Biological treatment method for automobile electrophoretic coating wastewater

Abstract

The invention provides a biological treatment method for automobile electrophoretic coating wastewater. According to the method disclosed by the invention, a microbial complex microbial inoculant consisting of Bayelinkia (LM-W with the preservation number of CGMCC No.17168) and Brevimonas brevis (LM-R with the preservation number of CGMCC No.17167) which are obtained by separating, purifying and screening the bottom mud of the spray paint wastewater is introduced in the step of aerobic biological treatment, and the microbial complex microbial inoculant has the function of efficiently degrading acrylic resin, greatly improves the COD (Chemical Oxygen Demand) removal rate, and can be applied to the field of aerobic biological treatment. Chemical agents and corresponding precipitated sludge required by a traditional chemical oxidation treatment unit can be omitted, the sludge amount can be reduced by 50%-60%, the sludge viscosity can be reduced, and the MBR membrane assembly can intercept compound microbial flora, prolong the sludge retention time and strengthen biodegradation; the method can stably reach the standard for high-acid, high-salt, high-suspended-matter and other complex water quality, 60%-80% of effluent can be reused for an electrophoretic coating production line, fresh water consumption is reduced, and cost is saved.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering technology, specifically relating to a biological treatment method for automotive electrophoretic coating wastewater. Background Technology

[0002] Wastewater generated during the automotive electrophoretic coating process contains high concentrations of organic matter (such as epoxy resin and acrylic resin), pigments, heavy metal ions (such as lead and zinc), surfactants, and small amounts of solvents. It is characterized by high COD (2000-5000 mg / L), poor biodegradability, and high toxicity (containing heavy metals and recalcitrant organic matter). Direct discharge can lead to eutrophication of water bodies, accumulation of heavy metals, and ecotoxicity, threatening human health.

[0003] Currently, a combined process of "coagulation sedimentation + chemical oxidation + activated sludge process + advanced treatment" is generally used to treat automotive electrophoretic coating wastewater. This process has the following problems:

[0004] 1. High reagent costs: Chemical oxidation requires large amounts of oxidant (such as Fenton's reagent), resulting in high processing costs;

[0005] 2. Low biological treatment efficiency: The traditional activated sludge process is insufficient in degrading acrylic acid substances in electrophoretic wastewater, with a COD removal rate of only 60%-70%.

[0006] 3. Large sludge production and high treatment costs. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a biological treatment method for automotive electrophoretic coating wastewater, so as to solve the problems of high dependence on chemical agents, high treatment cost, low degradation efficiency of organic matter (especially acrylic substances), high sludge production, and non-reusable wastewater in the existing technology.

[0008] To achieve the above objectives, the solution adopted by the present invention is as follows:

[0009] This invention provides a biological treatment method for automotive electrophoretic coating wastewater, comprising the following steps:

[0010] Step (1), coagulation and sedimentation pretreatment: Add reagents to the wastewater to generate flocculent precipitates from suspended solids, sparingly soluble metal salts and heavy metal ions in the wastewater. After solid-liquid separation, the treated effluent enters the next step.

[0011] Step (2), aerobic biological treatment: add microbial compound agent to the wastewater to efficiently decompose acrylic acid and other resin-like organic matter in the wastewater, and efficiently reduce CODcr, BOD5 and ammonia nitrogen in the wastewater; wherein, the microbial compound agent is composed of Bacillus baileyi (LM-W, accession number: CGMCC No.17168) and Bacillus brevis (LM-R, accession number: CGMCC No.17167) obtained by separation, purification and screening of the bottom sludge of the self-spraying paint wastewater;

[0012] Step (3), MBR membrane separation treatment: The wastewater treated in step (2) is filtered through an MBR membrane, and the COD of the effluent is less than 300 mg / L.

[0013] Preferably, in step (1), the agent includes a flocculating complex salt and a pH adjuster, wherein the flocculating complex salt is selected from at least one of ferrous sulfate, polyaluminum chloride (PAC) and polyacrylamide (PAM), and the pH adjuster is selected from at least one of sodium hydroxide, calcium hydroxide, sulfuric acid and hydrochloric acid.

[0014] Preferably, in step (1), the initial wastewater influent has a pH of 2-5, a COD of 2500-5000 mg / L, a color of 600 times, a total phosphorus (TP) of 12000-22000 mg / L, and a suspended solids (SS) of 300-2000 mg / L; the effluent has a pH of 7.5-11.5, a COD reduction of 30%-40%, a color reduction of 150 times, a total phosphorus (TP) reduction to below 5 mg / L, and a suspended solids (SS) reduction to 150-200 mg / L.

[0015] Preferably, in step (2), the bacterial concentration of *Baiyelinkie* in the treated wastewater is 10. 8 -10 10 CFU / mL, the bacterial concentration of the *Bacillus brevis* is 10. 8 -10 10 CFU / mL, the ratio of the number of colonies of the *Bacillus baileyi* to the number of colonies of the *Bacillus brevis* is 1:(0.1-10).

