Evaluating Removal Efficiency of Heavy Metals in Constructed Wetlands

Abstract

In recent decades, there has been a growing interest in using constructed wetlands (CWs) for the treatment of contaminated waters. There has been an increase in the use of wetland technology because of its low greenhouse effects, low maintenance and operational costs, and energy efficiency. However, there exists a level of uncertainty in regards to the performance of CWs and in some cases, CWs act as sources of contaminants. To address the issue, this paper presents the removal efficiencies for different heavy metal elements and identifies the factors affecting the removal processes. Using the San Joaquin Marsh constructed wetlands, removal efficiencies for four heavy metal elements—Cd, Cu, Pb and Zn—were evaluated. It was found that the effluent metal concentrations were not substantially lower than the influent. The removal efficiencies of 23.9%, 10.6%, and 17.6% were found for Cd, Cu, and Zn, respectively. No significant reduction was observed for concentrations of Pb. Different aspects of the removal mechanisms and possible factors controlling them were addressed and some recommendations were made to increase the removal efficiency of such systems. The results indicated that factors such as low metal loadings and algal growth in the marsh could be responsible for low removal rates of Pb.