Treatment system and method for water-based cleaning waste liquid in automobile coating production line

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly relates to a treatment system and method for water-based cleaning waste liquid in an automobile coating production line. The system comprises a waste liquid collection and homogeneous regulation unit, a multi-stage pretreatment unit, a secondary biochemical treatment unit and an intelligent control unit which are connected in sequence. The multi-stage pretreatment unit adopts a special A / B agent composite formula to perform efficient demulsification and coagulation; the secondary biochemical treatment unit adopts a combined process of hydrolytic acidification, contact oxidation and MBR (Membrane Bioreactor) for deep degradation. Through innovative integration of physicochemical and biochemical processes, the treatment problem of the high-concentration and strong-emulsification water-based cleaning waste liquid is effectively solved, efficient removal (gt, 99%) of COD, water resource recycling and hazardous waste reduction are achieved, and the method has the advantages of being good in treatment effect, low in operation cost, environmentally friendly and the like and is suitable for wastewater treatment and recycling in the automobile coating industry.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a system and method for treating water-based cleaning wastewater in automotive painting production lines. Background Technology

[0002] With the rapid development of new energy vehicles and intelligent manufacturing, automotive painting processes widely adopt robotic automated spraying systems and water-based coatings. During production, equipment such as cleaning robots and paint delivery pipelines generate large quantities of high-concentration, highly emulsified, and recalcitrant cleaning wastewater. This type of wastewater is characterized by extremely high chemical oxygen demand (COD) (300,000-600,000 mg / L), strong emulsification stability, complex composition, and poor biodegradability (B / C ratio 0.26-0.32), making it a typical example of difficult-to-treat industrial wastewater.

[0003] Currently, the industry mainly uses the following methods to treat this type of waste liquid: First, third-party transportation and disposal, which is costly, costing approximately 10,000 yuan per ton; second, direct incineration, which consumes a huge amount of energy and poses a risk of air pollution; and third, traditional coagulation and sedimentation, but with a low removal rate of only 20-30%. These existing methods all suffer from technical bottlenecks such as substandard treatment effects, high operating costs, inability to recover resources, and a high risk of secondary pollution.

[0004] For example, Chinese patent application CN118005204A discloses a "method for treating coating wastewater," but it mainly targets pretreatment electrophoresis wastewater and lacks specificity for the extremely high-concentration, strongly emulsifying aqueous cleaning wastewater generated by robotic cleaning, which is the focus of this invention. Its demulsification and treatment efficiencies are both insufficient. Therefore, developing an integrated treatment technology that can efficiently demulsify, deeply degrade, reuse resources, and has low operating costs is urgently needed. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a treatment system and method for water-based cleaning wastewater from automotive painting production lines, characterized by high processing efficiency, low operating costs, and the ability to achieve water resource reuse and hazardous waste reduction. The specific technical solution is as follows: A system for treating water-based cleaning wastewater in an automotive painting production line includes the following components connected sequentially via pipelines: Waste liquid collection and homogenization unit: including a mixing tank, a booster pump and a conditioning tank equipped with a stirring device and an online pH monitor, used to collect and equalize water quality and quantity; Multi-stage pretreatment unit: includes at least one reactor equipped with a stirring device, a dosing device for adding agent A and agent B, an inclined plate sedimentation tank and a centrifugal dewatering machine for demulsification, coagulation and solid-liquid separation; Secondary biochemical treatment unit: includes a hydrolysis acidification reactor, a contact oxidation tank and a membrane bioreactor (MBR) connected in sequence, for degrading organic matter and deep purification; Clean water reuse unit: includes a clean water tank and a reuse water pump, used for storing and reusing qualified produced water; Intelligent control unit: It adopts a PLC controller and is electrically connected to the pH online monitor, flow meter, and liquid level sensor. It is used to automatically control the dosage, stirring speed, water pump start and stop, and system operating parameters according to preset parameters.

[0006] Furthermore, Agent A comprises polyaluminum chloride (PAC), modified diatomaceous earth, and the pH adjuster citric acid; Agent B comprises cationic polyacrylamide (CPAM), nano-ferric oxide (Fe3O4), and a demulsifier.

