Removal of arsenic from drinking water supplies: Chile experience

In the north of Chile arsenic occurs naturally in surface water resources, principally in inorganic and pentavalent form As(V). In this zone 400 000 people live and for their drinking water supply treatment utilities for arsenic removal have been operating since the 1970s. The process used in Chile for arsenic removal is coagulation. Addition of coagulants to raw water facilitates the conversion of soluble As species into insoluble reaction products which are termed through adsorption mechanisms on to coagulated floc, which are then separated by filtration. The efficiency of arsenic removal by this process depends on the formation of insoluble products, arsenic adsorption on to particulates and separation of the resulting particulate As. Any problem arising in these processes decrease the efficiency of the arsenic removal process. Recent studies have shown that with an improvement of the current coagulation process (optimising raw water pH and dosage of chemical agents) the arsenic removal may be increased to 92.5-95.0%.