration of suspended solids in the mixed liquor is controlled at 3000-4000 mg / L, and the sludge age is 15-20 days. Furthermore, the segmented mixing adopts an adjustable speed submersible mixer, which is installed at the bottom of the anaerobic mixing zone, the anoxic mixing zone and the aerobic mixing zone respectively. The number of submersible mixers in each zone is determined according to the volume of the tank to ensure that there are no dead zones in the mixing. Furthermore, the aeration in the aerobic mixing zone is achieved using microporous aerators, which are evenly distributed at the bottom of the aerobic mixing zone, and the aeration produces bubbles with a pore size of 10-20 μm. Furthermore, in the pretreatment stage, the bar screen is made of 10-20mm spacing, and the hydraulic retention time in the sedimentation tank is 20-30min. Furthermore, in the sludge treatment and resource recovery stage, the remaining sludge is concentrated for 12-18 hours. After concentration, the sludge moisture content drops to 95%-97%. After dewatering, the sludge moisture content drops to 75%-80%. The dewatered sludge is used as raw material for organic fertilizer.

[0006] The technical solution provided by this invention has the following advantages compared with the known prior art: This invention creates anaerobic, anoxic, and aerobic mixing zones within a single modified activated sludge reactor by dividing it with partitions. This eliminates the need for additional independent anaerobic or anoxic tanks, significantly reducing engineering investment costs. It also simplifies the process and reduces operational complexity. Wastewater flows naturally through the water holes at the bottom of the partitions, eliminating the need for additional wastewater lifting equipment and further reducing energy consumption and maintenance costs. This invention utilizes a compound microbial agent containing polyphosphate-accumulating bacteria, denitrifying bacteria, nitrifying bacteria, and aerobic heterotrophic bacteria. This agent functions in different areas of the reaction tank, simultaneously achieving the degradation, nitrification, denitrification, and phosphorus absorption of carbon source pollutants. Combined with the phosphorus adsorption effect of a modified adsorption carrier, this significantly improves the removal efficiency of nitrogen and phosphorus. Practical application verification shows that this method can achieve a COD removal rate of over 90%, an ammonia nitrogen removal rate of over 85%, and a total phosphorus removal rate of over 90%, consistently meeting stringent nitrogen and phosphorus emission standards. This invention employs a segmented stirring and aeration synergistic control method. By precisely controlling the dissolved oxygen concentration, stirring rate, and hydraulic retention time in each zone, as well as the reasonable mixed liquor recirculation ratio and sludge recirculation ratio, the process control is simple, the process stability is high, and the treatment effect is not easily reduced due to parameter fluctuations. At the same time, by maintaining a stable sludge concentration in the reaction tank through sludge recirculation, a sufficient number of microorganisms are ensured, further guaranteeing the stability of process operation. This invention incorporates a sludge treatment and resource recovery stage, which involves partial recirculation of settled sludge and resource utilization of excess sludge. This not only reduces sludge discharge and lowers sludge disposal costs but also achieves resource recycling, meeting the requirements of green environmental protection and sustainable development. Simultaneously, the sludge filtrate is recirculated to avoid secondary pollution and improve the overall removal rate of pollutants in wastewater. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0008] Figure 1 This is a schematic diagram of the system flow for urban domestic sewage treatment according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the system flow for the integrated wastewater treatment in an industrial park, as described in Embodiment 2 of the present invention. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0010] A wastewater treatment method based on the thorough mixing and degradation of organic matter by activated sludge Example 1: Treatment of Urban Domestic Sewage 1. Wastewater quality background The average daily discharge of domestic sewage in a certain town is 500m³. 3 The influent water quality indicators are as follows: COD 320-380 mg / L, ammonia nitrogen 35-45 mg / L, total phosphorus 6-9 mg / L, SS 100-130 mg / L, BOD5 150-180 mg / L. The water quality meets the characteristics of typical urban domestic sewage and needs to be treated to meet the Class A discharge standard of the "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants" (GB18918-2002). 2. Specific processing steps (1) Pretreatment stage Bar screen: It adopts a medium bar screen (20mm spacing) and is equipped with a mechanical slag removal device. The water depth in front of the screen is 1.2m and the flow velocity through the screen is 0.8m / s. The screen slag is cleaned regularly every day (about 0.5m³ / d) to remove large floating objects and suspended solids such as plastic bags, branches, and fabrics from the sewage. Grit chamber: A horizontal flow grit chamber is selected, with a length of 15m, a width of 2.5m, an effective water depth of 1.0m, and a hydraulic retention time of 30min. Inorganic impurities such as sand and gravel are removed by gravity sedimentation. The grit is separated by a sand-water separator and then transported off-site for disposal (the average daily grit volume is about 0.3m³ / d). After pretreatment, the COD of the