A sludge granulation enhancement system and an enhancement treatment method for biological treatment of food industry wastewater

Abstract

The application discloses a sludge granulation strengthening system and a strengthening treatment method for food industry wastewater biological treatment, and belongs to the technical field of wastewater treatment. The system comprises an AAO biochemical reaction tank, a vertical flow granular sludge screening tank and a secondary sedimentation tank which are sequentially connected along the water flow direction and are communicated through pipelines; the system further comprises a screening tank concentrated granular sludge return pipeline and a light sludge return pipeline; the vertical flow granular sludge screening tank is internally divided into a sedimentation separation zone, a sludge distribution zone and a sludge storage zone, and the rising flow rate is controlled through an internal circulation pump and a particle size automatic detection system, so that the granular sludge and the light sludge are efficiently separated. The treatment method enables the wastewater to be discharged up to the standard after the wastewater is sequentially subjected to AAO biochemical reaction, vertical flow granular sludge screening and secondary sedimentation tank sedimentation by improving the sludge granulation degree, optimizing the sludge return path and reaction conditions. The sludge settling performance and the nitrogen and phosphorus removal efficiency are improved, the energy consumption and the land area are reduced, the system impact load capacity is enhanced, and the system is suitable for various food industry wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and particularly relates to a sludge granulation enhancement system and enhancement treatment method for biological treatment of food industry wastewater. Background Technology

[0002] Food industry wastewater is complex in composition, primarily originating from the raw material washing, processing, cooking, and cooling stages of food production. This results in typical characteristics of food industry wastewater, including large flow rates, high levels of organic matter and suspended solids, high biochemical oxygen demand (BOD) and chemical oxygen demand (COD) values, low toxicity, and significant fluctuations in water quality and quantity. The AAO (Anaerobically-Aerobic) system is one of the core technologies for addressing easily biodegradable food industry wastewater. The AAO system is a biological treatment system based on an anaerobic-anoxic-aerobic process, which utilizes three reaction zones with different environments to sequentially remove pollutants using specific microbial communities.

[0003] Anaerobic digester-aerobic reactor (AAO) is a classic biological nitrogen and phosphorus removal process. However, in traditional AAO processes, the sludge mixture returned from the secondary sedimentation tank to the anaerobic tank via the external sludge return pipe includes high-density sludge with good settling properties, flocculent sludge with poor settling properties, aged sludge, and filamentous bacteria. In long-term operation, the traditional AAO process still has the following limitations when treating food wastewater: Low reactor volumetric loading and large footprint of treatment facilities: The system's treatment efficiency is affected by sludge concentration and activity, resulting in limited treatment capacity per unit time and per unit volume. To meet treatment requirements, the reactor volume needs to be increased, increasing construction land and treatment costs.

[0004] The system has high energy consumption: In order to maintain the dissolved oxygen required for the aerobic stage of biological treatment and to realize sludge return and circulation, the aeration device and circulation pump consume a lot of electricity. The carbon source required for phosphorus release in the anaerobic stage and denitrification in the anoxic stage is insufficient and needs to be added, which indirectly increases the system's energy consumption.

[0005] Poor sludge settling performance leads to system instability: As the only solid-liquid separation unit, the secondary settling tank is prone to the accumulation of lightweight sludge with poor settling performance, which easily re-enters the system with the return flow. This results in an increase in the sludge volume index (SVI), increasing the risk of sludge bulking and the burden on the secondary settling tank's solid-liquid separation capacity. Furthermore, it weakens the system's adaptability to fluctuations in water quality and quantity, and reduces its resistance to shock loads.

[0006] The efficiency and quality of sludge return need to be improved: the sludge returned from the secondary sedimentation tank may contain light flocculent sludge, aged and disintegrated sludge, and low levels of active components, which reduces the rate of biochemical reaction and restricts the efficiency of nitrogen and phosphorus removal. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a sludge granulation enhancement system and method for biological treatment of food industry wastewater, thereby increasing reactor volumetric load, reducing treatment energy consumption, and improving the degree of sludge granulation, thus solving the problems in the prior art.

[0008] This invention provides the following technical solution: A sludge granulation enhancement system for biological treatment of food industry wastewater is provided, which is connected in sequence along the water flow direction: an AAO biochemical reaction tank, a vertical flow granular sludge screening tank, and a secondary sedimentation tank connected by pipelines; the system also includes a granular sludge return pipeline for the screening tank and a light sludge return pipeline.

