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.

View full abstract

Recently, the cyanobacterium Anabaena has been observed to form bloom in reservoirs without artificial pollution sources such as the Urushizawa Dam. Morphological identification and sequencing of the 16S rDNA gene and rbcLX region of this microorganism were performed on 22 Anabaena strains isolated from the Urushizawa Dam and other lakes and reservoirs. Four species of Anabaena (A. circinalis, A. ucrainica, A. smithii and A. pseudocompacta), which are generally observed in eutrophic freshwater lakes and reservoirs in Japan, were isolated from the Urushizawa Dam. On the basis of the 16S rDNA and rbcLX gene sequences, the isolated Anabaena strains were classified into four and five clusters, respectively. Morphologically different species, namely, A. circinalis, A. ucrainica, A. crassa, A. mucosa, A. smithii and A. viguieri, were contained in the same cluster of the 16S rDNA tree. Most of the strains were contained in clusters that featured no capability for cyanotoxin production.

View full abstract

To ensure the quality of drinking water in private wells in the Tama District, Tokyo, the Tokyo Metropolitan Institute of Public Health has surveyed water quality for many years. The primary contaminants in 698 wells within the District were monitored for ten years (1997-2006). In 1997, 51% of the wells exceeded drinking water quality standards. The following items exceeded standard values: total coliforms (34.3%), standard plate count bacteria (11.2%), tetrachloroethylene (PCE, 11.2%), nitrate-nitrogen (nitrate-N, 8.5%), and trichloroethylene (TCE, 2.1%). Escherichia coli was used to replaced total coliform as a standard to increase the accuracy of fecal matter determination and, as a result, the percentage of wells exceeding standards decreased to 30% in 2004. It was rare for the concentration of nitrate-N, PCE, or TCE to decrease below standard values over time. These contaminants were particularly common in wells in northeastern Tama. Thus, it is necessary to continue monitoring wells where contaminants exceed standard values.

View full abstract