Struvite crystallisation could be a sustainable and economical alternative for recovering phosphorus from wastewater streams with high phosphate concentrations. Struvite is a magnesium ammonium phosphate salt (MgNH4PO4·6H2O) that usually crystallises in a reversible reaction and produces orthorhombic crystals with a Mg2+:NH4+:PO43− molar ratio of 1.0:1.0:1.0 (Equation (1)). Struvite crystallisation occurs when magnesium, ammonium and phosphate concentrations exceeds the struvite solubility product (Ksp) (Doyle and Parsons, 2002). The crystallisation of struvite is a complex process that depends on supersaturation, pH, temperature and the presence of foreign ions, such as calcium. Calcium ions could interfere in the struvite crystallisation process by promoting the formation of calcium phosphates (Bouropoulos and Koutsoukos, 2000).