[0009] Preferably, a method for enhancing sludge granulation in the biological treatment of food industry wastewater includes the following steps: S1, food industry wastewater enters the pre-anoxic tank of the AAO biochemical reactor after pretreatment and anaerobic treatment. S2, In the pre-anoxic tank, the influent described in step S1 is mixed with the external return sludge from the secondary sedimentation tank and the concentrated granular sludge from the sludge storage area of ​​the vertical flow granular sludge screening tank. Dissolved oxygen and nitrate are rapidly consumed within the hydraulic retention time of 30 minutes to form a strict anaerobic environment. S3, the mixed liquor enters the anaerobic tank, where phosphorus-accumulating bacteria release phosphorus under a strictly anaerobic environment, with a hydraulic retention time of 1.5-2 hours. It then sequentially passes through an anoxic tank for denitrification, with a hydraulic retention time of 2-4 hours. Finally, it enters an aerobic tank where the dissolved oxygen concentration is maintained at 2-3 mg / L for nitrification, organic matter oxidation, and aerobic phosphorus uptake, with a hydraulic retention time of 4-8 hours. Ca is added at the effluent outlet of the aerobic tank. 2+ Mg 2+ Their concentrations were 40 mg / L and 10 mg / L, respectively; S4, the mixed liquor at the end of the aerobic tank all enters the vertical flow granular sludge screening tank; In S5, the mixed liquor flows from bottom to top in the vertical flow granular sludge screening tank. The upward flow velocity on the surface of the sedimentation separation zone is controlled within the range of 1-8 m / h by the internal circulation pump and the inlet flow valve, so as to achieve gravity screening. The granular sludge with better performance settles into the sludge storage area, while the light sludge with poor performance is returned to the anoxic tank or directly guided to the secondary sedimentation tank through the pipeline at a return ratio of 100-400%. S6, through the automatic particle size detection system and the lowest sludge level sensor in the sludge storage area, monitors in real time and returns concentrated granular sludge that meets the particle size standard and has a concentration of 6000-12000 mg / L in the sludge storage area to the pre-anoxic tank at a return ratio of 10%-30%. S7, the supernatant from the vertical flow granular sludge screening tank enters the secondary sedimentation tank for final sedimentation. Part of the sludge at the bottom of the secondary sedimentation tank is returned to the pre-anoxic tank through the sludge external return pipe at a return ratio of 10%-90%. The remaining sludge is discharged from the system, and the supernatant from the secondary sedimentation tank is discharged as the final effluent that meets the standards.

[0010] Preferably, the AAO biochemical reactor includes a pre-anoxic tank, an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence. The hydraulic retention time of the pre-anoxic tank is no more than 30 minutes; the hydraulic retention time of the anaerobic tank is 1.5-2 hours; the hydraulic retention time of the anoxic tank is 2-4 hours; and the hydraulic retention time of the aerobic tank is 4-8 hours.

[0011] Preferably, calcium ions and magnesium ions are added to the effluent pipe of the aerobic tank at concentrations of 40 mg / L and 10 mg / L, respectively. The aerobic tank is provided with a mixed liquor outlet at the end, which is connected to the inlet of the vertical flow granular sludge screening tank through a pipeline.

[0012] Preferably, the vertical flow granular sludge screening tank has a three-dimensional tank structure, which is divided into three functional areas from top to bottom: an upper sedimentation and separation area, a middle sludge mixing area, and a lower sludge storage area.

[0013] Preferably, the vertical flow granular sludge screening tank is provided with an inlet, a supernatant outlet, and a concentrated granular sludge outlet. Part of the supernatant is connected to the inlet of the secondary sedimentation tank through an overflow weir pipeline. A circulation pump is installed outside the screening tank. The circulation pump returns the sludge from the sedimentation separation zone or the sludge mixing zone from the upper part of the tank to the sludge storage zone or the lower part of the inlet. The circulation pump is linked with the inlet flow control valve to coordinately adjust the upward flow velocity of the sedimentation separation zone and stabilize it within the range of 1-8 m / h.

[0014] Preferably, the sedimentation and separation zone of the vertical flow granular sludge screening tank is equipped with an automatic particle size detection system. This system detects the sludge particle size distribution and the signal from the lowest sludge level sensor, and then uses this information to adjust the flow rate of the circulating pump to change the upward flow velocity.

[0015] Preferably, the upper outlet of the vertical flow granular sludge screening tank is connected to the anoxic tank via a pipeline, and the reflux ratio is controlled at 100-400%; the concentrated granular sludge outlet at the bottom of the sludge storage area of ​​the screening tank is connected to the pre-anoxic tank via an external reflux pipeline for the screened sludge, the concentration of the concentrated granular sludge is 6000-12000 mg / L, and the reflux ratio is controlled at 10%-30%.

[0016] Preferably, the secondary sedimentation tank is provided with an outlet and a sludge outlet. The sludge outlet is connected to the pre-anoxic tank through a sludge external return pipeline. The return ratio is controlled at 10%-90%. The remaining sludge is discharged from the system. The supernatant outlet of the secondary sedimentation tank is the final outlet of the system.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a sludge granulation enhancement system and method for biological treatment of food industry wastewater, significantly improving sludge settling performance and effectively inhibiting sludge bulking. In traditional AAO processes, the secondary settling tank is the only solid-liquid separation unit. Lightweight flocculent sludge with poor settling performance easily accumulates in the system with the recirculation, leading to increased SVI values ​​and exacerbating the risk of sludge bulking. This invention achieves efficient dynamic separation of heavy granular sludge and lightweight sludge by setting up a vertical flow granular sludge screening tank after the aerobic tank and utilizing an internal hydraulic screening and automatic particle size detection system. High-density granular sludge with good performance is selectively retained and recirculated, while lightweight sludge is discharged from the system. This breaks the vicious cycle of lightweight sludge from the system structure, significantly improves the sludge settling performance of the system, and reduces the solid-liquid separation load of the secondary settling tank.

[0018] Enhancing System Stability and Shock Load Resistance: Traditional processes for food wastewater, characterized by large fluctuations in water quality and quantity, are prone to operational instability due to the loose structure and poor settling properties of the sludge. This invention optimizes the sludge return path, returning the low-dissolved oxygen mixed liquor from the upper part of the screening tank to the anoxic tank. This reduces the interference of the traditional aerobic tank-to-high-dissolved oxygen mixed liquor return to the anoxic tank's denitrification environment. Simultaneously, it continuously replenishes the system with highly active granular sludge obtained from screening and discharges aged and disintegrated sludge. This maintains the overall activity and structural stability of the sludge within the system, significantly improving the process's adaptability to influent fluctuations, enhancing its shock load resistance, and resulting in more stable and reliable operation.

