URBAN WATER RE-USE
resources are limited, delicate, and very unequally distributed across the
planet. During the second half of the 20th century, water demand increased
dramatically (Vargas-Yáñez et al., 2009). In many countries, water use
is approaching the limit of available resources. The water supply is endangered
by over-exploitation of renewable underground water (generating salt-water
intrusion) and the exploitation of non-renewable resources (including fossil
water) (Pereira & Paulo, 2004). Climate changes are expected to have even more
negative impacts. Agriculture, industry and domestic wastewater are making
clean water more scarce and intensifying pollution of water resources both
surface water and groundwater (UN, 2006; UN-Water, 2006, 2007). Water resource
management is increasingly reliant on techniques for augmenting the limited
natural water supply, such as, desalination, water reuse, rainwater harvesting,
enhanced groundwater recharge and inter-basin transfers (UN, 2006).
wastewater can be thought of as a ‘new/old’ water resource, which can be added
to the general water balance of a region. For example, it can replace potable
water for irrigation or for other purposes besides drinking. Doing so relieves
some of the demand on water resources (Asano, 1998). Thus, the benefits of
treated wastewater are manifold, especially to agricultural countries facing
chronic water shortage (Sipala et al., 2003). It’s estimated that global
freshwater withdrawals are around 4000 km³ per year: 44% of this water is
consumed, mainly by agriculture through evaporation in irrigated cropland. The
remaining 56% is released into the environment as wastewater in the form of
municipal and industrial effluent and agricultural drainage water (FAO’s
Given that half of the freshwater released into
the environment is released as wastewater, it makes sense to ask how much of it
is treated before being released?
On average, high-income countries treat about 70%
of the wastewater they generate. That figure drops to around 30% in middle
income countries. In low-income countries, only 8% of industrial and
municipal wastewater undergoes treatment of any kind (Sato et. al,
2013). This exacerbates the situation for in poor areas, particularly in slums,
where people are often directly exposed to untreated wastewater due to a lack
of water and sanitation services (UN-Water 2017).
The above 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, UN-Water 2017RJ1 ).
Based on data from
Sato et al. (2013), cited in the UN- Water report 2017
What is the environmental impact of
inadequately treated wastewater?
The discharge of untreated
wastewater into seas and oceans partially explains why de-oxygenated dead zones
are rapidly growing. An estimated 245,000 km2 of marine ecosystems
are affected, with consequences for fisheries, livelihoods, and food chains
(Corcoran et al., 2010; UN-Water 2017). Moreover, increased discharges
of inadequately treated wastewater are contributing to the further degradation
of water quality in surface and groundwater as water pollution critically
affects water availability. Water quality degradation, it takes the form of organic
pollution coming from wastewater that can have severe impacts on inland
fisheries, food security and notably livelihoods of poor rural communities.
Severe organic pollution already affects around one-seventh of all river
stretches in Africa, Asia and Latin America and has been steadily increasing
for years (UNEP, 2016).
Household sanitation facilities
globally have improved markedly since 1990. However, waste still poses
significant public health risks, due to poor containment, leakages during
emptying and transport, and ineffective sewage treatment. It is estimated that
only 26% of urban and 34% of rural sanitation and
wastewater services are managed with a good control and measures safety that
prevent human contact with excreta along the entire sanitation chain (Hutton
and Varughese, 2016)
Worldwide, the annual capital
expenditures on water infrastructure and wastewater infrastructure by utilities
have been estimated at US$100 billion and US$104 billion, respectively (Heymann
et al., 2010; UN-Water 2017).
The benefits to society of managing human waste are considerable, for
public health as well as for the environment. For every US$1 spent on
sanitation, the estimated return is US$5.5 (Hutton and Haller, 2004; UN-Water
If things carry on this way, the
risks will of course intensify. The question is how we can effectively limit
and reduce pollution by wastewater. The challenge is complex because the
concerns are varied and wide-ranging. Human health and preservation of the
environment are priorities, but they will have to be pursued in the context of
local regulatory frameworks, territorial constraints, and limited funding of wastewater
Water reuse after advanced
wastewater consists in decanting the particulate pollutants and extracting the
dissolved elements via many steps of treatments. Depending of the number and
the kind of steps the level of treatment pass from a simple one, primary
treatment, to a secondary one characterized by with physicochemical and
biological interventions. If the process includes disinfection,
denitrification, phosphorus removal steps the treatment is classified as a
can be classic solutions or more innovative processes, extensive or intensive,
and involving ecological engineering. Tertiary treatment is an advanced level
of wastewater treatment that is gaining importance. It is important to note that, of all the
wastewater produced worldwide, only a very small fraction actually undergoes
tertiary treatment and rarely adopted Because of its higher cost and
technically more difficult and managing authorities are looking for low cost
and low labor requiring technologies. Nevertheless, more research and
development programs are conducted worldwide looking for innovative solutions
of wastewater treatment optimizing cost and environmentally well adapted.
Marrakech urban wastewater treatment
Recycling wastewater components
There is another major upside to
wastewater treatment, besides water reuse. A surprising range of resources can
be recaptured in the process, including green energy, bio-plastics and other
organic materials. These by-products can be beneficial for agriculture,
industry and a variety of urban uses. In
the global context of resource scarcity, harnessing them not only limits the
environmental impact of wastewater discharge, it also recoups some of the
financial investment in wastewater treatment.
