Drains, soap, dye: What pollutes the Yamuna in Delhi

WHEN THE RIVER ENTERS DELHI AT PALLA, ITS WATER MEETS POLLUTION NORMS, BUT WHEN IT EXITS THE CITY, POLLUTANTS ARE 30 TIMES THE PERMISSIBLE LIMITS

- Jasjeev Gandhiok and Paras Singh

The difference in the Yamuna when it enters Delhi, and the form in which the river exits the city are stark - chemically, visually, and even by smell.

Spanning 22km through the Capital, the Yamuna encounters a major drain approximately every 1.2km, each adding to its contamination. This, along with other smaller sources of pollution, consistently chip away at the water quality as the river traverses the city.

The deterioration starts soon after the river meets the Najafgarh drain - the first and the largest polluting of the city's 18 drains - that ferries much of Delhi's sewage, industrial effluents and other toxic waste into the river.

When the river enters Delhi at Palla, its water meets pollution norms, with acceptable levels of biological oxygen demand (BOD) and dissolved oxygen (DO), no visible froth, and no foul smell. By the time it exits the city, the river's pollutants are as high as 30 times the permissible standards, and around this time of the year, there's a thick iceberg-like block of foam that blankets the surface.

The foam problem