Phosphate recovery from wastewaters comparing two different sources of magnesium oxide in the precipitation of struvite
Limited phosphate resources, increasing fertilizer prices and unsustainable methods of treating phosphates in wastewaters have resulted in the need for phosphate recovery technologies. One method involves the precipitation of a magnesium ammonium phosphate mineral called 'struvite' (MgNH 4PO4·6HO). Wastewaters often require an additional source of Mg2+ and a solution pH between 8 and 11 in order to achieve orthophosphate (OP) removal as struvite. This research examined 3 effluents to determine an ideal pH for producing the lowest residual values of OP. Two types of MgO were also tested for their ability to reduce OP concentrations: a pure chemical source and ground MgO refractories. Optimal pH levels were not determined, as it was likely that the supersaturation was too high to produce differences in OP removal. Chemical-grade MgO was more reactive than the refractories, and was therefore more effective in removing OP as struvite in wastes where Mg2+ was limiting. OP removal rates of >90% were achieved in each effluent.