STRUVITE (MGNH4PO4.6H2O) SOLUBILITY AND ITS APPLICATION TO A PIGGERY EFFLUENT PROBLEM

Struvite (MgNH4PO4.6H2O) solution chemistry was studied in order to understand a struvite scaling problem which exists in the pipe network of a series of 4 effluent lagoons at a piggery. The conditional solubility constant (P(s)=S(Mg).S(NH3-N).S(PO4-P), equilibrium S values (M)) was determined over a range of pH values (6.8-8.5) and solution concentrations of Mg, NH3-N and PO4-P close to field conditions, and at a temperature of 30-degrees-C. A comparison of field and laboratory data indicates struvite precipitates from the second lagoon onwards. The solubility data obtained also indicate potential for precipitation as a method of nutrient removal from wastewaters.