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

ABSTRACT

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 (nm_Ex/nm_Em) were moderately (correlation coefficient, R = 0.85 and 0.86) and fairly (R = 0.59, 0.67, and 0.75) correlated with DON reduction.

KEYWORDS:

• Dissolved organic matter
• fluorescence excitation-emission matrix
• humic and fulvic acids
• polyaluminium chloride
• powder activated carbon
• tryptophan

Acknowledgments

This research was funded by Prince of Songkla University (PSU) under contract number ENG550369S and by Center of Excellence on Hazardous Substance Management (HSM), Chulalongkorn University, with bilateral support by the Thailand National Research Fund project, Songkhla Lake, Songkhla Province. We would like to sincerely thank Associate Professor Seppo Karrila, Prince of Songkla University, for assistance with manuscript preparation.

Additional information

Funding

Prince of Songkla University (PSU) (ENG550369S) and Center of Excellence on Hazardous Substance Management (HSM), Chulalongkorn University.