Quantitative correlation of absolute hydroxyl radical rate constants with non-isolated effluent organic matter bulk properties in water

Absolute second-order rate constants for the reaction between the hydroxyl radical (^•OH) and eight water samples containing non-isolated effluent organic matter (EfOM) collected at different wastewater and reclamation sites were measured by electron pulse radiolysis. The measured rate constants ranged from 0.27 to 1.21 × 10⁹ Mc^-1 s^-1, with an average value of 0.86 (±0.35) × 10⁹ Mc ^-1 s^-1. These absolute values were 3-5 times faster than previously reported values using natural organic matter and wastewater isolates. The obtained rate constants were correlated (R² > 0.99) to bulk EfOM properties through an empirical equation that included terms relating to the polarity, apparent molecular weight, and fluorescence index of the effluent organic matter. The obtained data were used to model steady state ^•OH concentrations during UV advanced oxidation. The steady-state ^•OH concentration was lower than that obtained using previously reported values for the reaction with dissolved organic matter, indicating that accurate measurement of reaction rate constants at specific sites would greatly improve the design and prediction of the removal of organic contaminants. These results will improve the ability of researchers to accurately model scavenging capacities during the advanced oxidation process treatment of wastewaters.