Wastewater produced in the production of painting process is mainly divided into pretreatment wastewater, electrophoretic painting wastewater and spraying wastewater.

Pre-treatment wastewater from the paint before the surface treatment of degreasing, phosphating surface and other processes, containing emulsified oil, surfactants, phosphates, heavy metal ions filler, solvents and so on. Electrophoretic painting wastewater is generated from the floating paint attached to the painted parts and the cleaning process of the tank liquid, generally including to the ionic wash water and ultrafiltration solution; its composition is the same as the composition of the tank liquid, which contains water-soluble resins (e.g., epoxy resins, phenolic resins, etc.), pigments (e.g., carbon black, iron oxide red, lead and mercury, etc.), fillers (e.g., titanium dioxide, talc, etc.), co-solvents (e.g., triethanolamine, butanol, etc.) and a small amount of heavy metal ions.

Wet spraying room with water to wash the paint spray booth work area air, air paint and organic solvents are transferred to the water to form the wastewater; wastewater contains a large number of paint particles, the water quality by the paint used (nitro lacquer, amino lacquer, alkyd lacquer and epoxy lacquer-based) and solvents (such as ethanol, acetone, lipids, benzene, etc.), depending on the cosolvents.

Painting wastewater characteristics.
1. Coating wastewater types, water quality varies according to the materials used, only degreasing solution has a variety of formulations, paint types are more.
2. The discharge is irregular, except for part of the washing water continuous overflow discharge, coating line wastewater or waste liquid is mostly intermittent centralized discharge.
3. Water quality and quantity change greatly without regularity.