Effect of ozone exposure on the oxidation of trace organic contaminants in wastewater

Three tertiary-treated wastewater effluents were evaluated to determine the impact of wastewater quality (i.e. effluent organic matter (EfOM), nitrite, and alkalinity) on ozone (O-3) decomposition and subsequent removal of 31 organic contaminants including endocrine disrupting compounds, pharmaceuticals, and personal care products. The O-3 dose was normalized based upon total organic carbon (TOC) and nitrite to allow comparison between the different wastewaters with respect to O-3 decomposition. EfOM with higher molecular weight components underwent greater transformation, which corresponded to increased O-3 decomposition when compared on a TOC basis. Hydroxyl radical ((OH)-O-center dot) exposure, measured by parachlorobenzoic acid (pCBA), showed that limited (OH)-O-center dot was available for contaminant destruction during the initial stage of O-3 decomposition (t < 30 s) due to the effect of the scavenging by the water quality. Advanced oxidation using O-3 and hydrogen peroxide did not increase the net production of (OH)-O-center dot compared to O-3 under the conditions studied. EfOM reactivity impacted the removal of trace contaminants when evaluated based on the O-3:TOC ratio. Trace contaminants with second order reaction rate constants with O-3 (k(O3)) > 10(5) M-1 s(-1) and (OH)-O-center dot (k(OH)) > 10(9) M-1 s(-1), including carbamazepine, diclofenac, naproxen, sulfamethoxazole, and triclosan, were >95% removed independent of water quality when the O-3 exposure (integral O-3 dt) was measurable (0-0.8 mg min/L). O-3 exposure would be a conservative surrogate to assess the removal of trace contaminants that re fast-reacting with O-3. Removal of contaminants with k(O3) < 10 M-1 s(-1) and k(OH) > 10(9) M-1 s(-1), including atrazine, iopromide, diazepam, and ibuprofen, varied when O-3 exposure could not be measured, and appeared to be dependent upon the compound specific k(OH center dot) Atrazine, diazepam, ibuprofen and iopromide provided excellent linear correlation with pCBA (R-2 > 0.86) making them good indicators of (OH)-O-center dot availability. (C) 2008 Elsevier Ltd. All rights reserved.