Surface water pretreatment using floating media filter

Laboratory-scale experiments were conducted in contact flocculation filtration using a dual media filter operating in the upflow, saturated mode. The filter media was lighter than water; thus, the bed floated. Since coarse media remained at the bottom, the flow direction was upflow, which had the added advantage of the flow being in the direction of grain compression. Polypropylene and Polystyrene were the optimum combination of media, which due to their large density difference did not intermix even under severe agitation, thus eliminating the media intermixing problem common to dual media filters. The influent concentrations were kept constant and the flow velocity, and filter media size and shape were varied. The headless variation along the filter, the influent quality of two filter layers, and the effluent quality were studied. Filter runs exceeding 40 h were achieved before reaching breakthrough at conventional rapid sand filtration rates. Floating media obtained turbidity removal per unit headless in comparison to sand media, and floating media are proposed as a prefilter in surface-water filtration.