12 May 2010
Arsenic removal from water
Arsenic is a naturally occurring and highly poisonous contaminant found in subterranean water bodies in many parts of the world. Wikipedia reports that 137 million people are affected in 70 countries [arsenic in drinking water section] by drinking arsenic-contaminated water. In most affected countries, contaminated groundwater is the main source of water for the rural population. These communities urgently require a simple and affordable technology to remove arsenic from groundwater for both drinking and irrigation purposes. Therefore, a chemical and waste-free arsenic removal method could provide long-term water security to the affected people.
The conventional technologies used in South Asia, and elsewhere, for arsenic removal are based on the 'pump and treat' method involving either adsorption or membrane processes. Such plants are expensive to run and have problems associated with waste disposal and maintenance. In contrast, Subterranean Arsenic Removal (SAR) or ‘in-situ treatment’ plants neither use any chemicals, nor produce waste. Their installation is similar to a tube-well; all parts are easily available and can be installed by village technicians. Queen’s University Belfast is credited with setting-up the world’s first low cost and chemical free water treatment plant in the arsenic belt of India. Six such plants are now in operation in rural locations in West Bengal, close to the Bangladesh border, with the financial assistance of the World Bank. These plants are being managed by local water users’ associations and are being used to supply water to the local population ( Each plant can produce up to 6,000 litres of safe drinking water depending on the demand (arsenic concentration <10 ppb) with a typical production cost of US$1.00 for every 10,000 litres. Subterranean groundwater treatment is based on the principle of oxidation and filtration processes of conventional surface treatment plants for removal of iron and manganese from water, but has the added benefit of (i) enzymatic oxidation of As (III) to insoluble As (V), and (ii) huge adsorption space in the aquifer zone that removes arsenic along with iron and manganese in a manner that does not clog the aquifer.
The high concentration of arsenic in groundwater in South Asia is due to the presence of bacteria that use arsenic bearing minerals as a source of energy among one of the available sources, turning insoluble As(V) to soluble As(III). In the SAR process, the following takes place:
1.The underground aquifer is turned into a natural biochemical reactor that removes water-borne arsenic along with iron and manganese.
2.The oxidation processes are accelerated by the autocatalytic effect of the oxidation products and by the chemo-autotrophic micro organisms. No chemicals are used and no sludge is produced in the process, maintaining normal permeability of the aquifer.
Many of the villagers who started using water for cooking and drinking purposes from community plants in early 2008 are already showing signs of recovery from arsenicosis. Six plants are operational and six rural communities with a total population of more than 7,000 have been getting their water supply from ‘SAR’ plants ( and many more are now being installed in the Bengaldelta.
Large scale implementation of the technology is in the offing; numerous websites including Wikipedia (with both ‘arsenic’ and ‘groundwater in arsenic’ sections) have published information on this technology, which has generated interest in many communities.
This technology could transform the way arsenic is removed from groundwater, saving millions of lives in the Ganges, Brahmaputra and the Mekong delta where the arsenic is of arsenopyrite origin. This includes the affected areas of India, Bangladesh, Cambodia, Nepal, Vietnam and Thailand. The technology will soon be implemented in Cambodia and Burkina Faso with the help of Royal University of Phnom Penh and ‘Friends in Action International’ respectively. The technology is scalable from a production capacity of 10,000 litres per day (US$4,000) to 100,000 litres per day (US $20,000) for each plant, catering to the drinking water needs of 2,000 to 20,000 people.
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