Landfill leachate pretreatment process

Abstract

The invention discloses a landfill leachate pretreatment process, and belongs to the technical field of landfill leachate treatment.The landfill leachate pretreatment process comprises the following steps of S1, pre-oxidation and catalytic chain breaking, S2, dual-alkali calcium and magnesium removal, S3, magnetic flocculation and adsorption, S4, dynamic membrane filtration unit treatment and S5, control system integration. The mass transfer efficiency of an oxidizing agent and pollutants is enhanced, the dosing of the agent is dynamically regulated and controlled by combining an ORP (oxidation reduction potential) meter, so that parameters such as potential, pH value and temperature are kept in an optimal interval, the oxidation reaction is ensured to be fully carried out, macromolecular organic matters are efficiently decomposed, and a foundation is laid for subsequent treatment; the collision efficiency of calcium and magnesium ions is improved through the water distributor and the granular sludge bed, and meanwhile, the chemical dosage is dynamically controlled and the pH value is accurately adjusted through the sensor, so that the calcium and magnesium ions are efficiently removed, the chemical waste is reduced, and the operation cost is reduced.

Description

[0001] The present invention relates to the technical field of landfill leachate treatment, and more particularly to a landfill leachate pretreatment process. Background Art

[0002] Garbage refers to solid or fluid waste that has lost its use value and cannot be reused. This waste includes solid particles, garbage, slag, sludge, discarded products, broken utensils, defective products, animal carcasses, spoiled food, human and animal feces, etc., while leachate refers to a high-concentration organic wastewater formed in a landfill by the water contained in the garbage itself, rainwater and snow entering the landfill, and other water after passing through the garbage layer and the overburden layer. It mainly comes from the wastewater containing high concentrations of organic matter, inorganic matter and pollutants formed by biological decomposition, precipitation, groundwater, etc. during the stacking or landfill process of domestic garbage;

[0003] In the prior art, the patent document with the authorization announcement number CN114524536B discloses a "pretreatment process for landfill leachate", which includes the following steps: the landfill leachate is filtered and pre-separated, and then enters an electric flocculation treatment device for electric flocculation treatment; the effluent of the electric flocculation treatment device enters an ozone oxidation treatment device for ozone oxidation reaction; the effluent of the ozone oxidation treatment device is pH-adjusted and then enters an electro-Fenton treatment device for electro-Fenton reaction; the effluent of the electro-Fenton treatment device is pH-adjusted and then enters a flocculation precipitation treatment device for coagulation and precipitation with a coagulant, and the effluent of the flocculation precipitation treatment device is the landfill leachate that has completed the pretreatment;

[0004] Although existing technologies can achieve the simultaneous removal of pollutants such as suspended solids, COD, ammonia nitrogen, total phosphorus, and turbidity in wastewater, and can also improve the biodegradability of wastewater and reduce the subsequent treatment load, they mainly rely on electrochemical processes, resulting in high energy consumption, and the electrodes are easily corroded by high-salt environments and require maintenance; the cost of ozone dosing equipment is high, and the synergistic mechanism of tail gas and electro-Fenton has not been refined; the addition of reagents in the coagulation stage lacks dynamic regulation, which may cause waste or fluctuations in effect; the process is long and the pH adjustment link increases the complexity of operation, affecting continuity. Summary of the Invention

[0005] The present invention mainly provides a landfill leachate pretreatment process, which can solve the problems of high energy consumption, high cost and poor coordination proposed in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a landfill leachate pretreatment process, comprising:

