Integrated design of a constructed wetland system for decreasing concentrations and bioavailability of copper in water (Scirpus californicus)

This research focussed on design of a constructed wetland system for the A-01 outfall, a wastestream containing toxic levels of copper at the U.S. Department of Energy's Savannah River Site (SRS) in South Carolina. The South Carolina Department of Health and Environmental Control has established a discharge limit of 22 μg/L total copper for the A-01 outfall. This provided the opportunity to conduct research involving design of a constructed wetland system for limiting copper bioavailability and mitigating ecological risks to receiving-water organisms.; Design of the constructed wetland system involved theoretical modeling and strategic review of scientific literature to provide a conceptual design, which served as the basis for a physical model used to test hypotheses relative the wetland function and performance. Objectives were to evaluate contributions of wetland vegetation and hydrosoil in copper transfers and transformations, to compare performance of the physical model with a “site-specific” model constructed at SRS, and to confirm and enhance design specifications for the full-scale constructed wetland system. The physical model was designed on the basis of integrated processes inherent to wetland vegetation, hydrosoil, and hydroperiod that would promote copper transfers and transformations to limit copper bioavailability, such as sorption to organic matter and precipitation of copper as sulfide minerals. This model consisted of five pairs of wetland cells (378 L), each pair arranged in series providing a 48-h hydraulic retention time. Four pairs received 50 μg Cu/L (nominal) added to municipal water, while one pair received only municipal water. Wetland vegetation was Scirpus californicus (giant bulrush), and hydrosoil consisted of 85% sand, 15% silt/clay, 5% organic matter, and 5% sulfur (per top 10 cm). Hydrosoil and overlying water depths were 30 cm each.; Scirpus californicus contributed sorption sites for copper and provided organic matter for dissimilatory sulfate reduction, necessary for precipitating copper as sulfide minerals. Viable S. californicus shoot and root tissues sorbed 0.6% and 1.9%, respectively, of copper entering the system.; Performance of the physical model was compared with a site-specific model constructed at SRS. The site-specific model consisted of commercially available S. californicus, hydrosoil from the full-scale wetland construction site, and water from the A-01 outfall. Differences in performance of the site-specific and “generic” model systems enhanced full-scale design by highlighting critical aspects of wetland function and augmenting operation and maintenance plans for the full-scale system. (Abstract shortened by UMI.)...