Tertiary treatment forms the last stage in some treatment plants. It is sometimes necessary to meet with the strict treatment standard. The cost for this type of treatment is typically high.
The main purpose is to remove any recalcitrant contaminants from the wastewater. These contaminants can not be removed in the biological system during the available treatment time.
Another purpose is to remove any solids from the wastewater (these solids contribute to the Chemical Oxygen Demand).
Some of the processes that can be used are