Tertiary Treatment
Overview Nitrogen Removal Phosphorus Removal
Land Treatment Membrane Filtration References

Tertiary Treatment

When wastewater is to be recycled or when eutrophication of natural bodies of water is an issue, tertiary treatment can be used on wastewater effluent. Tertiary treatment removes contaminants that are remaining from the previous primary or secondary treatments.

The main contaminants of concern with tertiary treatment are nitrogen and phosphorus. In excess, they can cause harmful algae blooms in the natural receiving water that wastewater effluent will eventually flow into (Figure 1). This can lead to a dead zone in the receiving body where most naturally existing organisms have been died due to dissolved oxygen depletion caused by the algae.

Figure 1: A bloom in the Baltic viewed from space on July 13, 2005 (EAS 2008).

Many modern treatment methods incorporate physical, chemical, and biological processes in the same operation making the distinction between primary, secondary, and tertiary somewhat arbitrary (Tchobanoglous 1985). For purposes of this discussion, tertiary treatment is defined as an optional last step of a wastewater treatment process.