[0007] The present invention also provides a wastewater treatment method using the above system, comprising the following steps: S1 Wastewater Collection and Adjustment: The water-based cleaning wastewater generated from the automotive painting production line is collected to the wastewater collection and homogenization adjustment unit. The water quality is uniformly mixed by stirring, and the pH of the wastewater is adjusted to 4.5-5.5 by a pH online monitoring instrument and a dosing device. S2 Multi-stage Pretreatment: The waste liquid treated by S1 is transported to the reactor of the multi-stage pretreatment unit. First, agent A is added at 15-25 mL / L, followed by agent B at 5-8 mL / L, with a rate gradient G of 50-70 s. -1 Under the conditions of stirring reaction for 45-60 minutes, demulsification and coagulation are carried out; the mixture after reaction enters the inclined plate sedimentation tank for solid-liquid separation, the supernatant enters the subsequent unit, and the bottom sludge is dewatered by centrifugal dewatering machine and then transported off-site for disposal. S3 Secondary Biological Treatment: The supernatant obtained from S2 first enters the hydrolysis and acidification reactor, where hydrolysis and acidification are carried out under conditions of hydraulic retention time of 24-36 hours, temperature of 35±2℃, and pH of 5.5-6.5, converting recalcitrant large organic molecules into easily degradable small molecules. Subsequently, the effluent enters the contact oxidation tank for aerobic biological degradation to further remove organic matter. Finally, the effluent undergoes sludge-water separation through an MBR system. The designed flux of the MBR membrane is 15-20 L / (m²·h) to ensure the quality of the effluent. S4 Clean Water Reuse: The permeable water from the MBR system enters the clean water tank and is reused in the production process via a reuse water pump.

[0008] The beneficial effects of this invention are as follows: (1) Extremely high treatment efficiency. Through the innovative combination process of "physicochemical pretreatment + biochemical deep treatment", especially the optimized A / B agent composite formula, efficient demulsification and deep COD removal of strongly emulsified and high-concentration waste liquid are achieved. The total COD removal rate of the system is >99%, and the COD of the effluent is <50mg / L, which is stable and better than the national emission standard. (2) Significantly reduced operating costs. The treatment cost is reduced to about RMB57.8 / ton, which is more than 94% lower than the traditional external transportation and disposal method (about RMB10,000 / ton), resulting in huge economic benefits. (3) High degree of resource utilization. A high proportion of wastewater reuse is achieved (annual reuse can reach more than 20,000 m³). At the same time, the water content of the waste residue generated by pretreatment is <40% after dewatering, which achieves a great reduction in hazardous waste (reduction of more than 85%). (4) Stable and reliable system operation. The intelligent control system can adapt to water quality fluctuations and has strong resistance to shock loads, ensuring long-term stable operation that meets standards. (5) It is environmentally friendly, with no risk of secondary pollution throughout the process, and significantly reduces carbon emissions and the amount of hazardous waste disposed of externally, resulting in significant environmental benefits. Attached Figure Description

[0009] Figure 1 This is a process flow diagram of the secondary biochemical treatment system of the present invention. Detailed Implementation

[0010] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0011] A system for treating water-based cleaning wastewater in an automotive painting production line includes a wastewater collection and homogenization unit, a multi-stage pretreatment unit, a secondary biochemical treatment unit, and a clean water reuse unit connected in sequence via pipelines, as well as an intelligent control unit electrically connected to sensors and actuators in each unit.

[0012] The waste liquid collection and homogenization unit includes a mixing tank, a booster pump, and a conditioning tank. The conditioning tank is equipped with a stirring device 14 and an online pH monitor, which are used to collect the cleaning waste liquid generated by the production line, and to balance the water quality and quantity through stirring and mixing. At the same time, based on the feedback from the pH monitor, the intelligent control unit controls the addition of chemicals to initially adjust the pH of the waste liquid to a suitable range.

[0013] The multi-stage pretreatment unit comprises one or more reactors connected in series, each equipped with a stirring device. The reactors are connected to dosing devices for agent A and agent B via pipelines. The reactor outlet is connected to an inclined plate sedimentation tank, the sludge outlet of which is connected to a centrifugal dewatering machine, and the supernatant outlet is connected to the subsequent secondary biological treatment unit. This unit is used for efficient demulsification and coagulation of the wastewater, achieving solid-liquid separation.

[0014] The secondary biological treatment unit comprises a hydrolysis acidification reactor, a contact oxidation tank, and a membrane bioreactor (MBR) connected in sequence. The MBR incorporates membrane modules. This unit is used for the deep purification of pretreated wastewater, degrading dissolved organic matter.

[0015] The clean water reuse unit includes a clean water tank and a reuse water pump, which are used to store the product water of the MBR and reuse it according to production needs.

[0016] The intelligent control unit uses a PLC controller, which is electrically connected to the pH online monitor, flow meters and level sensors of each unit, as well as actuators such as water pumps and stirring motors. The PLC controller has preset control logic, which can automatically control the dosage, stirring speed, and water pump start and stop of each unit according to the received signals, so as to realize the automated operation of the system.

[0017] The above system was used to treat the robot water-based cleaning wastewater generated from an automotive painting production line. The raw water COD was approximately 450,000 mg / L.

[0018] The processing steps are as follows: (1) Collect the waste liquid into the equalization tank, mix it evenly by stirring, and adjust the pH to 5.0 by controlling the addition of acid through the intelligent control unit.

