Calcutta has no wastewater treatment plant. The integrated wetland system developed by the Calcutta Metropolitan Authority is a complex and cost- effective strategy for handling Calcutta’s solid waste and sewage. The wetlands are a patchwork of canals, vegetable plots, rice paddies and fish ponds covering some 12,000 hectares. When solid waste arrives, thousands of people comb through the debris removing what can be recycled. The remaining organic mass is used to support vegetable gardens irrigated with sewage water.
Raw sewage is decomposed in a 2,500 ha system of ponds and canals filled with algae. The algae are transformed into edible protein by fish that thrive on the thick algal soup such as Indian and Chinese carp and tilapias. The multiple stocking of fingerlings and multiple harvesting provides relatively high yields of 3-8 tons per hectare annually.
Through this process, the garbage fields produce 150 tons of vegetables per day, the fish ponds produce 3-8 tons per hectare annually, and the paddy fields produce 16,000 tons of rice. The project is managed by community groups, utilizes appropriate technology, with entrepreneurs taking away all sales proceeds in return for rental of land and water. Some 17,000 fishermen participate and produce 20 tons of fish daily.
Under the Ganga Action Plan, similar wetlands treatment facilities are being implemented in other municipalities to address pollution in the Ganges River.
Kolkata Municipal Development Authority
Prashasan Bhavan, Block-DD-1, Sector-I, Salt Lake
Ph # 2358 6314 www.cmdaonline.com