Ingenious system to manage sewage in Kolkata

Fisher folk of the East Kolkata Wetlands use sewage from the city’s lakes to rear fish. Watch an interview of the person who popularized this system that the locals invented years ago.
Fishermen use wastewater of Kolkata to rear fish Fishermen use wastewater of Kolkata to rear fish

They take your pain and give you what you need. They will absorb the excess showers that our cities can’t handle and replenish water underground when our taps run dry. Often underestimated, these shallow water bodies are also home to countless life forms and serve as winter destinations for distant migratory birds. Blame me for being philosophical but I equate wetlands to mothers.

Historically, wetlands have been victims of city expansions around the world. Closer to home too, some of these wetlands are making way for land reclamation. Despite these gnawing threats, the East Kolkata Wetlands have managed to stand out as a living and breathing example of the mutual love between man and nature. The earliest known accounts from 1748 show that these wetlands or salt lakes were spread over a vast area of about 20,000 acres stretching from near the river Hooghly for about 5-6 km to the east.

Bidhannagar or Salt Lake City (adjoining East Kolkata Wetlands) as it is popularly called, is a ‘planned’ satellite town in the Indian state of West Bengal (Wikipedia). Centuries ago however, fishermen who depended on these salt lakes ‘planned’ their own survival as well as that of the water bodies by creating an immaculate system - a system where the city's sewage would drain into these lakes so they could rear fish. The wastewater was then used for raising another crop of paddy! But, they say innovation is driven by scarcity. Fishermen in the salt lakes didn’t create this ensemble out of nothing. It was a crisis of livelihood that gave birth to such an invention. 

These wetlands on the east of Kolkata were once connected to the sea through a now-dry river, Bidyadhari. They received the tidal spill over of the Bidyadhari river that opened into the Bay of Bengal. Thus the lakes were a perfect place for brackish water fisheries (brackish water is that which has more salinity than fresh water, but not as much as seawater. It may result when fresh water meets seawater). When this connection with the sea was lost due to human interventions, the fishermen adapted. These water bodies were turned into sewage water fisheries. Since then, the lakes take in the city’s sewage and in return provide fish and vegetables by a completely natural process.

The man who interpreted the ingenuity of the local fishermen tells how this happened in the video below.

Dr. Dhrubajyoti Ghosh, a humble engineer-turned-ecologist in Kolkata, deciphered the truth behind this symbiotic system thriving in his own backyard. This was when he was assigned the task of recommending how the city’s wastewater could be utilized. He observed this striking phenomenon by which these large shallow water bodies were fed wastewater through a network of canals. This wastewater was detained for a stipulated time and fish was grown. He asserts that this pond system was exactly the one that works best in tropical sunshine to improve the quality of wastewater, better than any sewage treatment plant, provided the detention time is sufficient.

Recognizing this as the best wastewater utilization plan has changed the history of Kolkata city. "According to scientists, around 980 million litre of sewage is dumped into EKW daily and the 240 bheris in EKW produce 10,000 tonnes of fish annually. In addition, the farmlands produce 1,500 tonnes of rice and 55,000 tonne of vegetables" (Times of India). Thirty years hence, it is still the only Class I city by the river Ganga (Hoogly) where no fund has come to set up a conventional sewage treatment plant. The attached document: 'Ecological History of Calcutta's Wetland Conversion' by Dr. Dhrubajyoti Ghosh and Susmita Sen contains more information on this. 

Ghosh has spent thirty years of his life to understand the significance of this self-organising system. He renamed it to East Calcutta (Kolkata) Wetlands as he felt it was meaningless to call it ‘salt lakes’ because there was no trace of salinity in these water bodies now. He has religiously mapped the wetland area where wastewater was used either in fisheries or in paddy fields. This area was calculated as 12,500 hectares and he pursued the case to put this wetland on the global map as a Ramsar site in 2002.

This does not mean however, that the East Kolkata Wetlands are free from threats. Though they do have the protection from legislations and recognition from International conventions, the real estate boom is swallowing large chunks of these water bodies. About 10% of the East Kolkata Wetlands has been converted into concrete in just the last 10 years.

As mutual love slowly withers away and man’s greed takes over, the largest sewage-fed aquaculture in the world breathes in fear for its survival.

 

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