[0007] First, after pre-separation, the leachate is transported to the pre-oxidation reaction chamber by a centrifugal pump. The ultrasonic generator is turned on to enhance mass transfer, the frequency conversion stirrer is used to promote mixing, and the ORP meter is used to dynamically control the addition of oxidants to complete pre-oxidation and catalytic chain breaking. Then, the pre-oxidation effluent enters the fluidized bed reactor. After preliminary impurities are removed in the pre-precipitation area, the water distributor and the granular sludge bed are used to improve the collision efficiency of calcium and magnesium ions. Calcium hydroxide emulsion and sodium carbonate solution are dynamically added with the help of a pH meter and a calcium ion sensor to achieve double alkali decalcification and magnesium removal, and the precipitated sludge is discharged regularly. Subsequently, the decalcified effluent enters the magnetic In the flocculation reaction chamber, magnetic flocculants are first added to the mixing zone through turbine stirring, and then frame stirring and magnetic stirring are used in the flocculation zone to promote floc aggregation. Modified activated carbon is added for adsorption simultaneously, and the flocculant dosage is regulated by feedback from the turbidity meter. Afterwards, the effluent from the magnetic flocculation is pressurized by a centrifugal pump and enters the cross-flow dynamic membrane device for filtration. Pulse backwashing is automatically triggered based on the trans-membrane pressure difference, and regular chemical cleaning is performed to maintain the membrane flux. Finally, through the integration of the intelligent control system, data is collected by various sensors, and automatic adjustment of chemical addition, membrane backwash triggering and fault switching warning are realized through PLC to complete the pretreatment of landfill leachate.

[0008] Furthermore, when the pre-oxidation reaction chamber is in operation, the frequency of the ultrasonic generator is 30 kHz, the power is 10 kW, the speed of the variable frequency stirrer is 100 rpm, and the ORP meter monitors the potential of the reaction chamber in real time to maintain the potential in the range of +300 to +400 mV. At the same time, the pH value is monitored to maintain the pH value at 6.5 to 7.5 and the temperature is maintained at 20°C to 30°C.

[0009] Furthermore, the effective volume of the fluidized bed reactor is 15m 3 The pre-oxidation effluent enters through the overflow port and first passes through 7m 3 The pre-precipitation area initially removes large particles of impurities and then enters the 8m 3 In the fluidized bed area, the water distributor distributes water evenly at a flow rate of 0.5m / s. The granular sludge bed with a modified ceramsite filling rate of 30% is suspended by the impact of water flow, which improves the collision efficiency of calcium and magnesium ions. The sludge discharge cycle is 8 hours, and the sludge discharge volume each time is 0.5m 3 .

[0010] Furthermore, in the double-alkali method for decalcification and magnesium treatment, calcium hydroxide emulsion is added via a screw pump, with the initial dosage controlled at 10 kg / ton of leachate. The pH value of the pre-precipitation zone is monitored by a pH meter and maintained at 10.0-10.5. The dosage of sodium carbonate solution is dynamically adjusted based on the data from the calcium ion sensor. When the calcium ion concentration is greater than 1000 mg / L, the dosage is increased to 4 kg / ton of leachate to ensure that the pH of the fluidized bed zone is between 10.5 and 11.0.

[0011] Furthermore, the magnetic flocculation reaction chamber includes 1m 3 Mixed zone and 4m 3Flocculation zone; the turbine agitator in the mixing zone rotates at 200 rpm, and a 12% polyferric chloride-magnetic nanoparticle flocculant is added for 5 minutes; the frame agitator in the flocculation zone rotates at 30 rpm, and a magnetic stirring device with a magnetic field strength of 800 Gs is used to promote floc aggregation. The reaction time is 10 minutes, and modified activated carbon with a particle size of 1.0 mm is added simultaneously at a dosage of 80 mg / L. The adsorption time is 10 minutes, and the turbidity meter monitors and feedbacks. When the turbidity is greater than 20 NTU, the flocculant dosage is automatically increased by 50 mg / L.

[0012] Furthermore, when the dynamic membrane device is in operation, the magnetic flocculation effluent is pressurized to 0.2 MPa by a centrifugal pump and transported to a filter with a pore size of 0.1 μm and a filtration area of 50 m 2 The ceramic microfiltration membrane assembly maintains a membrane surface flow rate of 2.5m / s, the transmembrane pressure difference is controlled within 0.15MPa, and the produced water SS≤10mg / L, COD≤500mg / L, and turbidity≤1NTU.

[0013] Furthermore, the pulse backwash of the dynamic membrane filtration unit is automatically triggered when TMP≥0.15MPa; the water inlet pump is turned off and the flow rate is turned on at 3m 3 / h backwash pump, use pre-treated clean water to backwash the membrane surface for 30 seconds, the backwash frequency is 4 times / hour, the backwash water volume is 10% of the treatment volume, every three months, use 2% citric acid solution for 30 minutes of circulation cleaning and 1% sodium hypochlorite solution for 1 hour to maintain the membrane flux.

