A membrane bioreactor treatment method and field return system for wastewater from sheep slaughterhouses.

Abstract

This invention discloses a membrane bioreactor (MBR) treatment method and a field return system for wastewater from sheep slaughterhouses. After three-stage pretreatment, the wastewater undergoes two-stage anoxic-aerobic denitrification, with segmented influent and two-stage internal recirculation. A short-range nitrification window is created in the first-stage aerobic zone with low dissolved oxygen through intermittent aeration, while stable nitrification occurs in the second-stage aerobic zone. The biochemically treated effluent enters a PVDF submerged ultrafiltration (MBR), where the mixed liquor suspended solids concentration and flux are controlled. Backwashing / relaxation and chemical cleaning sequences are triggered by the increase in transmembrane pressure difference per unit time, enhancing shock and fouling resistance. MBR permeate is fed into a field return tank and connected to the field return system. Precise water and fertilizer return and salt control are achieved through rapid nitrogen and phosphorus measurement, application decision-making, and stratified drip irrigation valve control. This scheme can achieve effluent ammonia nitrogen ≤3 mg / L, high total nitrogen removal, and reduced membrane fouling and nitrogen loss.

Description

Technical Field

[0001] This invention belongs to the field of bio-environmental protection technology, and in particular relates to a membrane bioreactor treatment method and a system for returning wastewater from sheep slaughter to the field. Background Technology

[0002] The combined wastewater generated during the slaughtering and deep processing of Tan sheep typically contains biodegradable organic matter such as blood, grease, protein, and meat scraps, along with hair, suspended solids, and pathogenic microorganisms. It is characterized by high chemical oxygen demand (COD), high ammonia nitrogen concentration, strong shock load, and a tendency to putrefy and emit foul odors. Existing projects often employ a pretreatment-biochemical denitrification-deep treatment route. Among these, membrane bioreactors (MBRs) are used for upgrading and reusing slaughterhouse wastewater due to their high solid-liquid separation efficiency and low effluent turbidity.

[0003] For example, Chinese patent CN107244735B discloses a slaughterhouse wastewater treatment process, which constructs a series system of storage tank—anaerobic tank—microaerobic tank—sedimentation tank—aerobic tank—sedimentation tank and MBR, and achieves denitrification through nitrification liquor recirculation. This scheme can treat high-salt, high-ammonia-nitrogen slaughterhouse wastewater, but its process chain is long and relies on multi-stage sedimentation and recirculation. In scenarios where the oil / suspended solids in slaughterhouse wastewater fluctuate greatly, problems such as increased front-end separation load and difficulty in maintaining long-term stable dissolved oxygen and recirculation ratios in the subsequent biological treatment stage may occur. At the same time, the "discharge if compliant, otherwise enter MBR" diversion mode may cause the MBR to operate intermittently or under sudden load increases, resulting in fluctuations in effluent ammonia nitrogen, accelerated membrane fouling, and increased operating costs, making it difficult to balance continuous and stable compliance with standards and economic efficiency.

[0004] For example, CN206396015U discloses a two-stage AO-MBR combined wastewater treatment system, which sets up multi-stage anaerobic / aerobic reaction tanks and MBR membrane tanks, and is equipped with components such as pH adjustment and water level sensing. Although such devices can improve effluent quality, they mainly focus on the series structure of treatment units and the recirculation connection relationship, and still have shortcomings in addressing the engineering challenges of slaughterhouse wastewater with "high oil-high nitrogen-high shock": First, when the carbon source distribution and segmented influent strategy in the anoxic section are not targeted, the total nitrogen removal depth is easily limited and the demand for external carbon sources increases; Second, to ensure nitrification, the aeration intensity often needs to be increased, which increases energy consumption and makes it difficult to maintain energy-saving denitrification windows such as short-cut nitrification; Third, the MBR section mostly adopts fixed-cycle backwashing / chemical cleaning, lacking a pollution early warning and triggering mechanism based on the trend of transmembrane pressure difference changes, which easily leads to rapid irreversible pollution, increased cleaning frequency, and decreased membrane life under the shock of oil and colloids.

[0005] Furthermore, when slaughterhouse wastewater meets treatment standards and is used for farmland irrigation / returning, it is necessary to consider both nutrient utilization and salt control, as well as reduce the risk of pathogen transmission. However, existing technologies often separate "treatment to meet standards" from "field application and salt-controlled irrigation," lacking a closed-loop connection mechanism centered on rapid water quality testing, application decision-making, and valve-controlled drip irrigation. This leads to problems such as over-application, nitrogen loss, salt migration, and reliance on manual experience in the field return process. Therefore, it is necessary to propose a membrane bioreactor treatment and its return system that is more adaptable to slaughterhouse wastewater load fluctuations, balances deep denitrification and membrane anti-fouling, and can be safely and efficiently connected to the field return process. Summary of the Invention

[0006] To address the aforementioned technical issues, a two-stage anoxic-aerobic coupled MBR treatment system and its closed-loop return-to-field system for wastewater from sheep slaughterhouses under high-load fluctuation conditions are provided. This system aims to achieve stable deep denitrification, reduce membrane fouling and operating energy consumption, and support safe and efficient return-to-field utilization.

[0007] To achieve the above-mentioned technical objectives, the present invention provides the following technical solutions.

[0008] In a first aspect, the present invention provides a membrane bioreactor treatment method for wastewater from sheep slaughterhouses, comprising the following steps: S1, collect wastewater from the slaughter of Tan sheep, and perform three-stage pretreatment in sequence: screen interception, solid-liquid separation and air flotation oil removal to obtain pretreated wastewater; S2, the pretreated wastewater undergoes a two-stage anoxic-aerobic denitrification biological treatment, comprising a primary anoxic unit A1, a primary aerobic unit O1, a secondary anoxic unit A2, and a secondary aerobic unit O2. The pretreated wastewater is fed into A1 and A2 in a segmented influent manner, with the O1 mixture being refluxed back to A1 at the primary internal reflux ratio and the O2 mixture being refluxed back to A2 at the secondary internal reflux ratio. O1 is controlled to operate with low dissolved oxygen (DO) of 0.2–0.6 mg / L, and intermittent aeration is performed on O1 to inhibit nitrate-oxidizing bacteria and form short-cut nitrification dominated by nitrite. The dissolved oxygen (DO) of O2 is controlled to 1.2–2.0 mg / L to complete the nitrification of remaining ammonia nitrogen and stabilize the effluent. S3, O2 effluent is introduced into membrane bioreactor (MBR) for solid-liquid separation. The MBR uses a PVDF submerged ultrafiltration membrane module. The concentration of suspended solids in the mixed liquor of the membrane tank is controlled at 8-12 g / L and the membrane flux is 8-15 L / (m2·h). The increase in transmembrane pressure difference (TMP) per unit time is used as the membrane fouling criterion. When the increase in TMP per unit time exceeds a preset threshold, the backwashing / relaxation-recovery and chemical cleaning sequence of the membrane module is triggered. S4: Online collection of ammonia nitrogen and turbidity parameters of A1, A2, O1, O2 and MBR permeate; Closed-loop adjustment of the segmented influent ratio, the two-stage internal reflux ratio and the aeration intensity of O1 and O2 based on the target ammonia nitrogen ≤3mg / L and total nitrogen removal rate ≥90%. S5 transports the MBR permeate to the return-to-field water tank for use by the subsequent return-to-field irrigation system.

