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

摘要

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) exposure, measured by parachlorobenzoic acid (pCBA), showed that limited 'OH 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 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 (kO_3)>10~5 M~(-1) s~(-1) and 'OH (k_(OH)) > 10~9 M~(-1) s~(-1), including carbamazepine, diclofe-nac, naproxen, sulfamethoxazole, and triclosan, were >95% removed independent of water quality when the O_3 exposure (∫ O_3 dt) was measurable (0-0.8 mgmin/L). O_3 exposure would be a conservative surrogate to assess the removal of trace contaminants that are fast-reacting with O_3. Removal of contaminants with ko_3 < 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). Atrazine, diazepam, ibuprofen and iopromide provided excellent linear correlation with pCBA (R~2 > 0.86) making them good indicators of 'OH availability.