A method for treating non-biodegradable wastewater

Abstract

The present application belongs to the field of wastewater treatment, and provides a treatment method for refractory wastewater. Specifically, the method comprises three process steps of pretreatment, biochemical treatment and advanced treatment, and sequentially carries out pretreatment, biochemical treatment and advanced treatment on the refractory wastewater. In the pretreatment stage, the fluidized bed crystallization technology and Fenton-like reaction are used to obtain crystalline bodies with high catalytic activity and improve the B / C of the wastewater; the effluent from the pretreatment is subjected to neutralization, degassing, flocculation and precipitation and other treatment processes, and the degradable acetic acid remaining in the pretreatment stage is used as a carbon source to re-enter the biochemical treatment stage, which is treated by the AO process method, and has low carbon and economy; finally, the wastewater after the biochemical treatment enters the advanced treatment stage, and the high catalytic activity of the waste catalytic crystalline bodies in the pretreatment stage is used to carry out catalytic ozone micro-bubble treatment on the wastewater to reach the national discharge and reuse standards, and the waste catalysts can also be resourcefully utilized. The wastewater treatment process provided by the present application has high treatment efficiency and low cost, runs through the whole wastewater treatment process, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for treating recalcitrant wastewater. Background Technology

[0002] The treatment of recalcitrant industrial wastewater is a major issue restricting my country's economic development and environmental protection. Its basic characteristics are high organic matter concentration, many types of pollutants, low biodegradability, strong biological inhibition, and high salt content. Conventional treatment technologies are difficult to achieve efficient and stable operation. Generally, it is necessary to couple physical, chemical and biological treatment technologies to construct a three-stage treatment process of pretreatment-biological treatment-deep treatment.

[0003] Firstly, pretreatment is the first process step in wastewater treatment. Through physical methods such as filtration and sedimentation, and chemical methods such as oxidation and reduction, impurities and pollutants in wastewater can be initially removed, and the biodegradability of wastewater can be improved. However, the pretreatment process often only treats the surface of the wastewater and cannot solve the fundamental problem of recalcitrant organic matter in the wastewater.

[0004] The second process is biological treatment. This typically employs biological treatment methods such as activated sludge and biofilm processes. However, organic matter in recalcitrant wastewater can inhibit microorganisms, significantly reducing their efficiency in degrading pollutants. To maintain microbial activity, additional carbon sources are often required to provide sufficient energy and carbon to support microbial growth. This leads to a dependence on external carbon sources in the biological treatment process, thereby increasing treatment costs.

[0005] The third process is advanced treatment. After pretreatment and biological treatment, most organic pollutants in recalcitrant industrial wastewater have been degraded and removed, but some persistent recalcitrant components may still remain in the effluent at low concentrations. Commonly used advanced treatment processes mainly include advanced oxidation technologies, membrane separation, and adsorption. However, advanced oxidation technologies often require expensive catalysts, and the intermediate products generated require further treatment. Membrane separation technology also has certain limitations, such as the durability of membrane materials, membrane fouling problems, and high maintenance costs. Adsorption technology has advantages such as good treatment effect and simple operation, but it also has problems such as difficult adsorbent regeneration and high cost when the treatment volume is large.

[0006] In the treatment of recalcitrant organic wastewater, Fenton oxidation, as an advanced oxidation technology, is widely used in wastewater pretreatment due to its advantages such as fast reaction rate, strong oxidizing power, ability to improve the biodegradability of wastewater, and simple operation. In the traditional Fenton reaction, Fe... 2+Fe reacts with hydrogen peroxide under acidic conditions to generate highly reactive hydroxyl radicals, thereby degrading organic wastewater. However, in practical applications, the reaction often produces a large amount of iron sludge, leading to high costs for subsequent treatment and recycling, and limiting the continued progress of the reaction. In the fluidized bed Fenton reaction system, Fe... 3+ By attaching to the carrier surface of the fluidized bed through crystallization, the efficiency of the oxidation reaction can be improved, and the loss of iron ions in wastewater can be reduced, thereby effectively reducing the generation of iron sludge. However, Fenton fluidized bed technology has some potential drawbacks in wastewater treatment, including issues such as the selection of the support, the long crystallization cycle, and the waste generated during the crystal growth process through discharge, which urgently need to be studied and resolved.

