Haloacetamides Formation and Fate in Drinking Water Treatment Process of the Lower Nakdong River: Comparison of Summer and Winter Seasons

Abstract

Objectives : The formation characteristics and fate of haloacetamides (HAcAms), nitrogenous disinfection by-products (DBPs), were evaluated for each process in a drinking water treatment plant (DWTP) located downstream of the Nakdong River in summer and winter. In preparation for the gradually strengthening rules for DBPs, it was intended to be used as basic data for operating DWTPs.Methods : Seven HAcAms were monitored from the raw water to the clean water in the summer (Jul.∼Aug.) and winter (Dec.∼Jan.) at a large DWTP (180,000 m3/day) located downstream of the Nakdong River. Liquid-liquid extraction (LLE) method was used for sample extraction and GC-MS/MS was used for HAcAms analysis.Results and Discussion : The concentrations of HAcAms formed by the pre-Cl2 treatment in the DWTP in summer and winter were 9.4~27.2 µg/L and 1.4~3.5 µg/L, respectively, and were 7.7 times higher in summer than in winter. The HAcAms/TOX concentration ratio was 0.09~0.14 in summer compared to 0.01~0.02 in winter, and the HAcAms composition ratio among DBPs formed by the pre-chlorination increased rapidly in the summer. Five species of DCAcAm, BCAcAm, TCAcAm, DBAcAm, and BDCAcAm were formed in summer by the pre-chlorination, and five species of DCAcAm, BCAcAm, DBAcAm, DBCAcAm, and TBAcAm were formed in winter. The composition ratio of di-HAcAm species accounted for 91% and 66% in summer and winter, respectively, and the DCAcAm concentration was highest compared to other HAcAms species. In the batch biodegradation experiment, it was evaluated that the biodegradation of the HAcAms species was easy, and in the laboratory scale BAC process experiment (water temp. 20℃, EBCT 10~30 min.), di- and tri-HAcAms removal rate were 75~99% and 85~100%, respectively. In summer and winter, the removal rates of HAcAms in the BAC process of the DWTP were 81% and 54% on average, respectively. The HAcAm detection concentrations in the clean water ranged from 1.7 to 2.4 μg/L in summer and 0.7 to 1.2 µg/L in winter, which was twice as high in summer as was compared to winter.Conclusion : The formation concentration of HAcAms was higher than in winter by pre-chlorination, but it was easily removed in the BAC process in summer. However, in winter, the formation concentration of HAcAms was low by pre-chlorine treatment, but the removal rate in the BAC process was as low as 54%. The main removal process and mechanism of HAcAms in the DWTP were the BAC process and biodegradation. In a lab-scale BAC process simulation, a removal rate of more tthan 95% removal efficiency could be expected with the increase of EBCT to 30 minutes when HAcAms was highly formed in summer.