Maleic anhydride sewage multi-stage treatment system and process

Abstract

The maleic anhydride sewage multi-stage treatment system comprises a pretreatment module, an anaerobic treatment module, an aerobic treatment module, an advanced treatment module and an intelligent control module which are sequentially connected, the pretreatment module comprises a regulating tank, a coagulative precipitation tank and a micro-electrolytic tank, the micro-electrolytic tank is filled with iron-carbon filler, and the anaerobic treatment module is connected with the aerobic treatment module. The mass ratio of iron to carbon is 3: 1; the advanced treatment module comprises a catalytic ozonation unit and a biological aerated filter, a water outlet of the catalytic ozonation unit is communicated with a water inlet of the anaerobic treatment module through a reflux pipeline, the reflux ratio is 10%-30%, macromolecular pollutants are degraded through triple effects of chain scission, oxidation and flocculation, and the sewage treatment efficiency is improved. The enhanced chain breaking and biodegradability of micro-electrolysis synergistic coagulation are improved; and substrate mass transfer is accelerated by combining high-volume load, so that acid accumulation inhibition is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly to a multi-stage treatment system and process for maleic anhydride sewage. Background Art

[0002] Maleic anhydride is currently the third largest acid anhydride in the world after phthalic anhydride and acetic anhydride. It has a wide range of uses and is mainly used as a raw material for the production of 1,4-butanediol, unsaturated polyester resins, alkyd resins, etc. At the same time, it is also a copolymerization monomer of coatings, maleic rosin, and polymaleic anhydride, and can also be used as an organic chemical raw material for the production of ink additives, paper-making additives, plasticizers, etc., and can also be used in medicine and pesticides. At the same time, maleic anhydride is also used in the raw material production of fiberglass, petrochemical industry, food processing, medicine, building materials and other industries, and has extremely broad development and application prospects.

[0003] However, in the prior art, the maleic anhydride production process mainly uses solvent absorption, or uses a maleic anhydride device by the n-butane method to produce maleic anhydride. In this process, a large amount of maleic anhydride wastewater will be generated. Among them, the solvent absorption is mainly dibutyl phthalate / diisobutyl hexahydrophthalate (DIBE / DBP). The used solvent forms the main component of the sewage in the maleic anhydride production process. The used solvent contains impurities such as acetic acid, acrylic acid, n-butanol, and a small amount of maleic anhydride. Therefore, the maleic anhydride wastewater needs to be treated and discharged after reaching the discharge standard. Chemical Oxygen Demand (COD) is an important indicator of water body organic pollution and can reflect the pollution degree of the water body. When the maleic anhydride wastewater is reduced to less than 500 mg / L, it can be discharged.

[0004] It can be seen that in the prior art, whether using the biochemical method or physical and chemical methods such as concentration and evaporation to treat maleic anhydride wastewater, the physical and chemical methods are cumbersome to operate and have high treatment costs; the maleic anhydride wastewater treated by the biochemical method is difficult to meet the discharge standard of Chemical Oxygen Demand (COD).

[0005] Therefore, the related technologies of the current maleic anhydride sewage treatment process still need to be further improved. Summary of the Invention

[0006] Aiming at the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a multi-stage treatment system and process for maleic anhydride sewage, which solves the problems of removing high COD, difficult-to-degrade organic substances and biotoxic substances in the prior art.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions: On the one hand, the present invention provides a multi-stage treatment system for maleic anhydride sewage, including a pretreatment module, an anaerobic treatment module, an aerobic treatment module, a deep treatment module and an intelligent control module connected in sequence, wherein: The pretreatment module includes an adjustment tank, a coagulation sedimentation tank, and a micro-electrolysis tank. The micro-electrolysis tank is filled with iron-carbon filler, and the mass ratio of iron to carbon is 3:1; The advanced treatment module includes an ozone catalytic oxidation unit and an aerated biological filter. The outlet of the ozone catalytic oxidation unit is connected to the inlet of the anaerobic treatment module through a reflux pipeline, and the reflux ratio is 10%-30%.

[0008] On the basis of this technical solution, further preferably, the residence time of the micro-electrolysis tank is 2-4 h, the pH is controlled at 3-4, and the filling density of the iron-carbon filler is 60%-80%.

[0009] On the basis of this technical solution, further preferably, the anaerobic treatment module is an upflow anaerobic sludge bed reactor, and its operating parameters are: temperature 35-38 °C, hydraulic retention time 24-36 h; volumetric loading 5-7 kgCOD / (m²·d), and the biogas collected is used for system heating.

