Mechanistic studies of surface catalyzed H2O2 decomposition and contaminant degradation in the presence of sand

This study examined the mechanism and kinetics of surface catalyzed hydroge n peroxide decomposition and degradation of contaminants in the presence of land collected from an aquifer and a riverbed. Batch experiments were cond ucted using variable sand concentrations (0.2 to 1.0 g-sand/ml solution) an d phenol and quinoline as model contaminants. Inhibition and probe studies were conducted to ascertain the role of several oxygen radicals (e.g.(OH)-O -., (HO2)-H-./O-2(-)) on contaminant degradation. Phenol degradation produc ts were consistent with reaction with hydroxyl radical. Concordant with thi s, phenol degradation was greatly inhibited in the presence of the widely a ccepted hydroxyl radical scavenger butanol. Additional inhibition studies w ith superoxide dismutase (SOD) support the conclusion that superoxide anion participates in the formation of hydroxyl radical. It is postulated that t he relatively long-lived superoxide anion is capable of leaving the vicinit y of the sand surface into bulk solution, where it may react with hydrogen peroxide to form hydroxyl radical and contribute to contaminant degradation . A mechanism is formulated and evaluated which accounts for these observat ions, as well as hydrogen peroxide decomposition kinetics and the complex d ecay behavior of phenol and quinoline in the presence of sand. (C) 1999 Els evier Science Ltd. All rights reserved.