[0019] (2) Pump the adjusted waste liquid into the reactor. First, add agent A (a mixture of PAC, modified diatomaceous earth, and citric acid) at 20 mL / L through the agent A dosing device, and then add agent B (a mixture of CPAM, nano Fe3O4, and demulsifier) ​​at 6.5 mL / L through the agent B dosing device. Under the action of the stirring device, control the rate gradient G value to 60 s⁻¹, and react for 50 minutes.

[0020] (3) The mixture after the reaction enters the inclined plate sedimentation tank for sedimentation and separation. The supernatant enters the hydrolysis acidification reactor, and the bottom sludge is discharged into the centrifugal dewatering machine for dewatering. The dewatered sludge (moisture content <38%) is transported off-site for disposal.

[0021] (4) The supernatant is kept in the hydrolysis acidification reactor for 30 hours, with the temperature controlled at 35℃ and the pH value at 6.0. The effluent enters the contact oxidation tank for aerobic treatment, and then enters the MBR for mud-water separation. The MBR membrane flux is controlled at 18 L / (m²·h).

[0022] (5) The permeate from the MBR enters the clear water tank. The COD is tested and found to be 45 mg / L, which meets the reuse standard. It is then pumped to the production workshop for reuse via a reuse water pump.

[0023] Calculations show that the system in this embodiment achieves a total COD removal rate of 99.99%, with a treatment cost of approximately RMB 57.8 per ton of wastewater, which is more than 99% lower than the cost of external disposal (approximately RMB 10,000 per ton). Over 20,000 cubic meters of wastewater can be reused annually, and hazardous waste generation is reduced by more than 85%, achieving significant economic and environmental benefits. Comparative Example

[0024] The same raw water as in Example 1 was used, but only a conventional coagulation and sedimentation process (with only PAC and PAM added) was employed for treatment. The results showed that the COD removal rate was only about 25%, and the effluent COD was still as high as 330,000 mg / L or more, which could not meet the requirements for subsequent treatment or discharge. Comparative Example

[0025] The same raw water as in Example 1 was used, but the multi-stage pretreatment unit only used the A / B agent described in this invention, without subsequent secondary biological treatment. The results showed that although the demulsification effect was good, the effluent COD was still as high as several thousand mg / L, making it unsuitable for direct reuse or discharge.

[0026] The preferred embodiments of this patent have been described in detail above. However, this patent is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this patent.

Claims

1. A system for treating water-based cleaning wastewater in an automotive painting production line, characterized in that, Including those connected sequentially via pipes: Waste liquid collection and homogenization unit: including a mixing tank, a booster pump, and a conditioning tank equipped with a stirring device and an online pH monitor; Multi-stage pretreatment unit: includes at least one reactor equipped with a stirring device, a dosing device for adding agent A and agent B, an inclined plate sedimentation tank, and a centrifugal dewatering machine; Secondary biochemical treatment unit: includes a hydrolysis acidification reactor, a contact oxidation tank and a membrane bioreactor (MBR) connected in sequence. Clean water reuse unit: includes a clean water tank and a reuse water pump; Intelligent control unit: It adopts a PLC controller and is electrically connected to the pH online monitor, flow meter, and liquid level sensor. It is used to automatically control the dosage, stirring speed, water pump start and stop, and system operating parameters according to preset parameters.

2. The system for treating water-based cleaning wastewater in an automotive painting production line according to claim 1, characterized in that, Agent A contains polyaluminum chloride (PAC), modified diatomaceous earth, and the pH adjuster citric acid; Agent B contains cationic polyacrylamide (CPAM), nano-ferric oxide (Fe3O4), and a demulsifier.

3. A wastewater treatment method using the system described in claim 1 or 2, characterized in that: Includes the following steps: S1 Wastewater Collection and Conditioning: Collects the water-based cleaning wastewater generated from the automotive painting production line to the wastewater collection and homogenization conditioning unit, and adjusts the pH of the wastewater to 4.5-5.5; S2 Multi-stage Pretreatment: The waste liquid after S1 treatment is transported to the multi-stage pretreatment unit reactor, and agent A (15-25 mL / L) and agent B (5-8 mL / L) are added successively. The reaction is carried out for 45-60 minutes under a rate gradient G of 50-70 s⁻¹. The mixture after the reaction is separated into solid and liquid in an inclined plate sedimentation tank. The supernatant enters the subsequent unit, and the bottom sludge is dewatered by a centrifuge and then transported off-site for disposal. S3 Secondary biological treatment: The supernatant obtained from S2 is sequentially fed into the hydrolysis acidification reactor, the contact oxidation tank and the MBR system for treatment; S4 Clean Water Reuse: The permeable water from the MBR system enters the clean water tank and is reused in the production process via a reuse water pump.

4. The method according to claim 3, characterized in that, In step S3, the conditions for the hydrolysis-acidification reaction are: hydraulic residence time of 24-36 hours, temperature of 35±2℃, and pH of 5.5-6.

5.

5. The method according to claim 3, characterized in that, In step S3, the membrane design flux of the MBR system is 15-20 L / (m²·h).

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