Uso di risorse idriche non
convenzionali in agricoltura: un'alternativa imprescindibile
Antonio Lopez, CNR
IRSA, Bari
Water is an
increasingly scarce and valuable resource. Of principal concern is
our failure to recognize and accept that there is a finite supply of
water. The consensus is that the growing water scarcity and misuse of
freshwater pose serious threats to sustainable development.
In the coming years
the increase in water demand will likely be driven by population
growth (increasing the demand for drinking water supply and
agricultural production), changes in food preferences (change in food
habits toward richer and more water demanding diets), economic growth
(raising the water demand for industrial production and power
generation, including bioenergy). In addition, as society becomes
more aware and concerned about the potential impacts of human
activities on the environment, the demand for water to support
aquatic ecosystems and in-stream water uses will also rise (resulting
in environmental regulations such as establishing minimal flows and
levels for streams, or more restrictive water quality regulations).
Other factors that
could reduce the stock of available water resources are weather and
climate. Although the forecasts on regional scale are subject to
considerable uncertainty, it is expected that climate changes and
rising sea levels in coastal areas will intensify negatively
affecting quali-quantitatively local water resources.
Competition among
agriculture, industry and cities for limited water supplies will
obviously intensify as consequence of all the above factors.
As for agriculture,
taking into account that more than two-thirds of the water withdrawn
from the earth's rivers, lakes and aquifers is used for irrigation,
to meet the future challenge of reduced water availability the use of
alternative or unconventional water resources will play an ever more
important role in satisfying the increasing water requirements
particularly in arid and semi-arid regions, as most of the
Mediterranean countries.
It is quite
difficult to make a classification of unconventional water resources.
Water quality is the most important factor dealing with
unconventional water resources: quality is a complex factor since
there are many water quality parameters which vary with continuity.
Very often, not water quantity, but inadequate water quality and
water transport energy are limiting factors (“Water-Energy Nexus”).
Two major categories
of unconventional water resources can be identified, the first
including waters with high organic matter and microorganisms content
(such as municipal wastewater) and the second one including waters
with high saline concentration (such as sea and brachisk water, some
industrial and agro-industrial wastewater, etc.).
In many
Mediterranean countries municipal wastewater reuse has been practiced
for a long time and actually represents the most relevant use of
unconventional resources. Particularly in the absence of
environmentally safe recipients for the effluents, irrigation is
regarded as a sanitary mean of disposal, which makes wastewater
treatment economical. The nutrients content of municipal effluents is
also appreciated. Water scarcity has driven farmers, engineers,
scientists and government officers to collaborate in developing wide
scale wastewater reuse operations and associated equipment and
control methodologies.
As for desalination
of seawater and brackish water, it is progressively becoming a
technologically and economically available solution to water scarcity
particularly as a source of drinking water. In fact, desalination for
drinking purposes is a practice widely implemented. On the contrary,
for many countries, the current costs of such technology is
unaffordable for irrigation purposes.
In
any case, the choice of the most appropriate alternative water
resource is clearly a site-specific question to be managed carefully
comparing not only the cost-effectiveness of alternative option but
even the local socio-economic context.
Photo Credits: "Reverse osmosis desalination plant" by James Grellier - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons
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