Constructed wetlands can be an important tool for low-energy water treatment in urban environments. Versatile design of sub-units within a wetland system increases the range of possible treatment mechanisms. Among these units processes, sunlit wetland cells can be used to transform a range of trace organic compounds and to inactivate waterborne bacteria and viruses. Besides direct interactions of sunlight with contaminants, indirect processes involving natural photosensitizers [mostly dissolved organic matter (DOM)] may play an essential role in contaminant removal.  To better understand and quantify photochemical processes occurring in sunlit wetlands, the light-induced formation of reactive species [singlet oxygen (1O2), triplet state DOM (3DOM*) and hydroxyl radical (�OH)] in whole wetland water samples and isolated DOM from different cells of a pilot wetland system (vegetated/non-vegetated) fed by secondary treated waste water effluent, was determined. Spectroscopic parameters of DOM were collected as proxies to account for differences in DOM molecular size and aromaticity. Indirect light-induced inactivation of Enterococcus faecalis and MS2 bacteriophage was measured to quantify bacterial and viral attenuation, respectively. Results were benchmarked using standard DOMs (Suwannee River and Pony Lake fulvic acid).  Bacterial inactivation was strongly depended on the type of DOM. While standard DOMs did not significantly contribute to E. faecalis inactivation, DOM in whole water samples and DOM isolates from the wetland system contributed to inactivation. MS2 inactivation was highest using water that had passed through the wetland. Under environmental conditions 1O2 is believed to be an important participant in pathogen inactivation. Interestingly, 1O2 concentrations were similar for all DOMs, whereas [3DOM*] and �OH formation potential was higher for wetland DOMs. Other factors influencing indirect light-induced bacterial inactivation could be a smaller molecular size of wetland DOM (indicated by spectroscopic analysis) or an increased association of wetland DOM with the indicator organisms compared to standard DOM.

Natural photosensitizers in constructed unit process wetlands: Spectroscopic characterization, production of reactive species and effect on inactivation of indicator organisms

248th National Meeting (2014)

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