[0009] Specifically, the segmented water intake ratio is A1 water intake accounting for 50% to 80% of the total water intake, and A2 water intake accounting for 20% to 50% of the total water intake.

[0010] Specifically, the primary internal recirculation ratio and the secondary internal recirculation ratio are both 200% to 400%, and the internal recirculation ratio refers to the ratio of the recirculation flow rate of the corresponding aerobic unit to the total influent flow rate entering the corresponding anoxic unit.

[0011] Specifically, the intermittent aeration of O1 adopts an aeration-stop cycle control, with the ratio of aeration time to stop time being 1:(0.5~2).

[0012] Specifically, the PVDF submerged ultrafiltration membrane module has a membrane pore size of 0.03 to 0.10 μm, and the membrane surface shear is controlled by membrane tank aeration and scrubbing to reduce membrane fouling.

[0013] Specifically, the threshold for the increase of TMP per unit time is 0.5 to 3.0 kPa / hour; after triggering, backwashing, relaxation-recovery and chemical cleaning are performed sequentially, wherein the chemical cleaning agent includes at least one of hypochlorite solution or citric acid solution.

[0014] Specifically, the closed-loop regulation adopts a feedback control strategy based on online ammonia nitrogen and turbidity, and adjusts the aeration intensity of O1 and O2 in zones, and adjusts the segmented influent ratio in conjunction to ensure the supply of carbon source for denitrification in the anoxic zone.

[0015] Specifically, the odorous gases generated by the three-stage pretreatment, biochemical unit, or MBR membrane tank are subjected to a combined deodorization treatment of photocatalytic oxidation and chemically modified activated carbon adsorption before being discharged.

[0016] In a second aspect, the present invention also provides a membrane bioreactor treatment system for implementing the treatment method described in the first aspect, comprising: The three-stage pretreatment unit is used to perform bar screen interception, solid-liquid separation and air flotation oil removal on wastewater from Tan sheep slaughtering. The two-stage anoxic-aerobic biochemical unit includes A1, O1, A2, and O2, and is equipped with segmented water inlet pipelines and internal return pipelines that respectively return the O1 mixture to A1 and the O2 mixture to A2. Membrane bioreactor (MBR) equipped with PVDF submerged ultrafiltration membrane modules; The online monitoring and control unit is used to collect operating parameters including at least ammonia nitrogen, turbidity and transmembrane pressure difference (TMP), and output control commands for the segmented influent ratio, internal recirculation ratio and O1 and O2 aeration intensity. The water return pond is connected to the water outlet of the MBR and is used to store the MBR water and provide a water intake interface to the irrigation end.

[0017] Thirdly, the present invention also provides a system for returning wastewater from sheep slaughter to the field, comprising: The inlet interface is connected to the MBR permeate outlet or the return-to-field water tank of the system described in the second aspect, and is used to receive permeate after membrane bioreactor treatment. The fertilizer and water storage and distribution unit is used to buffer and store the received product water and provide a stable water supply during application. The nutrient rapid testing unit is used to quickly detect at least the nitrogen and phosphorus indicators of the produced water and output the test values; The application decision unit is communicatively connected to the nutrient rapid testing unit, and is used to generate a fertilizer and water application plan based on the detection value, and output a one-click application control command. The stratified drip irrigation distribution unit, connected to the fertilizer and water storage and distribution unit, includes shallow drip irrigation branches and deep drip irrigation branches as well as valve control components. It is used to implement integrated water and fertilizer stratified drip irrigation under the action of the distribution control command, and to control salt and inhibit salt migration by switching or coordinating water supply through shallow / deep branches. The Internet of Things (IoT) control unit is communicatively connected to the nutrient rapid testing unit, the application decision unit, and the stratified drip irrigation application unit. It is used to monitor and regulate via a mobile terminal, and to generate and issue application control commands within a preset response time after receiving the detection values.

[0018] This invention uses a three-stage pretreatment—two-stage A / O denitrification—MBR membrane separation—field return system as its main technical line. It optimizes the carbon source distribution in the anoxic section through segmented water intake and two-stage internal recirculation. In the first-stage aerobic zone, low-DO intermittent aeration is used to form a short-range nitrification window, and stable nitrification is achieved in the second-stage aerobic zone to balance energy saving and deep denitrification. In the MBR section, the TMP increase per unit time is used as the criterion for membrane fouling development, and a backwash / relaxation and chemical cleaning sequence is triggered to achieve continuous operation with shock resistance and fouling resistance. After the permeate enters the field return tank, it is interfaced with the field return system. It uses nitrogen and phosphorus rapid measurement—application decision-making—layered drip irrigation valve control to achieve precise water and fertilizer integration for field return and salt control.

[0019] Compared with conventional AO and MBR combination schemes, this invention can maintain stable compliance with standards under conditions of high oil content, high organic load, and fluctuating water quality in slaughterhouse wastewater: by segmented influent and short-cut nitrification-denitrification synergy, it improves total nitrogen removal and reduces aeration energy consumption and external carbon source requirements; by using a cleaning trigger mechanism based on TMP growth, it reduces the risk of irreversible membrane fouling, reduces downtime and cleaning chemical consumption, extends membrane life, and stably obtains low-turbidity permeate; and by linking with the closed-loop system at the field return end, it achieves precise application and stratified drip irrigation salt control according to water quality and soil conditions, reduces nitrogen loss, inhibits salt migration, and improves irrigation utilization efficiency. Attached Figure Description

[0020] Figure 1 A schematic diagram of the overall structure of a membrane bioreactor treatment method for wastewater from sheep slaughter and its return-to-field system.

[0021] Figure 2 : Schematic diagram of membrane bioreactor treatment process.

[0022] Figure 3 Schematic diagram of the structure and control process of the field return system based on wastewater from sheep slaughter. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0024] I. Terminology Explanation To enable those skilled in the art to implement this invention without creative effort, the frequently used terms in this invention are explained as follows.

[0025] Tan sheep slaughter wastewater: refers to the comprehensive wastewater generated in the slaughtering, cutting, cleaning, pre-cooling and packaging of Tan sheep. It is usually characterized by high organic load (blood, protein and fat), high suspended solids, oil content, high nitrogen and phosphorus concentration and large load fluctuation.

[0026] Three-stage pretreatment: refers to the combination of pretreatment steps for sheep slaughter wastewater, including screen interception, solid-liquid separation, and air flotation oil removal, to reduce large particulate impurities, fibers / hair, suspended solids, and floating oil, thereby creating stable influent conditions for subsequent biological and membrane treatment.

