Evaluating performance of a constructed wetland treatment system designed to decrease bioavailable copper in a waste stream

Published literature has indicated that when properly designed and maintained, constructed wetlands provide predictable water-quality improvement. However, because of the complexity or heterogeneity of wastewaters and the lack of quality data (both temporal and spatial) currently available from full-scale constructed wetland treatment systems, many constructed wetland designs fail to provide predictable water-quality improvement. By understanding internal thermodynamic processes and design criteria that affect the removal of targeted constituents in constructed wetlands, constructed wetland technology can be accurately and reliably transferred from site to site. Specific design parameters that should be identified when designing a constructed wetland include (1) character of the wastewater including the targeted constituents, (2) performance goals or desired levels of treatment, (3) transfer and transformation pathways, (4) flow rates and retention time required to achieve treatment, and (5) climate (i.e., temperature and precipitation). Using these guidelines, this research evaluated the performance of a constructed wetland treatment system for treatment of a copper-contaminatedwastewater. Specifically, this system was designed to achieve a regulatory limit of 22 mg/L total recoverable copper and eliminate toxicity in a waste streamby coupling the copper, sulfur, and carbon cycles, so that copper will be precipitated from thewater column and sequestered in the sediment in nonbioavailable forms. In this constructed wetland treatment system, average acid-soluble copper concentrations decreased by 85%, and soluble copper decreased by 83% from upstreamof the system to downstream, and the toxicity associatedwith the bioavailable fraction of copper was effectively removed. Environmental Geosciences, v. 15, no. 1 (March 2008), pp. 21–38 21 Copyright #2008. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved. DOI:10.1306/eg.07110707008