Oxidation of Trace Organic Contaminants (TrOCs) in Wastewater Effluent with Different Ozone-Based AOPs: Comparison of Ozone Exposure and ^•OH Formation

Abstract

Ozone-based advanced oxidation processes (AOPs), recognized as effective methods for tertiary water treatment in view of trace organic contaminant (TrOC) removal, were investigated in this study. By assessing and comparing different ozone-based AOPs for TrOC degradation in secondary wastewater effluent, criteria for appropriate AOP application and oxidant dose are provided. In this study, the value of the minimum ozone demand for formatted hydroxyl radical (•OH) to react with target contaminants was proposed and determined. The ozone exposure and •OH exposure were systemically investigated and compared in four types of different ozone-based AOPs (i.e., O3 only, O3/H2O2, O3/UV, and O3/H2O2/UV). The significant increase in •OH exposure was achieved by means of adding H2O2 and/or UV, which results in the increase of the eliminant efficiency of TrOCs. In particular, ozone-resistance compounds (e.g., atrazine and alachlor) were removed more efficient by combination O3 with H2O2 and UV than O3 only, O3/H2O2 and O3/UV at the equal ozone dose. Such as, the removal of atrazine and alachlor tripled after 2 min of treatment in the effluent by combining O3 with H2O2 and UV. Among the four ozone-based AOPs, the highest ozone exposure (3.27 mg min/L) was achieved by applying an O3:DOC of 0.9 O3 only. High ozone exposure is beneficial to enhance the abatement efficiency of high ozone-selective compounds (e.g., pentachlorophenol).