[0007] Catalytic ozone technology is widely used in advanced wastewater treatment, with advantages mainly reflected in its efficient oxidation of organic matter, removal of recalcitrant pollutants, and improved treatment efficiency. By introducing a catalyst, catalytic ozone technology can achieve a more efficient reaction rate than conventional ozone oxidation, contributing to the efficient degradation of specific wastewater components. However, catalytic ozone technology also has some drawbacks. The high cost of catalysts is one, especially the use of some precious metal catalysts, which increases operating costs. Furthermore, the short lifespan of the catalyst necessitates regular replacement or regeneration, increasing maintenance costs. Summary of the Invention

[0008] To address the above technical problems, this invention proposes a method for treating recalcitrant wastewater. The treated water, once meeting standards, can be directly discharged, which is beneficial for improving environmental quality. The treated wastewater contains largely removed harmful substances and pollutants, avoiding direct discharge and environmental pollution. Furthermore, the recycled treated water effectively alleviates water resource pressure and improves water resource utilization.

[0009] The purpose of this invention is to provide a method for treating recalcitrant wastewater, comprising the following steps:

[0010] S1: The recalcitrant wastewater is introduced into a fluidized bed reactor containing the original carrier, and a mixture of iron source and peracetic acid is added. The expansion effect of the fluidized bed is used to form a crystalline catalyst with catalytic activity to degrade the organic matter in the wastewater. After neutralization, degassing, flocculation and sedimentation processes are carried out to obtain the first wastewater containing acetic acid.

[0011] S2: The first wastewater containing acetic acid is sequentially fed into an anaerobic tank and an aerobic tank. In the anaerobic tank and the aerobic tank, microorganisms degrade the organic matter in the first wastewater to obtain the second wastewater.

[0012] S3: The second wastewater from S2 is fed into a microbubble catalytic ozone reactor containing the crystalline catalyst obtained in S1, and ozone is introduced through an ozone microbubble generator to achieve deep treatment of the wastewater. The resulting final wastewater is either directly discharged or recycled.

[0013] In this invention, in S1 and S2, peracetic acid oxidation produces acetic acid, a highly biodegradable product. In the anaerobic tank, denitrifying bacteria utilize organic matter in the wastewater and acetic acid produced by the decomposition of peracetic acid as carbon sources to promote the degradation of organic waste by microorganisms, thus possessing low carbon and economic benefits.

[0014] In this invention, in step S3, ozone is catalyzed by the highly catalytically active crystals from step S1, and ozone microbubbles are introduced to improve mass transfer and catalytic effect, thereby achieving the purpose of catalytic oxidation and degradation of residual organic matter, realizing the purpose of deep treatment of wastewater, and the wastewater can be directly discharged or recycled.

[0015] In some embodiments of the present invention, in S1, the pH value of the recalcitrant wastewater is 3-5;

[0016] And / or, the recalcitrant wastewater comes from one or more of the following: petrochemical wastewater, textile printing and dyeing wastewater, and pharmaceutical wastewater;

[0017] And / or, the original carrier is selected from one or more of building sand, sea sand, pyrite and zeolite particles;

[0018] And / or, the iron source is selected from iron-based raw materials;

[0019] And / or, the iron source is added in a sequential batch manner, with a dosing frequency of 18-24 hours / time, and no more iron-based raw materials are added after 5-7 days.

[0020] In some embodiments of the present invention, the iron-based raw material is selected from one or more of iron filings and pig iron powder. Pig iron powder is preferred, and the pig iron powder is a byproduct of carbon steel processing.

[0021] In some embodiments of the present invention, the iron source is modified by a mixture containing an oxidant and an accelerator;

[0022] And / or, the mass load of the modified iron source is 2-4 g / L.

