Anoxic storage to promote arsenic removal with groundwater-native iron

Storage containers are usually used to provide a constant water head in decentralized, community groundwater treatment systems for the removal of iron (Fe) and arsenic (As). However, the commonly practiced aeration prior to storage assists in rapid and complete Fe2+ oxidation, resulting in poor As removal, despite sufficient nativeFe(2+) in the source water. In this study, it was found that application of anoxic storage enhanced As removal from groundwater, containing >= 300 mu g/L of As(III) and 2.33 mg/L of Fe(2+ )in an As affected village of Rajshahi district in Bangladesh. Although the oxidation of Fe2+ and As(III) during oxic storage was considerably faster, the As/Fe removal ratio was higher during anoxic storage (61-80 +/- 5 mu gAs/mgFe) compared to the oxic storage (45 +/- 5 mu gAs/mgFe). This higher As removal efficacy in anoxic storage containers could not be attributed to the speciation of As, since As(V) concentrations were higher during oxic storage due to more favorable abiotic (As(III) oxidation by O-2 and Fenton-like intermediates) and biotic (As(III) oxidizing bacteria, e.g., Sideroxydans, Gallionella, Hydrogenophaga) conditions. The continuous, in-situ hydrous ferric oxide floc formation during flowthrough operation, and the favorable lower pH aiding higher sorption capacities for the gradually formed As (V) likely contributed to the improved performance in the anoxic storage containers.

Automated summary

Anoxic storage containers can enhance arsenic removal in groundwater treatment systems, even when the oxidation process is slower compared to aerobic storage. Aeration prior to storage may lead to rapid oxidation of Fe2+ and impact the removal efficiency of As.