IWRA World Water Congress 2008 Montpellier France
6. Water Conservation and Demand Management
Below 25 years old.
Research Assistant, Centre for Built
Environment and Convenor - Youth Water Forum, Kolkata, India.
Aquaculture, Photosynthesis, Resource Recovery, Urban Agriculture, Sustainability
AbstractECOLOGICAL RECYCLING OF
WASTEWATER FOR URBAN FOOD PRODUCTION
Ms. Arunima Guha
Convenor, Youth Water
W3R 4/7 Phase VII, Golfgreen, Kolkata 700 095, India
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
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.
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
(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.
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
(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