A laboratory study of factors affecting the applicability of direct filtration water treatment

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Virginia Polytechnic Institute and State University


The purposes of the study reported in this thesis were to determine the limiting raw water turbidity that could be treated using selected direct filtration treatment schemes and to compare the results of direct filtration and conventional water treatment. A dual media, granular filter employing coal and sand was used to treat New River water with turbidity adjusted by addition of bentonite. Besides influent turbidity, other variables of interest were coagulant choice, inclusion of flocculation with direct filtration, and the hydraulic loading rate applied to the filter.

Results indicated that direct filtration treatment may be an attractive treatment alternative for raw water of influent turbidity less than 5-8 Ntu. Alum appeared to be the coagulant of choice because the selected high molecular cationic polymer system exhibited too rapid headless in the relatively fine grained filter. Flocculating the coagulated water for 30 minutes allowed direct filtration treatment of raw water with turbidity of 15 Ntu when polymer coagulant was used.