[0010] On the basis of this technical solution, further preferably, the aerobic treatment module is composed of a moving bed biofilm reactor and a membrane bioreactor in series. Among them: the packing filling rate of the moving bed biofilm reactor is 50%-70%, and the dissolved oxygen is controlled at 2-4 mg / L; the membrane pore size of the membrane bioreactor is 0.1-0.4 μm, and the backwashing period is 6-12 h.

[0011] On the basis of this technical solution, further preferably, the catalyst of the ozone catalytic oxidation unit is manganese-iron bimetallic oxide supported on titanium dioxide, the catalyst filling rate is 30%-50%, the ozone dosage is 50-80 mg / L, and the reaction time is 30-60 min.

[0012] On the basis of this technical solution, further preferably, the intelligent control module includes: An on-line sensor group, at least including a pH sensor, an oxidation-reduction potential sensor, a dissolved oxygen sensor, and an ozone concentration analyzer; An actuator, at least including an ozone generator, an aeration blower, and a chemical dosing pump; A controller, which dynamically adjusts the ozone dosage, the aeration intensity, and the coagulant dosage based on the fuzzy PID algorithm.

[0013] Secondly, the present invention also provides a multi-stage treatment process for maleic anhydride wastewater, including the following steps: S1, pretreatment stage: After the wastewater is introduced into the adjustment tank to equalize the water quality, polyaluminum chloride 200-300 mg / L and polyacrylamide 1-2 mg / L are added in sequence for coagulation sedimentation, and then enter the micro-electrolysis tank for treatment for 2-4 h; S2, anaerobic treatment stage: control the UASB reactor temperature to 35-38 ° C, hydraulic retention time to 24-36h, volumetric load to 5-7 kgCOD / (m 3 d); S3, advanced treatment stage: the effluent from the ozone catalytic oxidation unit is partially refluxed to the UASB reactor with a reflux ratio of 10%-30%, and the remaining effluent enters the aerated biological filter for treatment until the COD is ≤50mg / L; S4, intelligent control stage: use PID algorithm to adjust the control strategy for subsequent processing.

[0014] On the basis of this technical solution, it is further preferred that the operating parameters of the ozone catalytic oxidation unit in step S3 are: the ozone dosage is dynamically adjusted according to the influent COD concentration, when COD>200 mg / L, the ozone dosage is 60-80 mg / L; when COD≤200 mg / L, the ozone dosage is 30-50 mg / L.

[0015] On the basis of this technical solution, further preferably, the control strategy of the intelligent control module includes: When the ORP sensor detection value is >400 mV, the backwash procedure of the aeration biological filter is triggered and the ozone dosage is reduced by 20%-40%; when the pH sensor detection value is <3, the dosing pump is started to add sodium hydroxide solution until the pH returns to 3-4.

[0016] On the basis of this technical solution, it is further preferred that the preparation method of the iron-carbon filler is: iron filings and activated carbon are mixed in a mass ratio of 3:1, soaked in 0.1 mol / L hydrochloric acid for 30 minutes, and calcined to 500-600°C under nitrogen protection for 2 hours.

[0017] The multi-stage treatment system and process of maleic anhydride wastewater of the present invention has the following beneficial effects compared with the prior art: (1) Compared with the existing processes that rely on coagulation and precipitation (such as PAC and PAM), the pretreatment module in the treatment system of the present invention utilizes the electron transfer effect of iron-carbon micro-electrolysis: Fe-C forms a tiny galvanic cell under acidic conditions, and Fe is oxidized as the anode (Fe → Fe²+2e - ), carbon acts as a cathode to adsorb H* to generate active hydrogen (2H + +2e - →2[H]); active hydrogen [H] and Fe 2+ Synergistically attack the molecular chains of organic matter (such as phthalates), degrade macromolecular pollutants through the triple action of bond breaking-oxidation-flocculation, and thoroughly enhance the chain breaking and biodegradability of electrolysis and synergistic coagulation.

