Removal of Pharmaceutical and Endocrine Disrupting Chemicals by Sequential Photochemical and Biological Oxidation Processes.

Abstract

The presence of biochemically active compounds (BACs) such as endocrine disrupting chemicals (EDCs) and antimicrobial compounds in the aquatic environment is an issue of great concern. For example, EDCs can cause gender bending in aquatic life, and antimicrobial compounds may lead to the evolution of antimicrobial resistant bacteria. The principal objective of this research was to quantify the effectiveness of combining UV/H2O2 and biological oxidation processes for the mineralization of BACs that commonly occur at trace levels in municipal wastewater and in drinking water sources. Initially, the photolysis and UV/H2O2 photooxidation rates of six BACs [the antimicrobial compounds sulfamethoxazole (SMX), sulfamethazine (SMZ), sulfadiazine (SDZ), and trimethoprim (TMP), the EDC bisphenol-A (BPA), and the analgesic diclofenac (DCL)] were determined. Experiments were conducted in ultrapure water, lake water (Lake Wheeler, NC) and wastewater treatment plant effluent (North Cary Water Reclamation Facility, Cary, NC). Photolysis and UV/H2O2 oxidation rates of BACs were quantified with a quasi-collimated beam (QCB) apparatus equipped with low pressure UV lamps, and the effects of the following factors on the BAC oxidation rates were evaluated: (1) pH, (2) H2O2 concentration, and (3) presence/absence of background organic matter. With the QCB apparatus, parameters such as quantum yields and second order rate constants describing the reaction between hydroxyl radicals and BACs were determined. With these parameters the level of BAC transformation at different UV fluences and H2O2 concentrations was predicted. For example, at treatment conditions used at a full-scale UV/H2O2 plant in the Netherlands (UV fluence = 540 mJ cm-2, H2O2 dose = 6 mg L-1), the following BAC transformation percentages would be obtained in NC lake water: ∼98% for DCL, ∼79% for SMX, ∼60% for SMZ, ∼51% for SDZ, ∼43% for TMP, and ∼46% for BPA. In wastewater treatment plant effluent, predicted BAC transformation percentages were lower at the same treatment conditions because hydroxyl radical scavengers were present at higher concentrations. Apart from determining parent compound removal rates in UV photolysis and UV/H2O2 photooxidation processes, antimicrobial activity removal was quantified by conducting growth inhibition assays. Using the Enterobacteriaceae organism E. coli ATCC® 25922, growth inhibition assay data showed that the antimicrobial activity in photochemically treated water samples was principally a result of the parent compound concentration that remained upon treatment. Therefore, no measurable antimicrobial activity was exerted by the photolysis and UV/H2O2 oxidation products of the studied sulfonamides and TMP. These results were consistently obtained for the different background water matrices and solution pH values that were studied. Finally, the mineralization potential of three 14C-labeled BACs (sulfadiazine, bisphenol-A, and diclofenac) after UV/H2O2 treatment was examined with a consortium of lake water bacteria and with bacteria associated with lake sediments. Upon UV/H2O2 oxidation, mineralization of 14C-labeled BAC oxidation intermediates by lake water bacteria was extremely slow (<1.1% for SDZ, <0.8% for BPA and <0.8% for DCL in 30 days). The use of lake sediments enhanced the biodegradation rate of sulfadiazine and its UV/H2O2 oxidation intermediates, but mineralization rates were still slow (1.1% for SDZ and 5.2% for SDZ UV/H2O2 oxidation intermediates after 30 days). Overall, the results of this research suggest that the UV/H2O2 process is able to remove BAC parent compounds and, for antibiotics, antimicrobial activity; however, oxidation intermediates may be persistent in the environment. Additional studies should be performed to determine the effects of these intermediates on aquatic life and their toxicological importance in the context of direct or indirect potable water reuse.