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namely Australia, Namibia and Singapore,
are already drinking treated wastewater, as
are some populations in the US, including in
California, Virginia and New Mexico.
It is usually safe, but public opinion is swayed
by those who refer to ‘toilet to tap’ reuse as a
way to discourage use. Indirect potable reuse
(IPR), whereby treated wastewater is added to
ground or surface sources (where it receives
additional treatment) and eventually ends up
as drinking water, has become increasingly
common (Box 2).
After tertiary treatment, the water is
discharged to a storage reservoir for a
period of six months or more. This level of
treatment seems to assuage public fears
about ‘toilet to tap’ concerns. In reality, a
large proportion of treated and untreated
wastewater ends up being discharged into
a watercourse and used downstream as a
water supply.
Non-potable reuse: industrial, commercial,
recreational and peri-urban agriculture
Local reuse becomes more economically
feasible if the point of reuse is close to the point
of production. Many industrial and commercial
establishments are in need of process
water and can institute better housekeeping
procedures to reduce their dependence on
water consumption and wastewater production,
as well as the associated costs.
Businesses can directly reuse some untreated
wastewater, provided it is of adequate
quality. Good sources include process water
for cooling or heating, and rainwater from
industrial/commercial roof collection or airport
aprons and runways. Industrial symbiosis
is often used to describe partnerships and
cooperation between two or more different
industries to enhance both environmental
performance and competitive capacity by
exchanging and optimising mutual material,
energy and water flows.
BOX 3: SEWAGE-FED AQUACULTURE SYSTEMS OF KOLKATA:
A CENTURY-OLD INNOVATION OF FARMERS
Farmers around Kolkata city in India
developed a technique of using domestic
sewage for fish culture and other agricultural
purposes, almost a century ago.
This technique is widely used to meet the
growing demand for fish in this densely
populated Indian city. The technique is
considered to be unique and is the largest
operational system in the world to convert
waste into consumable products.
Wastewater and urban runoff from
Metropolitan Kolkata (over 13 million
inhabitants) generate about 600 million
litres of sewage per day. Large-scale
usage of sewage for fish culture began in
the 1930s.
Early success of fish culture in stabilised
sewage ponds, which were used as a
source of water for growing vegetables,
provided stimulus for the large-scale
expansion of sewage-fed fish culture
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system. The area under this unique
system of culture peaked at 12 000ha,
but in recent years there has been a steep
decline in the area due to the increasing
pressure from urbanisation.
Currently, the area under the sewage
fed culture system has been reduced to
less than 4 000ha and the poor people
dependent on these wetlands for their
livelihood have been severely affected.
However, even today, a considerable amount
of fish consumed in Kolkata city is produced
from this system.
There are appeals to the government to
declare the existing sewage fed aquaculture
area as sanctuaries and to protect them
from further encroachment by the rapidly
expandin g population of Kolkata city. In
addition, 12 000ha are also cultivated for
growing vegetables.
Source: Extracted from Nandeesha (2002)
October 2018 Volume 24 I Number 8