Role of the propagation reactions on the hydroxyl radical formation in ozonation and peroxone (ozone/hydrogen peroxide) processes

To better predict the elimination of highly ozone-refractory organic micro-pollutants from wastewater in ozonation and peroxone (O-3/H2O2) processes, it is important to understand the OH center dot formation therein. Nevertheless, the contribution of the propagation reactions (in brief, OH center dot + DOM (Dissolved Organic Matter) + O-2 -> O-2(center dot-), O-3 + O-2(center dot-) -> O-3(center dot-) -> OH center dot) to the OH. yields (O) in these two processes has not received great attention so far. In this study, >25% of O-3 was estimated to be consumed via the propagation reactions in ozonation of wastewater effluents. The competition method (taking the OH center dot exposure and scavenging capacity of water matrix into account) was recommended to determine the O values, and thus the relatively higher values (i.e., 33-58% vs. 6-24%) in ozonation were obtained as compared with the tert-Butanol (tBuOH) assay (with excess tBuOH to scavenge OH center dot producing stoichiometric formaldehyde), where the contribution of the propagation reactions was otherwise neglected when excess tBuOH completely scavenged OH center dot. In peroxone of wastewater effluents, the rate constant of O-3 consumption increased significantly with the increase of H2O2 concentration ([H2O2]:[O-3]) = 0.1-0.35). However, compared to ozonation alone, the improvement of the Phi values was negligible over a wide range of [H2O2]:[O-3] = 0.1 -2.0. This discrepancy was mainly ascribed to the fact that substantial O-3 consumption via the propagation reactions resulted in comparable 0 values in peroxone vs. ozonation processes. (C) 2014 Elsevier Ltd. All rights reserved.