Most of the drinking water is supplied from groundwater in Bangladesh, where the arsenic polluted groundwater has been found in 60 districts out of a total of 64 districts. It is estimated that about 40 million people are currently exposed to the risk of arsenic poisoning. We have been making detailed surveys and experiments with AAN (Asia Arsenic Network) in model villages in Jessore district from March 1997 to get the arsenic pollution mechanism and arsenic-free water. We have developed Pond Sand Filter (PSF), which makes drinking water from arsenic free pond water, in Bangladesh since 1999. The pond water, however, dries up at the end of dry season and the use of PSF becomes difficult. In order to utilize PSF all the year round, we attempted to put the arsenic contaminated well water into PSF. After the fundamental tests about the arsenic removal performance of gravel tanks (2000~2001), we installed the gravel and sand tanks, which had the same size and structure as PSF, at Marua village in December 2002. We named it as GSF (Gravel Sand Filter). The arsenic removal performance was tested from 19 December 2002 to 4 January 2003 to obtain the performance data for the initial stage of the GSF operation. And, we have now the one year performance data for the arsenic removal of GSF.

This paper first shows the arsenic removal performance of GSF. It was seen that GSF could remove arsenic very well. The arsenic concentration of groundwater decreased from 0.25mg/L to 0.01~0.05mg /L after the gravel tanks and less than 0.01mg/L after the sand tank. The co-precipitation of arsenic with ferric iron is discussed with the effect of DO, As and Fe concentration values in the tanks. The one year performance data shows that PSF can be operated through a year by using pond water in rainy season and groundwater in dry season with a periodical maintenance of GSF like drainage from the gravel tank and cut of the surface sand of sand tank. Besides, we installed a smaller GSF, used exclusively for the removal of arsenic.

Secondly, The paper shows and discusses the leaching tests of the ferric-arsenic sludge from GSF and the solidified sludge with cement. The leaching ratio of arsenic to that in the sludge were 5–9% for the former and less than 5 % for the later. This means the co-precipitation of arsenic with ferric iron forms a strong chemical bond and the treatment of the sludge may not be difficult.