wastewater is reduced to 300-350mg / L and the SS is reduced to 80-100mg / L. (2) Modified activated sludge reaction stage Reactor parameters: The total effective volume of the modified activated sludge reactor is 100m³, which is divided into an anaerobic mixing zone (20m³), an anoxic mixing zone (25m³), and an aerobic mixing zone (55m³) by partitions. The bottom of the partitions is equipped with 100mm diameter water passage holes (spaced 1.5m apart) to ensure natural flow of sewage. Chemical dosing: The compound microbial agent is prepared by mixing Pseudomonas polyphosphate-accumulating bacteria, Alcaligenes denitrifying bacteria, Nitrosomonas-Nitrobacterium mixed nitrifying bacteria (mass ratio 1:1), and Bacillus aerobic heterotrophic bacteria in a ratio of 1:1.2:0.8:2.0. The dosage is 0.1 g / L (i.e., 100 g of agent per 1 m³ of wastewater treated), with a daily dosage of 50 kg. The modified diatomaceous earth (100 mesh particle size) is added at a dosage of 0.5 g / L, with a daily dosage of 250 kg. It is evenly added to the inlet of the reaction tank through an automatic dosing device. Partition control: Anaerobic mixing zone: Two 1.5kW submersible mixers (30r / min) are installed, the dissolved oxygen concentration is controlled at 0.1mg / L, the hydraulic retention time is 1.5h, polyphosphate-accumulating bacteria release phosphorus in this zone, and modified diatomaceous earth initially adsorbs organic pollutants and phosphorus. Anoxic mixing zone: Two 2.0kW submersible mixers (40r / min) are installed, with a dissolved oxygen concentration of 0.2mg / L and a hydraulic retention time of 2h. The aerobic zone mixture is refluxed via a return pump at a 100% return ratio (i.e., 500m³ / h). 3 / d) is returned to this area, where denitrifying bacteria use BOD5 (approximately 120-150 mg / L) to convert nitrate nitrogen into nitrogen gas; Aerobic mixing zone: Equipped with 3 submersible mixers (50 rpm) and microporous aerators (10-20 μm pore size, 50 aeration heads evenly distributed on the bottom of the tank), with an aeration intensity of 1.5 m. 3 / (m 2 h), dissolved oxygen concentration 2 mg / L, hydraulic retention time 4 h, aerobic heterotrophic bacteria degrade COD, nitrifying bacteria convert ammonia nitrogen into nitrate nitrogen, polyphosphate-accumulating bacteria absorb excessive phosphorus, and modified diatomaceous earth further adsorbs phosphorus. Operating parameters: Mixed liquor suspended solids concentration (MLSS) is controlled at 3000 mg / L, sludge age (SRT) is 15 days, and DO and MLSS are monitored in real time through an online monitoring instrument to adjust the stirring speed and aeration intensity in a timely manner. (3) Precipitation and separation stage Secondary sedimentation tank: A radial flow secondary sedimentation tank is adopted, with a diameter of 8m, an effective water depth of 2.5m, a sedimentation time of 2h, and a surface loading rate of 1.2m. 3 / (m 2 h) The activated sludge and modified adsorption carrier are allowed to settle in the tank, and the thickness of the sludge layer is controlled within 0.5m to prevent the sludge from floating. Effluent collection: The supernatant is collected through the surrounding effluent tank and COD, ammonia nitrogen, total phosphorus and SS are detected in real time by the online water quality monitoring instrument. After meeting the standards, it is disinfected through the ultraviolet disinfection channel (contact time 30min). The final effluent COD≤30mg / L, ammonia nitrogen≤5mg / L, total phosphorus≤0.5mg / L, SS≤10mg / L. (4) Sludge treatment and resource recovery stage Sludge return: The sludge (moisture content 99.2%) at the bottom of the secondary sedimentation tank is returned to the anaerobic mixing zone by a sludge pump at a return ratio of 50% (250 m³ / d) to maintain the stability of MLSS in the reaction tank; Waste sludge treatment: The waste sludge (approximately 250 m³ / d) enters the sludge thickening tank (effective volume 20 m³, thickening time 12 h). After thickening, the sludge moisture content is reduced to 97%. Then, it is dewatered by a plate and frame filter press (filtration pressure 0.6 MPa, filtration time 2 h). After dewatering, the sludge moisture content is 80%. The sludge cake (approximately 5 m³ / d) is sent to an organic fertilizer plant for composting and fermentation (temperature 55-65℃, fermentation 15 days) to produce organic fertilizer. Filtrate treatment: The sludge filtrate produced by pressure filtration (COD 120 mg / L, ammonia nitrogen 15 mg / L, total phosphorus 3 mg / L) is collected and returned to the anaerobic mixing zone for further treatment to avoid secondary pollution. 3. Verification of treatment effect After 30 days of continuous operation, with daily sampling and testing (once each in the morning, noon, and evening), the results showed that the average COD of the effluent was 28 mg / L (removal rate 91.4%), the average ammonia nitrogen was 4.5 mg / L (removal rate 88.9%), the average total phosphorus was 0.45 mg / L (removal rate 92.8%), and the average SS was 8 mg / L (removal rate 93.3%). All indicators consistently met the Class A discharge standard, and there were no problems such as sludge bulking or uneven aeration during operation, indicating good process stability. Example 2: Treatment of comprehensive wastewater from an industrial park (mainly food processing) 1. Wastewater quality background An industrial park primarily focuses on food processing (meat products and beverage production), with a small number of supporting machinery processing enterprises. The average daily wastewater discharge is 300 cubic meters. 