The report of the Task Force appointed by the Planning Commission presents an action plan for removal of arsenic contamination in West Bengal. It looks at the extent of the problem, its intake sources, technologies available and the operation and maintenance (O&M) issues.

It outlines the diverse technologies based on various scientific principles, assesses them based on their scale of operation (domestic or community) on techno-economic considerations & infrastructure required and provides suggestions. Short, medium and long term measures are outlined for tackling the problem of arsenic contamination in drinking water supply in the state.

As per the report, seventy-nine blocks in eight districts of the State are severely affected due to drinking of water contaminated with arsenic (>0.05 mg/l) and this is five times the World Health Organisation’s (WHO) permissible limit of 0.01 mg/l. The source of contamination is geological and the situation gets aggravated as major water demands of the affected districts are met from groundwater. The taskforce reviewed processes of arsenic removal the world over and shortlists some processes specific to the State.

The scientific principles followed in arsenic removal technologies for groundwater revolve around basic principles like coagulation/co-precipitation, adsorption, sedimentation, ion exchange, membrane/reverse osmosis, biological treatment/ oxidation etc. Technologies based on coagulation/co-precipitation/adsorption entail pre-oxidation of trivalent As (III) to pentavalent As(V), the latter being less toxic and having better removal efficiency.

The taskforce rules out ion exchange and reverse osmosis processes because of high costs and non-applicability in the context of West Bengal. It looked at some nine technologies for community level plants and three technologies for domestic scale developed by various national and international agencies to suggest short-term remediation measures. These technologies have been compared with regard to their scale of operation, capital cost, process, media, capacity and cost.

Medium-term measures are recommended for promoting conjunctive use of ground and surface water and waste water recycling for use by communities for other purposes. Long-term measures suggested include tapping of surface water and shallow dug wells in West Bengal, which do not contain arsenic.

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