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ECOLOGICAL RECYCLING OF WASTEWATER FOR URBAN FOOD PRODUCTION

Congress: 2008
Author(s):
Below 25 years old. Research Assistant, Centre for Built Environment and Convenor - Youth Water Forum, Kolkata, India.

Keyword(s): Aquaculture, Photosynthesis, Resource Recovery, Urban Agriculture, Sustainability
Article:
AbstractECOLOGICAL RECYCLING OF WASTEWATER FOR URBAN FOOD PRODUCTION Ms. Arunima Guha Convenor, Youth Water Forum W3R 4/7 Phase VII, Golfgreen, Kolkata 700 095, India e-mail (arunima_g83@rediffmail.com) 1. Introduction Asia, the largest continent with largest population is undergoing accelerated urbanisation with economic growth and globalisation. There were 202 cities each with one million population in 2000 and some have more than 10 million each. By 2015 out of 26 largest citie, 17 will be located in Asia. These cities consume resources and produce waste both liquid and solid. The disposal has become a problem involving management, money, manpower and infrastructure. On the other hand about 2 billion people have no access to adequate water and sanitation. In the conventional water supply and sanitation plan for cities, use of wastewater is neglected. The World Health Organisation about two decades ago suggested reuse of wastewater for aquaculture and agriculture rather than expensive wastewater treatment method. Wastewater is being used in Asia for a longtime in various ways. Reuse or recycle of water, often mixed with sewage effluent has high potentiality for aquaagriculture. 2. Kolkata Examples Kolkata is one of the pioneers in utilisation of wastewater for fish and vegetable production. It has the largest recycling district in the world with indigenous wastewater treatment in anaerobic facultative pond system. Kolkata Municipal system produces 750 million litre of wastewater daily. There are several ponds 140 in number in the east Kolkata wetlands. The pond unit, each of lagoon type is to facilitate natural aeration and with a shallow depth of about 1.5m to allow sufficient sunlight to each its bottom to promote growth algae and photo- synthetic oxygen. This is fitted with inlet and outlet sluice boxes for periodical wastewater sewage feed exchange from its nearest drainage outfall and canals. Using aquatic plant like water hyacinth and duckweed dirt and some metals are removed and it is also purified by exposure to sunlight and aeration. The high productivity of these fish ponds (7-8 ton/ha/year) are mainly due to rich nutrient element in wastewater like nitrogen, phosphorous potash etc. It generates abundant quantity of algael photo-synthetic oxygen found to be 0. mg/l at the inlet point to 15-20 mg/l at the outlet zone. The bio-chemical oxygen demand (BOD), a critical parameter of wastewater quality is 150-180 mg/l of the inlet to about to about 15-32 mg/l at the outlet. Another important aspect of Kolkata’s waste recycling is the integration of aquaculture with agriculture especially green vegetables in urban food production system. Solid waste of the city (2500 ton) is dumped near the wetland. Poor people separate paper, plastic and metals and the waste is naturally composted. The natural compost is used in the production of good quality of vegetables 150 mt/day without adding any fertiliser. The nutrient – rich sewage – fed waste water is used for irrigation and often sludge of wetland fisheries is used. In Southeeast Kolkata a fishermen’s cooperative has taken lease of 15 ponds, 50 ha in area from Kolkata Port Trust where 25 million litres of sewage – fed waste water is treated in the same indigenous process. The area has been declared as nature park. The management is by the cooperative society without any external help. The recycling of wastewater for aquaculture in wetlands in other municipal areas and its coordination with irrigation and agriculture is being advocated in within metropolition Kolkata. Such projects with stakeholder participation – fishermen, farmers, State and Municipal governments and village councils is known as community Based Wetland Ecosystem first introduced in 1995 in Titagarh, a northern municipality. This is also known as Integrated Resource Recovery project. Titagarh, an industrial town has an old sewage treatment plant with a capacity to treat 9.08 million litres of sewage/day (mld) and a new stabilisation tank has been built in nearly Bandipur with capacity of 14.10 mld. This includes waste water treatment and reuse for agriculture. The integrated complex is leased out to 110 farmers who produce about 3000 tons of vegetables and stabilisation tanks to local fishermen which yields 7 tons per ha per year. 3. Lessons learned There are several lessons learnt from Kolkata examples (a) Wastewater can be a part of overall water resource plan especially in cities. It has many benefits, one of them is to replace freshwater supply for irrigation, aquqculture, industrial water use, landscape gardening, horticulture etc. (b) Instead of expensive wastewater treatment measures, indigenous technology can purify the waste water, with exposure to sunlight and use of aquatic plants. (c) Sewagefed wastewater can be utilised by recycle for production of fish and such water can be used with sludge and natural compost for production of vegetables. Increasingly such practice is being used in many countries in Asia, Africa and Latin America. (d) It provides employment and poor farmers and fishermen can organise themselves into cooperative society and it can be a best practice with multiple stakeholders. (e) It improves environment with more oxygen and controls pollution. (f) It is cost effective process. It eliminates transport, marketing and other costs. (g) It can be a tool of good land management, creates a buffer zone of green and blue between urban and rural areas and leads to sustainable development. (h) Health and hygiene aspects will be a lesson after necessary regulation, contral and standards.
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