ENVIRONMENT AND ENERGY
informally in many countries. Reuse in peri-urban areas
offers an opportunity to produce food close to the area
of consumption.
POTABLE WATER REUSE
The use of treated municipal wastewater for drinking is not
quite so common, though well established in some places.
The populations of some countries, namely Australia,
Namibia, and Singapore, are already drinking treated
wastewater, as are some populations in the USA, 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.
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. In the
case of water reuse, this occurs often at a local scale.
By-products of one industry become feedstocks in another.
Similarly, process cooling water may be used for heat
recovery or for productive use. Sometimes, partnerships
share the management of utilities or ancillary services.
The United States Environmental Protection Agency (US
EPA) gives a good account of urban reuse systems that
provide partially treated (fit-for-purpose) wastewater for
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various non-potable purposes, including irrigation of
public parks and recreation centres, athletic fields, school
yards and playing fields, highway medians and shoulders,
and landscaped areas surrounding public buildings and
facilities; irrigation of landscaped areas surrounding single-
family and multi-family residences, general washdown,
and other maintenance activities; irrigation of landscaped
areas surrounding commercial, office, and industrial
developments; irrigation of golf courses; commercial uses,
such as vehicle washing facilities, laundry facilities, window
washing, and mixing water for pesticides, herbicides,
and liquid fertilisers; and ornamental landscape uses and
decorative water features, such as fountains, reflecting
pools, and waterfalls.
In dual distribution systems, the partially treated wastewater
is delivered to customers through a parallel network of
distribution pipes separate from the community’s potable
water distribution system. The reclaimed water distribution
system becomes a third water utility, in addition to
wastewater and potable water. Reclaimed water systems
are operated, maintained, and managed in a way that is
similar to the potable water system.
Direct use of treated municipal wastewater has been
practised for some time. Supplying nutritionally adequate
and safe food to city dwellers poses a substantial
challenge. Peri-urban agriculture offers one solution but
requires adequate water. Municipal wastewater is often
(usually informally) used without treatment, resulting
in serious health risks for both farmers and those who
consume the food. Social customs and diets dictate how
risky this practice is.
MANAGING URBAN RUN-OFF
Climate change adaptation seeks to lower the flood risks
associated with extreme rain events, but if developed
in synergy with urban development, it can also address
some of the problems associated with urban wastewater
management. Cities are increasingly concerned with the
effects of climate change, which include higher risks
of flooding and raised temperatures, combined with
increasing demands for safe drinking water supplies.
Rainwater in the form of surface runoff can contribute to
cities’ water balance and be collected to create attractive
recreational areas. PA
It is better to restrict the
discharge of hazardous
substances to sewers,
particularly those that render
the wastewater difficult to treat.
February 2018 Volume 23 I Number 12