Environmental Engineering: Fundamentals and Design - Chapter 11

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TOC > Ch. 11 > 11.7 Removal of nutrients

# Chapter 11 Wastewater Treatment

James R. Mihelcic, David W. Hand and Martin T. Auer

## Removal of nutrients: nitrogen and phosphorus

Tertiary treatment, also called advanced waste treatment, provides contaminant removal beyond that achieved in primary (physical settling) or secondary (biological) treatment. It may include additional removal of organic matter or solids, reductions in the concentration of nutrients such as nitrogen and phosphorus or treatment of toxic substances.
Phosphorus removal is of special interest in the Great Lakes region where additions of this plant nutrient may stimulate nuisance algal growth. Treatment plants discharging to the Great Lakes or their tributary waters have limits placed on the amount of phosphorus in their effluent. Phosphorus is removed by adding aluminum (alum) or iron (ferric chloride) salts at some point in the primary or secondary treatment process. The salts form a precipitate with the phosphorus which settles out in the clarifiers and is removed with the sludge. | Nuisance growth of the attached alga Cladophora in Lake Erie

#### Credits

Cladophora in Lake Erie photo: Scott Higgins (University of Waterloo).

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