Africa Water, Sanitation & Hygiene 2014 Sept - Oct Vol. 9 No.5 | Page 16

Water in the Post 2015 Development Agenda

of the liquid or water-carried domestic, municipal
and industrial wastes, together with such
groundwater, surface water and storm water as may
be present.
• Population growth, rapid urbanization, and
increasing water supply and sanitation provision will
all generate increased problems from wastewater
pollution.
• It has been estimated that the total global volume
of wastewater produced in 1995 was in excess of
1,500 km3.
•

There is the understanding that each litre of
wastewater pollutes at least 8 litres of freshwater,
so that on this basis some 12,000 km3 of the
globe’s water resources is not available for use each
year. If this figure keeps pace with population
growth, then with an anticipated population of
9 billion by 2050, the world’s water resources would
be reduced by some 18,000 km3 annually.

•

At present, only about a tenth of the domestic
wastewater in developing countries is collected and
only about a tenth of existing wastewater treatment
plants operates reliably and efficiently.

• Some of the damage associated with inadequate
handling of wastewater are:
- increased direct and indirect costs caused by

-

-
-

increased illness and mortality
higher costs for producing drinking and industrial
water, resulting in higher tariffs
loss of income from fisheries and aquaculture
poor water quality, which deters tourists,
immediately lowering income from tourism
loss of valuable biodiversity
loss in real estate values, when the quality of the
surroundings deteriorates: especially important for
slum dwellers where housing is the primary asset.

•

Untreated sewage affects over 70% of coral reefs,
precious habitats are disappearing and biodiversity
is decreasing, fishing and agricultural potential are
being lost, while poor water quality is reducing
income from tourism and the value of real estate.

• The global burden of human disease caused by
sewage pollution of coastal waters has been
estimated at 4 million lost person-years annually.
•

In March 2003, the World Panel on Financing Water
Infrastructure estimated that US $56 billion was
needed annually for wastewater treatment in order
to achieve the target on sanitation.

•

In the State of Mexico (Mexico), wastewater is
generated approximately at the rate of 30 m3 per
second (m3/s), about 19% of which is directly
discharged without any kind of treatment.

Purifying Water with Nanotech
Members are working on ways to make water potable
By Kathy Pretz

One of the Grand Challenges for Engineering set forth
by the academy aims to develop technology that will make
polluted water potable.
It’s not that the world doesn’t have enough water. Globally,
water is abundant, but most of it is in the oceans, where
it’s unsuitable for drinking without expensive desalination.
Another problem for some developing countries is that
contaminated drinking water contains bacteria and other
pollutants. The application of nanotechnology to purify
water is the focus of many papers presented at IEEE
conferences and published in the IEEE Xplore Digital
Library. Two are described here.

When water molecules [red and white] and sodium and chlorine ions [green and
purple] in saltwater encounter a sheet of graphene with holes of the right size
[center], the water passes through from right to left, but the sodium and chlorine from
the salt are blocked. Image: David Cohen-Tanugi

A

bout 1 of every 6 people around the world has no
adequate access to water, and more than twice that
number lack basic sanitation, for which water is essential,
according to the U.S. National Academy of Engineering.
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Africa Water, Sanitation & Hygiene • September - October 2014

Jeffrey C. Grossman, MIT associate professor of power
engineering, and his graduate students David CohenTanugi and Shreya Dave are developing a filtration
material made of a sheet of nanoporous graphene.
The holes in the graphene—a one-atom thick form of
carbon—are small enough to block salt ions while letting
water molecules through. Smithsonian magazine called this
nanoporous form of carbon one of the top five surprising
scientific milestones of 2012.
Cohen-Tanugi presented their paper, “Water Desalination