Constructed Wetlands for the Removal of Heavy Metals

Over the past ten years, industrial facilities have faced more stringent restrictions on the discharge of treated wastewater containing heavy metals. Many of these facilities were already treating wastewater to comply with permits based on effluent guidelines for heavy metals. However, new or renewed permit limits are based on water quality criteria and often result in effluent limitations that are near laboratory detection levels. Most of the existing treatment systems were not designed, and are not adequate, to meet these new effluent limitations. Constructed wetlands have been used extensively for the treatment of domestic wastewater, and in the mining industry, for the treatment of acid mine drainage (AMD). The use of constructed wetlands for the treatment of heavy metals from industrial wastewater has not been as widely applied or studied. This may be due, in part, to the problems with passive wetland systems that have developed at AMD sites and the need for more predictable results and higher metal removal efficiencies for industrial facilities. Based on the completion of numerous pilot-scale tests and the favorable results from two full-scale systems constructed in Arkansas, it is proposed that the use of constructed wetlands for heavy metal treatment, when applied within a defined range of design parameters, is a viable and cost effective alternative for the treatment of low concentration heavy metals.