ARSENIC TREATMENT IN DRINKING WATER THROUGH IRON AND IRON COMPOUNDS

Abstract

Arsenic exposure from drinking water can occur from natural as well as anthropogenic sources. Arsenic is poisonous to humans and is dangerous for the environment. As arsenic is widely distributed throughout the earth's crust, the natural source originating from the soil and rocks containing arsenic compounds is challenging to deal with. Concentration of arsenic in natural surface and ground waters is commonly around 0.001 mg/L but may exceed Img/L where the arsenic level in soil is high. Although arsenic can exist in four valency states (0, -3, +3,+5); the trivalent arsenite (+3) dominates in reducing conditions in ground water and pentavalent (+5) arsenate dominates in oxidizing conditions in surface waters. The valency state of arsenic plays a vital role in determining its toxicity as trivalent arsenite is more toxic compared to pentavalent arsenate. In countries such as Bangladesh, a great percentage of ground water taken through wells is contaminated with arsenic and the health of a large portion of population has been affected and is still at risk. Recommended allowable concentration of arsenic in drinking water set by WHO is 0.01 mg/L. Various technologies are being used to keep the arsenic contamination level within the range in drinking water while novel and more innovative techniques are being explored which could be safe, effective and economical. One of the treatment methods tested in this research work is using iron and its compounds to chemically react, adsorb or precipitate the arsenic in drinking water to bring down the concentration of arsenic to the recommended level. Experimentally, a titration method was used to react with the iron compounds with dissolved arsenic at defined pH values. It was found that chemical reaction of arsenic