3 The influent water quality is as follows: COD is 450-550 mg / L, ammonia nitrogen is 50-60 mg / L, total phosphorus is 10-13 mg / L, SS is 150-200 mg / L, BOD5 is 220-250 mg / L, and it contains a small amount of oil, protein and food residue. It needs to be treated to meet the Class I standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996). 2. Specific processing steps (1) Pretreatment stage The screen pool uses fine screens (10mm spacing), with a water depth of 1.0m in front of the screen and a flow velocity of 0.6m / s through the screen. It is equipped with a high-frequency vibration slag removal device to prevent grease from adhering to the screen bars. The average daily slag production is 0.4m³ / d (containing a lot of food residue), which is regularly transported to the kitchen waste treatment plant. Grit chamber: A vortex grit chamber with a diameter of 3m, an effective water depth of 1.2m, and a hydraulic retention time of 20min is selected. The vortex effect enhances the separation of sand particles, and the moisture content of the settled sand is less than 60%. The average daily production is 0.2m³ / d. After pretreatment, the COD of the wastewater is reduced to 420-520mg / L, SS is reduced to 120-160mg / L, and the oil content is reduced to 5-8mg / L. (2) Modified activated sludge reaction stage Reactor parameters: Total effective volume 150m³, divided into anaerobic mixing zone (30m³), anoxic mixing zone (40m³), and aerobic mixing zone (80m³). The bottom of the partition is equipped with water passage holes with a diameter of 120mm (spaced 1.2m apart). The tank wall is equipped with observation windows for easy observation of the mixed liquor state. Chemical dosing: The compound microbial agent is formulated with a ratio of polyphosphate-accumulating bacteria: denitrifying bacteria: nitrifying bacteria: aerobic heterotrophic bacteria = 1:1.5:1.0:2.5, with a dosage of 0.3 g / L (300 g per 1 m³ of wastewater), and a daily dosage of 90 kg; modified diatomaceous earth (200 mesh particle size) is added at a dosage of 1.0 g / L, with a daily dosage of 300 kg. After mixing the agent with the adsorption carrier, it is injected into the front end of the anaerobic mixing zone through a pipeline. Partition control: Anaerobic mixing zone: 3 submersible mixers of 2.0kW (50r / min), dissolved oxygen concentration of 0.2mg / L, hydraulic retention time of 2.5h. For high concentrations of organic matter, the retention time is extended to ensure that polyphosphate-accumulating bacteria fully release phosphorus, and modified diatomaceous earth adsorbs oil and phosphorus. Anoxic mixing zone: 3 submersible mixers of 2.2kW each (60r / min), dissolved oxygen concentration 0.5mg / L, hydraulic retention time 3h, mixed liquor reflux ratio 200% (600m). 3 / d), utilizing high BOD5 (approximately 180-220 mg / L) to enhance denitrification, increasing nitrate nitrogen removal rate to over 90%; Aerobic mixing zone: 4 x 3.0kW submersible mixers (70r / min), microporous aerators (10-20μm pore size, 80 aeration heads), aeration intensity of 2.5m. 3 / (m 2 h), dissolved oxygen concentration 4 mg / L, hydraulic retention time 6 h, high aeration intensity ensures high concentration COD degradation, and nitrifying bacteria efficiently convert ammonia nitrogen; Operating parameters: MLSS controlled at 4000 mg / L, SRT 20d, sludge settling ratio (SV) monitored periodically (every 3 days). 30 Maintain the sludge concentration at 20%-30% to prevent sludge aging. (3) Precipitation and separation stage Secondary sedimentation tank: Horizontal flow secondary sedimentation tank, 20m long, 3m wide, effective water depth 1.5m, sedimentation time 3h, surface loading 0.8m. 3 / (m 2 h) A sludge scraper (walking speed 0.5m / min) is installed at the bottom of the pool to prevent sludge deposition; Effluent treatment: After being collected by the weir plate, the supernatant enters the activated carbon filter column (filled with columnar activated carbon with a particle size of 2-4mm and a filtration rate of 8m / h) to further remove residual organic matter and color. The final effluent has COD≤60mg / L, ammonia nitrogen≤15mg / L, total phosphorus≤0.5mg / L, and SS≤10mg / L. (4) Sludge treatment and resource recovery stage Sludge return: The sludge return ratio is 100% (300 m³ / d). The returned sludge is returned to the anaerobic zone after passing through a sludge conditioning tank (with the addition of 0.1% polyacrylamide to improve settling properties). Waste sludge treatment: The waste sludge (approximately 150 m³ / d) enters a thickening tank (effective volume 30 m³, thickening time 18 h), reducing the moisture content to 95%. It is then dewatered by a belt filter press (belt width 2 m, filter belt speed 1.5 m / min, pressing pressure 0.8 MPa). After dewatering, the sludge moisture content is 75%, and the sludge cake (approximately 3 m³ / d) is sent to a biomass fuel plant to be made into briquettes. Filtrate and rinsing water: The filter press filtrate (COD 180 mg / L, ammonia nitrogen 20 mg / L, total phosphorus 5 mg / L) and filter cloth rinsing water (approximately 50 m³ / d) are collected together and returned to the front end of the bar screen in the pretreatment stage to achieve full-process pollutant control. 3. Verification of treatment effect After 45 days of continuous operation, the effluent indicators remained stable: COD averaged 52 mg / L (removal rate 90.2%), ammonia nitrogen averaged 12 mg / L (removal rate 81.3%), total phosphorus averaged 0.4 mg / L (removal rate 96.3%), and SS averaged 7 mg / L (removal rate 96.5%), meeting the Class I discharge standard. Moreover, the removal rate of characteristic pollutants (such as protein and oil) in food processing wastewater reached over 92%, and the process had strong resistance to shock loads (the effluent still met the standard even when the influent COD fluctuated by ±20%).