[0027] Two-stage A / O: This refers to dividing the biological system into two sets of anoxic and aerobic sections (A1 / O1, A2 / O2) connected in series. Through segmented water intake and two-stage internal recirculation, the denitrification carbon source distribution is optimized and the denitrification depth is improved.

[0028] Segmented influent: This refers to sending pretreated wastewater into A1 and A2 separately in proportion, instead of sending all of it into A1. This allows A2 to obtain fresh, biodegradable organic matter as a carbon source for denitrification, thereby reducing the need for external carbon sources and improving total nitrogen removal.

[0029] Internal recirculation ratio: refers to the ratio of the recirculation flow rate of the mixed liquor from the aerobic section to the corresponding anoxic section to the total influent flow rate into the corresponding anoxic section. It is used to provide nitrate / nitrite nitrogen electron acceptors to the anoxic section and enhance denitrification.

[0030] Low dissolved oxygen (low DO) and intermittent aeration: Maintaining low DO (e.g., 0.2–0.6 mg / L) in O1 and using an aeration-stop cycle operation makes the nitrification process biased towards short-cut nitrification, thereby reducing oxygen supply energy consumption and providing a better nitrogen form window for deep denitrification.

[0031] Membrane bioreactor (MBR): A unit that couples biological treatment with membrane separation. It uses a submerged ultrafiltration membrane module to separate the solid and liquid components of a mixed liquor to obtain permeate with low turbidity and low suspended solids. The MBR membrane of this invention is preferably made of PVDF material, with effluent suspended solids ≈ 0, and can retain pathogens.

[0032] PVDF submerged ultrafiltration membrane module: using polyvinylidene fluoride (PVDF) as the membrane material, with membrane pore size in the ultrafiltration range (e.g., 0.03-0.10μm), arranged in a membrane tank, and separation is completed by pumping in the permeate.

[0033] Mixed liquor suspended solids concentration (MLSS): refers to the total concentration of suspended solids (SS) in the mixed liquor of a biochemical reactor (especially an aerobic reactor or an MBR membrane reactor). It is mainly composed of activated sludge microbial flocs, undegraded organic particles, and inorganic particles. It is used to reflect the biomass level in the system and affects organic matter removal, nitrification and denitrification capacity, and membrane fouling risk. MBR often uses a higher MLSS to enhance shock resistance, but too high a MLSS will increase viscosity, aggravate membrane fouling, and increase energy consumption.

[0034] Sludge retention time (SRT): The average time that activated sludge is retained in a biological system, also known as solids retention time, usually measured in days (d). The longer the sludge retention time, the more conducive it is to the enrichment of slow-growing microorganisms such as nitrifying bacteria. However, too long a sludge retention time may lead to sludge aging, increased viscosity, and increased risk of membrane fouling.

[0035] Transmembrane pressure difference (TMP) and its increase per unit time: TMP is a parameter characterizing the loss of membrane filtration driving force; the increase per unit time is used to characterize the rate of membrane fouling development and serves as a criterion for triggering backwashing / relaxation / chemical cleaning, which can improve the adaptability of cleaning timing under load fluctuation scenarios.

[0036] Nitrogen oxides NO X This refers to the general term for oxidized nitrogen commonly used in water treatment, typically including nitrate nitrogen (NO3). --N With nitrite nitrogen NO2 - -N.

[0037] Precision fertilization / fertilizer integration: This refers to using MBR permeate as irrigation water (or as a water-soluble fertilizer carrier), combined with rapid nutrient testing and application decisions, to achieve closed-loop management of "testing-calculation-application-irrigation" in the drip irrigation system.

[0038] Layered drip irrigation for salt control: This refers to the installation of drip irrigation branches (shallow / deep) in different soil layers, which alter the distribution of the wetting front through valve-controlled switching or coordinated water supply, thereby inhibiting the upward movement of salts with evaporation and improving the efficiency of water and nutrient utilization in the root zone.

[0039] One-click application and response time: refers to the decision-making unit quickly generating application instructions based on rapid measurement data and issuing them to the valve control, metering, and pump station execution terminals to achieve convenient operation.

[0040] II. System Structure The present invention comprises at least two parts: a membrane bioreactor treatment system; and a field return system, which is connected to the MBR permeate outlet or the field return pool of the treatment system to achieve precise and safe return of fertilizer and water to the field.

[0041] like Figure 1 As shown, the system of the present invention may include the following modules: Water intake collection and homogenization unit: including collection well, equalization tank and booster pump; used to collect wastewater from various drainage points in the slaughterhouse and balance fluctuations in water volume and quality.

[0042] The three-stage pretreatment unit includes a bar screen, solid-liquid separation equipment, and dissolved air flotation device (including a dosing and dissolved air system).

[0043] Two-stage A / O biological treatment unit: including A1 (primary anoxic tank), O1 (primary aerobic tank), A2 (secondary anoxic tank), and O2 (secondary aerobic tank); equipped with segmented inlet pipelines, primary internal return pump and return pipeline, secondary internal return pump and return pipeline, and can be equipped with external return and excess sludge discharge pipelines.

[0044] Membrane bioreactor (MBR) unit: includes membrane tank, PVDF submerged ultrafiltration membrane module, suction pump, permeate pipeline, backwashing and chemical cleaning device (chemical cleaning), and membrane tank aeration system.

[0045] Return-to-field water tank: Connected to the MBR permeate outlet, it is used for permeate buffer storage and provides a water intake interface to the downstream return-to-field system.

[0046] Odor collection and deodorization unit: used to collect and purify odors escaping from pretreatment, biochemical treatment, membrane tanks, etc.; a combination of photocatalytic oxidation and chemically modified activated carbon adsorption can be used.

[0047] Online monitoring and control unit: including PLC, industrial computer, data acquisition unit, online ammonia nitrogen / nitrite nitrogen / turbidity / TMP / DO / ORP / pH sensors, flow meter, valve and fan / blower frequency converter, etc.

[0048] IoT and mobile terminal unit: used for mobile phone monitoring and control, and can be combined with mini-program decision-making terminals, etc.

[0049] Returning water system: Connected to the returning water tank, including fertilizer and water storage and distribution, rapid nutrient testing, application decision-making, stratified drip irrigation and valve-controlled pumping station, etc.

[0050] III. Specific Technical Route for Implementing the Method of the Invention The logic of the membrane bioreactor treatment method of the present invention is as follows: Figure 2 The specific technical implementation route is as follows.

[0051] S1: Three-stage preprocessing 1. Grille interception (1) Set up coarse grid and fine grid in series: the gap of the coarse grid can be 10-20mm, which is used to intercept bone debris, hair clumps, packaging fragments, etc.; the gap of the fine grid can be 1-3mm, which is used to intercept fine fibers and hair.