[0016] Preferably, the ratio of the number of colonies of *Bacillus baileyi* to that of *Bacillus brevis* is 1:1.

[0017] Preferably, in step (2), the wastewater is further filled with biological contact oxidation packing material, and the microbial composite agent is attached to the surface of the biological contact oxidation packing material in the form of a biofilm.

[0018] Preferably, in step (2), the dissolved oxygen (DO) content is also controlled to be 2-4 mg / L; the hydraulic retention time (HRT) in step (2) is 36-98 hours.

[0019] Preferably, in step (3), a hollow fiber ultrafiltration membrane with a pore size of 0.05-0.15 μm and a flux of 15-20 L / (m²) is used. 2 ·h), the effluent can be reused in the electrophoretic coating production line.

[0020] Preferably, after step (3), the following steps are also included: the sludge generated in steps (1) and (3) is fed into a screw press dewatering machine for dewatering treatment, and the moisture content of the dewatered sludge is reduced to below 60%.

[0021] Preferably, the sludge generated in step (3) is also returned to step (2).

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The biological treatment method for automotive electrophoretic coating wastewater provided by this invention introduces a microbial composite agent composed of *Bacillus baileyi* (LM-W, accession number: CGMCC No. 17168) and *Bacillus brevis* (LM-R, accession number: CGMCC No. 17167), obtained by separation, purification, and screening of sediment from spray paint wastewater, in the aerobic biological treatment step. This agent has the function of efficiently degrading acrylic resin, significantly improving the COD removal rate, and can eliminate the need for chemical agents and corresponding sedimented sludge required by traditional chemical oxidation treatment units. It can reduce the amount of sludge (by 50%-60%) and sludge viscosity. The MBR membrane module can retain the composite microbial community, prolong the sludge retention time, and enhance biodegradation. It can stably meet the standards for complex water qualities such as high acidity, high salinity, and high suspended solids. 60%-80% of the effluent can be reused in the electrophoretic coating production line, reducing fresh water consumption and saving costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the biological treatment system for automotive electrophoretic coating wastewater according to the present invention.

[0025] Figure 2 This is a schematic diagram of the process flow for the biological treatment method of automotive electrophoretic coating wastewater according to the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] This invention provides a biological treatment method for automotive electrophoretic coating wastewater, employing, as follows: Figure 1 The shown automotive electrophoretic coating wastewater biological treatment system combines Figure 2 It includes the following steps:

[0028] Step (1), coagulation and sedimentation pretreatment: Add reagents to the wastewater to generate flocculent precipitates from suspended solids, sparingly soluble metal salts and heavy metal ions in the wastewater. After solid-liquid separation, the treated effluent enters the next step.

[0029] In this step, the initial wastewater is sent to a coagulation sedimentation pretreatment tank 1 for pretreatment. The coagulation sedimentation pretreatment tank 1 includes a coagulation tank 11, a flocculation tank 12, and an inclined tube sedimentation tank 13, which are separated by baffles and connected in a flow-through manner. In some embodiments, a first reagent pipeline 14 is provided on the coagulation tank 11, and a second reagent pipeline 15 is provided on the flocculation tank 12. The first reagent pipeline 14 is connected to a coagulant storage tank 16 for adding coagulant solutions such as ferric chloride (FC), polyaluminum chloride (PAC), and polyferric sulfate (PFS). The second reagent pipeline 15 is connected to a flocculant storage tank 17 for adding flocculant solutions such as polyacrylamide (PAM). In some embodiments, the coagulant storage tank 16 is also connected to the coagulant preparation tank 18, where the coagulant solution is prepared and then the prepared coagulant solution is passed into the coagulant storage tank 16 for storage; the flocculant storage tank 17 is also connected to the flocculant preparation tank 19, where the flocculant solution is prepared and then the prepared flocculant solution is passed into the flocculant storage tank 19 for storage.

[0030] According to the present invention, the coagulant solution is introduced into the coagulation tank 11 through the first reagent pipe 14. In the coagulation tank 11, the coagulant reacts with the wastewater to form fine suspended solids. The coagulant solution is introduced into the flocculation tank 12 through the second reagent pipe 15. In the flocculation tank 12, the coagulant reacts with the wastewater to generate flocculent suspended solids and precipitates with larger particle sizes. The effluent from the coagulation tank 11 and the flocculation tank 12 is sent into the inclined tube sedimentation tank 13. The inclined tube sedimentation tank 13 is equipped with hexagonal honeycomb inclined tube packing 131. Solid-liquid separation is performed by inclined tube sedimentation to remove flocculent precipitates. The supernatant enters the next step.

