Effects of Season and Photoperiod on Emerging Contaminants in Treatment Wetland Mesocosms Receiving Secondarily Treated Municipal Wastewater or Surface Water From an Urban Stream

Abstract

Treatment wetlands (TWs) are widely used to treat municipal wastewater and urban runoff influenced surface water. This study investigated the seasonal variation in the removal of emerging contaminants (ECs) and the effect of shading on treatment performance in free water surface (FWS) and subsurface flow (SSF) TW mesocosms at the Norman Water Reclamation Facility (NWRF). Fifty TW mesocosms with five replicates of three hydrologic regimes (FWS, SSF and open water controls (OWC)), crossed with two vegetation plantings (planted (PL) and unplanted (UP)), and two source waters (urban runoff influenced surface water and secondarily treated municipal wastewater) were examined. Two experiments were conducted. The first experiment assessed the seasonal removal of about 90 ECs (pharmaceuticals and personal care products, pesticides, and per- and polyfluoroalkyl substances (PFAS)) to assess the influence of temperature and photoperiod. The second experiment examined the role of sunlight on carbamazepine and sulfamethoxazole concentrations in shaded and unshaded TW mesocosms. Influent and effluent water samples were analyzed for ECs, nutrients (PO43-, NO3-, NO2-), a suite of trace metals, and total suspended solids. Data analyses included the Shapiro-Wilk test, Q-Q plots, and histograms to determine normality and homogeneity of the collected data. Kruskal-Wallis test and Dunns post-hoc test with Bonferroni corrections were used to determine whether statistical differences between influent and effluent concentrations from FWS-PL, FWS-UP, SSF-PL, SSF-UP, and OWC existed. Some ECs exhibited variability between seasons, TWs, and water sources. The shaded and unshaded FWS-PL, FWS-UP, SSF-PL, and SSF-UP did not exhibit significant differences in the treatment of ECs. Carbamazepine was resistant to removal while sulfamethoxazole exhibited differences in concentrations from influent and effluent between the shaded and unshaded conditions. These findings contribute to understanding the role of seasonal variation and shading in the performance of TWs. The results offer insights to help optimize and improve wetland design for efficient removal of ECs under various environmental conditions.