The Removal of Phosphate by Hydroxyapatite and Struvite Crystallisation in South Africa

Nutrient removal by chemical means has, over the past decade, become an expensive practice owing to the scarcity of chemicals. A new method of phosphate removal by hydroxyapatite [Ca5(PO4)3OH] crystallisation has gained increasing interest as the need for the implementation of clean technology has become more apparent as we move into the environmentally conscious nineties. This method as well as another method, viz. struvite [NH4MgPO4-6H2O] crystallisation, will be discussed using results obtained from a laboratory scale study using three types of effluent, two demonstrating hydroxyapatite crystallisation and the third, struvite crystallisation. While it has been proven that phosphate crystallisation does work as a tertiary treatment (Van Dijk and Wilms, 1991) this paper will also show that the positioning of the crystalliser can vary to suit the need of the industry for which it has been designed.