Impacts of coagulation on upflow roughing filtration in layers

In community water supplies, technologies that are people-centred are encouraged to ensure sustainability. Upflow roughing filtration in layers (URFL) is a simple pre-treatment process applied to reduce raw water turbidity without the aid of coagulation to levels acceptable for effective slow sand filtration (SSF). However, practical applications of URFL are limited to raw waters with turbidity < 20 - 50 NTU. Incorporation of simple coagulation, achieved by gravity dosing equipment, can provide an opportunity for URFL to treat higher turbidity raw waters. This paper present results of a study carried out on the impacts of low-dosage simple coagulation on URFL performance. The main evaluation criterion was the effluent turbidity. Intermittent coagulation was studied as well, including its effect on, headloss and filter media cleaning. The URFL unit was regularly challenged with high turbidity loads without adjusting coagulant dosages. Coagulation was achieved with lower-than conventional dosages. URFL effluents were sent to SSF, whose effluent turbidity was analysed.