Chemical conditioning for dewatering municipal wastewater sludges

The feasibility of using ferric chloride in conjunction with a polymer for conditioning the Regina wastewater treatment plant sludge was examined. Specific resistance to filtration, capillary suction time, and time-to-filter were evaluated. Optimum dosages of ferric chloride, Percol 755 and Percol 757 were found to be 80.6, 2.9 and 2.7 kg/t of dry solids, respectively. Optimum dosing resulted in complete charge neutralization. Dual-chemical conditioning showed that a combination of 50% of optimum dosage of FeCl 3 and 50% of optimum dosage of Percol 757 had the lowest CST, SRF and TTF values. A percentage of the optimum dosage of polymer could be replaced by a similar percentage of the optimum dosage of FeCl 3 without adversely affecting the dewatering efficiency. A good correlation could be found between the CST and SRF data.