ABSTRACT
The first observations of biological phosphate removal were made in high rate activated sludge plants designed and operated to limit nitrification. In 1974, J. L. Barnard suggested that it was necessary for the sludge or mixed liquor of an activated sludge plant to pass through an anaerobic phase absent of dissolved oxygen or nitrate and then through an aerated phase in order to activate the phosphorus removal mechanism. As the role of volatile fatty acids became evident, researchers demonstrated the relationship between acetate addition and phosphorus release. The role of short chain carbohydrates was best demonstrated by Gerber et al. who fed nitrates together with various short chain carbohydrates to sludge from a biological phosphorus removal plant. Much of what is known today about biological phosphorus removal has been learned through experiences in full-scale operations. A large number of plants have been constructed all over the world for the removal of phosphorus, in conjunction with nitrogen removal.