[0018] (2) Multi-stage anaerobic metabolic pathway: UASB is enriched with hydrolytic bacteria (such as Clostridium), acidogenic bacteria (such as Syntrophobacter) and methanogenic bacteria (such as Methanothrix) in layers, and the multi-stage synergy of hydrolysis-acidification-methane production is achieved. The temperature and load are coordinated to optimize the activity of the spraying bacteria at 35-38 °C, combined with a high volumetric load of 6 kgCOD / (m 3 d) Accelerate substrate mass transfer and avoid acid accumulation inhibition. Compared with traditional anaerobic processes, the bacterial community structure is not optimized and the volume load is only 3-4 kgCOD / (m 3 d) and biogas is not recycled for heating.

[0019] (3) Free radical pathway of Mn-Fe / TiO2 catalyst: Mn-Fe bimetallic Oxides activate ozone through surface hydroxyl groups to generate ·OH and ·O2 - Free radicals attack C=C double bonds and benzene ring structures in organic matter, achieving targeted mineralization (e.g., γ-butyrolactone → CO₂ + H₂O). BAF bioaugmentation and ozone recirculation: A portion of the ozone effluent is recirculated to the UASB, where alternating anaerobic and aerobic exposures induce microbial exoenzyme secretion, enhancing the degradation of recalcitrant compounds (e.g., ring opening of tetrahydrofuran). Traditional ozone hydrogenation relies on homogeneous reactions (e.g., O₃ alone), has low catalyst efficiency (e.g., TiO₂ alone), and lacks closed-loop synergy with biological treatment.

[0020] (4) Fuzzy logic of ORP and ozone dosing: When ORP>400 mV, it is judged that ozone is excessive (oxidation potential is too high), triggering BAF backwashing and reducing ozone dosage (such as from 60 to 48 mg / L) to avoid ineffective oxidation; PID adjustment of pH and dosing: When the pH of the micro-electrolysis cell is less than 3, NaOH solution is added, and the PID algorithm is used to dynamically adjust the dosing pump frequency according to the pH deviation to maintain Fe 2+ Optimal dissolution rate; compared to traditional control that relies on fixed thresholds (such as timed backwashing), it cannot dynamically respond to changes in water quality, resulting in waste of reagents or incomplete treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a process flow chart for the multi-stage treatment of maleic anhydride wastewater as described in Example 2 of the present invention. Detailed implementation mode

[0023] Next, in combination with the implementation modes of the present invention, the technical solutions in the implementation modes of the present invention will be clearly and completely described. Obviously, the described implementation modes are only a part of the implementation modes of the present invention, rather than all the implementation modes. Based on the implementation modes in the present invention, all other implementation modes obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0024] The present invention provides a multi-stage treatment system and process for maleic anhydride sewage. Through the modular combination of pretreatment, anaerobic, aerobic, and advanced treatment modules, combined with the ozone catalytic oxidation - BAF collaborative process and intelligent control technology, efficient, stable, and low-consumption sewage treatment is achieved. In particular, by returning the effluent from the ozone unit to the anaerobic section, the cyclic degradation of refractory organic matter is promoted, and the treatment cost is reduced. This system is applicable to the up-to-standard discharge and reuse of high-concentration maleic anhydride production wastewater.

[0025] In a preferred implementation mode, a multi-stage treatment system for maleic anhydride sewage includes a pretreatment module, an anaerobic treatment module, an aerobic treatment module, an advanced treatment module, and an intelligent control module connected in sequence, where: The pretreatment module includes an adjustment tank, a coagulation sedimentation tank, and a micro-electrolysis tank. The micro-electrolysis tank is filled with iron-carbon packing, and the mass ratio of iron to carbon is 3:1; The advanced treatment module includes an ozone catalytic oxidation unit and a biological aerated filter. The outlet of the ozone catalytic oxidation unit is connected to the inlet of the anaerobic treatment module through a reflux pipeline, and the reflux ratio is 10% - 30%.

[0026] In a preferred implementation mode, specifically, the residence time of the micro-electrolysis tank is 2 - 4 h, the pH is controlled at 3 - 4, and the packing density of the iron-carbon packing is 60% - 80%.

[0027] In a preferred implementation mode, specifically, the anaerobic treatment module is an upflow anaerobic sludge bed reactor, and its operating parameters are: temperature 35 - 38 °C, hydraulic retention time 24 - 36 h; volumetric loading 5 - 7 kgCOD / (m²·d), and the biogas collected is used for system heating.

[0028] In a preferred implementation mode, specifically, the aerobic treatment module is composed of a moving bed biofilm reactor and a membrane bioreactor connected in series, where: the packing filling rate of the moving bed biofilm reactor is 50% - 70%, and the dissolved oxygen is controlled at 2 - 4 mg / L; the membrane pore size of the membrane bioreactor is 0.1 - 0.4 μm, and the backwashing period is 6 - 12 h.

