Abstract
An arsenic removal unit (GSF) was constructed by the Miyazaki University research group in the Marua village in Bangladesh. The sludge drained from the GSF was directed to a sludge tank and allowed to settle down. Then the supernatant in the tank was released to an artificial pond. The water, sediment and sludge samples from the pond and tank were analyzed, and the microbial statuses of the pond and tank were examined. The ORP result was observed to have changed from the reduction state to the oxidation state in the tank within one year from 2005 and 2006. Therewith, the concentration of soluble arsenic and iron in the tank decreased compared with those one year ago. The amount of arsenic included in the entire pond hardly changed in 2005 and 2006. From the result of an enrichment culture using sediment from the pond, monomethylarsonic acid and dimethylarsinic acid were detected in the medium, and the amount of total arsenic compounds in the medium decreased. It is thought that this loss was contributed by biogenic activity induced by inorganic arsenic biomethylation to gasified volatile organic species, such as monomethylarsine and dimethylarsine. These results suggested that the natural attenuation of arsenic in the pond was performed by biologic gasification.