[0052] (2) The grating residue can be dewatered by screw conveyor pressing and then transported off-site or treated in conjunction with the solid waste system.

[0053] (3) A water collection well and a booster pump should be installed behind the screen, and a liquid level interlock control should be configured; when the liquid level is too high, an alarm will be triggered and the standby pump will be switched in conjunction with the alarm.

[0054] 2. Solid-liquid separation Solid-liquid separation equipment includes: hydrocyclones, screw extrusion separators, rotary drum screens, and screw presses. It is recommended to place the solid-liquid separation unit before air flotation to reduce the air flotation load and minimize the risk of flocs / fibers clogging the dissolved air release device.

[0055] For workshop drainage containing a large amount of hair and fiber, rotary drum screen (screen hole 0.5-1.0mm) or screw press solid-liquid separator can be preferred. For slaughterhouse wastewater with high oil content, an oil separation / buffer section can be added after solid-liquid separation to reduce instantaneous oil shock.

[0056] 3. Air flotation for oil removal The preferred flotation device is dissolved air flotation (DAF). The preferred configuration is as follows: (1) Set up a dosing and mixing zone at the front end of the air flotation: Inorganic coagulants (such as polyaluminum chloride and polyferric sulfate) and coagulant aids (such as anionic PAM) can be added to promote the flocculation and flotation of oil / protein colloids; (2) The pressure of the dissolved air system can be 0.35 to 0.55 MPa; the reflux ratio can be 20% to 50%; and the air-to-water ratio can be 0.02 to 0.08. (3) The surface load of air flotation can be 5 to 12 m. 3 / (m 2 •h), residence time 15-30min; the scum scraper operates continuously or intermittently to discharge the scum into the scum tank for dewatering treatment; (4) The effluent from the air flotation enters the equalization tank, and the need to add alkalinity is determined by online pH and ORP monitoring to meet the subsequent nitrification requirements.

[0057] S2: Two-stage A / O denitrification 1. Overall Configuration A1 / O1 / A2 / O2 can be a continuous flow plug flow system or a multi-cell series system. To balance carbon source utilization and denitrification depth, the configuration is as follows: The total hydraulic retention time is 6–18 hours, of which 2–6 hours is in section A and 4–12 hours is in section O. The sludge age is 8–25 days, and is adjusted through the discharge of excess sludge. It can operate at temperatures of 10-35℃. In low-temperature seasons, nitrification capacity can be maintained by increasing sludge age and reducing load. The pH should be controlled between 7.0 and 8.2; if the alkalinity is insufficient, NaHCO3 or lime milk can be added to adjust it.

[0058] 2. Segmented water intake The pretreated wastewater is divided into two streams: one stream goes into A1, and the other stream goes into A2. Recommended ratio: A1 accounts for 50%–80%, and A2 accounts for 20%–50%.

[0059] The mechanism is that A2 obtains readily degradable organic matter from the fresh inlet as an electron donor for denitrification, which can significantly improve total nitrogen removal and reduce the amount of added carbon source; at the same time, it can mitigate the problem of insufficient denitrification at the back end caused by the excessive consumption of carbon source at the front end of A1.

[0060] Two variable frequency influent pumps are preferred, and the distribution ratio is controlled by online flow meter feedback. When the total nitrogen or nitrate nitrogen is too high, the proportion of A2 entering can be increased to enhance the downstream denitrification.

[0061] 3. Two-stage internal reflux O1 mixture is refluxed to A1, and O2 mixture is refluxed to A2. The internal reflux ratio in the first stage and the internal reflux ratio in the second stage can both be 200%-400%.

[0062] The primary internal reflux mainly carries the NOx produced by nitrification into A1, achieving front-end denitrification; The secondary internal recirculation mainly achieves deep denitrification. In particular, under segmented influent, A2 has a stronger denitrification capacity, which can further reduce the total nitrogen in the effluent.

[0063] To avoid the reflux carrying too much dissolved oxygen and inhibiting anoxic denitrification, the reflux inlet can be set at the front end of section A and a submerged reflux pipe can be used, or the reflux mixture can be degassed by energy dissipation; at the same time, the anoxic environment can be stabilized by controlling the stirring intensity of section A.

[0064] 4. Low DO and intermittent aeration create a short nitrification window. O1 is set to the low DO operating zone, with DO controlled at 0.2-0.6 mg / L, and intermittent aeration (aeration-stop cycle) is adopted, with an aeration-stop ratio of 1:(0.5-2).

[0065] Control objectives include: (1) The activity of nitrate-oxidizing bacteria is inhibited under low DO conditions, so that ammonia-oxidizing bacteria preferentially oxidize NH4. + Converted to NO2 - This leads to short-range nitrification, primarily composed of nitrite. (2) Reduce oxygen supply energy consumption and lower the overall aeration volume; (3) Provides more easily reduced NO2 for subsequent A2 denitrification - Improve the denitrification efficiency by optimizing the pathway.

[0066] During implementation, O1 can be achieved using fine bubble aeration and a variable frequency blower; during the aeration shutdown phase, stirring should be maintained or mixing should be achieved using reflux mixing. To prevent excessively low dissolved oxygen during aeration shutdown, which could lead to filamentous bacteria expansion or foaming, a minimum stirring power and an ORP lower limit interlock can be set.

[0067] 5. O2-stabilized nitration and polishing O2 serves as the stabilizing aerobic stage for nitrification / polishing, with DO controlled at 1.2–2.0 mg / L to complete the nitrification of residual ammonia nitrogen and stabilize the effluent. When O1 short-cut nitrification leads to NO2… - If the DO (dissolved oxygen) level is too high and the effluent ammonia nitrogen level is already low, the DO level can be appropriately increased to 1.8–2.5 mg / L to promote some NO2 production. - To NO3 - The process involves conversion and, in conjunction with A2 deep denitrification, balances the risk of nitrite.

[0068] 6. Denitrification carbon source management When the quality of slaughterhouse wastewater fluctuates significantly, if there is insufficient carbon source for denitrification, it is usually manifested as high nitrate nitrogen or total nitrogen in the A2 effluent. The following strategies can be adopted.

[0069] Preferred strategies: Increase the proportion of A2 stage influent, or reduce the internal recirculation ratio of the first stage and increase the internal recirculation ratio of the second stage, so that the carbon source is more concentrated for downstream deep denitrification; Auxiliary strategies: Add small amounts of external carbon sources, such as sodium acetate, glucose, or fermentation broth. The preferred addition point is the A2 inlet, and the addition should be linked to the NOx online monitoring system for as-needed addition.

[0070] S3: MBR Solid-Liquid Separation and Membrane Fouling Control 1. Membrane module The MBR uses PVDF submerged ultrafiltration membrane modules with membrane pore sizes ranging from 0.03 to 0.10 μm; the membrane tank is equipped with an aeration and scrubbing system to reduce deposits on the membrane surface.

