If suspended throughout the wastewater, grease and oil removal becomes more difficult, requiring physical and chemical treatment. Solids suspended in wastewater are typically the result of Priming and Finishing at a vehicle assembly facility. Sprayed paints and coatings not transferred to parts may be captured by a water curtain surrounding the application units. To facilitate water recycling, these solids must be removed by filtration or through the addition of other chemicals which result in precipitation of solids. Additions of chemicals causes some contaminants to form Solids or clumps of solids.
Neutralization is a simple example of chemical treatment.
Note that each of these wastewater pre-treatment methods generates a sludge which must be properly managed. The implementation of pollution prevention options at the source would reduce or eliminate the need for wastewater pre-treatment, and thus also reduce or eliminate the generation of wastewater sludge.