[0019] To improve granulation efficiency: In addition to the vertical flow screen trapping granular sludge, add an appropriate amount of Ca to the effluent from the aerobic tank. 2+ Mg 2+ The addition of this substance further promoted the formation of granular sludge.

[0020] Reducing system energy consumption, increasing volumetric loading, and decreasing footprint: Traditional AAO processes rely on internal reflux of nitrification liquor to meet denitrification requirements, resulting in high energy consumption. This invention optimizes this internal reflux path, using the supernatant from the screening tank with lower dissolved oxygen for reflux, thus reducing reflux energy consumption while maintaining denitrification efficiency. Furthermore, by optimizing and concentrating sludge in the screening tank, the system can maintain a higher activated sludge concentration and a better sludge community structure, thereby increasing the volumetric loading and treatment capacity of the bioreactor without increasing the tank volume, contributing to a reduction in the overall footprint of the wastewater treatment facility. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a sludge granulation enhancement system for biological treatment of food industry wastewater according to the present invention. Figure 2 This is a schematic diagram of the vertical flow granular sludge screening tank structure of the present invention. Figure 3 This is a schematic diagram of the sludge granulation enhancement method of the present invention. Detailed Implementation

[0023] 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 a part of the embodiments of the present invention, not all of them. 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.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in Embodiments 2-4, preferred embodiments are described in this invention to avoid redundancy. However, this invention is not limited to these, but can be specifically implemented in other ways within the scope of the technical solutions defined in the appended claims.

[0026] Example 1: like Figure 1-2 As shown, a sludge granulation enhancement system for biological treatment of food industry wastewater is sequentially connected along the water flow direction: an AAO biochemical reaction tank, a vertical flow granular sludge screening tank, and a secondary sedimentation tank, all connected by pipelines; the system also includes a granular sludge return pipeline for the screening tank and a light sludge return pipeline.

[0027] The AAO biochemical reactor comprises a pre-anoxic tank, an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence. The hydraulic retention time of the pre-anoxic tank is no more than 30 minutes; the hydraulic retention time of the anaerobic tank is 1.5-2 hours; the hydraulic retention time of the anoxic tank is 2-4 hours; and the hydraulic retention time of the aerobic tank is 4-8 hours.

[0028] Calcium and magnesium ions are added to the effluent pipe of the aerobic tank at concentrations of 40 mg / L and 10 mg / L, respectively. The aerobic tank has a mixed liquor outlet at the end, which is connected to the inlet of the vertical flow granular sludge screening tank through a pipeline.

[0029] The vertical flow granular sludge screening tank is a three-dimensional tank structure, internally divided into three functional areas from top to bottom: an upper sedimentation and separation zone, a middle sludge mixing zone, and a lower sludge storage zone. A "three-section" three-dimensional tank structure is proposed: the sludge mixing zone ensures uniform water distribution of the mixed liquor, avoiding the decrease in separation efficiency caused by uneven local flow velocities, and providing stable hydraulic conditions for subsequent separation; the sedimentation and separation zone utilizes the difference in gravity settling in the vertical flow direction to naturally classify granular sludge (settling velocity > rising velocity) and light sludge (settling velocity < rising velocity), conforming to the laws of fluid mechanics and sludge settling dynamics; the sludge storage zone serves as a "rich chamber" for high-quality granular sludge, achieving precise control of sludge volume through a minimum sludge level sensor, preventing granular sludge loss or excessive deposition. This structural design is not simply an addition of separation devices, but rather an integrated system of "separation-rich-recirculation" through functional zoning and hydraulic synergy, solving the technical bottlenecks of incomplete sludge separation and poor recirculation quality in traditional processes, representing a breakthrough reconstruction of the wastewater treatment system structure.

[0030] The vertical flow granular sludge screening tank is equipped with an inlet, a supernatant outlet, and a concentrated granular sludge outlet. Part of the supernatant is connected to the inlet of the secondary sedimentation tank through an overflow weir pipeline. A circulation pump is installed outside the screening tank. This circulation pump returns the sludge from the sedimentation separation zone or sludge mixing zone from the upper part of the tank to the sludge storage zone or the lower part of the inlet. The circulation pump is linked with the inlet flow control valve to coordinate and adjust the upward flow velocity in the sedimentation separation zone to keep it stable within the range of 1-8 m / h. The system adopts a three-dimensional tank structure to replace the traditional planar separation device, utilizing vertical space to achieve sludge separation and enrichment. The floor space required is only 1 / 3 to 1 / 2 of that of a planar device with the same processing capacity, solving the problem of large footprint of traditional processes. The three-stage zoned design specifically addresses the three major problems of uneven water distribution, imprecise separation, and insufficient enrichment: the sludge mixing zone uses an umbrella-shaped water distributor to ensure uniform rise of the mixed liquor; the height of the sedimentation separation zone is matched with the rising flow velocity to ensure critical separation of granular sludge settling and light sludge floating; the bottom of the sludge storage zone has a conical structure, which, together with the sludge pump, enables efficient discharge of concentrated sludge and avoids sedimentation and caking.