[0071] Preferred operating window: MLSS, 8–12 g / L; flux, 8–15 L / (m²) 2 •h); Filtration-relaxation cycle: 8-12 min for filtration, 1-3 min for relaxation; Dissolved oxygen in the membrane tank: 0.5-2.0 mg / L, mainly used for scrubbing and inhibiting anaerobic putrefaction, which can be adjusted according to the odor and foam situation of the system.

[0072] To reduce membrane fouling, the following measures can be further implemented: variable frequency control should be used for permeate pumping to keep the flux as constant as possible; Set up a combination of permeate backwash (permeate water reverse flushing of membrane pores) and air scrubbing; for water quality prone to scaling, the pH and hardness of the membrane tank can be managed, and if necessary, citric acid can be added to the chemical cleaning to remove inorganic scale.

[0073] 2. Cleaning strategy triggered by TMP growth slope This invention uses the increase in TMP per unit time as the criterion for membrane fouling, rather than solely relying on absolute TMP as the triggering condition. The mechanism is that under fluctuating slaughterhouse wastewater loads and grease shocks, the absolute value of TMP may be affected by short-term disturbances, but the rate (slope) of fouling development better reflects whether irreversible fouling has occurred, thus enabling more precise selection of cleaning timing.

[0074] The TMP growth rate indicator is defined as: ; in, For a moment The transmembrane pressure difference, For time intervals (e.g., 10-30 minutes). The unit can be kPa / hour.

[0075] when If the threshold (0.5–3.0 kPa / hour) is exceeded, a cleaning sequence is triggered. The cleaning sequence is as follows: (1) Backwashing: Use product water for backwashing, with an intensity of 1.5 to 2.5 times the flux, lasting 30 to 120 seconds; (2) Relaxation-recovery: Stop suction and continue aeration and scrubbing for 1-5 minutes to release reversible contaminants; (3) Chemical cleaning: including at least one of hypochlorite solution or citric acid solution.

[0076] Hypochlorite solution (calculated as available chlorine) can be 500–2000 mg / L, used to remove organic fouling and biofilm; Citric acid solution, at concentrations of 0.5% to 2.0% (mass fraction), is used to remove inorganic scale and metal deposits. Chemical cleaning can be performed by soaking for 0.5-2 hours or circulating cleaning for 0.5-1.5 hours. After cleaning, rinse with the produced water until the residual chlorine is within acceptable limits.

[0077] To reduce the frequency of chemical cleaning and extend membrane life, multi-level triggering can be further configured: for example, first using... Triggering backwash / relaxation, if multiple triggers still fail to achieve the desired result... Once the temperature drops below the threshold, chemical cleaning is triggered again.

[0078] 3. Sludge and return management in membrane tanks To prevent membrane tank sludge aging from increasing viscosity and exacerbating membrane fouling, the following can be done: The overall sludge age of the control system is within a reasonable range, such as 10–20 days; Regularly discharge excess sludge and replenish with fresh activated sludge; To prevent air flotation failure from causing a large amount of oil to enter the biochemical system.

[0079] S4: Online monitoring and closed-loop linkage control 1. Configuration of online monitoring points and sensors To achieve closed-loop regulation, online or semi-online monitoring points should be installed at A1, A2, O1, O2, and the MBR permeate, including at least: Ammonia nitrogen: Analyzed online using ion-selective electrode or colorimetric method; Nitrite nitrogen: analyzed using an online colorimetric analyzer; Turbidity: Used to determine membrane permeate stability and abnormal penetration; TMP: Differential pressure sensor at the inlet and outlet of the membrane module or conversion of negative pressure on the suction side; DO: O1, O2 and membrane pool; ORP: A1, A2; pH, temperature, flow rate: basic monitoring throughout the entire process.

[0080] 2. Control variables and actuators Control variables include: Segmented water intake ratio (The ratio of A1 to A2); First-stage internal reflux ratio Compared with the secondary internal reflux ratio ; O1 aeration intensity and O2 aeration intensity (blower frequency or valve opening); O1 Aeration Cycle Parameters (Aeration Time) With the end of exposure time ); Membrane suction flux With cleaning strategy parameters ( Threshold, backwash frequency, etc.

[0081] The actuators include: variable frequency inlet pump, variable frequency return pump, blower, aeration valve, electric regulating valve, membrane suction pump, backwash valve and chemical cleaning pump, etc.

[0082] 3. Control Logic (1) Ammonia nitrogen closed loop (using MBR permeate NH4) - (Main controller) If the effluent ammonia nitrogen concentration exceeds the target limit for ammonia nitrogen control, increase the O2 aeration intensity or extend the O2 aeration time; if necessary, increase the sludge age (reduce sludge discharge) to enhance the amount of nitrifying bacteria.

[0083] If the ammonia nitrogen concentration in the effluent is consistently lower than the set value and energy consumption is high, the O2 aeration intensity can be reduced and the aeration time and shutdown time optimized to save energy.

[0084] (2) Short-range nitrification window control Maintain the DO of O1 at 0.2–0.6 mg / L; If nitrite accumulates significantly at the O2 or effluent end (exceeding the safety threshold), the upper limit of DO at O1 can be appropriately increased or the aeration stop time can be shortened to inhibit nitrite accumulation. If the nitrate content is too high and the energy consumption is too high, the DO of O1 can be reduced and the aeration stoppage can be extended to enhance the short-range nitrification trend.

[0085] (3) Total nitrogen closed loop If the total nitrogen in the effluent is too high, prioritize increasing it. And increase the proportion of segmented influent entering A2. Enhance back-end denitrification; If the ORP in section A is too high, it indicates insufficient oxygen. In this case, reduce the impact of reflux oxygen carrying or increase the stirring and aeration shutdown strategy. If necessary, reduce the reflux flow into A1 and introduce more NOx into A2 for treatment. If there are obvious signs of insufficient carbon source, such as persistently high nitrate levels in the A2 effluent and low COD in the influent, a small dose of external carbon source can be added and interlocked with online NOx for on-demand addition.

[0086] (4) Closed-loop control of membrane fouling like If the threshold is exceeded (0.5–3.0 kPa / hour), backwashing / relaxation is performed; if continuous triggering fails to recover, chemical cleaning is performed. If turbidity increases or abnormal penetration occurs, a membrane module integrity check and bypass reflux to the front-end treatment are triggered to prevent substandard water from entering the return-to-field water tank.

[0087] S5: Production water inlet and connection to the field return water pond MBR permeate flows through permeate pipelines into the field irrigation tank, and provides two outlets: One route serves as a water intake system for returning water to the fields; the other route can be used for purposes such as greening, ecological restoration, or fire emergency reserves.

[0088] To prevent substandard water from accidentally entering the field return point, the following should be installed: Interlock for excessive turbidity / ammonia nitrogen in permeate: If the limit is exceeded, the electric valve will switch to the reflux or emergency tank. The water return tank is equipped with level and overflow alarms, and is linked to the front-end MBR suction to limit the flow. If necessary, UV or sodium hypochlorite micro-dose disinfection can be installed at the inlet of the water return pond to further reduce the risk of pathogens.