[0014] Furthermore, in the control system integration, the ORP meter, pH meter, calcium ion sensor, and flow sensor transmit data to the PLC via 4mA to 20mA signals, with an update frequency of 1 time per minute. The dosage of calcium hydroxide and sodium carbonate is automatically adjusted by the PID algorithm with a control accuracy of ±5%. The membrane backwash is triggered based on the TMP threshold, and the HMI displays a fault code when the equipment fails.

[0015] The beneficial effects of the landfill leachate pretreatment process of the present invention are:

[0016] First, the pre-oxidation and catalytic chain breaking process enhances the mass transfer efficiency between the oxidant and the pollutants through the cooperation of an ultrasonic generator and a variable frequency agitator. The ORP meter is used to dynamically control the dosage of the reagent, so that parameters such as potential, pH value and temperature are maintained in the optimal range, ensuring that the oxidation reaction proceeds fully and that large molecular organic matter is efficiently decomposed, laying the foundation for subsequent treatment. Next, the double-alkali decalcification and magnesium process utilizes the special structure of the fluidized bed reactor to improve the collision efficiency of calcium and magnesium ions through a water distributor and a granular sludge bed. At the same time, the sensor dynamically controls the dosage of the reagent and accurately adjusts the pH value. This not only effectively removes calcium and magnesium ions, but also reduces reagent waste and lowers operating costs.

[0017] In addition, the magnetic flocculation and dynamic membrane filtration process effectively removes pollutants such as suspended matter, colloids and color through gradient stirring in the mixing zone and flocculation zone, magnetic stirring device and adsorption of modified activated carbon. The water quality is then precisely filtered by the dynamic membrane device to ensure that the produced water meets the standards. Pulse backwashing and regular chemical cleaning maintain the membrane flux and ensure the stable operation of the filtration system. Finally, the intelligent control system integrates various sensors and PLCs to realize functions such as real-time data collection, automatic adjustment of chemical addition, membrane backwash triggering and fault switching warning, which greatly improves the automation level and stability of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0019] Figure 1 This is a schematic diagram of a process flow of a landfill leachate pretreatment process according to the present invention;

[0020] Figure 2 The present invention is a schematic flow chart of a method for pretreatment of landfill leachate. DETAILED DESCRIPTION

[0021] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1

[0023] like Figure 1-Figure 2 As shown, a technical solution is provided: a landfill leachate pretreatment process, comprising:

[0024] Step 1: Pre-oxidation and catalytic chain breaking

[0025] The landfill leachate is first filtered through a grid for pre-separation. After removing large particles of impurities, it is pumped by a centrifugal pump (with a flow rate of 5m 3 / h) to the pre-oxidation reaction chamber (volume 10m 3) for 2 hours, then turn on the ultrasonic generator (frequency 30kHz, power 10kW), generate cavitation effect through high-frequency vibration, form a local high-temperature and high-pressure microenvironment, enhance the collision frequency between the oxidant and the pollutant molecules, then add sulfate-nano-iron composite solution (concentration 25%) and start the frequency conversion stirrer (speed 100rpm) at the same time, so that the sulfate-nano-iron composite solution and the landfill leachate are fully mixed, and then the ORP meter monitors the reaction chamber potential in real time. When the potential is lower than +300mV, it indicates that the oxidant is insufficient, and the peristaltic pump automatically increases the dosage of the agent (initial The initial dosage is 600mg / L, about 30L / h); when it exceeds +400mV, the dosage is reduced. Through dynamic negative feedback control, the potential is maintained in the range of +300 to +400mV. This potential range can maximize the efficiency of iron ion circulation and ensure that the persulfate decomposition rate is ≥85%. Then, the pH value (6.5 to 7.5) and temperature (20℃ to 30℃) are monitored simultaneously. The pH value is maintained by automatically adding dilute sulfuric acid or sodium hydroxide solution, and the temperature is adjusted by a jacketed heat exchanger. In the event of an abnormality, an audible and visual alarm is triggered to prevent the decrease of free radical activity due to pH or temperature fluctuations.

