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 (O3) decomposition and subsequent removal of 31 organic contaminants including endocrine disrupting compounds, pharmaceuticals, and personal care products. The O3 dose was normalized based upon total organic carbon (TOC) and nitrite to allow comparison between the different wastewaters with respect to O3 decomposition. EfOM with higher molecular weight components underwent greater transformation, which corresponded to increased O3 decomposition when compared on a TOC basis. Hydroxyl radical (OH) exposure, measured by parachlorobenzoic acid (pCBA), showed that limited OH was available for contaminant destruction during the initial stage of O3 decomposition (t < 30 s) due to the effect of the scavenging by the water quality. Advanced oxidation using O3 and hydrogen peroxide did not increase the net production of OH compared to O3 under the conditions studied. EfOM reactivity impacted the removal of trace contaminants when evaluated based on the O3:TOC ratio. Trace contaminants with second order reaction rate constants with O3 (kO3kO3) > 105 M−1 s−1 and OH (kOH) > 109 M−1 s−1, including carbamazepine, diclofenac, naproxen, sulfamethoxazole, and triclosan, were >95% removed independent of water quality when the O3 exposure (∫O3ⅆt) was measurable (0–0.8 mg min/L). O3 exposure would be a conservative surrogate to assess the removal of trace contaminants that are fast-reacting with O3. Removal of contaminants with kO3<10M−1s−1 and kOH > 109 M−1 s−1, including atrazine, iopromide, diazepam, and ibuprofen, varied when O3 exposure could not be measured, and appeared to be dependent upon the compound specific kOH. Atrazine, diazepam, ibuprofen and iopromide provided excellent linear correlation with pCBA (R2 > 0.86) making them good indicators of OH availability.