The world’s largest sewage-fed aquaculture, a complex of wetlands located east of Kolkata, treating the city's sewage and utilising the nutrients to sustain fish farms and agriculture, generating significant environmental, economic, and social benefits for the community
Context
Ever since its establishment as a fort by British colonisers who ordered its marshlands to be drained, Kolkata, the capital of West Bengal in India, has faced problems with drainage when sewage and wastewater contaminate the Hooghly river in the western part of the city.
Dismissing local and situated knowledges when building imperial trading and military infrastructures, the British colonisers soon encountered the problems with sewage. In the early 20th century, British and Indian engineers therefore instigated a system of shallow canals, pumps, and sediment tanks to reroute the city’s wastewater to wetlands in the Bay of Bengal. The system worked with the land’s natural slope towards the east, becoming one of the world’s most multifunctional wetland ecosystems.
Practice
East Kolkata Wetlands (EKW) is one of the largest wastewater-fed aquaculture sites in the world, encompassing 12,500 hectares of land in the eastern part of the city. Its unique feature is fish-farming, or pisciculture. Beyond working with the land’s natural slope, EKW utilises the region’s local knowledge and skills in wetland management.
More than a century ago, farmers in the wetland region developed techniques of using domestic sewage to feed fish that served an increasing urban population. These sewage-fed fishponds, called bheris in Bengali, were adopted by EKW and continue to host numerous species of fish across more than 5,800 hectares.
An ancient technology with continued functionality, bheris also treat sewage and wastewater through natural processes of sunlight and algae. Specifically, the basins of bheris are sufficiently shallow to allow algae to grow through photosynthesis, whereby these algae act as a water purifier and source of nutrition for the fish population.
Kolkata’s municipality is responsible for channelling sewage and wastewater from the city’s underground sewers to pumping stations where bheri owners and local employees continue the processing. This relay employs over 60,000 people whose work provides the city with fresh fish, as well as vegetables grown in the wetlands.
In sum, EKW generates huge environmental, economic, and social benefits. Crucially, it harnesses traditional technological knowledge about fish farming to face an issue imposed originally by an external project of colonial infrastructure. Beyond facing the ongoing challenge of sewage management, EKW functions as a carbon sink for the city, its green space absorbing pollution and providing habitats for numerous flora and fauna. Dealing with long-standing challenges of sewage disposal and food provision, EKW therefore faces contemporary issues of climate breakdown, such as biodiversity loss and rising carbon emissions, with a regenerative ecological and social system.