The primary pollutants generated from industrial operations are oil and solids. Oily waste is generated from any number of sources around industrial facilities. Other than process waste, pollutants are generated by support operations such as equipment steam cleaning, maintenance wash down, and eyen natural occurrences such as rain water runoff.

"Specific Pollutant Limitations" and the "National Categorical Standards" limit the amount of "dispersed" and floatable oil and grease allowed to be discharged to public owned treatment works. Additionally, most sanitation districts limit the amount of solids that can be discharged.

The most consistent maintenance and operation-free method to remove these pollutants from waste water is through the use of gravity separation. Various methods of separation and applications to fit specific site conditions are illustrated in the Industrial Waste section of this website

Criteria for sizing these systems varies from district to district.