[0023] In some embodiments of the present invention, the oxidant is H2O2 and the promoter is FeSO4·7H2O.

[0024] In some embodiments of the present invention, the modification reaction time is 30 to 60 minutes. After completion, the modified iron-based raw material is taken out and air-dried for storage.

[0025] In some embodiments of the present invention, in S1, the mass concentration ratio of the iron-based raw material, peracetic acid, and COD in the recalcitrant wastewater is 2-4:2-4:1;

[0026] And / or, the residence time of the recalcitrant wastewater in the fluidized bed is 40 min to 60 min;

[0027] And / or, the reflux expansion rate of the fluidized bed is 50% to 80%.

[0028] In this invention, in S1, the wastewater at the current stage cannot directly enter the biochemical treatment process. It must undergo neutralization, degassing, flocculation and sedimentation processes. The main purpose is to remove some of the iron sludge and eliminate hydrogen peroxide in peracetic acid.

[0029] In some embodiments of the present invention, in S2, the microorganisms in the anaerobic tank are denitrifying bacteria. The denitrifying bacteria in the present invention are conventional denitrifying bacteria in the art and are not particularly limited. They can be denitrifying cocci or denitrifying pseudomonas. The denitrifying bacteria use the organic matter in the wastewater and the acetic acid produced by the decomposition of peracetic acid as carbon sources to promote the degradation ability of microorganisms on organic waste and complete the organic matter degradation and denitrification process.

[0030] And / or, the microorganisms in the aerobic tank are nitrifying bacteria. The nitrifying bacteria in this invention are conventional nitrifying bacteria in the art and are not particularly limited. They can be selected from nitrite bacteria, nitrate bacteria, etc.

[0031] And / or, the anaerobic tank and the aerobic tank are subjected to internal reflux of mixed liquor, with a mixed liquor reflux ratio of 300-400% and a sludge reflux ratio of 50-100%.

[0032] In some embodiments of the present invention, the water temperature of the anaerobic tank is 20-30℃, the dissolved oxygen (DO) is ≤0.4mg / L, the pH value is 7.0-8.5, and the wastewater retention time is 1-2h.

[0033] And / or, the water temperature of the aerobic tank is 20-30℃, the pH value is 7.0-8.0, the wastewater retention time is not less than 5-6h, and the dissolved oxygen (DO) is greater than 2mg / L;

[0034] And / or, the wastewater retention time ratio in the anaerobic tank and the aerobic tank is 1:5 to 8.

[0035] In some embodiments of the present invention, in S3, the pH value of the reaction system formed by the second wastewater and the crystalline catalyst is 6 to 9;

[0036] And / or, the wastewater retention time is 10-20 min; the wastewater retention time also has a significant impact on the ozone oxidation effect. If the wastewater retention time is too short, the ozone oxidation reaction will not proceed sufficiently, while if the wastewater retention time is too long, it may lead to the generation of oxidation byproducts, affecting the final treatment effect.

[0037] And / or, the volume ratio of the crystalline catalyst to the microbubble catalytic ozone reactor is 30% to 40%.

[0038] In some embodiments of the present invention, in step S3, the ratio of ozone dosage to COD concentration in the second wastewater is 2-3:1. An appropriate amount of ozone dosage ensures the oxidation reaction proceeds while avoiding resource waste due to excessive dosage.

[0039] And / or, the ozone dosing acceleration rate is 150–200 mg / (L·min);

[0040] And / or, the ozone flow rate is 0.3 to 0.5 L / min; an appropriate flow rate can ensure the uniform distribution of microbubbles in the reaction device, thereby increasing the contact area between ozone and reactants and promoting the increase of reaction rate.

[0041] The objective of this invention is to construct a comprehensive system and method for treating recalcitrant wastewater using fluidized bed crystallization coupled with catalytic ozone technology. This system aims to overcome the limitations of traditional Fenton wastewater treatment processes and offers the following advantages: First, it enables rapid crystal growth under peracetic acid stimulation, improving the biodegradability of wastewater during the pretreatment stage. Second, in the biochemical treatment stage, peracetic acid oxidation produces highly biodegradable acetic acid, serving as a carbon source and saving on the cost of external carbon source addition while maintaining microbial activity. Finally, in the advanced treatment stage, the fluidized bed crystals act as a catalytic ozone catalyst, effectively catalyzing the generation of hydroxyl radicals and other active species to mineralize recalcitrant organic matter, achieving national wastewater discharge standards.