[0026] The sulfate-nano-iron composite solution is prepared by dispersing nano-iron particles (particle size 20-50 nm, purity ≥99%) in deionized water at a concentration of 5% to 8% by mass of the composite solution, and ultrasonically dispersing for 30 minutes (frequency 40 kHz) to form a stable nano-iron suspension; then adding potassium persulfate (K2S2O8) to a total solution concentration of 25%, stirring and mixing uniformly (rotating speed 200 rpm, time 20 minutes) to fully dissolve the persulfate and form a homogeneous system with the nano-iron particles. The nano-iron acts as a catalyst to promote the decomposition of the persulfate to produce sulfate free radicals, which account for 5% to 8% of the composite solution mass. The persulfate content is 17% to 20%, and the balance is water. This ratio ensures maximum free radical yield while avoiding the problem of agglomeration and inactivation caused by excessive nano-iron.

[0027] Step 2: Double Alkali Decalcification and Magnesium

[0028] After pre-oxidation, the effluent enters the fluidized bed reactor (total volume 15m 3 ), first pass 7m 3 The pre-precipitation zone removes large particles of impurities with a particle size of more than 500 μm (such as sand particles and undecomposed garbage debris). The gravity sedimentation principle is used with a residence time of 30 minutes to reduce the suspended solids (SS) concentration in the leachate from 600 to 800 mg / L of pre-oxidation effluent to 300 to 400 mg / L. The water then flows into the 8m 3In the fluidized bed area, the water distributor adopts a porous uniform structure (aperture 20mm, opening rate 30%), and distributes water evenly at a flow rate of 0.5m / s, so that the water flow is in an upward flow state, driving the modified ceramsite (particle size 3-5mm, specific surface area ≥500m 2 / g, with a surface loaded calcium carbonate seed) filling rate of 30% granular sludge bed forming a suspended state, the bed expansion rate is controlled at 20% to 30%, and the collision and friction between particles promotes the contact area between calcium and magnesium ions and the reagent to increase by 2-3 times;

[0029] Then, a screw pump was used to add 6% calcium hydroxide emulsion (initial dosage 10kg / ton of leachate). The pH value of the pre-precipitation zone was monitored in real time by a pH meter and maintained at 10.0-10.5, so that magnesium ions were precipitated in the form of magnesium hydroxide (Mg(OH)2) (solubility ≤ 10mg / L). At the same time, some calcium ions began to form calcium carbonate crystal nuclei. Subsequently, in the fluidized bed area, the dosage of sodium carbonate solution (concentration 15%) was dynamically adjusted according to the data of the calcium ion sensor (detection accuracy ±5mg / L). When the calcium ion concentration is greater than 1000 mg / L, the dosage is increased to 4 kg / ton of leachate. The high pH environment (10.5-11.0) is used to promote carbonate ions and calcium ions to generate calcium carbonate precipitation (solubility ≤ 5 mg / L). At the same time, the seeds on the surface of the modified ceramsite can accelerate the crystallization process, so that the precipitation efficiency is increased by more than 40%. The calcium carbonate and magnesium hydroxide precipitation generated by the reaction are collected through the bottom conical bucket. The sludge discharge cycle is 8 hours (adjusted according to the feedback of the sludge concentration meter), and the sludge discharge volume each time is 0.5m 3 , the sludge moisture content is about 85%, which is 10% to 15% lower than the traditional sedimentation process;

[0030] The preparation method of the calcium hydroxide emulsion comprises the following steps: adding a fixed amount of deionized water to a stirring tank, turning on a stirrer (rotating speed 150-200 rpm), slowly adding calcium hydroxide powder (purity ≥95%) in an amount of 6% of the total mass of the solution, and continuously stirring for 40-60 minutes until the powder is completely dispersed to form a uniform emulsion. During the preparation process, the water temperature needs to be controlled at 20-30° C. to avoid a decrease in the solubility of the calcium hydroxide due to high temperature. The calcium hydroxide content is 6% of the mass of the emulsion, and the remainder is water. This concentration can ensure a sufficient calcium ion concentration to remove magnesium ions and part of the calcium ions, avoid the problem of clogging of the delivery pipeline due to excessively high concentration, and simultaneously ensure the fluidity and reactivity of the calcium hydroxide emulsion.

