Oxidation behavior of aqueous contaminants in the presence of hydrogen peroxide and filter media

Abstract

Hydrogen peroxide has been used as an oxidant to degrade contaminants in solutions and soils. A poor understanding of the numerous variables that are involved makes it difficult to determine dominant contaminant removal mechanisms. Our primary objective was to examine the relationship between contaminant (quinoline and nitrobenzene) degradation rate and the rate of hydrogen peroxide decomposition on filter media. Both batch and continuous flow column experiments were conducted. In general, the rate of contaminant degradation was proportional to the rate of hydrogen peroxide decomposition, but the mass of contaminant removed depended on the amount of hydrogen peroxide decomposed, filter medium concentration, and filter medium characteristics. For increasing filter medium concentration and equivalent loss of hydrogen peroxide, the mass of contaminant degraded was found to decrease. In addition, acid-hydroxylamine treatment of the selected filter medium, to examine the role of reducible metal oxide coatings, resulted in greater contaminant removals than the parent material despite a slower hydrogen peroxide decomposition rate. The observed hydrogen peroxide decomposition and contaminant oxidation results are consistent with a reaction scheme whose central elements include: (1) a rate limiting filter medium surface catalyzed reaction initiating hydrogen peroxide decomposition with the formation of a reactive intermediate, (2) a competing reaction of the intermediate with the filter medium surface, and (3) reaction of the same intermediate with the aqueous organic contaminant. Loss of quinoline and nitrobenzene is most likely a solution phase reaction because sorption of these compounds was small over the pH range 7–8 and oxidation efficiency did not increase with increasing filter medium concentration, which would be expected if the reactions were occurring on the surface. Finally, enhanced oxidation of quinoline and nitrobenzene on the treated material is explained by more efficient use of the reactive intermediates for contaminant oxidation due to a reduction in the number of scavenging sites associated with reducible metal oxide coatings.