CASE STUDY 1: East Kolkata Wetlands: A Resource Recovery System Through Productive Activities
By Nitai Kundu, Mausumi Pal, Sharmistha Saha
LOCATION AND AREA DISTRIBUTION
• East Kolkata Wetland encompasses a wide number of water bodies and is extended throughout the two districts of North 24 Parganas and South 24 Parganas in West Bengal. It covers an area of about 12,500 hectares and majority of the land is used for various purposes such as: agricultural fields, sewage fed aquaculture and fish farming, solid waste farms and rest is the built up area. It supports one of the world’s largest wastewater fed fishery system. 45.93% of the wetland area is manmade built up.
HYDROLOGY
• This wetland was earlier considered as a buffer zone, but later on all the urban waste and solid garbage was dumped there. As a result, the rise of Sewage fed pisciculture and agriculture made EKW a natural waste recycling system. As the waste water passes through the fishery ponds which are spread over 4000 ha, they facilitate the physical, chemical and biological treatment of water and improve its quality. Thus, EKW came to be known as “KIDNEY OF THE CITY”.
• Ramsar convention described it as: “one of the rare examples of environmental protection and development management where a complex ecological process has been adopted by local farmers for mastering resource recovery activities”. In August 2002 under the Ramsar convention guidelines it was recognized as a wetland of international importance under the article 8 of the convention.
• Maximum temperature during summers is 30oC and Minimum temperature during winters is 10oC. It has no catchment area of its own and about 250 million gallons of sewage per day is disposed in it. For groundwater recharging, there is no good aquifer present till the depth of 400feet. Water is present in perched aquifers. Sometimes the total dissolved solid content overshoots 1800ppm. Water table is present at a depth of 8m. Fishery pond water has an average pH of about 7.5 and BOD ranges from 35-50 ppm and COD is about 55-140 ppm. Soil has very high moisture content and is of mixed clay and alluvial type.
LAND USE PATTERN
• The wetland area is mainly classified as:
(1) Substantially water body oriented area – 47%
(2) Agricultural area – 38%
(3) Productive farming area – 5%
(4) Urban or rural settlements – 10%
ROLE OF CANALS IN URBAN AND RURAL SETTLEMENTS: Wide and deep canals help in fetching sewage while the narrow canals are used by fishery owners for aquaculture.
GOVERNANCE: Garbage dumping ground is under the jurisdiction of (K.M.A.) Kolkata Metropolitan Area and Kolkata Municipal Corporation (K.M.C.).
BIODIVERSITY: EKW is rich in biodiversity and has unique floral and faunal species that can be used as medicine, thatching materials, food and fodder, paper pulp extraction, manure, etc. and help in checking the rapid eutrophication of water bodies and control the soil erosion.
• Flora: 30 genera of phytoplankton, 96 sp of vascular plants, 55 species of Wetland plants, etc.
• Fauna: Zooplanktons (17), cladoceran (3), rotiferan (5), freshwater crustacean species (loss of brackish water crustacean sp. due to intervention by the fishery owners to grow only selected species), aquatic insects, fishes, amphibians, birds, reptiles, mammals, invertebrates and lower vertebrates.
• It provides a suitable habitat for various migratory and local birds and is a home for various endangered and threatened species such as marsh mongoose which is endemic to EKW.
EVOLUTION OF EKW AS A WASTE RECYCLING REGION
• At first, the city used to discharge all its effluents into the river Hooghly that instead of draining out the effluents lead to an annual saturation with colloids and solids occasioned by the rains and floods. Furthermore, addition of corpses and dead bodies into the river lead to its acute contamination.
• Thus, In 1857 William Clarke's scheme was adopted that was contrived for passing the sewage to the eastern side of the city which would modify the pollutant levels with time as the number of pumping stations increased. Later, the high population boom caused increased demand for water supply and the gradual filing up of the rain fed water systems became inundated with sewage effluents. Thus, the government pressurized the Kolkata co operation to dispense the rainwater into the circular canals.
• A new system was later adopted in which the city discharged its sewage to the SE river Bidyadhari from there to river Matla and then to Bay of Bengal. Various lock gates and canals controlled the water flow and the sewage was stored in various reservoirs and released only at low tides. Within approximately 10 years, river Bidyadhari started to heavily silt up at a particular lock gate at Dhapa that was used to synchronize the storage and release of storage during low tides. Thus the lock gates had to be opened to save the river but slowly due to heavy siltation, it was pronounces as untreatable and dead. A large area of this Salt Lake was used as a reservoir for the storage of sewage from urban and rural areas.
• First attempt at sewage fed fishery was during 1860s which didn’t turn out to be successful. A fish ghat on the Raja’s Khal was later established during 1872, which lead to flourishing fish markets.
• The first formal attempt at sewage fed aquaculture was done by Mr. Bidhu Bhushan Sarkar and later the land was taken to construct a SWF (Storm Water Flow) canal which lead to the disruption of both the market and the fish canal. However, this discharge of sewage through the canal into the brackish water bodies lead to a reduction in the salinity of water. Hence, over a period of time, the non saline water body gave rise to the carp culture in 1929.
• Subsequently, the adoption of Dr. B.N. Dey’s Outfall Scheme by the local people to start wastewater fed aquaculture helped in the generation of profits and improved the state economy.
MECHANISM OF WASTE WATER TREATMENT IN FISH PONDS
1. PISCICULTURE – WSP (WASTE STABILIZATION PONDS)
ANAEROBIC (PRIMARY)
FACULTATIVE (SECONDARY)
MATURATION (SECONDARY)
• The slow moving canal streams function as anaerobic and facultative ponds, while fishery ponds act as maturation ponds. The Anaerobic character leads to unsightly and smelly canals and Nitrogen and phosphorous get deposited into the pond as sediments. These stabilization ponds help in the removal of B.O.D. and pathogens.
2. INCORPORATION OF EFFLUENTS INTO ALGAL BIOMASS: (secondary aerobic treatment of waste).
3. INCORPORATION OF EFFLUENTS INTO FISH BIOMASS: (Incorporate nutrients and carbon in their body mass).
4. VOLATILIZATION: (some dissolved toxic compounds can evaporate).
MEASURES TAKEN UP BY GOVERNMENT AGENCIES
• Responsibilities of K.M.C. end when the effluents reach to the outfall channels. Thereafter sewage and waste water is drawn into fisheries of EKW by the fishery owners where within few days of detention, biodegradation of organic compounds of sewage and waste water takes place. The Cumulative efficiency in removing B.O.D. (measure of organic pollution) is above 80% and in reducing coli form bacteria are 99.99% on an avg.
• Sewage fed fisheries pond act as solar reactors where organic matter is taken up by the phytoplankton that are further taken up by fishes that check upon the population of phytoplankton and convert waste water to consumable forms.
Salt lake reclamation and Calcutta high court’s verdict
• In 1945, out of 20,000 acres of wetland 18,000 acres were used for sewage fed pisciculture by 350 fisheries. Chief minister Dr. Bhidan Chandra Roy proposed to build a satellite township name SALT LAKE. In Between 1962-1967, nearly 3000 acres of lake was filled up with silt from Hooghly and this area was converted into a major residential area SALT LAKE CITY.
At present only 6500 acres of wetland is left for sewage fed aqua culture and paddy cultivation.
CONCLUSION
EKW aims at:
• conservation of biodiversity;
• improvement of livelihood of local people;
• Management of wetlands under the Ramsar convention guidelines; and
• Establishment and maintenance of resource reuse system through productive activities.