Arsenic removal from water using advanced oxidation processes.

Consumption of groundwaters containing natural arsenic at several hundred microg/l (ppb) in countries such as Bangladesh has lead to the increased occurrence of many cancers particularly those of the skin and bladder, while concerns in the USA and Australia regarding the unknown health impact of drinking water containing tens of ppb of arsenic is leading to increasingly stringent maximum contaminant levels. The anaerobic conditions of these groundwaters result in the arsenic being present in its reduced form, hence the use of an oxidant is necessary if the arsenic is to be successfully removed by precipitation or ion exchange methods. Advance oxidation methods which utilise ultraviolet light and a photo absorber have been developed and patented, in which both iron salts and sulphite can be used as the photoabsorber.

Photochemical oxidation of arsenic by oxygen and iron in acidic solutions.

The rate of oxidation of As(III) to As(V) by oxygen is increased by several orders of magnitude by the presence of dissolved Fe(III) and illumination with near ultraviolet light. The oxidation reaction has been studied in acidic conditions in the absence and presence of dissolved oxygen. A reaction mechanism has been postulated in which Fe(III)-hydroxide and -chloride complexes first absorb photons to produce highly oxidising hydroxyl and dichloro radicals.