[0031] In this step, by adding coagulants, flocculants, and other agents to the wastewater, suspended solids, sparingly soluble metal salts, and heavy metal ions in the wastewater are converted into flocculent precipitates. Before adding coagulants, flocculants, and other agents to the coagulation tank 11 and the flocculation tank 12, the pH value of the wastewater also needs to be adjusted. pH adjusters such as sodium hydroxide, calcium hydroxide, sulfuric acid, and hydrochloric acid are added to the coagulation tank 11 and the flocculation tank 12. Specifically, the coagulation tank 11 and the flocculation tank 12 are respectively equipped with a third agent pipeline 101, a fourth agent pipeline 102, a fifth agent pipeline 103, and a sixth agent pipeline 104. The third agent pipeline 101 and the fifth agent pipeline 103 are connected to the alkaline solution storage tank 105 for adding alkaline solutions such as sodium hydroxide or calcium hydroxide. The fourth agent pipeline 102 and the sixth agent pipeline 104 are connected to the acid solution storage tank 106 for adding acid solutions such as sulfuric acid or hydrochloric acid. In some embodiments, the alkali storage tank 105 is also connected to the alkali preparation tank 107, for example, sodium hydroxide or calcium hydroxide alkali solution is prepared in the alkali preparation tank 107, and the prepared alkali solution is then passed into the alkali storage tank 105 for storage; the acid storage tank 106 is also connected to the acid preparation tank 108, for example, sulfuric acid or hydrochloric acid solution is prepared in the acid preparation tank 108, and the prepared acid solution is then passed into the acid storage tank 106 for storage.

[0032] In this step, the initial wastewater influent has a pH of 2-5, COD of 2500-5000 mg / L, color of 600 times, total phosphorus (TP) of 12000-22000 mg / L, and suspended solids (SS) of 300-2000 mg / L; the effluent has a pH of 7.5-11.5, COD reduced by 30%-40%, color reduced to 150 times, total phosphorus (TP) reduced to below 5 mg / L, and suspended solids (SS) reduced to 150-200 mg / L.

[0033] Step (2), aerobic biological treatment: add microbial compound agent to the wastewater. The microbial compound agent is composed of Bacillus baileyi (LM-W, accession number: CGMCC No.17168) and Bacillus brevis (LM-R, accession number: CGMCC No.17167) obtained by separation, purification and screening of the bottom sludge of the self-spraying paint wastewater.

[0034] In this step, the wastewater treated in step (1) enters the aerobic biological treatment tank 2. The aerobic biological treatment tank 2 is separated from the inclined tube sedimentation tank 13 of the coagulation sedimentation pretreatment tank 1 by a partition and connected by a baffle. The aerobic biological treatment tank 2 is equipped with biological contact oxidation packing 21 and aeration heads 22 are provided at the bottom of the tank. The wastewater in the tank is aerated through the aeration heads 22, and the dissolved oxygen (DO) content in the wastewater is adjusted to 2-4 mg / L by controlling the aeration rate.

[0035] In this step, a seventh agent pipeline 23 is also provided on the aerobic biological treatment tank 2. The seventh agent pipeline 23 is connected to the microbial agent storage tank 24 and is used to add microbial agents.

[0036] According to the present invention, the aerobic microbial agent used in the present invention is a specific microbial compound agent, which is composed of *Beijerinckia sp.* (LM-W, accession number: CGMCC No. 17168) and *Brachymonas sp.* (LM-R, accession number: CGMCC No. 17167) obtained by separation, purification and screening of sediment from spray paint wastewater.

[0037] According to the present invention, the microbial composite agent composed of *Beijerinckia sp.* (LM-W, accession number: CGMCC No. 17168) and *Brachymonas assp.* (LM-R, accession number: CGMCC No. 17167) obtained by separation, purification, and screening of bottom sludge from spray paint wastewater has the function of efficiently degrading acrylic acid and other resinous organic matter in wastewater, and can improve COD removal rate. Compared with traditional chemical oxidation treatment methods, it does not require environmentally harmful chemical agents, does not produce sedimented sludge, and greatly reduces sludge volume (by 50%-60%) and sludge viscosity.

[0038] According to the present invention, the *Beijerinckia* sp. (LM-W, accession number: CGMCC No. 17168) and *Brachymonas* sp. (LM-R, accession number: CGMCC No. 17167) used in the present invention are both derived from the separation, purification, and screening of paint spraying wastewater sludge, for example, from the sludge of exhaust gas scrubbing wastewater from automotive paint spraying booths.

[0039] According to the present invention, the method for obtaining *Beijerinckia sp.* (LM-W, accession number: CGMCC No. 17168) includes the following steps:

