Use of sidestream based MgSO₄ as chemical coagulant in the simultaneous removal of nitrogen and phosphorus from wastewaters

Abstract Phosphorus as phosphate and nitrogen as ammonium or nitrate are the main nutrients in wastewaters and agricultural sludges. They runoff easily to waterways and cause eutrophication in water bodies. However, ammonium and phosphate could be precipitated simultaneously and used as recycled nutrients. In this research, MgSO₄ solution obtained by treating fly ash or dolomite with sulfuric acid was used as a coagulant for simultaneous phosphorus and nitrogen removal from synthetic (NH₄)₂HPO₄ solution. Precipitation experiments were performed at room temperature (20 ± 2 °C) using different molar ratios Mg:P:N (1.1–1.6:1–2:1–2) and precipitation times (6–24 h). The pH was adjusted to 9.0 and kept constant. In all cases, there was only a minor changes in the removal of both ammonium and phosphate after 4 hours of reaction time. Highest ammonium removal percentages (75.5 %) were achieved for fly ash based MgSO₄ solution using molar ratios Mg:P:N 1.6:1:1 and 1.1:2:2. Also the highest phosphate removal percentages was achieved with these two molar ratios (84.5 % for 1.6:1:1 and 82.5 % for 1.1:2:2). Struvite was the only formed precipitation product in all cases as was confirmed by XRD. Results indicate that fly ash and dolomite based MgSO₄ solutions have great potential in the ammonium and phosphate precipitation from synthetic samples