[0089] IV. Odor Collection and Deodorization Slaughterhouse wastewater treatment systems easily generate hydrogen sulfide, ammonia, and organic amine odors. This invention installs enclosed gas collection hoods in pretreatment tanks, biological treatment tanks, and membrane tanks, collecting the odors through a negative pressure pipe network before they enter the deodorization unit. The deodorization unit can employ: Photocatalytic oxidation reactor: The carrier is coated with photocatalytic materials such as TiO2 and equipped with a UV light source; odorous gases are oxidized into CO2, H2O and low-odor small molecules in the reactor; Chemically modified activated carbon adsorber: deeply adsorbs residual odor molecules.

[0090] Parameter settings: Gas collection air volume, determined according to the surface area of ​​the tank and the number of air changes, can be 2-6 times / hour; Photocatalytic reactor residence time, 0.5-2s; Activated carbon bed air velocity, 0.1-0.3m / s; Activated carbon replacement / regeneration cycle: determined according to the changes in outlet odor concentration and pressure drop.

[0091] V. Returning to the Field System 5.1 Structure of the Return-to-Field System The inlet of the return-to-field system is connected to the MBR permeate outlet or the return-to-field water tank, such as... Figure 3 As shown, the return-to-field system may include: Water inlet and fertilizer / water storage and distribution unit: including water intake pump, filter, pressure stabilizing tank or variable frequency constant pressure water supply device, fertilizer / water storage and distribution tank, and metering pump.

[0092] Nutrient rapid testing unit: used for rapid detection of nitrogen, phosphorus and other indicators in the product water; portable spectral rapid testing or online water quality sensor can be used.

[0093] Application Decision Unit: Used to generate application plans based on rapid test results and output one-click application control commands; Layered drip irrigation distribution unit: includes shallow drip irrigation branches, deep drip irrigation branches, valve control components and field pipe network; salt control is achieved through valve-controlled switching / coordinated water supply.

[0094] IoT control unit: Communicates with rapid measurement, decision-making, and valve-controlled pump stations, and supports monitoring and control via mobile devices.

[0095] 5.2 Rapid Nutrient Test The nutrient rapid testing unit must output at least the detection values ​​for nitrogen and phosphorus. This includes, but is not limited to: 1. Rapid Spectral Measurement Method Light source: UV-Vis or near-infrared light source; Detection cell: optical path 1–10 mm; Acquisition: Acquire absorption spectra in the range of 200–800 nm (or wider); Inversion: Using pre-established calibration curves or regression models, spectral features are mapped to target indicators.

[0096] Disclosure of calibration / training dataset: Data source: MBR permeate samples (covering different operating conditions, seasons, and dilution ratios) were collected, and true values ​​were obtained using national / industry standard methods; Recommended data size: no fewer than 100 samples, covering concentration ranges and interfering factors; Feature selection: Absorbance at a characteristic wavelength or principal component can be used; Fitting methods: Partial least squares regression or multiple linear regression can be used; 2. Electrochemical / colorimetric rapid detection method Ammonia nitrogen: ion-selective electrode or colorimetric reagent kit; Phosphorus: colorimetric method or reagent kit; Output: Output to the decision unit in mg / L format.

[0097] 5.3 Allocation Decision Model This invention provides a configurable material flow model for developing a precision application system. It employs a mass conservation decision model based on "field-crop-soil-fertilizer and water," which includes at least input variables, constraints, and output instructions.

[0098] 1) Model input variables Water quality variables: (Nitrogen concentration in product water, mg / L) (Phosphorus concentration in the produced water, mg / L) (Electrical conductivity), etc.; Soil variables: (Soil salinity, electrical conductivity) (Soil moisture content), soil texture (sand, loam, clay), available phosphorus, etc.; Crop variables: crop type (corn, wheat, alfalfa, etc.), growth period Target output ; Irrigation variable: Irrigable area System traffic dripper flow rate ; Management constraints: Maximum irrigation time per session Risk threshold for salt content shift Pathogen risk level, etc.

[0099] 2) Core Decision Calculation (1) Nitrogen requirement estimation According to the crop's growth period Nitrogen requirement per unit area (kg / acre) Determine the nitrogen application target for this application: ; (2) The produced water can provide nitrogen. If the irrigation water volume this time is (m³), then the amount of nitrogen introduced into the produced water is: ;in Unit mg / L, after conversion The unit is kg.

[0100] (3) Correction of fertilizer supplementation amount and utilization rate Considering field utilization rate (e.g., 0.6–0.85), then the amount of nitrogen fertilizer needed to be supplemented is: ; (4) Irrigation volume under salt control constraints Based on soil salinity threshold and stratified drip irrigation strategy, the irrigation amount is given. ;when Approaching the threshold When using deep drip irrigation, prioritize deep drip irrigation and reduce the proportion of shallow water supply to prevent salt from rising upwards.

[0101] 3) Model parameter selection and calibration Source: Fitted using local agricultural technology recommendations or field trials; Calibration: Obtained through field comparative trials; Determined based on crop salt tolerance threshold and soil type; The above parameters can be stored in the crop-soil parameter database and managed separately by region and crop type.

[0102] 4) Output instructions The output of the decision unit should include at least: The irrigation mode for this application is: shallow / deep / synergistic. Irrigation volume Irrigation duration ; Fertilizer metering pump dosage (converted according to solution concentration); Valve opening degree and switching sequence; Safety interlocks: Irrigation can be stopped during rain, when turbidity exceeds the limit, or when soil moisture content exceeds the limit.

[0103] (v) Layered drip irrigation for salt control The tiered drip irrigation distribution unit can be constructed as follows: 1) Shallow drip irrigation branch: drip tape buried at a depth of 5-15cm, dripper spacing of 20-40cm, single dripper flow rate of ~3L / h; used for watering and fertilizing during the seedling stage or shallow root stage.

[0104] 2) Deep drip irrigation branch: The drip irrigation pipe is buried at a depth of 20-40cm (which can be adjusted according to the depth of the crop root system), and the dripper spacing is 30-60cm; it is used for the main water supply in the middle and late stages to form a deep moist body and reduce surface evaporation.

[0105] 3) Valve control components: The shallow valve group and the deep valve group are respectively equipped with electric valves or solenoid valves, which, together with pressure sensors and flow meters, realize pressure stabilization and fault diagnosis.

[0106] 4) Salt control strategy: when Increase the proportion of deep water supply when rising or evaporation is high; When shallow water supply is required during the seedling stage, a combination of short-term shallow water supply and long-term deep water supply should be used to ensure the root zone water content while inhibiting salt migration. A periodic salt flushing irrigation strategy is set up, and the decision to execute it is determined through a closed-loop system using soil EC sensors.

