Ozone and chlorine reactions with dissolved organic matter - Assessment of oxidant-reactive moieties by optical measurements and the electron donating capacities

Abstract

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 (UV or UV) 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. TheOH 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.

Molecular-Level Transformation of Dissolved Organic Matter during Oxidation by Ozone and Hydroxyl Radical

“…2 DOM analysis using bulk measurements provides insight into how ozonation alters DOM composition. Spectroscopic measurements of DOM after reaction with ozone consistently show decreases in fluorescence 12,13,31 and specific UV absorbance. 12,13,[16][17][18]21 Decreasing molecular weight is reported by size exclusion chromatography (SEC) coupled with organic carbon detection 13, and by sequential ultrafiltration, 14 while XAD fractionation shows a shift from hydrophobic to polar hydrophilic material.…”

“…12-14, 29, 33 Finally, electron donating capacity (EDC) of DOM decreases after oxidation, with large changes observed at low specific ozone doses. 31,34,35 EDC is an operationally-defined measurement of phenolic moieties in DOM that show antioxidant properties. [36][37][38] Phenols are highly reactive with ozone, 25,28,39 suggesting that these moieties are important targets for O3 oxidation.…”

“…Large decreases in EDC at low specific ozone doses are observed using SEC followed by spectrophotometric detection or flow injection analysis with electrochemical detection. 1,31,34,35 This is attributed to electrophilic attack on activated aromatic compounds (e.g., phenols) by ozone.…”

Comparison of the impact of ozone, chlorine dioxide, ferrate and permanganate pre-oxidation on organic disinfection byproduct formation during post-chlorination

“…The better performance of O 3 -t-BuOH at lower pH can be attributed to a higher stability of O 3 with a higher ozone exposure, leading to an enhanced cleavage of aromatic rings. 32,46 In contrast to O 3 , the stability of Fe(VI) decreases with decreasing pH. 33 However, the Fe(VI) reactivity towards a large selection of organic NOM moieties also increases with decreasing pH, while the O 3 reactivity tends to decrease with decreasing pH.…”

Improved Operation of Continuous Ozone Hydrate Production

“…Ozone (O 3 ) is known as a strong oxidant 1–3. It is harmless because it rapidly decomposes to oxygen (O 2 ) 4.…”