ENVIRONMENT AND ENERGY
While adequately treated wastewater is a resource that
can be used to address water supply shortages, the
level of wastewater treatment directly affects ambient
water quality, with implications on water availability.
GLOBAL WASTEWATER PRODUCTION AND TREATMENT
Although data on wastewater generation, collection, and
treatment is grossly lacking, it is clear that, worldwide, the
vast majority of wastewater is neither collected nor treated.
Furthermore, wastewater collection per se is not synonymous
with wastewater treatment. In many cases, collected
wastewater is merely discharged directly into the environment
without any treatment.
Agricultural run-off is almost never collected or treated, so
that metrics for these types of wastewater flows are practically
non-existent. The Aquastat database of the Food and Agriculture
Organization of the United Nations (FAO) estimates global
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freshwater withdrawals at 3 928km³ per year. An estimated
44% (1 716km 3 per year) of this water is consumed, mainly
by agriculture through evaporation in irrigated cropland. The
remaining 56% (2 212km 3 per year) is released into the
environment as wastewater in the form of municipal and
industrial effluent and agricultural drainage water.
A country’s level of industrial and municipal wastewater
treatment is generally a reflection of its income level. On
average, high-income countries treat about 70% of the
wastewater they generate, while that ratio drops to 38%
in upper middle-income countries and to 28% in lower
middle-income countries. In low-income countries, only 8% of
industrial and municipal wastewater undergoes treatment of
any kind (Sato et al., 2013). This exasperates the situation for
the poor, particularly in slums, who are often directly exposed
to wastewater due to a lack of water and sanitation services.
These estimates support the often-cited approximation that,
globally, it is likely that over 80% of wastewater is released to
the environment without adequate treatment (WWAP, 2012;
UN-Water 2015a).
There also appears to be significant variability across different
regions. In Europe, 71% of the municipal and industrial
wastewater generated undergoes treatment, while only 20%
is treated in the Latin American countries. In the Middle East
and North Africa (MENA), an estimated 51% of municipal
and industrial wastewater is treated. In African countries, the
lack of financial resources for the development of wastewater
facilities is a major constraint in managing wastewater, while
32 out of 48 sub-Saharan African countries had no data
available on wastewater generation and treatment.
The treatment of wastewater and its use and/or disposal in
the humid regions of high-income countries (for example
North America, northern Europe, and Japan) are motivated by
stringent effluent discharge regulations and public awareness
about environmental quality. The situation is different in high-
income countries in drier regions (for example parts of North
America, Australia, the Middle East, and southern Europe),
where treated wastewater is often used for irrigation, given
the increasing competition for water between agriculture and
other sectors.
The persistent expansion of sewerage and the consequent
increases in wastewater volume generate pressure on existing
treatment facilities, and in some cases, can lead to suboptimal
performance. Even when wastewater is collected and treated,
the final quality of the wastewater discharged may be affected
by poor operation and maintenance, as well as overflow during
The release of untreated wastewater from expanding
human settlements and increasing industrial production
generates physical, chemical, and biological pollution,
impacting both human and environmental health.
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October 2017 Volume 23 I Number 8