Preliminary evaluation of metals removal in three pilot-scale constructed wetland systems

Pilot-scale surface-flow, subsurface-flow and floating aquatic plant constructed wetland system designs were installed and evaluated to determine the effectiveness of constructed wetlands to immobilize and remove metals such as cadmium, zinc, copper, chromium, lead and nickel in tertiary effluent wastewater in a Midwestern US climate (central Illinois). Following wetland treatment, average concentrations of copper decreased from 56.6μg l in influent to 7.9μg l (86.0 per cent reduction) in the FAP system, 9.2μg l (83.7 per cent reduction) in the SSF system and 11.0μg l (80.6 per cent reduction) in the SF system, respectively. Results of ANOVA indicated that differences in concentration reduction of copper among the three wetlands were not statistically significant. The average concentration of chromium decreased from 1.31μg l in influent to 0.4μg l (69.5 per cent reduction) in all system designs. Copper concentrations were reduced consistently with increasing wetland retention time, with most of concentration reduction having occurred in the first wetland cell for all system designs.