[0107] (vi) Internet of Things Control and Execution The IoT control unit can use communication methods such as NB-IoT, 4G, and LoRa to synchronize rapid test data and decision results to the mobile device. The mobile interface can provide: Real-time water quality (nitrogen, phosphorus, turbidity), soil water and salinity, valve status, pump station pressure and flow rate; After selecting the field and crop, an application plan will be automatically generated. One-click execution with estimated completion time displayed; Abnormal alarms: Turbidity exceeding limits, abnormal pressure, valve not in position, pump overload, etc.

[0108] VI. Key Parameters and Examples 6.1 Key Parameters To facilitate the implementation of this invention, preferred ranges for key control parameters are given in Table 1.

[0109] Table 1 Key Control Parameters 6.2 Typical Implementation Examples 6.2.1 Example 1: Two-stage A / O and MBR treatment of wastewater from a 200-ton / day Tan sheep slaughterhouse to produce treated wastewater that meets standards 1. Scale and Objectives Processing capacity: 200t / d.

[0110] Use of produced water: It is used for dryland irrigation in the return-to-field water pond; the water quality is in accordance with the farmland irrigation water quality standard GB5084-2005.

[0111] 2. Influent water quality (7-day average) COD: 3600 mg / L; 5-day biochemical oxygen demand (BOD5): 1900 mg / L; SS: 1200 mg / L; animal and vegetable oils: 220 mg / L; ammonia nitrogen: 240 mg / L; total nitrogen: 410 mg / L; total phosphorus: 38 mg / L; pH: 6.8-7.4; 3. S1 Level 3 Preprocessing Operating Parameters Screen: 10mm coarse, 2mm fine; Solid-liquid separation: 0.8mm rotary drum screen; Air flotation: PAC dosage 150mg / L, PAM dosage 2mg / L; reflux ratio 30%, pressure 0.45MPa; residence time 20min.

[0112] Pretreated effluent (average): COD: 1900 mg / L, SS: 320 mg / L, oil: 55 mg / L.

[0113] 4. Key S2 Level A / O Settings Segmented water intake: A1 70%, A2 30%; Internal recirculation: , O1DO: 0.3~0.5mg / L, aeration-to-stop ratio 1:1; O2DO: 1.5-1.8mg / L; sludge age: 15d; water retention time: 12h total (4h total A, 8h total O).

[0114] 5. S3 MBR settings PVDF submerged ultrafiltration membrane; MLSS: 9.5~11g / L; flux: 10~12LMH; Threshold: 1.5 kPa / h; Backwash: Backwash for 60 seconds after filtration every 10 minutes; Relax for 2 minutes; Chemical cleaning: 1000 mg / L available chlorine once a month, 1% citric acid once every 2 months.

[0115] 6. After 30 days of continuous and stable operation, the effluent indicators (average values) are shown in Table 2.

[0116] Table 2. Effluent Indicators of Example 1 As shown in Table 2, the ammonia nitrogen in Example 1 was stable at 1.9 mg / L < 3 mg / L, the total nitrogen removal rate was approximately 93%, and the turbidity of the MBR permeate was < 1 NTU.

[0117] 6.2.2 Example 2 1. Operating Condition Settings Based on Example 1, the oil shock generated during the peak slaughter period was simulated: by introducing upstream oil separation fluctuations, the oil concentration in the influent was increased to 350-450 mg / L for 3 consecutive days, and the membrane operation was recorded.

[0118] 2. Using the present invention The result of triggering the strategy Day 1: TMP slowly increases from 12 kPa to 15 kPa. kPa / h; Day 2: A short period of accelerated pollution occurred. The peak pressure reached 1.7 kPa / h, triggering backwashing and relaxation. After 2 hours... It dropped back to 0.6 kPa / h; Day 3: If the threshold is exceeded again and three consecutive backwashes are ineffective, chemical cleaning (soaking in 1000 mg / L available chlorine for 1 hour) is triggered. After cleaning, TMP recovers to around 13 kPa, and flux returns to the set value. The system did not experience long-term membrane flux decline or abnormal permeate turbidity.

[0119] 6.2.3 Comparative Example 1 Under the same membrane module, flux setting, MLSS range, aeration and scrubbing intensity, and feedwater grease impact conditions as Example 1 and Example 2, the only difference was that the membrane fouling trigger criterion was changed from "TMP increase per unit time exceeding the threshold" to "TMP > 25 kPa triggers chemical cleaning". The results are as follows: Although the TMP did not exceed 25 kPa in the first two days, the accelerated rate of contamination forced the flux to be reduced. Chemical cleaning was only triggered after the TMP rapidly rose to 25 kPa on the 3rd day, during which there was a risk of increased turbidity in the permeate and short-term exceedance of the standard. Operators were forced to take manual intervention measures and shut down the machine for cleaning, which affected continuity.

[0120] This demonstrates that using TMP growth as a criterion can identify the pollution acceleration phase earlier and address it within the reversible pollution window, thereby improving the stability and safety of continuous operation.

[0121] 6.2.4 Example 3: Precision fertilization and water return to the field and stratified drip irrigation for salt control 1. Water sources and fields Water source: MBR permeate enters the field return water tank and is drawn from the field return system inlet; Field: 50 mu of dryland corn, soil is slightly saline-alkaline, topsoil... 2.0~3.5dS / m; 2. System Configuration Nutrient rapid test: Output using a rapid spectral measurement device. and ; Decision-making end: WeChat mini program and PLC linkage, response time ≤ 1 minute.

[0122] Layered drip irrigation: shallow layer buried at a depth of 10cm, deep layer buried at a depth of 30cm; valve-controlled switching.

[0123] 3. Application process The quick test yielded the following results: mg / L, mg / L; The decision-making unit estimates the nitrogen requirement for this week based on the crop's growth stage. kg (Zenda); Planned irrigation volume m³, then kg; Pick ,but kg (converted to urea or water-soluble fertilizer dosage); If soil If the water level rises close to the threshold, then use 80% deep water supply and 20% shallow water supply, and shorten the shallow water irrigation time to prevent salt from moving upwards.

[0124] Table 3 shows a comparison of the technical effects of Example 3 with the conventional stubble application scheme.