[0011] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wastewater treatment method based on the thorough mixing and degradation of organic matter by activated sludge, characterized in that, Includes the following steps: (1) Pretreatment stage: The wastewater to be treated is introduced into the grit chamber and the grit chamber in sequence to remove large floating objects, suspended solids and inorganic sand particles respectively; (2) Modified activated sludge reaction stage: The pretreated wastewater is introduced into the modified activated sludge reactor, and compound microbial agents and modified adsorption carriers are added to the reactor. The treatment is carried out by a segmented stirring and aeration synergistic control method. The modified activated sludge reactor is a single tank. The tank is divided into an anaerobic stirring zone, an anoxic stirring zone and an aerobic stirring zone by partitions. Water holes are provided at the bottom of the partitions. The partitions are made of reinforced concrete or fiberglass. The diameter of the water holes should be 100–150 mm, the spacing should be 1.0–1.5 m, and the holes should be located at the bottom of the partitions 0.3–0.5 m from the bottom of the tank to ensure natural flow of wastewater and avoid sludge deposition. Anaerobic mixing zone: Dissolved oxygen concentration ≤0.2mg / L, mixing rate 30-50r / min, hydraulic retention time 1.5-2.5h; Anoxic mixing zone: control dissolved oxygen concentration at 0.2-0.5 mg / L, stirring rate at 40-60 r / min, hydraulic retention time at 2-3 h, and return the mixture from the aerobic mixing zone to this zone at a reflux ratio of 100%-200%. Aerobic mixing zone: Dissolved oxygen concentration controlled at 2-4 mg / L, aeration intensity at 1.5-2.5 m / s. 3 / (m 2 h), stirring rate 50-70 r / min, hydraulic retention time 4-6 h; (3) Sedimentation and separation stage: The effluent from the modified activated sludge reactor is introduced into the secondary sedimentation tank and allowed to settle for 2-3 hours to achieve solid-liquid separation. The supernatant is the effluent that meets the standards. (4) Sludge treatment and resource recovery stage: A portion of the sludge settled at the bottom of the secondary sedimentation tank is returned to the anaerobic mixing zone at a return ratio of 50%-100%. The remaining sludge is concentrated and dewatered, and the sludge filtrate produced by dewatering is returned to the anaerobic mixing zone.

