H&T uses co-precipitation followed by filtration as the preferred method for removal of arsenic from drinking water. There are many methods available to remove arsenic including ion exchange, RO and adsorptive processes. However, we feel the co-precipitation process is the easiest to operate and most economical. Often, arsenic will be present in combination with iron and/or manganese. When iron and manganese are in the water, it is necessary to remove them first before using RO, ion exchange or an adsorptive process to extract the arsenic. Filtration done with GreensandPlus enables the iron, manganese and arsenic to be removed in one step. First, chlorine is fed to oxidize all the arsenite (+3) up to the arsenate (+5) state and to regenerate the catalytic GreensandPlus media. The iron is then oxidized and precipitated by the chlorine in the presence of the catalytic media. The arsenic in the +5 state combines with the iron floc and is filtered. Like the iron, manganese is oxidized and precipitated in the presence of chlorine and the catalytic media. In instances where there is not enough, or any, iron present to remove the arsenic, an iron coagulant like ferric chloride can be added to provide the floc necessary for arsenic removal. When no iron is present and ferric chloride is used to provide the floc, a dual media bed of sand and anthracite is used in lieu of GreensandPlus. However, the chlorine feed is still required in case any arsenic remains in the arsenite (+3) state.