Département Ressources aquatiques et eau potable

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.

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Oxidation processes are impacted by the type, concentration and reactivity of the dissolved organic matter (DOM). In this study, the reactions between various types of DOM (Suwannee River fulvic acid (SRFA), Nordic Reservoir NOM (NNOM) and Pony Lake fulvic acid (PLFA)) and two oxidants (ozone and chlorine) were studied in the pH range 2–9 by using a combination of optical measurements and electron donating capacities. The relationships between residual electron donating capacity (EDC) and residual absorbance showed a strong pH dependence for the ozone-DOM reactions with phenolic functional groups being the main reacting moieties. Relative EDC and absorbance abatements (UV₂₅₄ or UV₂₈₀) were similar at pH 2. At pH 7 or 9, the relative abatement of EDC was more pronounced than for absorbance, which could be explained by the formation of UV-absorbing products such as benzoquinone from the transformation of phenolic moieties. An increase in fluorescence abatement with increasing pH was also observed during ozonation. The increase in fluorescence quantum yields could not be attributed to formation of benzoquinone, but related to a faster abatement of phenolic moieties relative to fluorophores with low ozone reactivity.
The overall ^•OH yields as a result of DOM-induced ozone consumption increased significantly with increasing pH, which could be related to the higher reactivity of phenolic moieties at higher pH. The ^•OH yields for SRFA and PLFA were proportional to the phenolic contents, whereas for NNOM, the ^•OH yield was about 30% higher.
During chlorination of DOM at pH 7 an efficient relative EDC abatement was observed whereas the relative absorbance abatement was much less pronounced. This is due to the formation of chlorophenolic moieties, which exert a significant absorbance, and partly lose their electron donating capacity.
Pre-ozonation of SRFA leads to a decrease of chloroform and haloacetic acid formation, however, only after a threshold of > ∼50% abatement of the EDC and under conditions which are not precursor limited. The decrease in chloroform and haloacetic acid formation after the threshold EDC abatement was proportional to the relative residual EDC.