Non-target screening of dissolved organic matter in raw water, coagulated water, and chlorinated water by Orbitrap mass spectrometry.

This study aimed to classify the possible molecular formulas of precursors for disinfection by-products (DBPs) in raw, coagulated, and chlorinated water samples from the U-Tapao Canal, Songkhla, Thailand. The molecular formulas of DBPs in chlorinated water were investigated. Polyaluminum chloride (PACl) was employed as a coagulant. Orbitrap Fourier transform-mass spectrometry was able to estimate the composition of dissolved organic matter (DOM) with the carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) elements contained and DBPs at the molecular level. The molecular formulas of the DOM in the raw water primarily consisted of CHO and CHON when extracted by lichrolut EN. The CHO and CHON species were rich in lignin-, tannin-, and condensed aromatic-like substances. The DOM with high-molecular-weight from 300 to 500 Da were preferentially removed by coagulation. The PACl coagulation decreased the abundances of lignin-, tannin-, and condensed aromatic-like substances in the CHO formulas, while lignin- and condensed aromatic-like substances in the CHON formulas remained. The remaining precursors corresponded to CHON molecules in the coagulated water, which may result in the formation of some chlorine (Cl)-containing molecules. Several DBPs among the CHOCl and CHONCl species were produced in the chlorinated water through the addition reaction of chlorine. New chlorinated N-DBPs of 21 formulas were detected.

Emerging disinfection by-products' formation potential in raw water, wastewater, and treated wastewater in Thailand.

Raw water (RW) from the Bangkok and Sing Buri water treatment plants located on the Chao Phraya River, river water, domestic wastewater (WW), and treated wastewater (TWW) from two wastewater treatment plants in Thailand were collected three times to investigate disinfection by-products' (DBPs) formation potential (FP) including trihalomethane FP (THMFP), iodo-THMFP (I-THMFP), haloacetonitriles FP (HANFP), and trichloronitromethane FP (TCNMFP). High THMFP levels were observed in river water, WW, and TWW. Considering average value, the THMFP of TWW was about two times higher than that of RW. Relatively high levels of I-THMFP were found in WW and TWW. The I-THMFP of TWW was three to seven times higher than that of RW. The HANFP of TWW was one to three times higher than that of RW. High levels of TCNMFP were found in WW and TWW. TCNMFP of TWW was six to thirteen times higher than that of RW. The discharge of TWW to RW must be prevented and controlled. The moderately positive linear relationship was obtained between dissolved organic carbon and TCNMFP in TWW. Considering measured weight concentration, THMFP was found as the highest DBPs. The highest lethal concentration 50-weighted and lowest cytotoxicity-weighted concentrations of DBPs were determined for HANFP.

Reduction by enhanced coagulation of dissolved organic nitrogen as a precursor of N-nitrosodimethylamine.

Raw water from the Banglen (BL) water treatment plant (WTP) and Bangkhen (BK) WTP in central Thailand and Hatyai (HY) WTP in southern Thailand was investigated for dissolved organic nitrogen (DON) reduction. The DON(mg N/L) and the dissolved organic carbon (DOC)/DON ratio were 0.34 and 21, 0.24 and 18, and 1.12 and 3 for the raw waters from BL, BK, and HY WTPs, respectively. Polyaluminum chloride (PACl) dosages of 150, 80, and 40 mg/L at pH 7 were the optimal coagulation conditions for the raw waters from BL, BK, and HY WTPs, respectively, and could reduce DON by 50%, 42%, and 42%, respectively. PACl and powder activated carbon (PAC, both in mg/L) at 150 and 20, 80 and 20, and 40 and 60 could reduce DON in the raw waters from BL, BK, and HY WTPs by 71%, 67%, and 29%, respectively. DOC/DON values of water treated with PACl were similar to those of raw water. DOC/DON values of water treated with PACl and PAC were lower than those of raw water. N-nitrosodimethylamine (NDMA) formation potentials of raw water, water treated with PACl, or both PACl and PAC, and organic fractions of BL, BK, and HY WTPs were below the detection limits of 542 and 237 ng/L, respectively. Reductions in fluorescence intensities of tryptophan-like substances at peaks 240/350 and 280/350 (nmEx/nmEm) were moderately (correlation coefficient, R = 0.85 and 0.86) and fairly (R = 0.59, 0.67, and 0.75) correlated with DON reduction.

The presence of aliphatic and aromatic amines in reservoir and canal water as precursors to disinfection by-products.

This research aimed at determining the dimethylamine (DMA), diethylamine (DEA), dibutylamine (DBA), and aromatic aniline (AN) in reservoir and canal water in the U-Tapao River Basin, Songkhla, Thailand. The trihalomethane formation potential (THMFP) and N-nitrosodimethylamine formation potential (NDMA-FP) of the reservoir and canal water were analyzed. Water samples from two reservoirs and raw water from water treatment plants at upstream, midstream, and downstream locations of the canal were collected twice. The analysis of the DMA, DEA, DBA, and AN were conducted using gas chromatography and spectrofluorometry techniques. The DMA, DEA, and DBA levels in the reservoir and canal waters ranged from not detectable (ND) to 10 µg/L and from ND to 21.2 µg/L, respectively. AN was detected from 123 to 129 ng/L and from 112 to 177 ng/L in the reservoir and canal waters, respectively. The DMA, DEA, DBA, and AN exhibited two fluorescent peaks at 230nmEx/345nmEm and 280 nmEx/355nmEm. These two peaks corresponded to the peak positions of tryptophan. Detection limits of DMA, DEA, and DBA for fluorescent analysis were 500 µg/L whereas that of AN and tryptophan were 10 and 0.5 µg/L, respectively. The NDMA-FP measured in all the water samples was lower than the detection limit of 237 ng/L. THMFP ranged from 175 to 248 µg/L and 214 to 429 µg/L was detected in the reservoir and canal waters, respectively. The THMFP/dissolved organic carbon (DOC) of the reservoir and canal waters were comparable within the ranges of 73 to 131 µg THMFP/mg DOC.