Sunlight-mediated removal of emerging contaminants in treatment wetlands and surface waters

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Title: Sunlight-mediated removal of emerging contaminants in treatment wetlands and surface waters
Author: Aziz, Tarek; Sardana, Arpit
Abstract: In this project, we evaluated the photodegradation kinetics of wastewater derived emerging contaminants in treatment wetlands. We used dissolved organic matter (DOM) characterization tools and simulated irradiation experiments to investigate the relationship between photochemical behavior and wetland processing of wastewater effluents. Samples were collected from a treatment wetland site and a wastewater treatment plant (WWTP) in North Carolina. Cimetidine (CME), amoxicillin (AMX), 17𝞪-ethinyl-estradiol (EE2), and atenolol (ATL) were selected as target contaminants to evaluate photoreactivity of sampled waters. Target compounds were individually dissolved in the collected samples and their decay during irradiation was measured using HPLC methods. The direct photolysis photodegradation rates and quantum yields were calculated for AMX, EE2, and ATL, as these pharmaceuticals have been shown to undergo both direct and indirect photodegradation in sunlit waters. Photochemically produced reactive intermediates, such as excited triplet states of dissolved organic matter (3DOM*), singlet oxygen (1O2), and hydroxyl radical (•OH) were found to be substantially sensitized by both treatment wetland samples and WWTP effluents. •OH acted as the main photoreactant responsible for the phototransformation of AMX, ATL, and EE2. Photodegradation of CME was entirely due to singlet oxygen formation from irradiated DOM. Phototransformation rates and quantum yield coefficients were calculated to estimate the photochemical fate of the pharmaceuticals in sampled waters. Overall, photodegradation was fastest for CME, followed by EE2, and then AMX and ATL. It was observed that photoreactivity was higher in lagoon treated wastewaters than compared to vegetated wetland cells and secondary wastewater effluents. Some samples were observed to have an enhanced •OH formation yield which led to significantly higher phototransformation rates. This was suggested to be due to the activity of photo-Fenton reactions and DOM dependent hydroxylators. Optical indices for DOM characteristics were computed from ultraviolet–visible (UV-Vis) spectroscopy and excitation-emission matrix (EEM) fluorescence spectroscopy. ATL and EE2 photoreactivity was observed to be negatively correlated to humic and fulvic DOM components. The absorbance ratio (E2:E3) was found to be positively correlated only to CME phototransformation rates. Results from this study suggest that plant-derived organic matter from vegetated wetland cells can decrease photoreactivity of treatment wetland waters.
Publisher: NC Water Resources Research Institute
Date: 2020-09-04
Series/Report No.: UNC-WRRI;487
WRRI Project;19-05-U

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