The chemical enhancement of gravel (or roughing) filtration with coagulants, i.e. direct (gravel) filtration, has been proposed as a pre-treatment alternative for slow sand filters. However, studies have frequently focused on the efficiencies of the pre-filters in terms of reduction percentages. The effectiveness of the pre-treatment on the subsequent slow sand filtration is not usually cited or even evaluated. By incorporating a pilot-scale slow sand filter in our trials, both aspects of the pre-treatment process were assessed: efficiency and effectiveness. In terms of turbidity reductions, our results demonstrated that chemically enhanced pre-filtration was substantially more efficient (93.2 to 99.5%) than conventional pre-filtration (50.6 to 79.3); this was also observed in terms of reductions in the level of other parameters (i.e. thermotolerant faecal coliforms and dissolved organics). Yet, the use of a coagulant can have a negative impact on the slow sand filtration run.
Chemically enhanced gravel pre-filtration for slow sand filters: advantages and pitfalls
C.C. Dorea, B.A. Clarke; Chemically enhanced gravel pre-filtration for slow sand filters: advantages and pitfalls. Water Science and Technology: Water Supply 1 January 2006; 6 (1): 121–128. doi: https://doi.org/10.2166/ws.2006.029
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