[0031] The tank adopts a vertical flow design. The mixed liquor enters the sludge preparation zone from the inlet at the bottom of the tank. After being evenly distributed, it flows upward through the sedimentation and separation zone. Gravity settling is used to classify the sludge—granular sludge, due to its high density and fast settling velocity, settles downwards under gravity; lightweight sludge, due to its low density and slow settling velocity, flows upwards with the water flow, forming a separation pattern of "sinking granules and floating lightweight sludge." The lower sludge storage zone is used to store concentrated granular sludge. The tank structure design reduces sludge deposition and loss, ensuring effective enrichment of granular sludge. An external circulation pump is installed in the screening tank. This circulation pump is linked to the inlet flow control valve to return the sludge from the sedimentation and separation zone or the sludge preparation zone from the top of the tank to the sludge storage zone or the bottom of the inlet, forming a hydraulic recirculation within the tank. By adjusting the flow rate of the internal circulation pump, the surface upward flow velocity of the sedimentation separation zone is stabilized within the range of 1-8 m / h. When the upward flow velocity matches the difference in settling velocity between granular sludge and light sludge, granular sludge with a settling velocity greater than the upward flow velocity is effectively intercepted and settled into the sludge storage area, while light sludge with a settling velocity less than the upward flow velocity enters the upper outlet with the water flow, achieving dynamic and efficient separation. The upper outlet of the screening tank is connected to the anoxic tank through a pipeline, and light sludge is returned to the anoxic tank at a return ratio of 100%-400%. This not only replenishes the microorganisms required for denitrification, but also reduces the interference of high dissolved oxygen return from traditional aerobic tanks on the anoxic environment due to the low dissolved oxygen content of the return liquid, thereby enhancing the denitrification efficiency.

[0032] The concentrated granular sludge (concentration 6000-12000 mg / L) at the bottom of the sludge storage area is returned to the pre-anoxic tank through the external return pipeline of the screened sludge at a return ratio of 10%-30%. The directional return of highly active granular sludge ensures that the pre-anoxic tank can quickly consume dissolved oxygen and nitrates and form a strict anaerobic environment. At the same time, it enhances the phosphorus release reaction of polyphosphate-accumulating bacteria in the anaerobic tank and improves the synergistic effect of nitrogen and phosphorus removal.

[0033] The sedimentation separation zone of the vertical flow granular sludge screening tank is equipped with an automatic particle size detection system. This system detects the sludge particle size distribution and the signal from the lowest sludge level sensor, and then adjusts the flow rate of the circulating pump to change the upward flow velocity. The automatic particle size detection system monitors the sludge particle size distribution in the sedimentation separation zone in real time. When the proportion of granular sludge decreases, it adjusts the flow rate of the circulating pump to increase the upward flow velocity and quickly discharge the light sludge. When the sludge level in the storage zone is too low, it reduces the upward flow velocity and prolongs the settling time of the granular sludge. The essence of this mechanism is to keep the upward flow velocity in the optimal range of "granular sludge retention - light sludge separation" through real-time monitoring and dynamic adjustment, breaking the limitation of "fixed flow velocity" in the traditional separation process and achieving adaptive optimization of separation efficiency.

[0034] The upper outlet of the vertical flow granular sludge screening tank is connected to the anoxic tank via a pipeline, and the reflux ratio is controlled at 100-400%. The concentrated granular sludge outlet at the bottom of the sludge storage area of ​​the screening tank is connected to the pre-anoxic tank via an external reflux pipeline for the screened sludge, with a concentrated granular sludge concentration of 6000-12000 mg / L and a reflux ratio controlled at 10%-30%.

[0035] The secondary sedimentation tank is equipped with an outlet and a sludge outlet. The sludge outlet is connected to the pre-anoxic tank through a sludge external return pipeline. The return ratio is controlled at 10%-90%. The remaining sludge is discharged from the system. The supernatant outlet of the secondary sedimentation tank is the final outlet of the system.

[0036] Specifically, this technical solution, based on the principle of "sludge characteristics - reaction tank function" adaptation, proposes a precise recirculation strategy to concentrate granular sludge (high activity, high concentration) and recirculate it to the pre-anoxic tank. The high biomass of the granular sludge can rapidly consume dissolved oxygen and nitrates, creating a strictly anaerobic environment for phosphorus release by polyphosphate-accumulating bacteria in the anaerobic tank, which meets the metabolic needs of polyphosphate-accumulating bacteria. Light sludge (containing a large number of denitrifying bacteria) is recirculated to the anoxic tank. The low-oxygen environment and microbial community it carries can directly enhance denitrification and reduce the damage to the anoxic environment caused by the high-oxygen recirculation liquid of the traditional aerobic tank. The essence of this design is to classify and allocate sludge to the corresponding reaction tank according to "functional attributes", realize the precise matching of "sludge-reaction", break through the limitations of the traditional "mixed recirculation", and belong to the deep optimization of the biological treatment reaction mechanism.

[0037] This innovative design features three independent return pipelines, each equipped with precisely controlled valves and metering pumps, enabling independent adjustment of the return ratio (10%-30% for concentrated granular sludge, 100%-400% for light sludge, and 10%-90% for secondary sedimentation tank sludge). The return ratio of each path can be dynamically adjusted based on the influent water quality (e.g., COD, nitrogen and phosphorus concentrations) to meet the treatment needs of different types of food industry wastewater. The concentrated granular sludge return pipeline is located at the bottom of the sludge storage area, employing a high-flow sludge pump to ensure smooth transport of high-concentration sludge (6000-12000 mg / L) and prevent pipeline blockage. The light sludge return pipeline connects to the upper outlet of the screening tank, utilizing overflow pressure difference to achieve low-energy return and reduce system operating costs.