[0040] Take 10g from the bottom sludge of the exhaust gas scrubbing wastewater from an automotive paint spraying booth. Under aseptic conditions, add it to 250mL Erlenmeyer flasks containing 100mL of sterile liquid enrichment medium (including 5g, 10g, 20g, 30g, or 50g of acrylic acid for acclimatization and enrichment, 0.1g of CaCl2·6H2O, 0.25g of MgCl2, 1.5g of K2HPO4, 1g of NH4Cl, 9g of peptone, 500mL of H2O, pH=6.5-7.0). After culturing on a shaker at 30℃ and 180rpm for 7 days, transfer it to the next batch of enrichment medium at a 10% inoculum (acrylic acid gradient of 5, 10, 20, 30, or 50g / L) and acclimatize under the same conditions for 7 days. Then, at a 10% inoculum volume, transfer the culture to a sterile liquid basal medium containing 100 g / L acrylic acid (including 1.00 g NH4NO3, 0.5 g MgSO4·7H2O, 0.5 g (NH4)2SO4, 0.5 g KH2PO4, 0.5 g NaCl, 1.5 g K2HPO4, 1000 mL H2O, pH = 4.0), i.e., an acrylic acid concentration of 100 g / L basal medium. Continue culturing for 7 days. After two consecutive transfers, take 0.1 mL of the obtained fermentation broth and repeatedly streak it on a solid basal medium for separation and purification until a single colony is obtained. Inoculate the pure colony onto an agar slant and store it in a refrigerator at 40°C to obtain the final product.

[0041] Upon identification, the basic morphology of *Beijerinckia sp.*, LM-W (CGMCC No. 17168) obtained by the above method is as follows: the bacteria have a rough surface, do not produce spores, and have small capsules. They divide by binary fission (transverse division of a single cell into two daughter cells), are Gram-negative, and have a cell size of approximately (1.5–2.5) μm in length and (0.3–0.5) μm in width. On solid culture media, the colonies are round, with a raised, smooth surface, intact edges, and are milky white and opaque.

[0042] According to the present invention, the method for obtaining *Brachymonas sp.* (LM-R, accession number: CGMCC No. 17167) includes the following steps:

[0043] Take 10g from the bottom sludge of the exhaust gas scrubbing wastewater from an automotive paint spraying booth. Under aseptic conditions, add it to 250mL Erlenmeyer flasks containing 100mL of sterile liquid enrichment medium (including 5g, 10g, 20g, 30g, or 50g toluene for acclimatization and enrichment, 0.1g CaCl2·6H2O, 0.25g MgCl2, 1.5g K2HPO4, 1g NH4Cl, 9g peptone, 500mL H2O, pH=6.5-7.0). After incubating for 7 days on a shaker at 30℃ and 180rpm, transfer the medium to the next batch of enrichment medium at a 10% inoculum (toluene gradient of 5, 10, 20, 30, or 50g / L) and acclimatize for another 7 days under the same conditions. Then, at a 10% inoculum volume, transfer the culture to a sterile liquid basal medium containing 100 g / L toluene (including 1.00 g NH4NO3, 0.5 g MgSO4·7H2O, 0.5 g (NH4)2SO4, 0.5 g KH2PO4, 0.5 g NaCl, 1.5 g K2HPO4, 1000 mL H2O, pH = 4.0), i.e., a basal medium with a toluene concentration of 100 g / L. Continue culturing for 7 days. After two consecutive transfers, take 0.1 mL of the obtained fermentation broth and repeatedly streak it onto a solid basal medium for separation and purification until a single colony is obtained. Inoculate the pure colony onto an agar slant and store it in a refrigerator at 40°C to obtain the final product.

[0044] The basic morphology of *Brachymonas sp.* (LM-R, CGMCC No. 17167) obtained by the above method is as follows: This bacterium is a bacillus with a rough surface, does not produce spores and has a small capsule, is Gram-positive, and has a cell size of approximately (1.0–2.0) μm in length and (0.3–0.5) μm in width. On solid culture medium, the colonies are round, with a raised and smooth surface, intact edges, and are yellowish-brown and opaque.

[0045] According to the present invention, the microbial agent of the present invention is a composite agent composed of *Beijerinckia sp.* (LM-W, accession number: CGMCC No. 17168) and *Brachymonas sp.* (LM-R, accession number: CGMCC No. 17167) obtained by separation, purification and screening of sediment from spray paint wastewater. It has synergistic and enhanced degradation performance on acrylic acid and other resin-based organic matter in wastewater, and the degradation efficiency is higher than that of a single species.

[0046] According to the present invention, the above-mentioned microbial compound agent is added to the aerobic biological treatment tank 2 through the seventh agent pipe 23. In the wastewater treated in the aerobic biological treatment tank 2, the bacterial concentration of *Baiyelinkie* is 10. 8 -10 10CFU / mL, the bacterial concentration of the *Bacillus brevis* is 10. 8 -10 10 The CFU / mL ratio of *Bacillus baileyi* to *Bacillus brevis* colony count is 1:(0.1-10), preferably 1:(0.1-5), such as 1:0.5, 1:1, 1:2, 1:3, 1:4, etc. More preferably, when the ratio of *Bacillus baileyi* to *Bacillus brevis* colony count is 1:1, the microbial compound agent has stronger degradation performance on acrylic acid and other resin-based organic matter in wastewater.

