EFFECTS OF COLLOIDAL STABILITY ON CLARIFICATION AND DEWATERING OF ACTIVATED-SLUDGE

The effect of colloidal stability upon activated sludge properties for clarification and dewatering by filtration was investigated through c ontrolled chemical manipulations of sludge in laboratory scale. The ma nipulations resulted in changes of the surface charge density and the shear sensitivity, the latter indicating a weakening of the sludge fle e structure. The shear sensitivity was found to correlate with the res idual turbidity after settling as well as with sludge filterability ch aracteristics. The data strongly suggest the importance of blinding to increase with increasing shear sensitivity. The amount of fine partic les present in the sludge was found to increase when sludge was expose d to a shear of similar magnitude to the shear in the employed filtrat ion apparatus, indicating erosion of flocs during filtration to be imp ortant for blinding. Qualitatively similar results were obtained in fu ll scale investigations of sludge from a treatment plant with varying inlet wastewater composition, indicating the possible importance of co lloidal stability for solid/liquid separation processes in full scale wastewater treatment. Copyright (C) 1996 IAWQ. Published by Elsevier S cience Ltd.