[0031] The preparation method of sodium carbonate solution is as follows: adding a certain amount of warm water (temperature 30-40°C to improve dissolution efficiency) into a dissolution tank, turning on the agitator (speed 100-150rpm), adding sodium carbonate powder (purity ≥99%) in batches, the addition amount is 15% of the total mass of the solution, and continuously stirring for 30-40 minutes until it is completely dissolved to form a transparent solution. After the preparation is completed, the concentration of the solution is tested by a density meter to ensure that the sodium carbonate content is 15% (mass fraction), and the remainder is water. This concentration takes into account both solubility and reaction efficiency, which can not only avoid incomplete dissolution due to excessively high concentration, but also reduce the dilution step during subsequent addition, ensuring rapid reaction with calcium ions in the fluidized bed area to form calcium carbonate precipitate, while reducing the transportation and storage costs of the agent.

[0032] Step 3: Magnetic flocculation and adsorption

[0033] After decalcification and magnesium removal, the effluent enters the magnetic flocculation reaction chamber (mixing zone 1m 3 , flocculation zone 4m 3 In the mixing zone, the turbine agitator stirs at a high speed of 200 rpm to form a strong turbulent environment, so that 12% polyferric chloride-magnetic nanoparticle flocculant (dosage 250 mg / L, about 12.5 L / h) is quickly mixed with the wastewater. The electrical neutralization effect of polyferric chloride is used to break the charge of the colloidal particles. At the same time, magnetic nanoparticles (particle size 20-50 nm, Fe3O4 content ≥90%) initially form micro-flocculation through adsorption and bridging. The mixing time is 5 minutes to ensure that the dispersion uniformity of the agent is greater than 90%.

[0034] Then, after entering the flocculation zone, the frame stirrer stirs at a low speed of 30 rpm, and cooperates with a magnetic stirring device with a magnetic field strength of 800 Gs (using a neodymium iron boron permanent magnet array, a magnetic field gradient of ≥500 Gs / m) to promote the directional aggregation of magnetic micro-flocs in a low shear force environment to form magnetic flocs with a particle size of >50 μm. The reaction time is 10 minutes, so that the floc sedimentation rate is increased to more than 20 m / h. At the same time, modified activated carbon with a particle size of 1.0 mm (specific surface area ≥1200 m 2 / g, surface loaded iron oxide), with a dosage of 80mg / L (about 4kg / h), uses its porous structure to adsorb residual color (removal rate ≥80%) and dissolved organic matter (COD removal rate increased by 15% to 20%), and through the synergistic effect of magnetic particles and activated carbon, enhances floc density and sedimentation performance. Then, a turbidity meter (detection accuracy ±0.1NTU) is set at the end of the flocculation zone for real-time monitoring. When the turbidity is greater than 20NTU, the flocculant dosing system is automatically triggered to increase the dosage by 50mg / L. Dynamic adjustment is made through the PID algorithm to ensure that the effluent turbidity is stable ≤10NTU. This design uses a three-level mechanism of "high shear mixing + low shear flocculation + magnetic enhancement". Compared with the traditional flocculation process, the floc formation speed is increased by 30% and the sludge volume is reduced by 25%. At the same time, the magnetic flocs can be intercepted by the magnetic field of the subsequent dynamic membrane filtration unit, further improving the solid-liquid separation efficiency.

[0035] The preparation method of the polyferric chloride-magnetic nanoparticle flocculant is as follows: adding deionized water to a reactor, turning on a stirrer (rotating speed 200-250rpm), first adding polyferric chloride (FeCl3 content ≥30%) to a solution mass concentration of 10%-11%, stirring and dissolving for 30 minutes; then adding magnetic nanoparticles (Fe3O4 content ≥90%, particle size 20-50nm) to control the amount of magnetic nanoparticles to account for 1%-2% of the total mass of the solution, continuing stirring for 60 minutes, and uniformly dispersing the magnetic particles in the polyferric chloride solution by ultrasonic dispersion (frequency 40kHz, power 500W) to form a stable composite flocculant, wherein the polyferric chloride content is 10%-11%, the magnetic nanoparticle content is 1%-2%, and the balance is water. This ratio not only ensures the electrical neutralization and flocculation ability of the polyferric chloride, but also improves the floc strength and sedimentation velocity through the adsorption and bridging effect of the magnetic particles. The composite flocculant is suitable for treating landfill leachate with high suspended matter and colloid content.

