Improving the Initial Effluent Quality of a Dual‐Media Filter by Coagulants in Backwash

The purpose of the research described in this article was to develop a revised conceptual theory for filter ripening and to evaluate the effect of adding various coagulants to backwash water as a means of reducing the magnitude and duration of the filter ripening sequence. It was found that the use of coagulants in backwash water can be very effective in improving initial effluent quality, with the optimum coagulant type being alum or the primary coagulant. The time for injection of the coagulant into the backwash water, the volume of water used for backwashing, and the remnant volume above the filter media after backwashing were also optimized.