Sedimentation: by means of gravity, heavier particles settle to the bottom of the sedimentation tanks for removal from the wastewater.
Effluent equalization: treatment processes are more effective if the wastewater inflow is standardized through equalization of the water stream. Wastewater treatment is normally optimized for limited concentration ranges of target pollutants.
Physical separation of components: larger particles settle and fats and oils rise to the surface and can be skimmed off. This settling process is aided in certain cases by the addition of specific chemicals or air.
Biological treatment: typically using a plentiful supply of air, microorganisms in biological treatment convert the remaining dissolved or colloidal organic matter into solids that can be precipitated.
Tertiary treatment (optional): eliminates undesirable elements, such as phosphorus, nitrates and certain compounds (pesticides, metals, detergents, etc.) and improves the quality of purified water before release into the environment or reuse.