Treatment of activated sludge using pure polyelectrolyte and its supernatant fluids for sludge dewatering was examined. The supernatant was used for treatment of fresh sludge for reducing the total cost of sludge conditioning by almost 50% and had great impact on wastewater treatment especially on that with large flow rate. The utilization of supernatant can be considered as a sustainable and economical method for pollution reduction especially in the developing countries. This would overcome the problem of imperfect mixing, difficulties in operated sludge conditioning, and utilized wasted polyelectrolyte. A slightly high positively charged polyelectrolyte was selected during this study. The results showed this polymer and the supernatant had significant influence on the sludge volume index (SVI) and sludge settling. The SVI and settling were improved by 50% and 60%, respectively. We found the sludge treated with supernatant showed a highest sludge settling properties compared with using pure polyelectrolyte especially for sludge samples with low total suspended solid (TSS) and SVI. Using mixed supernatant with pure polyelectrolyte showed higher settling compared to second treatment. Zeta potentials were measured, and increases in zeta potentials were observed for use of both pure polymer and supernatant fluids. The experiments of using supernatants for sludge treatment were found to reflect the use of waste for waste and principle of circulation cleaning; thus it can be a valuable reference for the researchers working in the field of sludge treatment.
Keywords: Activated sludge; Settling; Sludge volume index; Supernatant; Zeta potentials.