As wastewater enters a plant for treatment, it flows through a screen. This removes large floating objects, such as rags and sticks, which clog pipes or damage equipment. Once the wastewater has been screened, it passes into a grit chamber, where cinders, sand, and small stones settle to the bottom.

Processes commonly used in wastewater treatment include phase separation such as sedimentation, biological and chemical processes such as oxidation or polishing. The main by-product from wastewater treatment plants is a type of sludge that is usually treated in the same or another wastewater treatment plant.