Effects of Hydrology, Vegetation, and Aeration on Emerging Contaminant Removal from Secondarily Treated Wastewater Effluent in Treatment Wetland Mesocosms

Abstract

Indirect potable reuse is an expanding practice which returns portions of treated wastewater to municipal supplies. However, traditional wastewater treatment is not designed to remove the wide variety of “emerging contaminants” (EC), including personal care products, pharmaceuticals, industrial and agricultural compounds, and their transformation byproducts, found in modern wastewater. Treatment wetlands are an ecologically engineered approach designed for water quality improvement via natural biogeochemical, physiochemical, microbiological, and ecological processes, including sorption, volatilization, photodegradation, biodegradation, and phytoremediation. Mesocosm-scale wetlands provide the experimental flexibility required to identify appropriate combinations of wetland design parameters (e.g., hydrologic design, vegetation scheme, hydraulic retention time (HRT)) that optimize EC removal. A mesocosm treatment wetland compound comprised of 52 individual 220-L batch reactors was constructed at the Norman Water Reclamation Facility. This research focused on half of the mesocosms which received secondarily treated municipal wastewater. The experimental design included five open water control (OWC), ten free water surface (FWS) and ten subsurface flow (SSF) mesocosms. Half of each of the FWS and SSF mesocosms were planted with soft rush (Juncus effusus), while the remaining half remained unplanted. After an initial experiment determined an appropriate HRT of seven days, an aeration experiment was conducted in which active aeration was provided to 14 of the mesocosms by solar powered fish-pond aerators. Evaluation of removal efficiencies for sulfamethoxazole (SMZ), carbamazepine (CMP), and bisphenol-A (BPA) was conducted by measuring influent and effluent aqueous concentrations via enzyme linked immunosorbent assay (ELISA) testing. SMZ removal was greater in FWS and OWC, averaging 83% and 82% respectively, compared to 16% in SSF and was not significantly affected by vegetation (p = 0.303) or aeration (p = 0.228). CMP removal was impacted by hydrologic design, with removal rates in FWS, SSF, and OWC averaging 73%, 66%, and 56%, respectively, with a significant difference ( p = 0.001) between OWC (56%) and FWS (73%). CMP removal was not affected by vegetation or aeration. The BPA concentration in 84% of the effluent samples was below the minimum detection limit (MDL) of 50 ng/L, limiting BPA removal efficiency calculations to a maximum removal efficiency of 64%. BPA removal efficiency averaged 50% or greater for all treatment combinations. BPA removal efficiency was not affected by hydrology, vegetation, or aeration. Greater removal efficiencies for all target ECs as compared to previous studies may be due to a combination of factors including the high quality of the influent, extended hydraulic retention time, maturity of the systems, or other environmental influences. The results of this study provided evidence for the effectiveness of TWs for the removal of ECs from secondarily treated wastewater.