[0038] The synergistic principle of chemical coagulation and physical enrichment is used to construct a bidirectional enhanced granulation mechanism: Ca is added to the effluent of the aerobic tank. 2+ With Mg 2+It can neutralize the negative charge of bacterial flocs and extracellular polymeric substances (EPS), eliminating interparticle repulsion. Simultaneously, it promotes floc aggregation through ion bridging, laying the structural foundation for granular sludge formation. The vertical flow granular sludge screening tank selectively intercepts and enriches the initially formed micro-granular sludge, allowing the granular sludge to continuously proliferate within the system, forming a virtuous cycle of "formation-interception-proliferation-stabilization." This solves the problems of easy loss of micro-granular sludge and slow granulation process in traditional processes. Precise control of reagent dosing parameters: Ca is added to the effluent pipe of the aerobic tank (at the inlet of the screening tank). 2+ (40 mg / L) and Mg 2+ (10mg / L) This concentration range has been verified by a large number of experiments. It can effectively promote granulation without causing sludge calcification or EPS decomposition due to excessive concentration, thus solving the problem of optimizing the dosage of the agent. The agent addition and the screening tank function form a sequential synergy: After the agent is added, the mixed liquor directly enters the screening tank. At this time, the flocs are in the initial stage of coagulation. Through the hydraulic conditions and interception function of the screening tank, the flocs are further promoted to coagulate into stable granular sludge. This avoids the breakage of the agglomerates caused by hydraulic disturbance after the agent is added, and realizes the sequential connection of "chemical promotion-physical solidification".

[0039] refer to Figure 3 As shown, a method for enhancing sludge granulation in the biological treatment of food industry wastewater includes the following steps: S1, food industry wastewater enters the pre-anoxic tank of the AAO biochemical reaction tank after passing through the pretreatment unit. S2, In the pre-anoxic tank, the influent described in step S1 is mixed with the external return sludge from the secondary sedimentation tank and the concentrated granular sludge from the sludge storage area of ​​the vertical flow granular sludge screening tank. Dissolved oxygen and nitrate are rapidly consumed within the hydraulic retention time of 30 minutes to form a strict anaerobic environment. S3, the mixed liquor enters the anaerobic tank, where phosphorus release by polyphosphate-accumulating bacteria occurs under strictly anaerobic conditions, with a hydraulic retention time of 1.5-2 hours. It then sequentially passes through an anoxic tank for denitrification, with a hydraulic retention time of 2-4 hours. Finally, it enters an aerobic tank where the dissolved oxygen concentration is maintained at 2-3 mg / L for nitrification, organic matter oxidation, and aerobic phosphorus uptake, with a hydraulic retention time of 4-8 hours. Ca is added at the effluent outlet of the aerobic tank. 2+ Mg 2+ Their concentrations were 40 mg / L and 10 mg / L, respectively; S4, the mixed liquor at the end of the aerobic tank all enters the vertical flow granular sludge screening tank; In S5, the mixed liquor flows from bottom to top in the vertical flow granular sludge screening tank. The upward flow velocity on the surface of the sedimentation separation zone is controlled within the range of 1-8 m / h by the internal circulation pump and the inlet flow valve, so as to achieve gravity screening. The granular sludge with better performance settles into the sludge storage area, while the light sludge with poor performance is returned to the anoxic tank or directly guided to the secondary sedimentation tank through the pipeline at a return ratio of 100-400%. S6, through the automatic particle size detection system and the lowest sludge level sensor in the sludge storage area, monitors in real time and returns concentrated granular sludge that meets the particle size standard and has a concentration of 6000-12000 mg / L in the sludge storage area to the pre-anoxic tank at a return ratio of 10%-30%. S7, the supernatant from the vertical flow granular sludge screening tank enters the secondary sedimentation tank for final sedimentation. Part of the sludge at the bottom of the secondary sedimentation tank is returned to the pre-anoxic tank through the sludge external return pipe at a return ratio of 10%-90%. The remaining sludge is discharged from the system, and the supernatant from the secondary sedimentation tank is discharged as the final effluent that meets the standards.

[0040] Example 2: Treatment of pork slaughtering and processing wastewater The food wastewater generated by a pork slaughtering and processing plant was tested and found to contain COD of 2000 mg / L, ammonia nitrogen of 100 mg / L, total phosphorus of 22 mg / L, and was characterized by high levels of oil and suspended solids. The water quality and quantity fluctuated significantly.

[0041] The pretreatment unit consists of a fine screen with a 5mm gap, an oil separator, an equalization tank, a dissolved air flotation (DAF) tank, and a UASB tank. The equalization tank has a hydraulic retention time of 8 hours, the DAF tank has a reflux ratio of 0.3, and the DAF tank is supplemented with 50 mg / L polyaluminum chloride and 2 mg / L anionic polyacrylamide, effectively removing most of the grease and suspended solids. The UASB tank has a hydraulic retention time of 24 hours for further removal of organic matter.

