Abstract

Sand filter capping had been tried as an alternative for the currently practiced rapid sand filters. A 1000 m³/day capacity pilot plant constructed similarly to full scale water treatment plants was used for this purpose. Four levels of sand material with respect to grain size and thickness were used. Capping filter was represented by one level of anthracite coal with one thickness. In order to optimize the most efficient combination(s) of the two materials for maximum filter performance in terms of quality and quantity, four filtration rates were tried. A series of forty test runs and experiments exceeding 120 using different filter configurations were tried. Filters were operated in pairs and subjected to the same conditions. Filters consisting of 20 cm anthracite coal (0.91 mm E.S.) over 40 cm of sand (0.69 mm E.S.) appeared to be the best fit configuration among tried filters. Considerable economical consequences could be achieved using sand filter capping. This was reflected in reducing filter numbers or increasing the plant capacity by two folds in the minimum. Economic revenue was gained through reduction of disinfection doses as well as reduction in filter sand material. Runtimes of filters were increased by 2 - 3 folds indicating capability of more furnished water productivity and less amount for backwash need. Above all the water produced was of very good quality that met the most stringent specifications and promoted health. Capping sand filters were proven to suitably operate under varying conditions of influent turbidity and filtration rates.

Key words: Drinking water filtration, rapid sand filtration, dual-media filtration, multi-media filters, water treatment, filter media, gravity filtration.