[0029] In a preferred embodiment, specifically, the catalyst in the ozone catalytic oxidation unit is a manganese-iron bimetallic oxide supported on titanium dioxide, the catalyst filling rate is 30%-50%, the ozone dosage is 50-80 mg / L, and the reaction time is 30-60 min.

[0030] In a preferred embodiment, specifically, the intelligent control module includes: An on-line sensor group, including at least a pH sensor, an oxidation-reduction potential sensor, a dissolved oxygen sensor, and an ozone concentration analyzer; An actuator, including at least an ozone generator, an aeration blower, and a chemical dosing pump; A controller that dynamically adjusts the ozone dosage, aeration intensity, and coagulant dosage based on the fuzzy PID algorithm.

[0031] In a preferred embodiment, specifically, a multi-stage treatment process for maleic anhydride wastewater is also provided, including the following steps: S1, Pretreatment stage: After the wastewater is introduced into the regulating tank to equalize the water quality, polyaluminum chloride 200-300 mg / L and polyacrylamide 1-2 mg / L are added in sequence for coagulation precipitation, and then it enters the micro-electrolysis cell for treatment for 2-4 h; S2, Anaerobic treatment stage: Control the temperature of the UASB reactor at 35-38 °C, the hydraulic retention time at 24-36 h, and the volumetric loading at 5-7 kgCOD / (m 3 ·d); S3, Advanced treatment stage: A part of the effluent from the ozone catalytic oxidation unit is refluxed to the UASB reactor, and the reflux ratio is 10%-30%. The remaining effluent enters the biological aerated filter for treatment until COD ≤ 50 mg / L; S4, Intelligent control stage: Use the PID algorithm to adjust the control strategy for subsequent treatment.

[0032] In a preferred embodiment, specifically, the operating parameters of the ozone catalytic oxidation unit in step S3 are as follows: The ozone dosage is dynamically adjusted according to the influent COD concentration. When COD > 200 mg / L, the ozone dosage is 60-80 mg / L; when COD ≤ 200 mg / L, the ozone dosage is 30-50 mg / L.

[0033] In a preferred embodiment, specifically, the control strategy of the intelligent control module includes: When the detected value of the ORP sensor > 400 mV, trigger the backwashing program of the biological aerated filter and reduce the ozone dosage by 20%-40%; when the detected value of the pH sensor < 3, start the chemical dosing pump to add sodium hydroxide solution until the pH is restored to 3-4.

[0034] In a preferred embodiment, specifically, the preparation method of the iron-carbon filler is as follows: Mix iron filings and activated carbon in a mass ratio of 3:1, soak them in 0.1 mo1 / L hydrochloric acid for 30 min, and then calcine them at 500-600 °C for 2 h under nitrogen protection.

[0035] Example 1 A multi-stage treatment system for maleic anhydride wastewater includes: Pretreatment module: Regulating tank: with a volume of 50 m 3 , equipped with a liquid level sensor and a stirrer; Coagulation sedimentation tank: Add 250 mg / L of polyaluminum chloride (PAC); 1.5 mg / L of polyacrylamide (PAM); Micro-electrolysis cell: with dimensions of 5 m × 2 m × 3 m, filled with iron-carbon filler (mass ratio of iron filings to activated carbon = 3:1, calcined and modified), a residence time of 3 h, and the pH is controlled at 3.5.

[0036] Anaerobic treatment module: UASB reactor: with a volume of 300 m 3 , the temperature is controlled at 37 ± 0.5 °C, the hydraulic retention time is 30 h, the volume loading is 6 kgCOD / (m 3 ·d), and the biogas is collected and used for the heating system.

[0037] Aerobic treatment module: MBBR: The packing filling rate is 60%, and the dissolved oxygen (DO) is controlled at 3 mg / L; MBR: The membrane pore size is 0.2 μm, and the backwashing period is 8 h.

[0038] Advanced treatment module: Ozone catalytic oxidation unit: The catalyst is Mn-Fe / TiO2 (filling rate 40%), the ozone dosage is 60 mg / L, the reaction time is 45 min, and the effluent is refluxed to the UASB (reflux ratio 20%); Aerobic biological filter: The thickness of the ceramsite filter layer is 2.5 m, and the air-water ratio is 5:1.

