Primary treatment is where liquids and solids are separated using fine screens.
Any leftover materials from the primary treatment are removed using an activated sludge process. Bacteria naturally treats the sewage using a bioreactor and settling tanks, and nutrients such as nitrogen and phosphorus are removed.
In tertiary treatment, the sewage undergoes processing to make it safer for release into the environment.
This can include removing bacteria by filtering and disinfecting the wastewater before release.