Abstract

This research provided an approach for designing a constructed wetland system for treatment of copper-contaminated wastewater and was mostly based on (1) a review of scientific literature, (2) theoretical modeling, and (3) verification of performance via a pilot system. The pilot system consisted of five pairs of 378-L (100-gal) wetland cells, each pair arranged in series with a 48-hr hydraulic retention time. Four pairs received local municipal water amended with 50 μg Cu/L (nominal) as CuSO4·5H2O. The remaining pair received only municipal water, which provided an untreated control. Wetland hydrosoil was 85% sand and 15% silt and clay-size particles amended with agricultural lime (CaCO3), gypsum (CaSO4·2H2O), and Osmocote time-release fertilizer. Organic matter content was 3% by weight. Hydrosoil and overlying water depths were 30 cm (12 in.) each. Wetland vegetation was Schoenoplectus californicus (giant bulrush). Performance objectives were to decrease total copper to less than 22 μg/L and to eliminate toxicity to Ceriodaphnia dubia based on organism survival and reproduction. Total (acid-soluble) copper concentrations associated with wetland inflow averaged 46 ± 9 μg/L, whereas outflow concentrations were 12 ± 7 μg/L. Overall total copper removal from influent water was 73 ± 14%. Although inflow water was toxic to C. dubia, no toxicity was observed in outflow water after 1 month. Diagnostic measurements of wetland function (e.g., hydrosoil redox potential and sulfide formation) indicated that copper bioavailability was likely limited by copper precipitation as sulfidic minerals. This constructed wetland design was implemented at the U.S. Department of Energy's Savannah River Site to mitigate risks to receiving-water biota.

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