[0042] The hydraulic retention time (HRT) in the pre-anoxic tank of the AAO biochemical reactor is set to 10 minutes. Its main function is to rapidly consume residual dissolved oxygen in the influent and return flow, creating a strictly anaerobic environment for the anaerobic tank. Influent and externally returned sludge from the secondary sedimentation tank are mixed in the pre-anoxic tank at a 70% return ratio with high-quality granular sludge from the vertical flow granular sludge screening tank at a 30% return ratio. The anaerobic tank has a HRT of 1.5 hours and dissolved oxygen <0.2 mg / L, where rapid phosphorus release and further hydrolysis and acidification of complex organic matter are achieved. The anoxic tank has a HRT of 3 hours and dissolved oxygen <0.5 mg / L, receiving light sludge from the upper part of the vertical flow granular sludge screening tank with a return ratio of 200%. The aerobic tank has a HRT of 4 hours, controlling dissolved oxygen at 2.0-2.5 mg / L. To promote the formation of aerobic granular sludge, calcium chloride and magnesium sulfate are continuously added to the effluent from the aerobic tank to maintain calcium levels. 2+ The concentration is 50 mg / L, Mg 2+At a concentration of 15 mg / L, the appropriate concentration of Ca 2+ Mg 2+ Crosslinking extracellular polymers through bridging neutralizes negative charges, promotes coagulation, and constructs a rigid framework that facilitates the formation of aerobic granular sludge.

[0043] The effluent from the aerobic tank enters the vertical flow granular sludge screening tank. The surface upward flow velocity of the sedimentation separation zone is controlled to be 5 m / h by the circulating pump. The target particle size of the automatic particle size detection system is set to >200 μm. The concentration of concentrated sludge in the sludge storage zone is maintained at 6500 mg / L.

[0044] The surface hydraulic loading of the secondary sedimentation tank is 0.8m. 3 / (m 2 ·d), a portion of the sludge is returned to the anoxic tank at a 70% return ratio, and the remaining sludge is discharged.

[0045] After 60 days of continuous and stable operation, the average effluent quality was as follows: COD 43 mg / L, ammonia nitrogen 3 mg / L, total nitrogen 15 mg / L, and total phosphorus 0.4 mg / L. The COD removal rate was 97.85%, the ammonia nitrogen removal rate was 97%, and the total phosphorus removal rate was 98.18%. The system's sludge volume index (SVI) stabilized at 80 mg / L from an initial 150 mg / L, with aerobic granular sludge accounting for over 70%. The system demonstrated good tolerance to periodic influent load shocks, i.e., COD fluctuations up to 3000 mg / L.

[0046] Example 3: Treatment of chicken slaughtering and processing wastewater Food wastewater from a chicken slaughtering and processing plant was tested and found to contain COD of 1700 mg / L, ammonia nitrogen of 85 mg / L, total phosphorus of 15 mg / L, and a large amount of non-degradable organic matter and suspended solids from feathers, blood, etc.

[0047] The pretreatment unit consists of a fine screen with a 3mm gap, an equalization tank, an dissolved air flotation (DAF) tank, and a UASB tank. The equalization tank has a hydraulic retention time of 10 hours. The DAF tank is treated with 80 mg / L of composite decolorizing coagulant and 1.5 mg / L of polyacrylamide to effectively remove colloidal substances such as blood proteins. The UASB tank has a hydraulic retention time of 36 hours to further remove organic matter.

[0048] The hydraulic retention time (HRT) in the pre-anoxic tank of the AAO biochemical reactor is set to 10 minutes. Its main function is to rapidly consume residual dissolved oxygen in the influent and return flow, creating a strictly anaerobic environment for the anaerobic tank. Influent and externally returned sludge from the secondary sedimentation tank are mixed in the pre-anoxic tank at a 70% return ratio with high-quality granular sludge from the vertical flow granular sludge screening tank at a 30% return ratio. The anaerobic tank has a HRT of 1.5 hours and dissolved oxygen <0.2 mg / L, where rapid phosphorus release and further hydrolysis and acidification of complex organic matter are achieved. The anoxic tank has a HRT of 3.5 hours and dissolved oxygen <0.5 mg / L, receiving light sludge from the upper part of the vertical flow granular sludge screening tank with a return ratio of 250%. The aerobic tank has a HRT of 4.5 hours, controlling dissolved oxygen at 2.5-3.0 mg / L. To promote the formation of aerobic granular sludge, calcium chloride and magnesium sulfate are continuously added to the effluent from the aerobic tank to maintain calcium levels. 2+ The concentration is 80 mg / L, Mg 2+ At a concentration of 10 mg / L, the appropriate concentration of Ca 2+ Mg 2+ Crosslinking extracellular polymers through bridging neutralizes negative charges, promotes coagulation, and constructs a rigid framework that facilitates the formation of aerobic granular sludge.

[0049] The effluent from the aerobic tank enters the vertical flow granular sludge screening tank. The surface upward flow velocity of the sedimentation separation zone is controlled to be 4 m / h by the circulating pump. The target particle size of the automatic particle size detection system is set to >180 μm. The concentration of concentrated sludge in the sludge storage zone is maintained at 6800 mg / L.

[0050] The surface hydraulic loading of the secondary sedimentation tank is 0.7m. 3 / (m 2 ·d), a portion of the sludge is returned to the pre-anaerobic tank at a return ratio of 70%, and the remaining sludge is discharged.

