Fate of Wastewater-Derived Contaminants in Surface Waters.

To assess the role of the amount and type of biodegradable dissolved organic carbon (BDOC) in biotransformation of WWDCs in effluent-dominated surface waters, microcosm experiments were conducted with 10 pharmaceuticals and 5 steroid hormones typically detected in wastewater effluent. The role of BDOC was evaluated by monitoring the loss of WWDCs when a bacterial inoculum was introduced to microcosms containing BDOC from different sources. Five of the compounds underwent rapid biotransformation under all conditions (i.e., estrone, 17beta-estradiol, progesterone, testosterone and triclosan) while one compound (i.e., carbamazepine) was always resistant to biotransformation. For the remaining compounds, the rate of biotransformation was related to the amount and type of BDOC. For microcosms containing BDOC from the same source, the rates of biotransformation of the WWDCs increased as the initial concentration of wastewater BDOC increased, indicating that it may be possible to use BDOC to predict the rate of biotransformation of WWDCs in surface waters. Furthermore, BDOC derived from aquatic plants resulted in more loss of certain refractory compounds (i.e., gemfibrozil, sulfamethoxazole, 17alpha-ethinyl estradiol and trimethoprim) as compared to BDOC derived from wastewater effluent. The varying biotransformation rates of test compounds in microcosms containing different sources of BDOC may be explained by differences in microbial diversity and functionality among the microcosms. These observations have significant implications for the biotransformation rates of WWDCs in effluent-dominated surface waters where wastewater treatment processes affect the initial BDOC concentration of the wastewater effluent at the discharge point, and where BDOC may be provided by decaying plants and algae in the surface water. The observations also raise the possibility that engineered treatment wetlands and open ponds could be used to enhance natural attenuation of WWDCs in surface waters. To assess the importance of wetland plants and indigenous microbes in the transformation of steroid hormones in engineered treatment wetlands, microcosm experiments were performed using wastewater effluent and wetland plants from an adjacent pilot-scale wetland as sources of BDOC and microorganisms. The biotransformation rates of test compounds in microcosms containing microorganisms with plants and with microorganisms only were similar with testosterone and progesterone undergoing transformation at faster rates than 17beta-estradiol, and ethinyl estradiol being the most persistent steroid hormone. In the microcosms containing wastewater effluent, cattail extract, microorganisms and plants, similar biotransformation rates were observed for all compounds except ethinyl estradiol, which showed a slightly slower transformation rate. The slower transformation rate was attributed to an increase in light attenuation that slowed or prevented photolysis. This effect was not evident for the other hormones because they underwent biotransformation at relatively high rates. Higher biotransformation rates were not observed in the microcosms amended with BDOC because the inoculum used was extremely low in density and diversity and therefore was insensitive to differences in initial BDOC concentration. A field experiment was conducted at a pilot-scale constructed wetland in Denton (Texas) to investigate the fate of steroid hormones in treatment wetlands. A substantial fraction of the tracer and test compounds passed through the wetland before sampling began due to an unexpectedly high degree of short-circuiting. The wetland mean hydraulic retention time (HRT) and its variance...