Transformation of arsenic in the presence of cow dung and arsenic sludge disposal and management strategy in Bangladesh

Abstract

Summary With increasing use of arsenic (As) removal units for treatment of As-contaminated groundwater in rural Bangladesh, concerns have been raised regarding safe disposal of the As-rich wastes from such units and possible contamination of the environment. In the absence of any clear guideline for safe disposal of wastes generated from As removal units, the wastes are usually disposed of in the open environment, often on cow dung beds in the backyard. Short term (up to 6 weeks) batch experiments performed in this study suggest that bio-chemical (e.g., bio-methylation) processes in the presence of only fresh cow dung may lead to a significant removal of As, both from aqueous solution and As-rich treatment wastes. Arsenic removal appears to increase with decreasing As to cow dung weight ratio. This study also suggests that arsenate transforms to arsenite before removal from aqueous As solution in the presence of cow dung. In most cases majority of As removal takes place during first few days. Removal of As under cap-open (to facilitate aerobic condition) and cap-closed conditions (to facilitate aerobic condition) were found to be similar. No significant variation was observed in the removal As from aqueous solution and from treatment wastes (As bound to iron solids). This study concludes that disposal of As-rich treatment wastes to cow dung pits could be an effective option of As sludge disposal and management in rural areas of Bangladesh.