Reactivity of Chlorine Radicals (Cl^• and Cl₂^•–) with Dissolved Organic Matter and the Formation of Chlorinated Byproducts

Abstract

Chlorine radicals, including Cl• and Cl2 •–, can be produced in sunlight waters (rivers, oceans, and lakes) or water treatment processes (e.g., electrochemical and advanced oxidation processes). Dissolved organic matter (DOM) is a major reactant with, or a scavenger of, Cl• and Cl2 •– in water, but limited quantitative information exists regarding the influence of DOM structure on its reactivity with Cl• and Cl2 •–. This study aimed at quantifying the reaction rates and the formation of chlorinated organic byproducts produced from Cl• and Cl2 •– reactions with DOM. Laser flash photolysis experiments were conducted to quantify the second-order reaction rate constants of 19 DOM isolates with Cl• (k DOM–Cl•) and Cl2 •– (k DOM–Cl2•–), and compare those with the hydroxyl radical rate constants (k DOM–•OH). The values for k DOM–Cl• ((3.71 ± 0.34) × 108 to (1.52 ± 1.56) × 109 MC –1 s–1) were orders of magnitude greater than the k DOM–Cl2•– values ((4.60 ± 0.90) × 106 to (3.57 ± 0.53) × 107 MC –1 s–1). k DOM–Cl• negatively correlated with the weight-averaged molecular weight (M W) due to the diffusion-controlled reactions. DOM with high aromaticity and total antioxidant capacity tended to react faster with Cl2 •–. During the same experiments, we also monitored the formation of chlorinated byproducts through the evolution of total organic chlorine (TOCl) as a function of chlorine radical oxidant exposure (CT value). Maximum TOCl occurred at a CT of 4–8 × 10–12 M·s for Cl• and 1.1–2.2 × 10–10 M·s for Cl2 •–. These results signify the importance of DOM in scavenging chlorine radicals and the potential risks of producing chlorinated byproducts of unknown toxicity.

Rate Constants and Mechanisms for Reactions of Bromine Radicals with Trace Organic Contaminants

“…An LKS80 laser flash photolysis system (Applied Photophysics, U.K.) was employed to determine the second-order reaction rate constants of Br • and Br 2 •– with TrOCs using methods previously published, , but summarized in Text S2. All of the laser experiments were performed under conditions for pseudo-first-order kinetics and at room temperature (25 ± 2 °C).…”

“…•− with TrOCs using methods previously published, 26,34 but summarized in Text S2. All of the laser experiments were performed under conditions for pseudo-first-order kinetics and at room temperature (25 ± 2 °C).…”

The role of trace N-Oxyl compounds as redox mediator in enhancing antiviral ribavirin elimination in UV/Chlorine process

“…The second order rate constants of Cl• and ClO• vs. RBV ( and ) are 5.30×10 8 M -1 ·s -1 and 5.58×10 7 M -1 ·s -1 , respectively. The second order rate constant of Cl 2 •- vs. RBV ( ) is 2.83×10 5 M -1 ·s -1 , indicating that this radical will affect the degradation of RBV only when the steady state concentration of Cl 2 •- is high [33] , [35] , [36] , [37] . Besides, the second order rate constant of RBV vs. free chlorine ( ) is 4.0 M -1 ·s -1 .…”

Role of trace TEMPO as electron shuttle in enhancing chloroquine phosphate elimination in UV-LED-driven persulfate activation process

“…DOM is ubiquitous in real surface water, and different molecular weight DOM play different roles in AOPs [39] , [42] . Thus, DOM in three molecular weight ranges (< 1 kDa, 1 – 3 kDa and 3 – 5 kDa) were separated by ultrafiltration membrane (molecular weight cut-off), and were added in deionized water to reveal the effect of different molecular weight DOM on CP degradation in UV 305 /PDS and UV 305 /PDS/TEMPO processes.…”

“…High concentration chloride ion could react with SO 4 •– to yield Cl·, which would further transform into Cl 2 •– as the (9) , (10) . Thus, SO 4 •– could be scavenged by Cl – [42] , [45] . As shown in Fig.…”