THERE is a good chance the leafy vegetables that make it to your salad bowls were irrigated using untreated or partially treated sewage. Each day an estimated 20,000 million litres of sewage is used for irrigation—five times what Delhi generates each day—but more than half of it is untreated.
Faecal matter in sewage has millions of coliform bacteria which can cause diarrhoea, typhoid or other diseases. The Union Ministry of Environment and Forests (MoEF) has set standards for permissible limits of organic and inorganic pollutants in treated sewage, but it is yet to decide on coliform.
Why the long wait
In 1989, the World Health Organization (WHO) issued guidelines setting coliform limit at less than 1,000 most probable number (MPN) per 100ml of water to be used for irrigation of crops likely to be eaten uncooked. Following the suit, the environment ministry constituted a committee in 1999 which recommended desirable limit of coliform at 1,000 MPN/100ml and maximum permissible limit at 10,000 MPN/100ml for discharge of treated sewage into a waterbody or for agriculture, aquaculture or forestry.
Subsequently, the Ministry of Urban Development formed a committee in 2004 which recommended desirable limit at 500 MPN/100ml and maximum permissible limit at 2,500 MPN/100ml for discharge into the Yamuna stretch in Delhi. As a follow up to the recommendations, the Central Pollution Control Board (CPCB) sponsored a project to study reduction of coliform through conventional treatment technologies being adopted in India.
The three-year study, published in 2008, was carried out by Anna University in Chennai and the Indian Institute of Technology, Roorkee. It concluded that treatment facilities could remove a maximum of 99 per cent coliform. But sewage contains coliform upwards of 10 million MPN/100ml, so a 99 per cent removal would not be enough to meet standards.
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