Struvite precipitation runs were carried out in an 8 L batch reactor with a similar setup to the system used for the MgO suspension experiments. The system was agitated (200 rpm) at a constant temperature of 251C. The precursors were added to H2NH4PO4–H2O solution maintained at constant initial concentra- tion of 32 mmol L 1. To investigate the impact of magnesia, the amount of MgO or MgCl2 added to the system was varied to determine its influence on struvite crystallization. Therefore, different volumes of the MgO suspension or 200 mL solutions with an adjusted MgCl2 concentration were added. In this study, the amount of added magnesium is referred to as the molar ratio Mg:P, where Mg is the magnesium amount in all suspended MgO