[0036] The PID algorithm dynamic adjustment uses the deviation (e(t) = SP-PV) between the real-time monitoring value (PV) of the turbidity meter and the target value (SP = 10NTU) as input, and calculates the control amount (flocculant increment Δu(t)) through the three links of proportion (P), integration (I), and differentiation (D). The specific formula is:

[0037]

[0038] where k p is the proportional coefficient, which amplifies the current deviation and quickly responds to turbidity changes. i is the integral coefficient, eliminating steady-state errors and accumulating historical deviations, k d is the differential coefficient, which predicts the deviation trend and suppresses overshoot.

[0039] Step 4: Dynamic Membrane Filtration Unit

[0040] The magnetic flocculation effluent is pressurized to 0.2 MPa by a centrifugal pump and transported to the ceramic microfiltration membrane assembly (pore size 0.1 μm, α-Al2O3 material, porosity 40% to 45%) at a membrane surface flow rate of 2.5 m / s, with a filtration area of 50 m 2 , design flux 100~200L / m 2 h. In actual operation, the transmembrane pressure (TMP) is maintained in the range of 0.10-0.15 MPa by adjusting the frequency of the centrifugal pump. The calculation formula of TMP is:

[0041]

[0042] The inlet pressure, concentrate pressure and product water pressure are respectively monitored in real time by a pressure transmitter with an accuracy of 0.1 level to ensure that the thickness of the filter cake layer on the membrane surface is controlled at 0.1-0.3mm to avoid flux attenuation caused by excessive compaction. The filtered water product indicators are SS ≤ 10mg / L, COD ≤ 500mg / L, and turbidity ≤ 1NTU, which meet the subsequent DTRO or biochemical treatment water requirements. When TMP ≥ 0.15MPa, the PLC triggers the pulse backwash program: close the water inlet valve, start the backwash pump (flow rate 3m 3 / h), use pre-treated clean water (SS≤50mg / L) to flush the membrane surface at a reverse flow rate of 1.2m / s for 30 seconds, and the backwash water volume each time is 0.5m 3 (accounting for 10% of the treatment capacity), the loose filter cake on the membrane surface is removed by hydraulic shearing action, and the backwash frequency is 4 times / hour, which can make the membrane flux recovery rate reach more than 90%;

[0043] At the same time, chemical cleaning is performed every three months: first, a 2% citric acid solution (pH 2-3) is circulated and cleaned at a flow rate of 1.5m / s for 30 minutes to remove metal hydroxide deposits; then, a 1% sodium hypochlorite solution (effective chlorine concentration 1000-1500ppm) is soaked for 1 hour to kill biofilm and oxidize organic matter, and finally, rinsed with clean water until the conductivity is less than 100μS / cm. Chemical cleaning can restore the membrane flux to 95% of the initial value, extending the service life of the membrane module to more than 3 years;

[0044] The preparation method of citric acid solution is as follows: add a certain amount of deionized water to the cleaning tank, turn on the stirrer (speed 100-150rpm), slowly add food-grade citric acid powder (purity ≥99%), the addition amount is 2% of the total mass of the solution, and continue stirring for 20-30 minutes until it is completely dissolved to form a transparent acidic solution. No heating is required during the preparation process, and the dissolution can be completed at room temperature (20-25℃). The citric acid content is 2% of the solution mass, and the rest is water. This concentration can effectively dissolve metal oxides (such as Fe 3 +、Ca 2+ deposition), and avoid chemical erosion of the ceramic membrane due to excessive concentration, ensuring a balance between cleaning effect and membrane component safety;

[0045] The sodium hypochlorite solution is as follows: add a certain amount of clean water to a corrosion-resistant storage tank, turn on the agitator (speed 80-120rpm), slowly add sodium hypochlorite stock solution with an effective chlorine content ≥10%, the addition amount is 10% of the total mass of the solution (that is, 100kg stock solution to 900kg water), stir and mix evenly to form a solution with an effective chlorine concentration of 1%. Wear protective equipment during preparation and operate in a ventilated environment to avoid contact of the stock solution with the skin or mucous membranes. Among them, the sodium hypochlorite (calculated as effective chlorine) content is 1% of the solution mass, and the balance is water. This concentration can effectively kill bacteria, fungi and other microorganisms on the membrane surface, inhibit the growth of biofilm, and at the same time reduce the risk of oxidative damage to the membrane material, taking into account both cleaning efficiency and membrane component life protection.

