The purpose of this investigation was to study the removal of phosphorus by chemical precipitation with sodium aluminate and alum in the activated sludge aeration chamber, and determine the effect of the aluminum to phosphorus ratio and the mixed liquor suspended solids concentration on the phosphorus removal efficiency and the effect of the precipitants on the removal of organic pollutants in the activated sludge process. The studies were conducted on settled domestic sewage in three bench-scale continuous flow activated sludge units supplemented with jar tests. Major parameters employed included influent and effluent total phosphorus and chemical oxygen demand (COD), mixed liquor total and volatile suspended solids, pH, and sludge volume index. Both sodium aluminate and alum were found effective in reducing the phosphorus content of the sewage and aluminum to phosphorus ratios of 1.3 and 1.9 were required with alum and sodium aluminate to produce a minimum residual phosphorus concentration in the range of 1.0 mg/l P (q reduction of approximately 90 percent). On an available aluminum basis, alum was more effective than sodium aluminate; however, when molecular weight and cost were considered, sodium aluminate cost about one-half as much as alum for equivalent phosphorus removal. Variation of the mixed liquor suspended solids concentration had no significant effect on the removal of phosphorus. The addition of chemical did not adversely affect the removal of COD which averaged in excess of 90 percent throughout the studies; pH was also unaffected and remained in the 7.3 to 8.2 range --Abstract, page ii
