Design and Performance of a Pilot-Scale Constructed Wetland Treatment System for Simulated Bangladesh Groundwater

Abstract

Constructed wetland treatment systems (CWTSs) may offer an effective approach to treating arsenic-contaminated groundwater in Bangladesh. The objectives of the current study were to (1) design and construct a pilot-scale CWTS to reduce the concentration of arsenic in a simulated Bangladesh groundwater from ~200 µg/L to \u3c 10 µg/L, (2) assess arsenic removal performance by determining removal extents, efficiencies, and rates, and (3) evaluate biogeochemical removal processes based on the fate and distribution of arsenic in the CWTS. Two treatment series were designed to promote co-precipitation and sorption of arsenic with iron oxyhydroxides under oxidizing conditions, while two series were designed to promote precipitation of arsenic with sulfide under reducing conditions. Addition of zero-valent iron (ZVI) significantly improved (α = 0.05) performance of both oxidizing and reducing series. Arsenic removal performance was significantly greater (α = 0.05) in the oxidizing series amended with ZVI than in any other series, with removal extents, efficiencies, and rate coefficients ranging from 5-60 µg/L, 51-95 %, and 0.18-0.77 1/d, respectively. Results of this pilot-scale study demonstrate that a CWTS could be used successfully to reduce the concentration of arsenic in simulated Bangladesh groundwater to below the USEPA drinking water standard of 10 µg/L