[0046] Step 5: Control System Integration

[0047] ORP meter, pH meter, calcium ion sensor (detection range 0 ~ 2000mg / L, accuracy ± 2%), electromagnetic flow sensor (range 0 ~ 10m 3 / h, accuracy ±0.5%) transmits data in real time to the PLC (using Siemens S7-300 series, scanning cycle 50ms) via 4mA~20mA standard industrial signals. The data is updated once per minute to ensure real-time monitoring of process parameters. The PLC has a built-in PID control module that automatically adjusts the dosage of calcium hydroxide and sodium carbonate through an incremental PID algorithm with a control accuracy of ±5%. For example, when the calcium ion concentration is higher than the set value, the PLC calculates the required increase in sodium carbonate dosage and outputs a 4mA~20mA signal to the screw pump inverter, realizing dynamic optimization of reagent dosage. The PID algorithm formula is:

[0048] Δu(k)=K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-1)]

[0049] Where e(k) is the deviation value at the kth sampling moment, e(k-1) and e(k-2) are the deviation values at the k-1th and k-2th sampling moments.

[0050] The membrane backwash control logic based on the TMP threshold (0.15 MPa) is as follows: the pressure transmitter monitors the transmembrane pressure difference in real time. When the TMP is ≥ 0.15 MPa, the PLC triggers the digital output module, closes the water inlet valve, and starts the backwash pump to execute a 30-second pulse backwash program. This logic can avoid increased membrane fouling caused by manual intervention and maintain the membrane flux at more than 90% of the design value.

[0051] Equipment fault diagnosis: When the operating current of the dosing pump exceeds the rated value (monitored in real time by the frequency converter) or the bearing temperature of the membrane water inlet pump exceeds 60°C (detected by the PT100 temperature sensor), the PLC determines that it is an equipment fault and automatically cuts off the power supply of the faulty equipment. The HMI interface (using the Weiluntong MT8102iE) then displays the fault code in real time (such as E01: dosing pump blockage; E02: membrane pressure difference exceeds the limit) and sends a text message containing the fault type and occurrence time to the operation and maintenance personnel via the built-in GSM module (such as "Warning: Fluidized bed area dosing pump is blocked, code E01, time 2023-10-05 14:30"). The response time is less than 2 minutes.

[0052] The above embodiments only express several implementation methods of the present invention, and their description is relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention,

[0053] Under the above conditions, several modifications and improvements can be made, which all fall within the scope of protection of the present invention.

[0054] Therefore, the scope of protection of the patent for this invention should be based on the attached claims.

Claims

1. A landfill leachate pretreatment process, characterized by: First, after pre-separation, the leachate is transported to the pre-oxidation reaction chamber by a centrifugal pump. The ultrasonic generator is turned on to enhance mass transfer, the frequency conversion stirrer is used to promote mixing, and the ORP meter is used to dynamically control the addition of oxidants to complete pre-oxidation and catalytic chain breaking. Then, the pre-oxidation effluent enters the fluidized bed reactor. After preliminary impurities are removed in the pre-precipitation area, the water distributor and the granular sludge bed are used to improve the collision efficiency of calcium and magnesium ions. Calcium hydroxide emulsion and sodium carbonate solution are dynamically added with the help of a pH meter and a calcium ion sensor to achieve double alkali decalcification and magnesium removal, and the precipitated sludge is discharged regularly. Subsequently, the decalcified effluent enters the magnetic In the flocculation reaction chamber, magnetic flocculants are first added to the mixing zone through turbine stirring, and then frame stirring and magnetic stirring are used in the flocculation zone to promote floc aggregation. Modified activated carbon is added for adsorption simultaneously, and the flocculant dosage is regulated by feedback from the turbidity meter. Afterwards, the effluent from the magnetic flocculation is pressurized by a centrifugal pump and enters the cross-flow dynamic membrane device for filtration. Pulse backwashing is automatically triggered based on the trans-membrane pressure difference, and regular chemical cleaning is performed to maintain the membrane flux. Finally, through the integration of the intelligent control system, data is collected by various sensors, and automatic adjustment of chemical addition, membrane backwash triggering and fault switching warning are realized through PLC to complete the pretreatment of landfill leachate.