[0042] The technical solution of the present invention has the following advantages compared with the prior art:

[0043] (1) This invention overcomes the limitations of traditional Fenton wastewater treatment: Traditional Fenton wastewater treatment methods have some drawbacks, such as the reaction often producing a large amount of iron sludge and high cost of chemical reagents. However, this invention utilizes in-situ crystallization technology, which greatly reduces the generation of iron sludge and lowers the subsequent treatment cost of iron sludge. At the same time, the crystals have highly efficient catalytic activity, which can improve the wastewater treatment effect and reduce the use of chemical reagents, thereby reducing operating costs.

[0044] (2) Rapid growth of crystals by the high efficiency catalyst of the present invention: During the crystal growth process, peracetic acid can generate free radicals through decomposition. The free radicals react with the crystal surface to form an active growth interface. At the same time, the catalytic effect of peracetic acid makes the crystal surface rougher, promoting the rapid growth of the crystal.

[0045] (3) Improve the biodegradability of wastewater: After pretreatment, the biodegradability of wastewater is improved. At the same time, peracetic acid oxidation produces acetic acid, a highly biodegradable product, which can be used as a carbon source in the biochemical treatment stage. This helps to improve the degradation process of organic matter in water and saves the cost of adding external carbon sources.

[0046] (4) Waste crystals are used as catalytic ozone catalysts for deep treatment to achieve resource reuse: By introducing crystals into the deep treatment stage as catalytic ozone catalysts, the degradation efficiency of recalcitrant substances in wastewater is improved.

[0047] (5) Improve catalytic treatment efficiency by using ozone microbubble technology: Ozone microbubble technology utilizes the high oxidizing properties of ozone to effectively decompose organic matter in wastewater. At the same time, microbubbles can provide a larger contact surface area, promote the reaction rate, and thus enhance the wastewater treatment effect.

[0048] (6) It runs through the entire wastewater treatment process: This invention is not limited to wastewater treatment at a specific stage, but can run through the entire wastewater treatment process, from pretreatment to advanced treatment, to achieve the comprehensive effect of the entire wastewater treatment process. Attached Figure Description

[0049] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0050] Figure 1 This is the overall flowchart of the present invention.

[0051] Figure 2 This is a detailed diagram of the preprocessing stage of the present invention.

[0052] Figure 3 This is a detailed diagram of the biochemical treatment stage of the present invention.

[0053] Figure 4 This is a detailed diagram of the deep processing stage of the present invention.

[0054] Figure 5 This is a comparison chart of crystallization rates in various examples during the pretreatment stage of this invention.

[0055] Figure 6 This is a comparison chart of COD removal rates in various cases during the pretreatment stage of this invention.

[0056] Figure 7This is a comparison chart of COD removal rates in various cases during the biochemical treatment stage of this invention.

[0057] Figure 8 This is a comparison chart of COD removal rates in the deep treatment stage of the embodiments and comparative examples of the present invention. Detailed Implementation

[0058] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0059] Example 1

[0060] A fluidized bed crystallization coupled with catalytic ozone technology is used to construct a comprehensive system and method for treating recalcitrant wastewater, comprising the following steps:

[0061] Wastewater quality for treatment: Pharmaceutical wastewater, COD = 1200 mg / L, BOD5 = 200 mg / L, pH = 6, B / C = 0.16, TN = 800 mg / L, NH3-N = 500 mg / L.

