The objective of this research was to determine the coagulation effects of alum, ferric chloride, and cationic polymer when the coagulants are added to a sludge which has bulked due to a high bound water content. The effect of coagulant addition upon microbial metabolism was studied using dissolved oxygen uptake.

Coagulant dosages ranging from 200 mg/l to 700 mg/l were added to 1000 mg/1 and 2000 mg/l mixed liquor volatile suspended solids (MLVSS) concentration sludges, while dosages ranging from 200 mg/l to 1100 mg/l were added to 3000 mg/l MLVSS concentration sludges. The settling parameters studied included settling curves, half-hour and hour sludge volume indexes, and supernatant volatile suspended solids.

It was discovered that while good separation of microbial solids could be accomplished through the use of ferric chloride and a synthetic cationic polymer, alum coagulation was ineffective and coagulation addition in the range of dosages used brought about a reduction in the dissolved oxygen uptake rate of the microorganisms. The data presented includes dissolved oxygen uptake rates, uptake rates expressed as a percentage of the uptake rate in the coagulated sample, and supernatant pH.