2. A landfill leachate pretreatment process according to claim 1, characterized in that: When the pre-oxidation reaction chamber is in operation, the frequency of the ultrasonic generator is 30 kHz, the power is 10 kW, the speed of the variable frequency stirrer is 100 rpm, and the ORP meter monitors the potential of the reaction chamber in real time to maintain the potential in the range of +300 to +400 mV. At the same time, the pH value is monitored to maintain the pH value at 6.5 to 7.5, and the temperature is maintained at 20°C to 30°C.

3. The landfill leachate pretreatment process according to claim 1, wherein: The effective volume of the fluidized bed reactor is 15m 3 The pre-oxidation effluent enters through the overflow port and first passes through 7m 3 The pre-precipitation area initially removes large particles of impurities and then enters the 8m 3 In the fluidized bed area, the water distributor distributes water evenly at a flow rate of 0.5m / s. The granular sludge bed with a modified ceramsite filling rate of 30% is suspended by the impact of water flow, which improves the collision efficiency of calcium and magnesium ions. The sludge discharge cycle is 8 hours, and the sludge discharge volume each time is 0.5m 3 .

4. The landfill leachate pretreatment process according to claim 1, wherein: In the double-alkali decalcification and magnesium process, calcium hydroxide emulsion is added via a screw pump, with an initial dosage controlled at 10 kg / ton of leachate. The pH value of the pre-precipitation zone is monitored by a pH meter and maintained at 10.0-10.

5. The dosage of sodium carbonate solution is dynamically adjusted based on the data from the calcium ion sensor. When the calcium ion concentration is greater than 1000 mg / L, the dosage is increased to 4 kg / ton of leachate to ensure that the pH of the fluidized bed zone is between 10.5 and 11.

0.

5. The landfill leachate pretreatment process according to claim 1, characterized in that: The magnetic flocculation reaction chamber includes 1m 3 Mixed zone and 4m 3 Flocculation zone; the turbine agitator in the mixing zone rotates at 200 rpm, and a 12% polyferric chloride-magnetic nanoparticle flocculant is added for 5 minutes; the frame agitator in the flocculation zone rotates at 30 rpm, and a magnetic stirring device with a magnetic field strength of 800 Gs is used to promote floc aggregation. The reaction time is 10 minutes, and modified activated carbon with a particle size of 1.0 mm is added simultaneously at a dosage of 80 mg / L. The adsorption time is 10 minutes, and the turbidity meter monitors and feedbacks. When the turbidity is greater than 20 NTU, the flocculant dosage is automatically increased by 50 mg / L.

6. The landfill leachate pretreatment process according to claim 1, characterized in that: When the dynamic membrane device is running, the magnetic flocculation effluent is pressurized to 0.2 MPa by a centrifugal pump and transported to a filter with a pore size of 0.1 μm and a filtration area of 50 m 2 The ceramic microfiltration membrane assembly maintains a membrane surface flow rate of 2.5m / s, the transmembrane pressure difference is controlled within 0.15MPa, and the produced water SS≤10mg / L, COD≤500mg / L, and turbidity≤1NTU.

7. The landfill leachate pretreatment process according to claim 1, characterized in that: The pulse backwash of the dynamic membrane filtration unit, when TMP ≥ 0.15MPa, the PLC is automatically triggered; the water inlet pump is turned off and the flow rate is turned on 3m 3 / h backwash pump, use pre-treated clean water to backwash the membrane surface for 30 seconds, the backwash frequency is 4 times / hour, the backwash water volume is 10% of the treatment volume, every three months, use 2% citric acid solution for 30 minutes of circulation cleaning and 1% sodium hypochlorite solution for 1 hour to maintain the membrane flux.

8. The landfill leachate pretreatment process according to claim 1, characterized in that: In the control system integration, the ORP meter, pH meter, calcium ion sensor, and flow sensor transmit data to the PLC via 4mA-20mA signals, with an update frequency of 1 time per minute. The dosage of calcium hydroxide and sodium carbonate is automatically adjusted using a PID algorithm with a control accuracy of ±5%. Membrane backwash is triggered based on the TMP threshold, and a fault code is displayed on the HMI when a device malfunctions.

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