Formation of brominated trihalomethanes during chlorination or ozonation of natural organic matter extracts and model compounds in saline water

Oxidation experiments (chlorine, ozone and bromine) were carried out with synthetic saline waters containing natural organic matter (NOM) extracts and model compounds to evaluate the potential of these surrogates to mimic the formation of brominated trihalomethanes (Br-THMs) in natural saline waters. Synthetic saline water with Pony Lake fulvic acid (PLFA) showed comparable results to natural brackish and sea water for Br-THMs formation during chlorination and ozonation for typical ballast water treatment conditions ([Cl2]0 ≥ 5 mg/L or [O3]0 ≥ 3 mg/L). The molar CHBr3 yield in synthetic saline waters is higher for chlorination than for ozonation, since ozone reacts slower with bromide and faster with THM precursors. For bromination, the molar yields of CHBr3 for the NOM model compounds phenol, resorcinol, 3-oxopentanedioic acid and hydroquinone are 28, 62, 91 and 11%, respectively. CHBr3 formation is low during chlorination or ozonation of resorcinol-containing synthetic saline waters due to the faster reaction of resorcinol with these oxidants compared to the bromine formation from bromide. Oxidation experiments with mixtures of hydroquinone and phenol (or resorcinol) were conducted to mimic various functional groups of NOM reacting with Cl2 (or O3) in saline water. With increasing hydroquinone concentrations, the CHBr3 formation increases during both chlorination and ozonation of the mixtures, except for chlorination of the mixture of hydroquinone and resorcinol. The formation of THMs during chlorination of the mixture of hydroquinone and resorcinol is similar to that of resorcinol alone due to the much faster reaction of HOX with resorcinol compared to hydroquinone. In general, PLFA seems to be a reasonable DOM surrogate to simulate CHBr3 formation for realistic ballast water treatment. During chlorination, CHBr3 formations from phenol- and PLFA-containing synthetic brackish waters are comparable, for similar phenol contents.