[0039] Intelligent control module: Sensor group: Real-time monitor pH, ORP, DO and ozone concentration; Controller: Dynamically adjust the ozone dosage (±10 mg / L), aeration intensity (±0.5 mg / L DO) and dosing pump frequency based on the fuzzy PID algorithm.

[0040] Table 1 Treatment results Index Inlet concentration Outlet concentration Removal rate COD 15000 ≤50 ≥99.7% <![CDATA[BOD5]]> 3500 ≤10 ≥99.7% Total nitrogen 180 ≤15 ≥91.7% Operating cost -- 3.2 yuan / ton 35% lower than the industry average

[0041] Example 2

[0042] A multi-stage treatment process for maleic anhydride wastewater, which is applied to an integrated system in a large industrial park with a daily treatment capacity of 1000 tons, includes: S1, enhanced pretreatment: The micro-electrolysis cell is connected in series in two stages: the pH of the first stage is 3.0 (enhanced chain breaking), the pH of the second stage is 4.0 (promoting flocculation), the calcination temperature of the iron-carbon filler is increased to 600 °C (the porosity is increased to 65%), and the filler life is extended to 8 months.

[0043] S2, anaerobic-aerobic cooperation: A hydrolysis acidification tank (HRT 6h) is added between the UASB and the MBBR to further decompose refractory organic matter; the MBR uses a submerged ultrafiltration membrane (pore size 0.05 μm), and the backwashing period is extended to 12h.

[0044] S3, advanced treatment upgrade: The ozone catalytic oxidation unit is equipped with ultraviolet light assistance (wavelength 254 nm), and the generation efficiency of ·OH on the catalyst surface is increased by 30%; The biological aerated filter uses a multi-layer combined filter material, namely ceramsite + activated carbon, and the COD removal rate is increased to 95%.

[0045] S4, intelligent control strategy: Introduce an AI algorithm to predict water quality fluctuations and adjust the ozone dosage in advance (for example, when the COD suddenly increases to 20000 mg / L, the ozone automatically increases to 80 mg / L); Membrane fouling warning: When the transmembrane pressure difference (TMP) of the MBR > 30 kPa, trigger the chemical cleaning procedure (soak in 0.5% sodium hypochlorite for 2h).

[0046] Table 2 Comparison of treatment effects Index Example 2 Traditional process COD removal rate ≥99.8% ≤95% Water consumption per ton (kWh / ton) 1.8 3.0 Sludge production (kgDS / ton) 0.15 0.35 Catalyst life 12 months 6 months As can be seen from Table 2, utilize the synergy of micro-electrolysis and ozone for chain breaking: through the electron transfer of the iron-carbon filler and the synergistic effect of the free radical oxidation of the catalyst life Mn-Fe / TiO2, break the stubborn structures such as benzene ring ester bonds in maleic anhydride wastewater (such as phthalic anhydride → oxalic acid), energy-material closed-loop design: biogas recycling for heating (UASB gas production 2.5m 3 / m 3 ·d); oxygen effluent reflux induces enhanced microbial metabolism (the COD degradation rate is increased by 20%).

[0047] Intelligent dynamic control: The fuzzy PID algorithm improves the system's anti-shock load capacity to ±50% COD fluctuations, avoiding the treatment failure caused by sudden water quality changes in traditional processes, and can adjust parameters according to the sewage characteristics (such as salinity, toxic substance content), for example, high-salt wastewater (Cl -When ( > 5000 mg / L), the pH of the micro-electrolytic cell needs to be strictly controlled at 3.0 - 3.2 to prevent iron passivation.

[0048] In summary, the present invention discloses a multi-stage treatment system and process for maleic anhydride sewage, including a pretreatment module, an anaerobic treatment module, an aerobic treatment module, a deep treatment module, and an intelligent control module connected in sequence. Through the triple effects of chain breaking - oxidation - flocculation, macromolecular pollutants are degraded, enhancing the enhanced chain breaking and biodegradability of micro-electrolysis synergistic coagulation; combined with a high volume load to accelerate substrate mass transfer and avoid acid accumulation inhibition.

