THM precursor removal in raw water by up-flow pelletization process

Abstract

To reduce, trihalomethane (THM) formation in drinking water treatment, the presence of THM precursors in raw water must be minimized. This paper describes pilot scale studies carried out raw waters from Pra-Pa canal to assess the effectiveness of up-flow pelletization in THM precursors removal. The experiments were conducted with different dosages of coagulant (Polyaluminium chloride) and coagulant aid (nonionic polymer). In addition, the effects of number of paddles and up-flow velocity on the performance of the pelletizer were investigated. Process effectiveness was evaluated in terms of effluent turbidity, THM precursors removal and characteristics of pellets. Three parameters were used to quantify THM precursors concentration: total organic carbon (TOC), trihalomethane formation potential (THMFP) and ultraviolet absorbance at 260 nm (UV260). An up-flow velocity of up to 10 m/h, together with lower dosages of PAC1 and nonionic polymer found to be 5 mg/L and 0.2 mg/L, respectively was shown to be effective in the process. The removal efficiencies up to 43.2% THMFP, 48.6% TOC, 78.9% UV260 and 98.0 % turbidity were obtained. The diameter and settling velocity of pellets created in this study were 0.19-0.33 mm and 19.66-53.96 m/h, respectively