TREATMENT OF N-NITROSODIMETHYLAMINE PRECURSORS IN COAGULATED WATER BY NANOFILTRATION AND REVERSE OSMOSIS MEMBRANES

Abstract

This research is aimed at investigating the removal of N-Nitrosodimethylamine (NDMA) precursors in raw water supplies from the Bangkhen water treatment plant (WTP) and the Banglen WTP by polyaluminum chloride (PACl) coagulation combined with nanofiltration (NF) and reverse osmosis (RO) membrane. Raw water supplies were collected once time. The PACl of 80 mg/L at pH 7 and PACl of 150 mg/L at pH 7 were conducted as pre-treatment for raw water of the Bangkhen WTP and the Banglen WTP, respectively. NF270 and TW30 membranes were used in NF and RO experiments, respectively. The operating pressure of 4 bars was used. Dissolved organic carbon (DOC) of 4.2 mg/L and dissolved organic nitrogen (DON) of 0.24 mg/L were found in raw water of the Bangkhen WTP. DOC and DON of raw water of the Banglen WTP were 7.9 and 0.28 mg/L, respectively. The coagulation reduced DOC and DON from raw water of the Bangkhen WTP and the Banglen WTP by 32 and 34% and 41 and 37%, respectively. In the case of the Bangkhen WTP, the coagulation combined with NF reduced DOC and DON by 92 and 69%, respectively. DOC of 95% and DON of 85% could be reduced by coagulation combined with RO filtration. For the Banglen WTP, coagulation combined with NF reduced DOC and DON by 97 and 70%, respectively. DOC of 97% and DON of 79% could be reduced by coagulation combined with RO filtration. The PACl coagulation combined with RO filtration showed better results on DON removal when compared with coagulation combined with NF filtration. DOC of hydrophobic organic fraction (HPO) of 2.0 mg/L and DOC of hydrophilic organic fraction (HPI) of 2.2 mg/L were detected in raw water of the Bangkhen WTP. DOCHPO and DOCHPI of raw water of the Bangkhen WTP were 3.7 and 3.9 mg/L, respectively. The PACl coagulation, alone, showed better result on reduction of HPO than that of HPI. The PACl coagulation combined with RO filtration could reduce nearly 100% of both HPO and HPI. NDMA formation potential of raw water supplies, coagulated waters, and permeate waters could not be detected under the detection limit of the method at 542 ng/L.