Interaction between organic species in the formation of haloacetic acids following disinfection.

The formation of haloacetic acids (HAAs) from the chlorination of individual and binary mixtures of organic fractions obtained from the intake of Bangkhen Water Treatment Plant in Bangkok, Thailand was investigated. Experimental results revealed that, as an individual fraction, hydrophobic base (HPOB) was the most active in forming HAAs (approx. 200 microg/mg) whereas hydrophilic acid (HPIA) was the least (approx. 40 microg/mg). In binary mixtures, acid fractions exhibited stronger inhibitory effect in forming HAAs than base fractions. With the set of experimental data obtained from this work, no relationships between specific HAA formation potential and various organic fractions concentrations in binary mixtures could be formulated. Among the various individual HAA species obtained from the chlorination of each individual organic fraction, dichloroacetic acid (DCAA) was found to be predominant. On the other hand, the chlorination of binary organic fraction mixtures often led to the formation of monochloroacetic acid (MCAA) as the predominant HAA species.

FTIR evaluation of functional groups involved in the formation of haloacetic acids during the chlorination of raw water.

This work investigated the formation potential of haloacetic acid (HAA) compounds in the raw water for the Bangkhen water treatment plant (Bangkok, Thailand). The resin adsorption technique (with three different types of resins, i.e. DAX-8, AG-MP-50 and WA-10) was employed to characterize the organic content in the raw water into six fractions, i.e. hydrophobic neutral (HPON), hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophilic neutral (HPIN), hydrophilic acid (HPIA) and hydrophilic base (HPIB). Hydrophilic species appeared to be the predominant organic species in this water source (approximately 60%) with the neutral fraction being the most abundant (approximately 40%). Hydrophobic species, on the other hand, played the most important role in the formation of haloacetic acids as they contributed to as much as approximately 56% of total HAA formation potential. Among the three hydrophobic species, the hydrophobic base exhibited the highest specific HAA formation with 208mugHAAs/mg of dissolved organic carbon (DOC). Each organic fraction was examined for its associated functional groups by Fourier transform infrared (FTIR). The investigation of the formation of HAAs was achieved by tracking the changes in the FTIR results of the same water sample before and after the chlorination reaction. Based on the results obtained from this study, carboxylic acids, ketone, amide, amino acids and aromatic characteristic organics seemed to be the main precursors to HAA formation.

Characterization of haloacetic acid precursors in source water.

Raw water from the Bangkok (Thailand) main municipal water supply canal was examined for its natural organic composition by fractionation with adsorption resins. DAX-8 resin was the first resin employed to fractionate the hydrophobic fractions. Fractionation at neutral pH resulted in the separation of the hydrophobic neutral components; at a high pH level (approx. 10) separation of the hydrophobic base components occurred; and at a low pH level (approx. 2) the hydrophobic acid components were separated. AG-MP-50 cationic resin was then used to separate the hydrophilic base components, and WA-10, a weak anionic resin, was applied finally to fractionate the hydrophilic acid and neutral components. Subsequently, each fraction was tested for its chlorine disinfection by-product (DBP) formation potential. The HAA formation tests demonstrated that the various organic fractions had different reactivity levels for the formation of haloacetic acids (HAAs). For this source water, the hydrophilic neutral fraction dominated over the other five fractions in being the main organic component and the most significant precursor of HAAs formation. On the other hand, in terms of specific HAA formation potential (FP), the hydrophobic and hydrophilic base fractions were the most reactive precursors to the formation of HAAs. In all cases, the quantity of HAAs formed depended linearly upon the amount of organic constituents in the water sample.