[0047] In this step, the aforementioned microbial compound agent is added to the aerobic biological treatment tank 2 through the seventh agent pipe 23. In the aerobic biological treatment tank 2, the microbial compound agent adheres to the surface of the biological contact oxidation packing 21 in the form of a biofilm. It mainly utilizes the biofilm on the packing to degrade pollutants such as organic matter and ammonia nitrogen. It also has a high removal rate for CODcr, BOD5, and NH3-N in wastewater, degrading organic matter in wastewater into non-toxic and harmless carbon dioxide, water, and nitrogen-containing compounds. The quality of the packing determines whether microorganisms can be adsorbed and whether they can grow and reproduce well. High-density ecological packing can be used. For example, at a water depth of 2.0m, the packing layer height is set at 1.6m. This packing has a long service life, a large specific surface area, a certain degree of flexibility and rigidity, good resilience, and the material used is lighter than water. It can spread evenly in water and can densely and multi-layerly cut air bubbles, greatly improving the dissolved oxygen transfer coefficient, reducing aeration volume, and saving energy consumption.

[0048] In this step, the hydraulic retention time (HRT) is 36-98 hours, COD is reduced to below 500 mg / L, COD removal rate exceeds 80%, and color is further reduced by 50 times.

[0049] Step (3), MBR membrane separation treatment: The wastewater treated in step (2) is filtered through an MBR membrane, and the COD of the effluent is less than 300 mg / L.

[0050] In this step, the wastewater treated in step (2) enters the MBR membrane bioreactor 3. The MBR membrane bioreactor 3 is separated from the aerobic biological treatment tank 2 by a partition and is connected by a baffle. An MBR membrane module 31 is installed in the MBR membrane bioreactor 3. According to the scheme of the present invention, the MBR membrane module 31 adopts a hollow fiber ultrafiltration membrane with a pore size of 0.05-0.15μm and a flux of 15-20L / (m³). 2 After the wastewater is filtered through the MBR membrane module 31, the COD of the effluent can be less than 300 mg / L. The effluent can be reused in the electrophoretic coating production line, which can reduce the fresh water consumption of the electrophoretic coating production line and save production costs.

[0051] According to the present invention, the microbial compound agent added to the wastewater in the aerobic biological treatment tank 2 contains *Beijerinckia sp.*, LM-W (accession number: CGMCC No. 17168) with a cell size of approximately (1.5–2.5) μm in length and (0.3–0.5) μm in width, and *Brachymonas*... The cells of *Sp. LM-R* (accession number: CGMCC No. 17167) are approximately 1.0–2.0 μm long and 0.3–0.5 μm wide. The MBR membrane module 31 used in the MBR membrane bioreactor 3 is a hollow fiber ultrafiltration membrane with a pore size of 0.05–0.15 μm. Therefore, this membrane can retain complex microbial communities in wastewater, thereby prolonging the residence time of complex microbial communities in sludge, increasing the biomass of specific bacteria in the treatment system, enhancing biodegradation, further improving COD removal rate and total phosphorus (TP) removal rate, and ensuring water quality stability.

[0052] According to the present invention, a sludge return pipe 32 is also provided at the bottom of the MBR membrane bioreactor 3. The sludge return pipe 32 leads from the bottom of the tank to the aerobic biological treatment tank 2, and the sludge generated in step (3) is returned to step (2) for recycling.

[0053] Step (4) involves sending the sludge produced in steps (1) and (3) into the screw press dewatering machine 4 for dewatering treatment.

[0054] Specifically, in this step, each of the coagulation sedimentation pretreatment tank 1 in step (1) and the MBR membrane bioreactor 3 in step (3) is equipped with a sludge discharge pipe 41 at the bottom of the tank. Each sludge discharge pipe 41 is connected to the sludge tank 5. Each sludge discharge pipe 41 is equipped with a sludge discharge pipe valve 42 and a sludge discharge pump 43. The sludge tank 5 is connected to the screw press dewatering machine 4 through a pipe 44. The sludge in the sludge tank 5 is sent to the screw press dewatering machine 4 for dewatering treatment. The moisture content of the dewatered sludge is reduced to below 60%.

[0055] The biological treatment system and method for automotive electrophoretic coating wastewater provided by this invention introduces a microbial composite agent composed of *Bacillus baileyi* (LM-W, accession number: CGMCC No. 17168) and *Bacillus brevis* (LM-R, accession number: CGMCC No. 17167), obtained by separation, purification, and screening of sediment from spray paint wastewater, into the aerobic biological treatment section. This agent has the function of efficiently degrading acrylic resin, significantly improving COD removal rate, and can eliminate the need for chemical agents and corresponding precipitated sludge required by traditional chemical oxidation treatment units. It can reduce sludge volume (by 50%-60%) and sludge viscosity. The MBR membrane module can retain the composite microbial community, prolong sludge retention time, and enhance biodegradation. It can stably meet standards for complex water qualities such as high acidity, high salinity, and high suspended solids. 60%-80% of the effluent can be reused in the electrophoretic coating production line, reducing fresh water consumption and saving costs.

