Detailed introduction:
Spraying and painting wastewater is a kind of organic wastewater that is discharged by absorbing spray and organic solvent generated during workpiece spraying into water in the way of using water as absorbent in the painting process. This type of water is generally recycled, and its concentration will change during the recycling process. The content of organic pollutants and other pollutants will increase to saturation. It is necessary to regularly replace clean water. Replacing the discharged wastewater will seriously damage the ecological environment and must be treated harmless before discharge.
1、 Overview of Spray Painting Wastewater Pollution
Spraying and painting wastewater is a kind of organic wastewater that is discharged by absorbing spray and organic solvent generated during workpiece spraying into water in the way of using water as absorbent in the painting process. This type of water is generally recycled, and its concentration will change during the recycling process. The content of organic pollutants and other pollutants will increase to saturation. It is necessary to regularly replace clean water. Replacing the discharged wastewater will seriously damage the ecological environment and must be treated harmless before discharge.

2、 Source and pollution characteristics of spray painting wastewater
Source of sewage:
It mainly comes from the waste water generated after the paint spraying water curtain cabinet absorbs spray.
Water quality characteristics of spray painting wastewater:
1. Indirect discharge of wastewater results in significant changes in the concentration of pollutants in spray painting wastewater over time, resulting in significant changes in overall water quantity and quality, making biochemical treatment of wastewater more difficult.
2. The concentration of organic matter is high, mostly macromolecular organic matter, and the biodegradation rate is slow.
3. The composition of project wastewater is complex, containing substances such as petroleum that are difficult to biodegrade, making treatment difficult.
4. The nutrient composition in sewage is single, lacking some nutrients necessary for microbial production.
5. The organic compounds contained in this wastewater are highly soluble in water, and the treatment of low volatile organic compounds is relatively difficult compared to high volatile organic compounds, making it difficult to separate them from water, resulting in certain treatment difficulties.
6. Spray contains a large number of spray particles, so the concentration of suspended solids is high and the color is large.
7. It contains some toxic substances, which can affect the biochemical effect when the toxicity is high. In this case, effective absorption and reaction must be carried out before treatment.

3、 Difficulties in Treating Spray Painting Wastewater
Although the organic matter content of water-based paint has been greatly reduced compared to organic solvent paint, there are still significant difficulties in treating this type of wastewater. The difficulties in treating this type of paint spraying wastewater include high organic concentration, significant changes in water quantity and quality, low biodegradation efficiency, lack of nutrients, and the presence of toxic substances.
4、 Spraying and painting wastewater treatment process
There are several types of treatment methods for domestic paint wastewater:
1. Coagulation+Fenton oxidation method+filtration
Advantages: High removal rate (generally 60% -80% treatment efficiency), small footprint, simple equipment, and no secondary pollution;
Disadvantage: High dosing cost;
Scope of application: Factories with small water volume and low concentration.
2. Phosphorus removal reaction+air flotation+sand filtration method
Advantages: Stable treatment effect, low operating cost, small footprint, simple equipment, and low investment;
Disadvantages: Difficulty in achieving ideal treatment results;
Applicable to: phosphating paint wastewater.
3. Coagulation+air flotation+pressurized aeration+coagulation method
Advantages: high removal rate, fast degradation rate, small footprint, and large volumetric load;
Disadvantages: Large oxygen supply;
Not applicable to: low concentration organic wastewater.
4. Coagulation+hydrolysis acidification+aerobic biochemical method
Advantages: Stable treatment effect, high efficiency, economy, safety, no secondary pollution, and simple operation;
Disadvantages: Large footprint and large one-time investment;
Suitable for factories with high water volume and low concentration.
5. Air flotation (spray painting wastewater)+biochemical method (spray painting wastewater and domestic wastewater)
Advantages: Good treatment effect (treatment effect can reach 97% -99%), stable, efficient, economical, safe, no secondary pollution, and simple operation;
Disadvantages: Large footprint;
Suitable for: comprehensive treatment of a large amount of domestic sewage.
6. Paint mist coagulant (A/B agent)+physical method
The paint mist coagulant mainly consists of debonding agent, pH adjusting agent, and flocculant. By adding a paint mist coagulant, the paint mist and water-soluble organic matter charges in the wastewater are destroyed, lose their viscosity, and separated. Then, air flotation and coagulation are added to separate the paint residue. Paint mist coagulant belongs to a type of flocculant for sewage treatment.
Advantages: high removal rate (up to 99%), fast rate, simple equipment, beneficial for improving the activity of circulating water, improving the biodegradability of wastewater, and reducing wastewater treatment costs;
Disadvantages: Highly affected by microorganisms, requiring sterilization/inhibition before use;
Suitable for: various types of paints, various types of spray paint circulating water reuse, etc.