[0062] (1) Pretreatment stage: ① The pig iron powder is pretreated by repeatedly cleaning with detergent to remove oil stains, then treated with 1 mol / L sodium hydroxide and hydrochloric acid at pH=1 to eliminate oil stains, and finally washed until neutral. ② Modification treatment: The pretreated iron-based raw material is placed in a mixed solution containing 0.10 wt% oxidant H2O2 and 0.05 wt% accelerator FeSO4·7H2O, where the mass ratio of oxidant to accelerator is 2:1. The modification reaction takes 60 min. After completion, it is taken out and air-dried for storage to obtain modified iron-based raw material. ③ Using modified iron-based raw materials as the iron source, modified pig iron powder and peracetic acid are added to a fluidized bed (wherein, the mass concentration ratio of pig iron powder: peracetic acid: COD = 4:4:1). Building sand is used as a carrier, and a mass loading of 300 g / L of building sand is added. The expansion effect of the fluidized bed is used to keep the carrier in a suspended expansion state. ④ Pharmaceutical wastewater is introduced into the fluidized bed. The wastewater retention time is 60 min, the reflux expansion rate is 50%, the pH value of the reaction system is adjusted to 3.5, the frequency of dosing of modified pig iron powder is 24 hours / time, and the fluidized bed Fenton reactor is run continuously for 7 days. The crystallized catalyst is taken out, washed, and air-dried to obtain crystals with high catalytic activity. In the pretreatment stage, the COD removal rate reaches 55%, and the B / C ratio is increased to 0.35. Add 30% sodium hydroxide solution to adjust the pH of the wastewater to 7.0, then aerate and deaerate for 20 minutes, and finally enter the flocculation sedimentation tank with 2 mg / L PAM added. The sedimentation time is 1.5 hours for coagulation and sedimentation treatment to obtain the first wastewater, which then enters the biological treatment section.

[0063] (2) Biochemical treatment stage: The first wastewater obtained in step (1) is fed into a biochemical tank. The anaerobic tank has a water temperature of 25℃, dissolved oxygen (DO) of 0.3 mg / L, a pH of 7.0, and a hydraulic retention time of 1 h. The aerobic tank has a water temperature of 25℃, a pH of 7.5, a hydraulic retention time of 6 h, dissolved oxygen (DO) of 3 mg / L, a mixed liquor reflux ratio of 300%, and a sludge reflux ratio of 80%. The COD removal rate reaches 70% in the biochemical treatment stage, resulting in the second wastewater. The anaerobic bacteria are Bacillus subtilis, and the aerobic bacteria are Nitrosomonas europaea and Nitrobacter winogradskyi.

[0064] (3) Advanced treatment stage: The second wastewater obtained in step (2) is fed into a microbubble catalytic ozone reactor containing the highly catalytically active crystals obtained in step (1). The pH of the reaction system is adjusted to 8, the wastewater residence time is 15 min, the ozone dosing rate is 180 mg / (L·min), the microbubble gas flow rate is 0.3 L / min, and the filling ratio of the highly catalytically active crystals in the microbubble catalytic ozone reactor is 30%. In the advanced treatment stage, the COD removal rate reaches 50%.

[0065] Example 2

[0066] A fluidized bed crystallization coupled with catalytic ozone technology is used to construct a comprehensive system and method for treating recalcitrant wastewater, comprising the following steps:

[0067] Wastewater quality for treatment: Textile dyeing and printing wastewater, COD = 1500 mg / L, BOD5 = 220 mg / L, pH = 5, B / C = 0.15, TN = 750 mg / L, NH3-N = 450 mg / L.

