The removal of arsenic and metals from highly acidic water in horizontal subsurface flow constructed wetlands with alternative supporting media

Abstract

A laboratory-scale horizontal subsurface flow constructed wetland system was used to quantify the arsenic removal capacity in the treatment of highly acidic, arsenic and metal-rich water: pH ≈ 2, Fe ≈ 57 mg/L, Pb ≈ 0.9 mg/L, Zn ≈ 12 mg/L. The system was operated in two stages, being As ≈ 2.1 mg/L in stage one, and ≈ 3.7 mg/L in stage 2. Limestone and zeolite were employed as main supporting media to build non-vegetated and vegetated cells with Phragmites australis. The system was very effective in the removal of arsenic and iron (> 96%), and lead (> 94%) throughout the whole experimental period, having the four treatment types a similar performance. The main effect of the media type was on the pH adjustment capacity: limestone cells were able to raise the pH to ≈ 7.1, whereas zeolite cells raised it to ≈ 3.8. The contribution of plant uptake to the overall removal of As, Fe and Zn was minor; accounting for less than 0.02%, 0.07% and 0.7% respectively. As such, pollutants were mainly retained in the wetland beds. Our results suggest that limestone is recommended over zeolite as wetland medium mainly due to its neutralization capacity.