[0056] The biological treatment system and method for automotive electrophoretic coating wastewater provided by this invention employs the synergistic effect of two microbial species in the aerobic biological treatment section, which can efficiently degrade acrylic acid and other resin-based organic substances in the electrophoretic wastewater. The MBR membrane module replaces the traditional secondary sedimentation tank, which can retain the composite microbial community, prolong the residence time of the microbial composite agent in the sludge, increase the biomass of specific microbial species in the treatment system, enhance biodegradation and biological phosphorus removal, and ensure the stability of water quality.

[0057] The biological treatment system and method for automotive electrophoretic coating wastewater provided by this invention employs the synergistic effect of two microbial strains in the aerobic biological treatment section. The microorganisms used are non-toxic and harmless, decomposing organic matter and ammonia nitrogen in the waste gas into non-toxic and harmless carbon dioxide, water, and nitrogen-containing compounds. The metabolic products of the microbial community (such as carbon sources and nitrogen sources) can also be recycled, reducing the addition of external agents and making the entire waste gas treatment process more environmentally friendly, without producing secondary harmful substances.

[0058] The biological treatment system and method for automotive electrophoretic coating wastewater provided by this invention utilizes the synergistic effect of two microbial strains in the aerobic biological treatment section. This efficiently degrades acrylic acid and other resin-based organic substances in the electrophoretic wastewater, increasing the COD removal rate to over 95% and the acrylic acid degradation rate to >90%. It can also stably meet standards for complex water qualities such as high acidity, high salinity, and high suspended solids. 60%-80% of the effluent can be reused in the electrophoretic coating production line, reducing fresh water consumption and saving operating costs by 40%. Furthermore, it eliminates the need for chemical agents and corresponding precipitated sludge required by traditional chemical oxidation treatment units, reducing sludge volume (by 50%-60%) and sludge viscosity. The effluent meets the Class II standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996), and 60% of the effluent can be reused in the electrophoretic coating production line, achieving water resource recycling.

[0059] The present invention will be further illustrated below with reference to specific embodiments. The purpose of these embodiments is to provide a better understanding of the content and essential features of the present invention. Therefore, the examples given should not be considered as limitations on the scope of protection of the present invention. Any product identical or similar to the present invention, derived by any person based on the teachings of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0060] For experiments not specifically described in the examples, the procedures or conditions can be performed according to the conventional experimental steps and conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0061] Example 1:

[0062] A biological treatment method for automotive electrophoretic coating wastewater includes the following steps:

[0063] Influent water quality: pH=2, COD=3200mg / L, total phosphorus (TP)=14000mg / L, suspended solids (SS)=400mg / L;

[0064] Step (1), coagulation and sedimentation pretreatment: Add reagents to the wastewater to generate flocculent precipitates from suspended solids, sparingly soluble metal salts and heavy metal ions in the wastewater. After solid-liquid separation, the treated effluent enters the next step.

[0065] Add 23 g / L calcium hydroxide, 350 mg / L polyaluminum chloride (PAC), and 5 mg / L polyacrylamide (PAM) to adjust the pH to 8.9;

[0066] Total phosphorus (TP) was reduced to 2.8 mg / L (removal rate 99%), and suspended solids (SS) were reduced to 150 mg / L;

[0067] Step (2), aerobic biological treatment: add microbial compound agent to wastewater, and fill the wastewater with biological contact oxidation packing. The microbial compound agent is attached to the biological contact oxidation packing in the form of a biofilm and is aerated to efficiently decompose acrylic acid and other resin-like organic substances in the wastewater, and efficiently reduce CODcr, BOD5 and ammonia nitrogen in the wastewater.

[0068] The ratio of colony counts of the added microbial compound agent (Beijerinckia sp., LM-W, accession number: CGMCC No. 17168) and Brachymonas sp., LM-R, accession number: CGMCC No. 17167) was 1:1, and the bacterial concentration of each agent was 5 × 10⁻⁶. 9With CFU / mL, dissolved oxygen (DO) controlled at 3.5 mg / L, hydraulic retention time (HRT) of 60 hours, COD was reduced to 350 mg / L (removal rate of 86%).

[0069] Step (3), MBR membrane separation treatment: The wastewater treated in step (2) is filtered through an MBR membrane, and the sludge generated in step (3) is returned to step (2);

[0070] Hollow fiber membranes with a pore size of 0.1 μm were used, and the flux was 18 L / (m²). 2 The effluent COD was 280 mg / L, total phosphorus (TP) was 0.6 mg / L, and the effluent pH was 7.5.

[0071] Step (4), sludge treatment:

[0072] The sludge produced in steps (1) and (3) is fed into a screw press dewatering machine for dewatering treatment, and the moisture content of the resulting sludge cake is reduced to 53%.

[0073] Example 2:

[0074] A biological treatment method for automotive electrophoretic coating wastewater includes the following steps:

[0075] Influent water quality: pH=3.5, COD=5000mg / L, conductivity=12000μS / cm, color=600 times, suspended solids (SS)=1200mg / L;

[0076] Step (1), coagulation and sedimentation pretreatment: Add reagents to the wastewater to generate flocculent precipitates from suspended solids, sparingly soluble metal salts and heavy metal ions in the wastewater. After solid-liquid separation, the treated effluent enters the next step.

