Survey of Automotive Coating Wastewater Treatment Process

With the rapid development of science and technology, the development of the automobile industry can effectively stimulate the comprehensive development of a country's economy and promote the development of science and technology. Therefore, all countries have made the automotive industry one of the pillar industries. In 2013, China produced a total of 23,722,900 cars and sold 23,491,900 cars. The vigorous development of the automobile industry has provided strong support for the economic growth of the entire country. But everything is divided into two, and the rapid development of the automobile industry has also brought about certain negative effects. With the rapid development of the automobile industry, the contradiction between the automobile industry and energy consumption and environmental pollution has become increasingly prominent. At present, automobile manufacturing is generally divided into four major processes: stamping, bodywork, painting and assembly. The coating process is the process that produces the most wastewater. Coating wastewater contains contaminants such as resins, surfactants, heavy metal ions, oils, phosphates, paints, pigments, organic solvents, etc. The CODcr value is high. If it is not properly treated, it will cause serious pollution to the environment. How to effectively deal with the harmful substances in car painting wastewater has become an important issue for automobile manufacturers. Domestic and foreign parties have also attached great importance to this and have made great progress in engineering practice and scientific research. This article reviews the research and practical progress of wastewater treatment in automotive coating processes.

1 Characteristics of coating process wastewater

1.1 The source of coating wastewater: The automotive coating is an important part of the automobile production process. It consists of a series of chemical anti-corrosion treatment of the exposed steel plate car body. Finally, several layers of chemistry are formed on the substrate surface of the vehicle steel plate including the inner cavity. The main role of the coating and related protective media is to prevent corrosion of the body steel plate and beautify the appearance of the car body. The automotive coating process includes pretreatment, electrophoretic coating, electrophoretic polishing, PVC material sealing, middle coating, middle coating polishing, color paint coating, varnish coating, baking, filing, point repair, Black lacquer lining, cavity wax injection, assembly repair, etc., its process flow chart.

Survey of Automotive Coating Wastewater Treatment Process

The coating wastewater mainly comes from the vehicle body pre-treatment process (pre-degreasing, degreasing, surface conditioning, phosphating, passivation, etc.), cathodic electrophoresis process, and intermediate coating and spray-painting processes. Degreasing agents, phosphating agents, surface conditioners, and phosphoric acid are major pollutants in automotive paint wastewater.

1.2 Wastewater Composition and Characteristics: The main toxic and hazardous substances contained in the waste water are as follows: pre-coating treatment: nitrite, phosphate, emulsified oil, surfactant, Ni2+, Zn2+; primer: low-solvent cathodic electrophoretic film, Lead-free cathodic electrophoretic paint film, pigment, powder, epoxy resin, butanol, ethylene glycol monobutyl ether, isopropyl alcohol, dimethyl ethanol amine, polybutadiene resin, dimethyl alcohol, paint, etc.; , topcoat: xylene, banana water and other organic solvents, paint films, pigments, powders. The automotive painting wastewater has the following characteristics: There are many types of wastewater, and the composition is complex. There are many types of wastewater discharged from automobile coating lines. Each wastewater quality (component concentration) varies depending on the materials used; emissions are irregular. Except for part of the water washing continuous overflow discharge, the coating wastewater is mostly discharged intermittently; the amount of water and water quality change greatly. Due to various wastewater components and concentrations, and irregular discharge, the water volume and quality of water in the automotive coating line vary greatly, and there are no rules to follow.

2 Processing Technology and Its Research Progress

At present, there are a variety of technologies for the comprehensive treatment of coating wastewater or the deepening of a certain component. The scope of its research and engineering practice involves physical, chemical and biological methods.

2.1 Physicochemical treatment methods: The physicochemical method generally adopts two-stage coagulation sedimentation. By adding the coagulant in the waste water, the contaminants form agglomerates of large particles and are removed through precipitation and filtration. The principle of physical chemical method is simple, the investment is saved, and the area is small. It can generally be used in wastewater treatment projects with low emission requirements. However, physical treatment alone is difficult to achieve higher water quality requirements. The production sewage treatment station of a car manufacturing plant in Tianjin was selected to separately perform nickel pretreatment on the formed wastewater. The main body adopts the first-stage reaction, coagulation and sedimentation, secondary reaction, and gas-floating physicochemical process. After monitoring, the water quality can stably reach the tertiary emission standard in GB 8978-1996 Integrated Wastewater Discharge Standard. The heavy metal nickel in the phosphating wastewater is a type of pollutant controlled by the state. According to the regulations of the national environmental protection department, this factory has set up a pretreatment system to treat the metal nickel ion concentration to below 1.0 mg/L to meet the national requirements.

Cai Ying et al. used resin, surfactants, heavy metal ions, oils, pigments, and other contaminants in the coating wastewater of automobiles, especially the electrophoresis wastewater and paint wastewater, which are complex in composition and high in concentration, and have poor biodegradability. The coagulation and sedimentation, coagulation flotation, sand filtration and other processes applied to the treatment of coating wastewater have achieved good results: CODcr removal rate is greater than 80%.

2.2 Biological treatment methods: Biological treatment methods use microorganisms to degrade organic matter in water. The advantages of this method are low operating costs, high removal of organics, and low energy consumption during processing. However, microorganisms require high environmental conditions and have a long processing cycle. Jiangling Group Co., Ltd. produces a large amount of coating wastewater during its production process. The wastewater contains toxic substances such as emulsified oils, surfactants, water-soluble resins, pigments, and paints. The company invested in aeration biological filter (BIOFOR) wastewater treatment facilities in August 2004. Since its completion, it has been operating in a good condition. All indicators of the system's effluent meet the Class I emission standard for comprehensive wastewater discharge standards. The entire wastewater treatment project has the advantages of strong treatment capacity, good treatment effect, impact-resistant load, no secondary sedimentation tank, and simple process flow. Its process flow.