Evaluation of alternative pretreatment methods for use in direct filtration water treatment

The purpose of this study was to evaluate the performance of alum alone, alum in conjunction with a polymeric coagulant aid, and a primary coagulant polymer in the coagulation-flocculation-sedimentation portion of a water treatment process and to study the implications of the results with respect to future use in direct filtration. The performance of the coagulant, coagulant aid, and primary coagulant polymer was evaluated by altering the flocculation and sedimentation retention times in the pretreatIDEnt process chain. Among the water quality parameters monitored were turbidity, pH, total alkalinity, total hardness, and total solids. A brief literature review for direct filtration and coagulation-flocculation theory was also conducted.

The results of this investigation indicated that reduced retention times in the pretreatment process chain treated the selected raw waters sufficiently to enable consideration of direct filtration a viable treatment alternative. Analysis of data obtained indicated the use of polyelectrolyte as a primary coagulant or coagulant aid produced a pinpoint floc which is essential to successful utilization of direct filtration and that the floc formed settled more rapidly than floc from use of aluminum sulfate alone. The use of a polyelectrolyte as a primary coagulant or coagulant aid also reduced the chemical dosages required to provide appropriate turbidity removals.