[0077] Add 400 mg / L of polyaluminum chloride (PAC) and 6 mg / L of polyacrylamide (PAM) to adjust the pH to 8.2;

[0078] Suspended solids (SS) decreased to 200 mg / L, and color decreased by 150 times;

[0079] Step (2), aerobic biological treatment: add microbial compound agent to wastewater, and fill the wastewater with biological contact oxidation packing. The microbial compound agent is attached to the biological contact oxidation packing in the form of a biofilm and is aerated to efficiently decompose acrylic acid and other resin-like organic substances in the wastewater, and efficiently reduce CODcr, BOD5 and ammonia nitrogen in the wastewater.

[0080] The ratio of colony counts of the added microbial compound inoculant (Beijerinckia sp., LM-W, accession number: CGMCC No. 17168) and Brachymonas sp., LM-R, accession number: CGMCC No. 17167) was 1:1, and the bacterial concentration of each was 8 × 10⁻⁶. 9 CFU / mL, dissolved oxygen (DO) controlled at 4.0 mg / L, hydraulic retention time (HRT) of 36 hours, COD reduced to 400 mg / L, and color further reduced to 50 times;

[0081] Step (3), MBR membrane separation treatment: The wastewater treated in step (2) is filtered through an MBR membrane, and the sludge generated in step (3) is returned to step (2);

[0082] Hollow fiber membranes with a pore size of 0.1 μm were used, and the flux was 15 L / (m²). 2 The effluent COD is 75 mg / L, color is <10 times, conductivity is reduced to 5000 μS / cm, effluent pH is 7.8, and the effluent can be reused as workshop flushing water;

[0083] Step (4), sludge treatment:

[0084] The sludge produced in steps (1) and (3) is fed into a screw press dewatering machine for dewatering treatment, and the moisture content of the resulting sludge cake is reduced to 55%.

[0085] Example 3:

[0086] A biological treatment method for automotive electrophoretic coating wastewater includes the following steps:

[0087] Influent water quality: pH=4, COD=2800mg / L, total phosphorus (TP)=20000mg / L, suspended solids (SS)=2000mg / L;

[0088] Step (1), coagulation and sedimentation pretreatment: Add reagents to the wastewater to generate flocculent precipitates from suspended solids, sparingly soluble metal salts and heavy metal ions in the wastewater. After solid-liquid separation, the treated effluent enters the next step.

[0089] Add 42 g / L calcium hydroxide, 230 mg / L polyaluminum chloride (PAC), and 4 mg / L polyacrylamide (PAM) to adjust the pH to 7.8;

[0090] Total phosphorus (TP) was reduced to 400 mg / L (removal rate 98%), and suspended solids (SS) were reduced to 180 mg / L;

[0091] Step (2), aerobic biological treatment: add microbial compound agent to wastewater, and fill the wastewater with biological contact oxidation packing. The microbial compound agent is attached to the biological contact oxidation packing in the form of a biofilm and is aerated to efficiently decompose acrylic acid and other resin-like organic substances in the wastewater, and efficiently reduce CODcr, BOD5 and ammonia nitrogen in the wastewater.

[0092] The ratio of colony counts of the added microbial compound agent (Beijerinckia sp., LM-W, accession number: CGMCC No. 17168) and Brachymonas sp., LM-R, accession number: CGMCC No. 17167) was 1:1, and the bacterial concentration of each agent was 1×10⁻⁶. 10 With CFU / mL, dissolved oxygen (DO) controlled at 2.5 mg / L, hydraulic retention time (HRT) of 44 hours, COD was reduced to 320 mg / L (removal rate of 89%).

[0093] In step (3), the wastewater treated in step (2) is filtered through an MBR membrane, and the sludge generated in step (3) is returned to step (2).

[0094] Hollow fiber membranes with a pore size of 0.1 μm and a flux of 20 L / (m²) were used. 2 The effluent COD is 85 mg / L, total phosphorus (TP) is 0.8 mg / L, and pH is 7.0. The effluent can be directly reused in the pretreatment process of the electrophoresis tank.

[0095] Step (4), sludge treatment:

[0096] The sludge produced in steps (1) and (3) is fed into a screw press dewatering machine for dewatering treatment, and the moisture content of the resulting sludge cake is reduced to 56%.

[0097] Examples 4-6:

[0098] Based on Example 1, in step (2), the ratio of colony counts of the added microbial compound inoculant (Beijerinckia sp., LM-W, accession number: CGMCC No. 17168) and Brachymonas sp., LM-R, accession number: CGMCC No. 17167) was 1:0.5, 1:1.5, and 1:2, and the bacterial concentration of Beijerinckia sp. (LM-W) was 5 × 10⁻⁶. 9 The CFU / mL concentration of *Leptobacillus brevis* (LM-R) was 2.5 × 10⁻⁶. 9 CFU / mL, 7.5×10 9 CFU / mL, 1×10 10CFU / mL, otherwise the same as in Example 1;

[0099] The COD values ​​of the wastewater after step (2) are listed in Table 1.

