The influence of calcium to the map precipitate recycled from wastewater

The advantage of magnesium ammonium phosphate (MAP) precipitation method is the integrate of wastewater treatment and resources recovery. But generally, there have Ca²⁺ and Mg²⁺ in the wastewater, so there may have MAP and hydroxyapatite (HAP) simultaneously in the precipitate. The MAP can be used as slow release fertilizer directly; the HAP is just used as industrial raw material. So, the value of MAP is higher relatively. In order to get pure MAP, it is necessary to find out the influence of Ca²⁺ to MAP precipitation. The precipitation experiments under different Ca²⁺ concentration and different pH value were respectively conducted in simulation wastewater and landfill leachate. The NH₃-N removal rate, precipitation productivity and constituents were analysed, the influence of Ca²⁺ to MAP precipitation were summarized in this paper.