The use of simultaneous chemical precipitation in modified activated sludge systems exhibiting biological excess phosphate removal Part 4: Experimental periods using ferric chloride

Abstract

The effect of simultaneous ferric chloride (FeCl3) dosing on biological phosphorus (P) removal was investigated in an activated sludge system at pilot scale. Additional removal due to chemical precipitation was measured as the difference in system P removal between parallel test and control systems. Both systems strongly exhibited biological excess P removal (BEPR). The extent of Prelease in the anaerobic reactors of the two systems was compared by mass balance, as one indicator of the “magnitude” of BEPR. Phosphorus fractionation of the mixed liquor also served as an indicator of the biological and chemical mechanisms. Evidence was found that the BEPR mechanism is partially inhibited by simultaneous FeCl3 addition, even in the absence of effluent phosphate limitation. However, the degree of inhibition was relatively low, ranging from 3 to 20% (approximately) for FeCl3 doses in the range ca. 10 to 20 mg/l as Fe, with a system P removal of 20 to 30 mgP/l in the control.

Authors

Categories