SOLIDIFICATION AND NATURAL TREATMENT OF ARSENIC SLUDGE PRODUCED FROM

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We have established the design chart of the arsenic removal unit, Gravel Sand Filter (GSF), by examining the arsenic removal performance of 4 GSFs installed in Bangladesh these 4 years. These GSFs are community-based units and have supplied arsenic-safe water to villagers in these years. GSF is composed of gravel tanks and sand tank. The arsenic in groundwater is to be settled in the gravel voids of gravel tanks by co-precipitation with iron, which exits naturally in groundwater with higher concentration.The iron and arsenic in groundwater are first to be oxidized at the inlet tank of GSF. The aeration, contact between iron and arsenic, and the concentration of competition ions as phosphate are key points for the performance of GSF. The design methods for these poi its are proposed in this research. The performance of GSF is usually O.K with 10 value of ratio, Fe/As, in groundwater. The ratio of Fe/As should be, however, bigger 30 for the groundwater with high concentration of phosphat … More e. The box filled with large amount of used iron nails is to be set in the inlet tank in the design chart of GSF, when GSF has to be installed at the cite where the groundwater has less ratio of 30 under the higher concentration of phosphate.Arsenic sludge from GSF is to be settled in the sludge tank installed in the GSF cite through draining. The supernatant of the sludge tank is flowed to the artificial pond where the natural treatment of arsenic is examined. The settlement of the sludge tank is solidified by cement. The 90% of arsenic in the settlement is shut out without cement but the arsenic concentration of the leaching test was 0.05〜0.65mg/L, showing beyond values of standards 0.05mg/L in Bangladesh. The leaching tests for the 2% mixing of cement show 0.05〜0.11mg/L, which is less than the second standard for land contamination in Japan, 0.30mg/L..The pH of the tests shows 10.5-10.9.The treatment method, here, is to mix the sludge settlement with 2% cement and deposit without contact to water until the establishment of waste treatment management in Bangladesh.We have estimated the accumulation of arsenic at the bottom of the artificial pond and looked for the micro-organism in the bottom soil which can change the inorganic arsenic to organic one. We can detect some of Monomethylarsine(MMA) andDimethylarsine(DMA) in both of sludge tank and artificial pond. And, the micro-organism strong to arsenic was confirmed, which can live under the condition of arsenic concentration of 1000mg/L. Less