[0051] After 60 days of continuous and stable operation, the average effluent quality was as follows: COD 40 mg / L, ammonia nitrogen 2.7 mg / L, total nitrogen 12 mg / L, and total phosphorus 0.3 mg / L. The COD removal rate was 97.65%, the ammonia nitrogen removal rate was 96.82%, and the total phosphorus removal rate was 98%. The sludge volume index (SVI) stabilized at 85 mg / L from the initial 150 mg / L, and the aerobic granular sludge accounted for more than 60%, demonstrating the system's strong resistance to shock loads.

[0052] Example 4: Treatment of beverage factory wastewater The food wastewater generated by a beverage processing plant has good biodegradability, i.e., BOD / COD=0.7. The raw water was tested and found to contain COD of 2300mg / L, ammonia nitrogen of 35mg / L, total phosphorus of 10mg / L, and also contains easily degradable organic matter such as sugars and acids.

[0053] The pretreatment unit is equipped with a 5mm gap screen and an equalization tank. The hydraulic retention time in the equalization tank is 6 hours. Due to the low amount of suspended solids, no advanced physical and chemical treatment is performed.

[0054] The hydraulic retention time (HRT) in the pre-anoxic tank of the AAO biochemical reactor is set to 10 minutes. Its main function is to rapidly consume residual dissolved oxygen in the influent and return flow, creating a strictly anaerobic environment for the anaerobic tank. Influent and externally returned sludge from the secondary sedimentation tank are mixed in the pre-anoxic tank at a 70% return ratio with high-quality granular sludge from the vertical flow granular sludge screening tank at a 30% return ratio. The anaerobic tank has a HRT of 1 hour and dissolved oxygen <0.2 mg / L, where rapid phosphorus release and further hydrolysis and acidification of complex organic matter are achieved. The primary anoxic tank has a HRT of 2.5 hours and dissolved oxygen <0.5 mg / L, receiving light sludge from the upper part of the vertical flow granular sludge screening tank with a return ratio of 200%. The aerobic tank has a HRT of 4 hours, controlling dissolved oxygen at 2.0-2.5 mg / L. To promote the formation of aerobic granular sludge, calcium chloride and magnesium sulfate are continuously added to the effluent of the aerobic tank to maintain calcium levels. 2+ The concentration is 60 mg / L, Mg 2+ At a concentration of 15 mg / L, suitable concentrations of Ca2+ and Mg2+ crosslink extracellular polymers through bridging, neutralize negative charges to promote coagulation, and construct a rigid framework that is conducive to the formation of aerobic granular sludge.

[0055] The effluent from the aerobic tank enters the vertical flow granular sludge screening tank. The surface upward flow velocity of the sedimentation separation zone is controlled to be 5 m / h by the circulating pump. The target particle size of the automatic particle size detection system is set to >220 μm. The concentration of concentrated sludge in the sludge storage zone is maintained at 6800 mg / L.

[0056] The surface hydraulic loading of the secondary sedimentation tank is 1.0m. 3 / (m 2 ·d), a portion of the sludge is returned to the pre-anoxic tank at a return ratio of 70%, and the remaining sludge is discharged.

[0057] After 60 days of continuous and stable operation, the average effluent quality was as follows: COD 60 mg / L, ammonia nitrogen 2.1 mg / L, total nitrogen 10 mg / L, and total phosphorus 0.5 mg / L. The COD removal rate was 97.39%, ammonia nitrogen removal rate was 94%, and total phosphorus removal rate was 95%. The system's sludge volume index (SVI) remained stable at 75 mg / L for a long period, with aerobic granular sludge accounting for over 60%, demonstrating strong resistance to shock loads. Compared to the traditional AAO process, under the same treatment capacity, the reaction volume is reduced by approximately 25%, and aeration energy consumption is reduced by approximately 15%. The conventional AAO process was used as comparative examples 2, 3, and 4 to treat the wastewater from examples 2-4 above. Under the same treatment conditions, the treatment effects of the system and method of the present invention and the conventional AAO process were compared. The results are shown in the table below: As shown in the table above, compared with the traditional AAO process, the sludge granulation enhancement system and enhanced treatment method for biological treatment of food industry wastewater have the following advantages: Significantly improved nitrogen and phosphorus removal efficiency: COD, ammonia nitrogen, and total phosphorus removal rates are all higher than those of the traditional AAO process, resulting in better effluent quality and stable compliance with standards. Improved sludge settling performance: The system's sludge volume index (SVI) is much lower than that of the traditional AAO process, effectively inhibiting sludge bulking and significantly increasing the proportion of aerobic granular sludge. Reduced energy consumption and land area: Under the same treatment capacity, the reaction volume is reduced, aeration energy consumption is lower, saving construction land and operating costs. Enhanced resistance to shock loads: It can adapt to the large fluctuations in water quality and quantity of food industry wastewater, resulting in higher operational stability.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sludge granulation and enhancement system for biological treatment of food industry wastewater, characterized in that, The system is connected sequentially along the water flow direction: an AAO biochemical reaction tank, a vertical flow granular sludge screening tank, and a secondary sedimentation tank, all connected by pipelines; the system also includes a granular sludge return pipeline for the screening tank and a light sludge return pipeline.

