Polymer impact on filter blinding during alum sludge filtration

This paper describes an experimental investigation into the factors which control clogging phenomenon of the filter medium during alum sludge filtration under conditions of excess polymer dosing. Preliminary studies showed that the hydraulic resistance of the filter medium was associated with the amount of polymer trapped, but was not uniquely determined by the quantity of polymer trapped in the filter. Subsequent investigations showed that filter blinding can arise from the interaction of residual polymer and a colloidal fraction. When either of these components was missing, the trapping efficiency of the filter was low. In particular, the study demonstrated that polymer coatings on the filter did not have any significant impact on the hydraulic resistance. Evidence indicated that clogging and polymer trapping was particle size driven, the aggregate size being dependent on the polymer dose. Diagnosis of trends in the filter resistance suggested that they were being influenced by polymer/colloidal solids ratio through its effects on particle size.