Abstract
The effects of magnesium and calcium ions on phosphorus removal by aluminium coagulation were investigated with various jar tests using settled raw sewage. Maximum TP (total phosphate) removal occurred at pH around 5~6 with aluminium coagulation, and it decreased above pH 6. TP and HnPO4 removal efficiencies, however, were kept above 95% at pH above 6 by adding the divalent metallic ions like magnesium or calcium ions on aluminium coagulation process. At molar ratio of Al/P (Al/ HnPO4) above 3, TP removal efficiency was as high as 80%, and residual TP less than 0.2 mg/L occurred at Al/P ratio above 6. TP removal efficiency was improved by adding magnesium or calcium ions and the optimum Al/Mg and Al/Ca ratios were about 2. The required dose of aluminium coagulant was reduced for equivalent amount of TP removal by adding magnesium or calcium ions, as a result sludge generation was also reduced.
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