2. A method for enhancing sludge granulation in the biological treatment of food industry wastewater, employing the enhancement system as described in claim 1, characterized in that, Includes the following steps: S1, food industry wastewater enters the pre-anoxic tank of the AAO biochemical reactor after pretreatment and anaerobic treatment. S2, In the pre-anoxic tank, the influent described in step S1 is mixed with the external return sludge from the secondary sedimentation tank and the concentrated granular sludge from the sludge storage area of ​​the vertical flow granular sludge screening tank. Dissolved oxygen and nitrate are rapidly consumed within the hydraulic retention time of 30 minutes to form a strict anaerobic environment. S3, the mixed liquor enters the anaerobic tank, where phosphorus-accumulating bacteria release phosphorus under a strictly anaerobic environment, with a hydraulic retention time of 1.5-2 hours. It then sequentially passes through an anoxic tank for denitrification, with a hydraulic retention time of 2-4 hours. Finally, it enters an aerobic tank where the dissolved oxygen concentration is maintained at 2-3 mg / L for nitrification, organic matter oxidation, and aerobic phosphorus uptake, with a hydraulic retention time of 4-8 hours. Ca is added at the effluent outlet of the aerobic tank. 2+ Mg 2+ Their concentrations were 40 mg / L and 10 mg / L, respectively; S4, the mixed liquor at the end of the aerobic tank all enters the vertical flow granular sludge screening tank; In S5, the mixed liquor flows from bottom to top in the vertical flow granular sludge screening tank. The upward flow velocity on the surface of the sedimentation separation zone is controlled within the range of 1-8 m / h by the internal circulation pump and the inlet flow valve, so as to achieve gravity screening. The granular sludge with better performance settles into the sludge storage area, while the light sludge with poor performance is returned to the anoxic tank or directly guided to the secondary sedimentation tank through the pipeline at a return ratio of 100-400%. S6, through the automatic particle size detection system and the lowest sludge level sensor in the sludge storage area, monitors in real time and returns concentrated granular sludge that meets the particle size standard and has a concentration of 6000-12000 mg / L in the sludge storage area to the pre-anoxic tank at a return ratio of 10%-30%. S7, the supernatant from the vertical flow granular sludge screening tank enters the secondary sedimentation tank for final sedimentation. Part of the sludge at the bottom of the secondary sedimentation tank is returned to the pre-anoxic tank through the sludge external return pipe at a return ratio of 10%-90%. The remaining sludge is discharged from the system, and the supernatant from the secondary sedimentation tank is discharged as the final effluent that meets the standards.

3. A sludge granulation enhancement system for biological treatment of food industry wastewater according to claim 1, characterized in that, The AAO biochemical reactor comprises a pre-anoxic tank, an anaerobic tank, an anoxic tank, and an aerobic tank connected in sequence. The hydraulic retention time of the pre-anoxic tank is no more than 30 minutes; the hydraulic retention time of the anaerobic tank is 1.5-2 hours; the hydraulic retention time of the anoxic tank is 2-4 hours; and the hydraulic retention time of the aerobic tank is 4-8 hours.

4. A sludge granulation enhancement system for biological treatment of food industry wastewater according to claim 3, characterized in that, Calcium and magnesium ions are added to the effluent pipe of the aerobic tank at concentrations of 40 mg / L and 10 mg / L, respectively. The aerobic tank has a mixed liquor outlet at the end, which is connected to the inlet of the vertical flow granular sludge screening tank through a pipeline.

5. A sludge granulation enhancement system for biological treatment of food industry wastewater according to claim 1, characterized in that, The vertical flow granular sludge screening tank has a three-dimensional tank structure, which is divided into three functional areas from top to bottom: the upper sedimentation and separation area, the middle sludge mixing area, and the lower sludge storage area.

6. A sludge granulation enhancement system for biological treatment of food industry wastewater according to claim 1, characterized in that, The vertical flow granular sludge screening tank is equipped with an inlet, a supernatant outlet, and a concentrated granular sludge outlet. Part of the supernatant is connected to the inlet of the secondary sedimentation tank through an overflow weir pipeline. A circulation pump is installed outside the screening tank. This circulation pump returns the sludge from the sedimentation separation zone or sludge mixing zone from the upper part of the tank to the sludge storage zone or the lower part of the inlet. The circulation pump is linked with the inlet flow control valve to coordinate and adjust the upward flow velocity of the sedimentation separation zone to keep it stable within the range of 1-8 m / h.

7. A sludge granulation enhancement system for biological treatment of food industry wastewater according to claim 5, characterized in that, The sedimentation and separation zone of the vertical flow granular sludge screening tank is equipped with an automatic particle size detection system. This system detects the sludge particle size distribution and the signal from the lowest sludge level sensor, and then uses this information to adjust the flow rate of the circulating pump to change the upward flow velocity.

8. A sludge granulation enhancement system for biological treatment of food industry wastewater according to claim 1, characterized in that, The upper outlet of the vertical flow granular sludge screening tank is connected to the anoxic tank via a pipeline, and the reflux ratio is controlled at 100-400%. The concentrated granular sludge outlet at the bottom of the sludge storage area of ​​the screening tank is connected to the pre-anoxic tank via an external reflux pipeline for the screened sludge, with a concentrated granular sludge concentration of 6000-12000 mg / L and a reflux ratio controlled at 10%-30%.

9. A sludge granulation enhancement system for biological treatment of food industry wastewater according to claim 1, characterized in that, The secondary sedimentation tank is equipped with an outlet and a sludge outlet. The sludge outlet is connected to the pre-anoxic tank through a sludge external return pipeline. The return ratio is controlled at 10%-90%. The remaining sludge is discharged from the system. The supernatant outlet of the secondary sedimentation tank is the final outlet of the system.

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