Heavy metals-induced deflocculation of activated sludge

Abstract

Batch experiments were conducted to assess the influence of shock loads of mercury, cadmium, and zinc on the temporal settling capabilities of otherwise normal activated sludge. Sludge that contained heavy metals was never observed to bulk when it was allowed to settle for one-half hour. Deflocculation as measured by supernate suspended solids was observed at all metals concentrations. Deflocculation increases with time to a maximum and subsequently decreases to a constant level, however, elevated above the norm. This maximum was shown to increase at higher metals concentrations. This fact implies a potential for metals-laden sludge loss over the weir in conventional gravity cell separators. Compaction properties of the metals-laden sludges as measured by the standard sludge volume index test were observed to be improved with increasing metals concentrations, however.