Removal of arsenic from drinking water and soil bioremediation

Various countries in America have reported the existence of people suffering chronic exposure to levels of arsenic in drinking water that are higher than those envisaged in international standards. This is the case in Canada, the United States, Chile, Peru, Bolivia, Mexico, El Salvador and Nicaragua. Some of these countries have solved, either fully or in part, the problem of technology availability, depending on whether the affected population lives in rural or urban areas. There are around 14 methods of removing arsenic from water, with efficiencies that range from 70 to 99%. Coagulation-flocculation and lime softening are the methods most used in large systems, and not only to remove arsenic. Small systems can use ion exchange, activated alumina, reverse osmosis, nanofiltration and reverse electrodialysis. New technologies include sand covered with iron oxides, granular ferric hydroxide, iron packets, iron modified by sulfur, zeolite filtration, iron addition with direct filtration and conventional removal of iron and manganese. In Latin America studies have concentrated on the use of chemical coagulation with aluminum sulfate, hydrated lime and sodium polyelectrolyte, and have achieved arsenic levels of 0.12-0.15 mg/l. Direct coagulation over filters and coagulation-flocculation have reached values below 0.05 mg/l. Removal through adsorption uses hematites and materials with a high iron content and positively charged surfaces (natural green clay, activated clays, natural and activated zeolite and bone charcoal). In Latin America, Chile is the most experienced country in treating water for urban areas since it has four plants for removing arsenic from the water supply (0.40 mg/l) which together treat 2000 l/s and produce drinking water with 0.040 mg As/l. Improving the system by adding reverse osmosis (post treatment) and desalination has also been evaluated. In Peru there is one plant for removing arsenic that treats the water with ferric chloride and sulfuric acid. CEPIS-BS/SDE/PAHO has developed and patented a product called ALUFLOC, which is a mixture of an oxidant, activated clays and a coagulant (aluminum sulfate or ferric chloride).This is a simple, low-cost methodology which, at a household level, removes the natural arsenic present in groundwater that is consumed by the rural population. Up to 98% has been removed using Al2(SO)3 and FeCl3 as coagulants. As far as soil remediation in contaminated areas is concerned, studies have been carried out on the ability of certain plants to absorb and concentrate toxic substances. The University of Florida has identified a fern which absorbs and hyper-accumulates arsenic from contaminated soil. Techniques used to restore and stabilize arsenic in sludge, soil and industrial waste generally involve precipitation with lime and caustic soda. This is followed by sedimentation and/or filtration. In Mexico an insoluble arsenic compound has been produced which can also be used as a raw material in the manufacture of solid products for use in construction or disposed of in a landfill (Sandoval 2000). In addressing the problem of drinking water, the characteristics of the water source, water treatment, and methods for distribution and/or consumption must be taken into account, as well as the type of technology to be employed, which will depend on the characteristics of the location. Latin American countries have the experience and ability to develop technologies, but are limited by a lack of financial resources, facilities and, above all, state policies to facilitate and direct the development of such technologies which will lead to an effective solution to the problem or to satisfy existing needs. The people who are most affected are scattered over rural areas, consume untreated water and are unaware of the risks to which they are exposed. Pilot studies must be carried out on an ongoing and sustained basis until a solution is found that can be recommended for implementation in national programs to remove arsenic from drinking water.