A natural system to recycle waste water

Barely 5 km from the eastern edge of Kolkata is a spectacle that often takes the unwary visitor by surprise. One finds very large shallow ponds, with sparkling water, wrapped in an eerie silence.

But the importance of these ponds – or bheris as they are called locally – goes beyond their natural beauty.

The wetlands nurture the world’s largest waste water-fed aquaculture system. The sewage that is sent to the wetlands is subjected to solar purification, followed by natural oxidation, after which the water is conducive for the growth of algae and plankton, the primary food of fishes.

Research suggests that the wetlands provide a “very cheap, efficient and eco-friendly system of solid waste and sewer treatment system” for Kolkata and the city’s periphery. On August 19, 2002, the East Kolkata Wetlands was included in the Ramsar list of ‘Wetlands of International Importance’.

But there are problems galore for the wetlands. And encroachment is the single largest threat that the East Kolkata Wetlands face. According to Naba Dutta, environmental activist and member of green platform Sabuj Mancha, 4,500-5,000 sq m of wetlands have already been encroached upon or filled up.

In fact, he claims, there were initially 264-odd ponds, which have now come down to 202. “Some 62 water bodies have been filled up.”

The East Kolkata Wetlands Management Authority (EKWMA), a government body set up to protect the wetlands, has filed 87 cases of violation of environmental norms and encroachment in the wetlands area over an 18-month period (January 2016 to June 2017).

“This apart, there is rampant construction, such as parks and beautification of banks, which is only harming the fragile ecosystem,” Dutta alleges.

In the absence of official surveys, gauging the extent of encroachment is difficult. A 2016 survey conducted by SCOPE (an NGO) at Bhagwanpur — one of the 32 mouzas , the local word for settlement — revealed that the water cover had got reduced from 88 per cent in 2002 to 19 per cent in 2016.

The other question is also that of the quantity of the solid waste and sewer. The late Dhrubajyoti Ghosh, well-known champion of the wetlands, had, in his book, Ecology and Traditional Wetland Practice — Lessons from Wastewater Utilisation in the East Calcutta Wetlands, raised the issue of toxicity threat in the region. “It is well understood that the toxicity threat to the quality of fish and vegetables comes essentially from industrial effluents,” he mentions in his book.

The storm drainage system set up in the eastern part of the city in the 70s and 80s has turned into unauthorised sewer connections for small and medium industries.

Untreated industrial waste water reaches the fish-ponds and agricultural lands, leading to metal deposition. This, in turn, reduces the edible quality of fish and vegetables grown in the region.

In Bengaluru, the municipal sewage in Vrishabhavati river, which flows through the south-western part of the city, sustains vegetable farming in the southern fringes. But industrial effluents have raised concerns about toxicity levels in the food chain.

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