A Pilot Study of the Sludge Recycling Enhanced Coagulation-Ultrafiltration Process for Drinking Water: The Effects of Sludge Recycling Ratio and Coagulation Stirring Strategy

The pilot-scale study on a sludge recycling enhanced coagulation-ultrafiltration (UF) process for surface water treatment is investigated in this paper. The impact of the sludge recycling ratio and coagulation stirring strategy on removal, sedimentation efficiency, and membrane fouling control was studied in this work. Sludge recycling ratios of 0%, 5%, 10%, 15%, and 20% were applied, and the optimal ratio was found to be 10%. Moreover, four stirring strategies were also applied, and the best stirring strategy for coagulation was found to be rapid mixing (velocity gradient: 280 s(-1)), which is quite different from the coagulation stirring strategy without sludge recycling. This suggests that the adsorption effect of sludge could play a leading role during the procedure. Moreover, shortening the coagulation process makes it possible to reduce energy consumption.