The influence of media type on removal of arsenic, iron and boron from acidic wastewater in horizontal flow wetland microcosms planted with Phragmites australis

Abstract

In this study, horizontal flow wetland microcosms were used to test the effectiveness of two media types: (1) zeolite and (2) a series of limestone and cocopeat in the removal of arsenic (As), boron (B) and iron (Fe) from contaminated acidic waters such as those associated with mine waste. The wetlands were operated under a hydraulic loading of 30 mm/d, to treat acidic water with As = 2.3 mg/L, Fe = 97.3 mg/L and B = 30.8 mg/L at pH 2 ± 0.2. Both media were highly effective in the removal of As and Fe. The zeolite wetlands removed 99.9%, 96.1% and 12% of As, Fe and B respectively, whereas the removal efficiencies of the limestone/cocopeat wetlands were 99.8%, 87.3% and 17%. The contribution of plant uptake to As, Fe and B removal in both wetland types was almost negligible (<3% in all cases). The results confirm the key role of the wetland media in fostering specific removal processes. These processes include As co-precipitation with Fe due to pH adjustment provided by limestone, and As and Fe removal facilitated by the cation exchange capacity of the zeolite. Limestone/cocopeat wetlands may offer a more suitable treatment, given the neutral pH achieved and the slightly higher B removal, but zeolite wetlands are able to achieve lower concentrations of Fe, despite the acidic water in the treated effluent.