2. The wastewater treatment method according to claim 1, characterized in that, The compound microbial agent is prepared by mixing polyphosphate-accumulating bacteria, denitrifying bacteria, nitrifying bacteria, and aerobic heterotrophic bacteria in a mass ratio of 1:(1.2-1.5):(0.8-1.0):(2.0-2.5); wherein the polyphosphate-accumulating bacteria are Pseudomonas strains, the denitrifying bacteria are Alcaligenes strains, the nitrifying bacteria are a mixture of Nitrosomonas and Nitrifying Bacillus strains in a mass ratio of 1:1, and the aerobic heterotrophic bacteria are Bacillus strains.

3. The wastewater treatment method according to claim 1, characterized in that, The modified adsorbent carrier is modified diatomaceous earth, and its preparation method includes: ① Pulverize diatomaceous earth to 100-200 mesh, add 5%-10% hydrochloric acid solution, stir and react at 80-90℃ for 2-3 hours, wash with deionized water until neutral, and dry at 105-110℃. ② Add a 3%-5% ferric chloride solution to the dried diatomaceous earth. The mass-volume ratio of diatomaceous earth to ferric chloride solution is 1g:(10-15)mL. Stir and react at 60-70℃ for 1.5-2h, then calcine at 500-600℃ for 2-3h. After cooling, the modified diatomaceous earth is obtained.

4. The wastewater treatment method according to claim 1, characterized in that, The dosage of the compound microbial agent is 0.1-0.3g per liter of pretreated wastewater.

5. The wastewater treatment method according to claim 1, characterized in that, The modified adsorbent carrier is added at a rate of 0.5-1.0 g per liter of pretreated wastewater.

6. The wastewater treatment method according to claim 1, characterized in that, During the operation of the modified activated sludge reactor, the concentration of suspended solids in the mixed liquor is controlled at 3000-4000 mg / L, and the sludge age is 15-20 days.

7. The wastewater treatment method according to claim 1, characterized in that, The segmented mixing uses an adjustable-speed submersible mixer, which is installed at the bottom of the anaerobic mixing zone, the anoxic mixing zone, and the aerobic mixing zone. The number of submersible mixers in each zone is determined according to the volume of the tank to ensure that there are no dead zones in the mixing.

8. The wastewater treatment method according to claim 1, characterized in that, The aeration in the aerobic mixing zone is achieved using microporous aerators, which are evenly distributed at the bottom of the aerobic mixing zone. The aeration produces bubbles with a pore size of 10-20 μm.

9. The wastewater treatment method according to claim 1, characterized in that, In the pretreatment stage, the bar screen is 10-20mm apart, and the hydraulic retention time in the sedimentation tank is 20-30min.

10. The wastewater treatment method according to claim 1, characterized in that, In the sludge treatment and resource recovery stage, the remaining sludge is concentrated for 12-18 hours. After concentration, the sludge moisture content drops to 95%-97%. After dewatering, the sludge moisture content drops to 75%-80%. The dewatered sludge is used as raw material for organic fertilizer.

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