REDUCTION OF N-NITROSODIMETHYLAMINE PRECURSORS IN RAW WATER SUPPLY BY ENHANCED COAGULATION WITH POWDER ACTIVATED CARBON

Abstract

This research is aimed at determining the removal of N-nitrosodimethylamine (NDMA) precursors in raw water of the Bangkhen water treatment plant (WTP) and the Banglen WTP by enhanced coagulation with powder activated carbon (PAC) and coagulation followed by PAC adsorption. Alum and polyaluminium chloride (PACl) were used as coagulants. Raw water supplies were collected one time. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) of raw water of the Bangkhen WTP were 4.2 and 0.24 mg/L, respectively. DOC of 7.3 mg/L and DON of 0.34 mg/L were found in raw water of the Banglen WTP. The PACl of 80 mg/L at pH 7 could reduce DOC and DON from raw water of the Bangkhen WTP by 42 and 41%, respectively. The PACl of 150 mg/L at pH of 7 reduced DOC and DON in raw water of the Banglen WTP by 38, and 52%, respectively. The optimal condition at PACl of 80 mg/L combined with PAC of 20 mg/L at pH 7 could reduce DOC and DON in raw water of the Bangkhen WTP by 77 and 68%, respectively. For raw water of the Banglen WTP, the PACl of 150 mg/L combined with PAC 20 mg/L at pH 7 reduce DOC and DON by 85 and 70%, respectively. Percent reductions of DOC and DON by PACl coagulation followed by PAC adsorption were comparable to using PACl coagulation combined with PAC. DOCs of hydrophobic organic fraction (HPO) of 2.0 mg/L and hydrophilic organic fraction (HPI) of 2.2 mg/L were determined in raw water of the Bangkhen WTP. DOCHPI and DOCHPO in raw water of the Banglen WTP were 3.9 and 3.7 mg/L, respectively. For raw water of the Bangkhen WTP, the PACl coagulation reduced HPO and HPI by 47 and 31%, respectively. The PACl coagulation with PAC reduced HPO by 80% and HPI by 75%. For the Banglen WTP, the PACl coagulation reduced HPO by 45% and HPI by 42%. PACl coagulation with PAC reduced HPO and HPI by 89 and 83%, respectively. NDMA formation potentials in raw water, coagulated water, coagulated water at enhanced coagulation of Bangkhen and Banglen source waters were not detectable under detection limit of the methods of 542 ng/L.