Phosphorus removal characteristics of chemical coagulation process to decrease phosphorus loadings in stream water from agricultural area

Phosphorus (P) loadings, along with those of other nutrients, are a major cause of eutrophication. Operation reports of a phosphorus treatment pilot plant (PTPP) installed in Saemangeum Reservoir to decrease P loadings of stream water from an upstream agricultural area were examined. This was aimed at assessing the treatment efficiency and P removal characteristics of chemical coagulation for advanced nutrient removal and determining the optimal coagulant dose for P removal, based on the mole ratio of aluminum to phosphorus (Al:P). Aspects of coagulant dose operation for rainfall events and parameters affecting P removal efficiency were examined. Total phosphorus (TP) concentration of treated water in the PTPP was maintained below 0.1 mg/L; this satisfies the water quality criterion for TP discharge from wastewater treatment plants in the Saemangeum watershed. The P removal efficiency increased with increasing rainfall intensity because of the influent suspended solids washed out from non-point-source pollution by rainfall, whereas organic matter decreased P removal. The empirical molar Al:P vs. effluent-soluble TP associated with the minimal soluble P concentrations in treated water varied from 2–6:1, a high range compared with the typical coagulation process for P removal in municipal wastewater treatment plants.