The present dissolved organic matters (DOM) in real waters (e.g., wastewater) act important roles in hydroxyl radicals (OHrad) formation during ozonation and catalytic ozonation processes. Firstly, the DOM reacts with O3 yielding OHrad, acted as initiator of OHrad formation. The OHrad yield of initiation reactions was estimated to be 10~30% by “Tert-butonal (tBuOH) assay.” The formed OHrad reacts with DOM producing surperoxide radicals (O2,rad), which further reacts with O3 generating OHrad again (in brief, OHrad + DOM + O2 → O2,rad, O3 + O2,rad = O3,rad = OHrad). These reactions termed as propagation reactions, the OHrad yield of which was determined to be 100% according to the “Methanol assay.” Based on the kinetics of ozone decomposition, it was estimated that &gt;25% of O3 was consumed via the propagation reactions in ozonation of wastewater. The competition method (taking the OHrad exposure and scavenging capacity of water matrix into account) was recommended to determine the OHrad yields, and thus the relatively higher values (i.e., 33 ~58% vs. 6~24%) in ozonation were obtained as compared with the “tBuOH assay” (with excess tBuOH to scavenge OHrad producing stoichiometric formaldehyde), where the contribution of the propagation reactions was otherwise neglected when excess tBuOH completely scavenged OHrad. In catalytic ozonation and peroxone (O3/H2O2) processes, the catalysts and H2O2 only act as initiators for OHrad formation. Due to the great contribution of propagation reactions, the rate constant of O3 consumption increased significantly with the addition of catalysts or H2O2, while the improvement of the OHrad yields was negligible as compared to ozonation alone. The finding of this study may provide technical support for the application of catalytic ozonation processes in real waters, taking optimizing the dosage of catalysts as an example.

Role of the propagation reactions on the hydroxyl radical formation in the ozonation and catalytic ozonation of real waters

253rd National Meeting (2017)

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