To give one example, phosphorus is
widely used in the manufacture of fertilizers. Extractable phosphorus resources
are predicted to become scarce or exhausted in the next 50 to 100 years (Steen,
1998; Van Vuuren et al., 2010). Phosphorus recuperation from wastewater is suitable
and increasingly attractive alternative. An estimated 22% of global phosphorus demand
could be satisfied by recycling human urine and faeces worldwide according, to Mihelcic
et al., 2011.
Recovering phosphorus in this way
requires advanced technology. Scaling this technology to the required level is
undoubtedly a challenge, but significant progress has been made in recent years.
The payoffs are potentially great. Phosphorus is one example and this recovery
process may apply also for other nutrients.
Recycling nutrients or extracting
energy from wastewater constitute real opportunities for income generation, and
enlarges the resource base available to poor households (Winblad and
Simpson-Hébert, 2004). An example is composting toilets. These facilities offer
a low-cost route to increased agricultural productivity and improved nutrition.
At the same time, they can reduce the health and environmental risks from open
defecation, Kvarnström et al., 2014.
Re-use of treated wastewater has grown
significantly over the past decade and reduced significantly the pressure on
water resources in some regions. However, the reuse is associated with sanitary
and technical constraints depending on the targeted users: agricultural
irrigation, irrigation of parks and golf courses, industrial process or cooling
systems, cleaning of soils or roadways, aquifer recharge.
Municipal water demand corresponds to 11% of
global water withdrawal Out of this, quarter of this volume is consumed and the
rest is discharged as wastewater, representing 330 km³ per year (Mateo-Sagasta et
al., 2015) This could potentially irrigate 40 million hectares (with
approximately 8,000 m³ per hectare) (Mateo-Sagasta et al., 2015), or 15% of all
There is no comprehensive inventory of the amount
of treated or untreated wastewater used in agriculture. Estimates of the total
area that is being irrigated with raw and diluted wastewater are likely to
range between 5 and 20 million hectares, with the largest share probably in
China (Drechsel and Evans, 2010), which translates to between 2 to 7% of the
world’s total irrigated area (UN-Water, 2017).
The reuse of treated wastewater for irrigation is
not well controlled because of the inadequate wastewater treatment and the
resulting probable large-scale water pollution: many authors, among them
Drechsel and Evans, 2010; revealed that the area irrigated with unsafe
wastewater is probably ten times larger than the area using treated wastewater.
Due to the differences in the current levels of
wastewater treatment overall, the efforts required to achieve SDG Target 6.3
(related to wastewater management) will place a higher financial burden on
low-income and lower middle-income countries, putting them at an economic
disadvantage compared to high-income and upper middle income countries (Sato et
al., 2013; UN-Water 2017). If the upstream part of sanitation and water has
benefited from the dynamics of the UN Millennium Development Goals and is still
a matter of concern, collection and treatment-reuse should be placed at the
forefront of the international political agenda.
AQUASTAT, n.d.b. Food and Agriculture Organization of the United
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Corcoran E., Nellemann C., Baker E., Bos R., Osborn D., Savelli H.,
2010. Sick Water? The central role of wastewater management in sustainable
development. A Rapid Response Assessment. United Nations Environment Programme,
UN-HABITAT, GRID-Arendal. www.grida.noDrechsel P. & Evans A. E. V., 2010.
Wastewater use in irrigated agriculture. Irrig Drainage Syst (2010) 24:1–3.
Hutton G. and Varughese M., 2016. The Costs of Meeting the 2030
Sustainable Development Goal Targets on Drinking Water, Sanitation, and
Hygiene. World Bank, Washington, DC. © World Bank. https://openknowledge.worldbank.org/handle/10986/23681
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Lautze J., Cai X., and Matchya G. 2014. Water Productivity. In: Key
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Lautze, J. Ed. Routledge: New York, pp. 57-73.
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and sludge production, treatment and use. In Wastewater: Economic asset in an
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James R. Mihelcic ,Lauren M. Fry , Ryan Shaw, 2011. Global potential of
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Pereira, L.S., Paulo, A.A., 2004. Recursos hídricos,
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e Sociedade, Ed. Piaget, Lisboa, pp. 47-62.
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Sipala, S., G. Mancini and F.G.A.Vagliasindi. 2003. Development of
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van Vuuren D.P.‚ Bellevrat E.‚ Kitous A.‚ Isaac M.,
2010. Bio-energy use and low stabilization scenarios. The Energy
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Vargas-Yáñez M. , Moya F., Tel E., García-Martínez
M.C., Guerber E., Bourgeon M., 2009. Warming and salting in the
Western Mediterranean during the second half of the 20th century:
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WinbladU. and Simpson-Hebert M., 2004. Ecological Sanitation – Revised
and enlarged edition. Stockholm Environment Institute, Sweden
RJ1Interesting and alarming
RJ2I wondered if some of these
UN-sourced facts and figures could be collected into a separate text box as
bullet points. That way, the information would be highlighted and they wouldn’t
get in the way of the main narrative.