[0068] (1) Pretreatment stage: ① The pig iron powder is pretreated by repeatedly cleaning with detergent to remove oil stains, then treated with 1 mol / L sodium hydroxide and hydrochloric acid at pH=1 to eliminate oil stains, and finally washed until neutral. ② Modification treatment: The pretreated iron-based raw material is placed in a mixed solution containing 0.10 wt% H2O2 oxidant and 0.05 wt% FeSO4·7H2O accelerator, where the mass ratio of oxidant to accelerator is 2:1. The modification reaction takes 40 min. After completion, it is taken out and air-dried for storage to obtain the modified iron-based raw material. ③ Using modified iron-based raw materials as the iron source, modified pig iron powder and peracetic acid are added to a fluidized bed (wherein, the mass concentration ratio of pig iron powder: peracetic acid: COD = 3:3:1). Zeolite particles are used as carriers, and construction sand with a mass loading of 350 g / L is added. The expansion effect of the fluidized bed is used to keep the carrier in a suspended expansion state. ④ Pharmaceutical wastewater is introduced into the fluidized bed. The wastewater retention time is 40 min, the reflux expansion rate is 80%, the pH value of the reaction system is adjusted to 4.5, the frequency of dosing of modified pig iron powder is 24 hours / time, and the fluidized bed Fenton reactor is run continuously for 7 days. The crystallized catalyst is taken out, washed, and air-dried to obtain crystals with high catalytic activity. In the pretreatment stage, the COD removal rate reaches 45%, and the B / C ratio is increased to 0.36. Then, 30% sodium hydroxide solution was added to adjust the pH of the wastewater to 7.0. After degassing by blowing air for 20 minutes, the wastewater was finally introduced into a flocculation sedimentation tank with 2 mg / L PAM added. The sedimentation time was 1.5 hours for coagulation and sedimentation treatment to obtain the first wastewater. The effluent then entered the biological treatment section.

[0069] (2) Biochemical treatment stage: The first wastewater obtained in step (1) is fed into a biochemical tank. The anaerobic tank has a water temperature of 20℃, dissolved oxygen (DO) of 0.35 mg / L, a pH of 7.5, and a hydraulic retention time of 1 h. The aerobic tank has a water temperature of 25℃, a pH of 8, a hydraulic retention time of 5 h, dissolved oxygen (DO) of 3 mg / L, a mixed liquor reflux ratio of 350%, and a sludge reflux ratio of 90%. The COD removal rate reaches 75% in the biochemical treatment stage, resulting in the second wastewater. The anaerobic bacteria are Bacillus subtilis, and the aerobic bacteria are Nitrosomonas europaea and Nitrobacter winogradskyi.

[0070] (3) Advanced treatment stage: The second wastewater obtained in step (2) is fed into a microbubble catalytic ozone reactor containing the highly catalytically active crystals obtained in step (1). The pH of the reaction system is adjusted to 9, the wastewater residence time is 20 min, the ozone dosing rate is 200 mg / (L·min), the microbubble flow rate is 0.5 L / min, and the proportion of the highly catalytically active crystals filling the microbubble catalytic ozone reactor is 40%. In the advanced treatment stage, the COD removal rate reaches 60%.

[0071] Example 3

[0072] A fluidized bed crystallization coupled with catalytic ozone technology is used to construct a comprehensive system and method for treating recalcitrant wastewater, comprising the following steps:

[0073] Wastewater quality for treatment: petrochemical wastewater, COD = 1600 mg / L, BOD5 = 320 mg / L, pH = 8, B / C = 0.20, TN = 600 mg / L, NH3-N = 400 mg / L.

[0074] (1) Pretreatment stage: ① The pig iron powder is pretreated by repeatedly cleaning with detergent to remove oil stains, then treated with 1 mol / L sodium hydroxide and hydrochloric acid at pH=1 to eliminate oil stains, and finally washed until neutral. ② Modification treatment: The pretreated iron-based raw material is placed in a mixed solution containing 0.10 wt% oxidant H2O2 and 0.05 wt% accelerator FeSO4·7H2O, where the mass ratio of oxidant to accelerator is 2:1. The modification reaction takes 50 min. After completion, it is taken out and air-dried for storage to obtain modified iron-based raw material. ③ Using modified iron-based raw materials as the iron source, modified pig iron powder and peracetic acid are added to a fluidized bed (wherein, the mass concentration ratio of pig iron powder to peracetic acid to COD is 3:4:1). Pyrite is used as a carrier, and construction sand with a mass loading of 400 g / L is added. The expansion effect of the fluidized bed is used to keep the carrier in a suspended expansion state. ④ Pharmaceutical wastewater is introduced into the fluidized bed. The wastewater retention time is 50 min, the reflux expansion rate is 70%, the pH of the reaction system is adjusted to 5, and the frequency of adding modified pig iron powder is 24 hours / time. The fluidized bed Fenton reactor is run continuously for 7 days. The catalyst that has been loaded is taken out, washed, and air-dried to obtain crystals with high catalytic activity. In the pretreatment stage, the COD removal rate reaches 50%, and the B / C ratio is increased to 0.33. Add 30% sodium hydroxide solution to adjust the pH of the wastewater to 7.0, then aerate and deaerate for 20 minutes, and finally enter the flocculation sedimentation tank with 2 mg / L PAM added. The sedimentation time is 1.5 hours for coagulation and sedimentation treatment to obtain the first wastewater, which then enters the biological treatment section.