[0125] Table 3. Effect indicators of Example 3 In summary, under the conditions of high organic matter content, high oil content, and fluctuating load in 200t / d Tan sheep slaughter wastewater, the present invention, through the synergistic treatment of "three-stage pretreatment, two-stage anoxic-aerobic segmented influent and two-stage internal recirculation, one-stage aerobic low-DO intermittent aeration, and PVDF-MBR membrane separation," can achieve stable effluent compliance. The MBR permeate has low turbidity, near-zero suspended solids, and ammonia nitrogen stably controlled below 3mg / L with a total nitrogen removal rate exceeding 90%, thus meeting the water quality requirements for farmland application. Under adverse conditions such as oil shock, Example 2 demonstrates the use of an early warning-triggered cleaning mechanism based on the TMP increase per unit time. The backwash / relaxation-recovery and chemical cleaning sequence can be initiated in a timely manner during the accelerated fouling phase, avoiding forced flux reduction and abnormal permeate turbidity, significantly improving the system's continuous and stable operation capability and reducing the risk of irreversible membrane fouling. Furthermore, Example 3 shows that by connecting the MBR permeate to the field return system via a return-to-field water tank, combined with rapid nitrogen and phosphorus measurement, application decision-making, and stratified drip irrigation valve control, precise water and fertilizer return to the field and salt-controlled irrigation can be achieved. While ensuring crop yield, it significantly saves water, reduces fertilizer usage and nitrogen loss, and inhibits salt migration. This proves that the present invention has comprehensive technical effects of deep denitrification, stable achievement of standards, resistance to shock and membrane fouling, and safe and efficient return-to-field utilization.

[0126] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A membrane bioreaction treatment method based on Tan sheep slaughter wastewater, characterized in that, Includes the following steps: S1, collect wastewater from the slaughter of Tan sheep, and perform three-stage pretreatment in sequence: screen interception, solid-liquid separation and air flotation oil removal to obtain pretreated wastewater; S2, the pretreated wastewater undergoes a two-stage anoxic-aerobic denitrification biological treatment, comprising a primary anoxic unit A1, a primary aerobic unit O1, a secondary anoxic unit A2, and a secondary aerobic unit O2. The pretreated wastewater is fed into A1 and A2 in a segmented influent manner, with the O1 mixture being refluxed back to A1 at the primary internal reflux ratio and the O2 mixture being refluxed back to A2 at the secondary internal reflux ratio. O1 is controlled to operate with low dissolved oxygen (DO) of 0.2–0.6 mg / L, and intermittent aeration is performed on O1 to inhibit nitrate-oxidizing bacteria and form short-cut nitrification dominated by nitrite. The dissolved oxygen (DO) of O2 is controlled to 1.2–2.0 mg / L to complete the nitrification of remaining ammonia nitrogen and stabilize the effluent. S3, the O2 effluent water enters a membrane bioreactor MBR for solid-liquid separation, the MBR adopts a polyvinylidene fluoride PVDF material immersed ultrafiltration membrane module, the mixed liquid suspended solid concentration of the membrane tank is controlled to be 8-12 g / L, the membrane flux is controlled to be 8-15 L / (m 2 ·h), and the increase amount of the trans-membrane pressure difference TMP per unit time is taken as a membrane pollution criterion: when the increase amount of the TMP per unit time exceeds a preset threshold value, a backwashing / relaxation-recovery and chemical cleaning sequence of the membrane module is triggered; S4: Online collection of ammonia nitrogen and turbidity parameters of A1, A2, O1, O2 and MBR permeate; Closed-loop adjustment of the segmented influent ratio, the two-stage internal reflux ratio and the aeration intensity of O1 and O2 based on the target ammonia nitrogen ≤3mg / L and total nitrogen removal rate ≥90%. S5 transports the MBR permeate to the return-to-field water tank for use by the subsequent return-to-field irrigation system.

2. The method of claim 1, wherein: The segmented water intake ratio is as follows: A1 water intake accounts for 50% to 80% of the total water intake, and A2 water intake accounts for 20% to 50% of the total water intake.

3. The method of claim 1, wherein: The internal recirculation ratio of the first stage and the internal recirculation ratio of the second stage are both 200% to 400%, where the internal recirculation ratio refers to the ratio of the recirculation flow rate of the corresponding aerobic unit to the total influent flow rate entering the corresponding anoxic unit.

4. The method of claim 1, wherein: The intermittent aeration of O1 is controlled by an aeration-stop cycle, with the ratio of aeration time to stop time being 1:(0.5~2).

5. The method of claim 1, wherein: The PVDF submerged ultrafiltration membrane module has a membrane pore size of 0.03 to 0.10 μm, and the membrane surface shear is controlled by membrane tank aeration and scrubbing to reduce membrane fouling.

6. The method of claim 1, wherein: The threshold for the increase of TMP per unit time is 0.5 to 3.0 kPa / hour; after triggering, backwashing, relaxation-recovery and chemical cleaning are performed sequentially, wherein the chemical cleaning agent includes at least one of hypochlorite solution or citric acid solution.

7. The method of claim 1, wherein: The closed-loop regulation adopts a feedback control strategy based on online ammonia nitrogen and turbidity, and adjusts the aeration intensity of O1 and O2 in zones, and adjusts the influent ratio of each section in conjunction to ensure the supply of carbon source for denitrification in the anoxic section.

8. The method of claim 1, wherein: The odorous gases generated by the three-stage pretreatment, biochemical unit, or MBR membrane tank are subjected to a combined deodorization treatment of "photocatalytic oxidation - chemically modified activated carbon adsorption" before being discharged.

9. Membrane bioreactor system for carrying out the treatment method according to any one of claims 1 to 8, characterized in that, include: The three-stage pretreatment unit is used to perform bar screen interception, solid-liquid separation and air flotation oil removal on wastewater from sheep slaughtering. The two-stage anoxic-aerobic biochemical unit includes A1, O1, A2, and O2, and is equipped with segmented water inlet pipelines and internal return pipelines that respectively return the O1 mixture to A1 and the O2 mixture to A2. Membrane bioreactor (MBR) equipped with PVDF submerged ultrafiltration membrane modules; The online monitoring and control unit is used to collect operating parameters including at least ammonia nitrogen, turbidity and transmembrane pressure difference (TMP), and output control commands for the segmented influent ratio, internal recirculation ratio and O1 and O2 aeration intensity. The water return pond is connected to the water outlet of the MBR and is used to store the MBR water and provide a water intake interface to the irrigation end.

10. A system for applying Tan sheep slaughter wastewater to the field, characterized in that, include: The inlet interface is connected to the MBR permeate outlet or the return-to-field water tank of the system described in claim 9, and is used to receive permeate after membrane bioreactor treatment. The fertilizer and water storage and distribution unit is used to buffer and store the received product water and provide a stable water supply during application. The nutrient rapid testing unit is used to quickly detect at least the nitrogen and phosphorus indicators of the produced water and output the test values; The application decision unit is communicatively connected to the nutrient rapid testing unit, and is used to generate a fertilizer and water application plan based on the detection value, and output a one-click application control command. The stratified drip irrigation distribution unit, connected to the fertilizer and water storage and distribution unit, includes shallow drip irrigation branches and deep drip irrigation branches as well as valve control components. It is used to implement integrated water and fertilizer stratified drip irrigation under the action of the distribution control command, and to control salt and inhibit salt migration by switching or coordinating water supply through shallow / deep branches. The Internet of Things (IoT) control unit is communicatively connected to the nutrient rapid testing unit, the application decision unit, and the stratified drip irrigation application unit. It is used to monitor and regulate via a mobile terminal, and to generate and issue application control commands within a preset response time after receiving the detection values.

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