Trials using modified sequencing batch reactors were performed to study the influence of the amount of nitrified nitrogen on pH (and thus solubility of the phosphorus) and determine whether the pH was the main cause of the increased phosphorus dissolving. It was determined that the modified sequencing batch reactor process management (hydraulic retention time and anaerobic/aerobic step duration) did allow the control of the amount of nitrogen nitrified in one cycle and hence the amount of the phosphorus dissolved.