[0075] (2) Biochemical treatment stage: The first wastewater obtained in step (1) is fed into a biochemical tank. The anaerobic tank has a water temperature of 25℃, dissolved oxygen (DO) of 0.25 mg / L, a pH of 7.5, and a hydraulic retention time of 1 h. The aerobic tank has a water temperature of 25℃, a pH of 8, a hydraulic retention time of 6 h, dissolved oxygen (DO) of 3 mg / L, a mixed liquor reflux ratio of 400%, and a sludge reflux ratio of 90%. The COD removal rate reaches 78% in the biochemical treatment stage, resulting in the second wastewater. The anaerobic bacteria are *Nitrosomonas europaea*, and the aerobic bacteria are *Nitrosomonas europaea* and *Nitrobacter winogradskyi*.

[0076] (3) Advanced treatment stage: The second wastewater obtained in step (2) is fed into a microbubble catalytic ozone reactor containing the highly catalytically active crystals obtained in step (1). The pH of the reaction system is adjusted to 8, the reaction time is 18 min, the ozone dosing rate is 180 mg / (L·min), the microbubble gas flow rate is 0.4 L / min, and the filling ratio of the crystalline catalyst is 35%. In the advanced treatment stage, the COD removal rate reaches 55%.

[0077] Comparative Example 1 (compared to Example 1)

[0078] Comparative Example 1 adopted a conventional fluidized bed Fenton process + typical AO process + commercial catalyst catalytic ozone treatment process. The wastewater quality was: pharmaceutical wastewater, COD = 1200 mg / L, BOD5 = 200 mg / L, pH = 6, B / C = 0.16, TN = 800 mg / L, NH3-N = 500 mg / L.

[0079] (1) Pretreatment stage: The mass concentration ratio of pig iron powder:H2O2:COD = 4:4:1. Using construction sand as a carrier, a mass loading of 300g / L of construction sand was added. The expansion effect of the fluidized bed was utilized to keep the carrier in a suspended expansion state. The wastewater retention time was 60min, the reflux expansion rate was 50%, and the pH value of the reaction system was 3.5. The fluidized bed Fenton reactor was run continuously for 7 days. In the pretreatment stage, the COD removal rate reached 30%, and the B / C ratio was increased to 0.30. 30% sodium hydroxide solution was added to adjust the pH of the wastewater to 7.0. After aeration and degassing for 20min, the wastewater was finally added to the flocculation sedimentation tank with 2mg / L PAM. The sedimentation time was 1.5h for coagulation and sedimentation treatment to obtain the first wastewater. The effluent entered the biological treatment section.

[0080] (2) Biochemical treatment stage: The first wastewater obtained in step (1) is fed into the biochemical tank. The water temperature in the anaerobic tank is 25℃, the dissolved oxygen (DO) is 0.3 mg / L, the pH is 7.0, and the hydraulic retention time is 1 h. The water temperature in the aerobic tank is 25℃, the pH is 7.5, the hydraulic retention time is 6 h, the dissolved oxygen (DO) is 3 mg / L, the mixed liquor reflux ratio is 300%, the sludge reflux ratio is 80%, and methanol is added as a supplementary carbon source. The COD removal rate reaches 65% in the biochemical treatment stage, and the second wastewater is obtained. The anaerobic bacteria are Bacillus subtilis, and the aerobic bacteria are Nitrosomonas europaea and Nitrobacter winogradskyi.