[0100] Table 1

[0101]

[0102] As can be seen from Table 1, the present invention employs two microbial compound agents in the aerobic biological treatment section, with the colony count ratio of Beijerinckia sp. (LM-W) and Brachymonas sp. (LM-R) being 1:1, which has the best COD removal efficiency.

[0103] Comparative Example 1:

[0104] Based on Example 1, in step (2), only the bacterial concentration was 5×10⁻⁶. 9 The microbial inoculum (Beijerinckia sp., LM-W, accession number: CGMCC No. 17168) at CFU / mL was the same as in Example 1.

[0105] The COD of the wastewater treated in step (2) was reduced to 1250 mg / L.

[0106] Comparative Example 2:

[0107] Based on Example 1, in step (2), only the bacterial concentration was 5×10⁻⁶. 9 The microbial inoculum (Brachymonas sp., LM-R, accession number: CGMCC No. 17167) at CFU / mL was used, and the rest was the same as in Example 1;

[0108] The COD of the wastewater treated in step (2) was reduced to 1050 mg / L.

[0109] As can be seen from Comparative Examples 1 and 2, the present invention uses two microbial compound agents in the aerobic biological treatment section, which has a significant synergistic effect on COD removal efficiency compared with the use of a single microbial species.

[0110] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A biological treatment method for automotive electrophoretic coating wastewater, characterized in that, Includes the following steps: Step (1), coagulation and sedimentation pretreatment: Add reagents to the wastewater to generate flocculent precipitates from suspended solids, sparingly soluble metal salts and heavy metal ions in the wastewater. After solid-liquid separation, the treated effluent enters the next step. Step (2), aerobic biological treatment: add microbial compound agent to the wastewater to efficiently decompose acrylic acid and other resin-like organic matter in the wastewater, and efficiently reduce CODcr, BOD5 and ammonia nitrogen in the wastewater; wherein, the microbial compound agent is composed of Bacillus baileyi (LM-W, accession number: CGMCC No.17168) and Bacillus brevis (LM-R, accession number: CGMCC No.17167) obtained by separation, purification and screening of the bottom sludge of the self-spraying paint wastewater; Step (3), MBR membrane separation treatment: The wastewater treated in step (2) is filtered through an MBR membrane, and the COD of the effluent is less than 300 mg / L.

2. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, In step (1), the agent includes a flocculating compound salt and a pH adjuster. The flocculating compound salt is selected from at least one of ferrous sulfate, ferric chloride (FC), polyaluminum chloride (PAC), polyferric sulfate (PFS), and polyacrylamide (PAM). The pH adjuster is selected from at least one of sodium hydroxide, calcium hydroxide, sulfuric acid, and hydrochloric acid.

3. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, In step (1), the initial wastewater influent has a pH of 2-5, COD of 2500-5000 mg / L, color of 600 times, total phosphorus (TP) of 12000-22000 mg / L, and suspended solids (SS) of 300-2000 mg / L; the effluent has a pH of 7.5-11.5, COD reduced by 30%-40%, color reduced by 150 times, total phosphorus (TP) reduced to below 5 mg / L, and suspended solids (SS) reduced to 150-200 mg / L.

4. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, In step (2), the bacterial concentration of *Baiyelinkie* in the treated wastewater is 10. 8 -10 10 CFU / mL, the bacterial concentration of the *Bacillus brevis* is 10. 8 -10 10 CFU / mL, the ratio of the number of colonies of the *Bacillus baileyi* to the number of colonies of the *Bacillus brevis* is 1:(0.1-10).

5. The biological treatment method for automotive electrophoretic coating wastewater according to claim 4, characterized in that, The colony count ratio of *Bacillus baileyi* to *Bacillus brevis* is 1:

1.

6. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, In step (2), the wastewater is also filled with biological contact oxidation packing material, and the microbial composite agent is attached to the surface of the biological contact oxidation packing material in the form of a biofilm.

7. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, In step (2), the dissolved oxygen (DO) content is controlled to be 2-4 mg / L; the hydraulic retention time (HRT) in step (2) is 36-98 hours.

8. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, In step (3), a hollow fiber ultrafiltration membrane with a pore size of 0.05-0.15 μm and a flux of 15-20 L / (m²) is used. 2 ·h), the effluent can be reused in the electrophoretic coating production line.

9. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, After step (3), the following steps are also included: the sludge generated in steps (1) and (3) is sent to a screw press dewatering machine for dewatering treatment, and the moisture content of the dewatered sludge is reduced to below 60%.

10. The biological treatment method for automotive electrophoretic coating wastewater according to claim 1, characterized in that, The sludge generated in step (3) is also returned to step (2).

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