Arsenic is found to exist within the shallow zones of groundwater in many countries and a large number of drinking water treatment units have been installed to combat this arsenic poisoning. Microbial activity can greatly affect the mobilization of arsenic under anaerobic conditions when coupled with the oxidation of organic matter. In this study, the bioleaching of arsenic in response to organic matter inclusion in a drinking water treatment process has been elucidated. The decomposition of organic matter due to the microbial action has led to an anaerobic condition within the accumulated sludge in the treatment unit and hence caused the bioleaching of arsenic, above 130 μg/L, with the effluent water. Nevertheless, the biofilm structure, related to the oxygen penetration, had significant influence on the bioleaching of arsenic even in the circumferential aerobic condition of the biofilm. For a biofilm thickness around 400 μm, an anaerobic bottom part was noticed and hence a clear step-up concentration of arsenic was observed in the associated bulk liquid. This study suggests that organic matter would have a sufficiently important influence on the microbiological transformation of arsenic to warrant its consideration in designing safe remediation strategies in the context of arsenic removal processes for drinking water.

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