[0081] (3) Deep treatment stage: The second wastewater obtained in step (2) is fed into a microbubble catalytic ozone reactor containing the highly catalytically active crystals obtained in step (1). The pH of the reaction system is adjusted to 8, the reaction time is 15 min, the ozone dosing rate is 180 mg / (L·min), the filling ratio of commercial OC type catalyst is 30%, and the COD removal rate reaches 35% in the deep treatment stage.

[0082] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for treating recalcitrant wastewater, characterized by, The method comprises the following steps: S1: introducing the refractory wastewater into a fluidized bed reactor containing original carriers, and adding a mixture of iron source and peroxyacetic acid, using the swelling effect of the fluidized bed to form a catalytically active crystalline catalyst, and degrading the organic matter in the wastewater, and then performing neutralization, degassing, flocculation and precipitation processes to obtain first wastewater containing acetic acid; S2: sequentially introducing the first wastewater containing acetic acid into an anaerobic tank and an aerobic tank, and degrading the organic matter in the first wastewater by microorganisms in the anaerobic tank and the aerobic tank to obtain second wastewater; S3: introducing the second wastewater in S2 into a micro-bubble catalytic ozone reactor containing the crystalline catalyst obtained in S1, and introducing ozone through an ozone micro-bubble generator to achieve advanced treatment of the wastewater, and the obtained final wastewater is directly discharged or recycled.

2. The treatment method according to claim 1, characterized in that, In S1, the pH value of the refractory wastewater is 3-5; And / or, the refractory wastewater is from one or more of petrochemical wastewater, textile printing and dyeing wastewater, and pharmaceutical wastewater; And / or, the original carrier is selected from one or more of building sand, sea sand, pyrite and zeolite particles; And / or, the iron source is selected from iron-based raw materials; And / or, the iron source is added in a sequencing batch mode, and the dosing frequency is 18-24 hours / time, and the iron-based raw materials are not added after 5-7 days.

3. The treatment method according to claim 2, characterized in that, The iron-based raw materials are selected from one or more of iron filings and pig iron powder.

4. The treatment method according to any one of claims 1 to 3, characterized in that, The iron source is modified by a mixed solution containing an oxidizing agent and a promoter; And / or, the mass loading of the modified iron source is 2-4 g / L.

5. The treatment method of claim 1, wherein In S1, the mass concentration ratio of COD in the iron source, peroxyacetic acid and refractory wastewater is 2-4:2-4:1; And / or, the residence time of the refractory wastewater in the fluidized bed is 40 min-60 min; And / or, the backflow swelling rate of the fluidized bed is 50%-80%.

6. The treatment method of claim 1, wherein In S2, the mixed liquid is backflowed between the anaerobic tank and the aerobic tank, and the mixed liquid backflow ratio is 300-400%, and the sludge backflow ratio is 50-100%.

7. The treatment method of claim 1, wherein The water temperature of the anaerobic tank is 20-30℃, the dissolved oxygen DO is ≤0.4 mg / L, the pH value is 7.0-8.5, and the wastewater residence time is 1-2 h; And / or, the water temperature of the aerobic tank is 20-30℃, the pH value is 7.0-8.0, the wastewater residence time is not less than 5-6 h, and the dissolved oxygen DO is >2 mg / L; And / or, the wastewater residence time ratio of the anaerobic tank to the aerobic tank is 1:5-8.

8. The treatment method of claim 1, wherein, In S3, the pH value of the reaction system formed by the second wastewater and the crystalline catalyst is 6-9; And / or, the wastewater residence time is 10-20 min; And / or, the volume ratio of the crystalline catalyst to the micro-bubble catalytic ozone reactor is 30%-40%.

9. The treatment method of claim 1, wherein, In S3, the ratio of ozone dosage to COD concentration in the second wastewater is 2-3:1; And / or, the ozone dosing rate is 150-200 mg / (L·min); And / or, the gas flow rate of ozone is 0.3-0.5 L / min.

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