The process of sewage treatment is generally divided into Primary , Secondary , and Tertiary Treatment; depending on the degree to which the effluent is purified:
How Does A Sewage Treatment Plant Work?
In primary treatment, screening and sedimentation remove some of the suspended solids and organic matter. The effluent from primary treatment will contain high amounts of organic matter.
Secondary sewage treatment is directed at the removal
of biodegradable organic and suspended solids, mainly using biological unit processes. Disinfection may be included in secondary sewage treatment.
Tertiary sewage treatment includes the removal
of nutrients, toxic substances including heavy metals and further removal of suspended solids and organic. Effluent from tertiary treatment is of a higher standard and generally suitable for reuse.