[0049] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A maleic anhydride sewage multi-stage treatment system, characterized in that, It includes a pre-treatment module, an anaerobic treatment module, an aerobic treatment module, a deep treatment module and an intelligent control module connected in sequence. Among them: the pre-treatment module includes an adjustment tank, a coagulation sedimentation tank and a micro-electrolysis tank. Iron-carbon fillers are filled in the micro-electrolysis tank, and the mass ratio of iron to carbon is 3:1; the deep treatment module includes an ozone catalytic oxidation unit and a biological aerated filter. The water outlet of the ozone catalytic oxidation unit is connected to the water inlet of the anaerobic treatment module through a reflux pipeline, and the reflux ratio is 10%-30%.

2. The maleic anhydride sewage multi-stage treatment system according to claim 1, characterized in that, The residence time of the micro-electrolysis tank is 2-4h, the pH is controlled at 3-4, and the filling density of the iron-carbon fillers is 60%-80%.

3. The maleic anhydride sewage multi-stage treatment system according to claim 2, characterized in that, The anaerobic treatment module is an upflow anaerobic sludge bed reactor, and its operating parameters are: temperature 35-38°C, hydraulic retention time 24-36h; volumetric loading 5-7 kgCOD / (m²·d), and the biogas collected is used for system heating.

4. The maleic anhydride sewage multi-stage treatment system according to claim 3, characterized in that, The aerobic treatment module is composed of a moving bed biofilm reactor and a membrane bioreactor connected in series. Among them: the filling rate of the fillers in the moving bed biofilm reactor is 50%-70%, and the dissolved oxygen is controlled at 2-4mg / L; the membrane pore size of the membrane bioreactor is 0.1-0.4 μm, and the backwashing period is 6-12h.

5. The maleic anhydride sewage multi-stage treatment system according to claim 4, wherein The catalyst of the ozone catalytic oxidation unit is manganese-iron bimetallic oxide supported on titanium dioxide, the catalyst filling rate is 30%-50%, the ozone dosage is 50-80 mg / L, and the reaction time is 30-60min.

6. The multistage treatment system for maleic anhydride sewage according to claim 5, characterized in that, The intelligent control module includes: An on-line sensor group, at least including a pH sensor, an oxidation-reduction potential sensor, a dissolved oxygen sensor and an ozone concentration analyzer; An actuator, at least including an ozone generator, an aeration blower and a chemical dosing pump; A controller, which dynamically adjusts the ozone dosage, aeration intensity and coagulant dosage based on the fuzzy PID algorithm.

7. A multi-stage treatment process for maleic anhydride wastewater, based on the multi-stage treatment system for maleic anhydride wastewater according to any one of claims 1-5, characterized in that, It includes the following steps: S1, pre-treatment stage: After the wastewater is introduced into the adjustment tank to balance the water quality, polyaluminum chloride 200-300mg / L and polyacrylamide 1-2mg / L are added in sequence for coagulation sedimentation, and then enter the micro-electrolysis tank for treatment for 2-4h; S2, Anaerobic treatment stage: Control the temperature of the UASB reactor at 35 - 38 °C, hydraulic retention time 24 - 36 h, volumetric loading 5 - 7 kgCOD / (m 3 ·d); S3, deep treatment stage: Part of the effluent from the ozone catalytic oxidation unit is refluxed to the UASB reactor, and the reflux ratio is 10%-30%. The remaining effluent enters the biological aerated filter for treatment until COD≤50mg / L; S4, intelligent control stage: Use the PID algorithm to adjust the control strategy for subsequent treatment.

8. The multi-stage treatment process for maleic anhydride wastewater according to claim 7, wherein, The operating parameters of the ozone catalytic oxidation unit in step S3 are: the ozone dosage is dynamically adjusted according to the influent COD concentration. When COD>200 mg / L, the ozone dosage is 60-80 mg / L; when COD≤200 mg / L, the ozone dosage is 30-50 mg / L.

9. The multi-stage treatment process for maleic anhydride wastewater according to claim 7, characterized in that The control strategy of the intelligent control module includes: When the detected value of the ORP sensor > 400 mV, trigger the backwashing program of the biological aerated filter and reduce the ozone dosage by 20%-40%; when the detected value of the pH sensor < 3, start the chemical dosing pump to add sodium hydroxide solution until the pH is restored to 3-4.

10. A maleic anhydride sewage multi-stage treatment process according to claim 7, characterized in that, The preparation method of the iron-carbon filler is as follows: Mix iron filings and activated carbon in a mass ratio of 3:1, soak them in 0.1 mo1 / L hydrochloric acid for 30 min, and then calcine them at 500-600 °C for 2 h under nitrogen protection.

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