NATURAL WASTE WATER TREATMENT
AND ITS
IMPACT ON ENVIRONMENTAL LIFE
Giuseppe Alonzo, Claudio De
Pasquale
ITAF Dept. – Faculty
of Agronomy –
90128 Palermo, Italy
alonzo@unipa.it, claudiodep@hotmail.com
The total volume of water on the Earth is vast, 1.4 billion km3 (1).However, the proportion of this
that is fresh and reasonably accessible is less than 1%, at 11 million km3.
There is, therefore, no shortage of water on this planet, just a lack of
accessibility to fresh water at some places at some times. Agriculture is the
largest user of freshwater, accounting for around three quarters of the entire
global consumption (2). However,
agriculture does not `consume' water in the conventional sense, since
(globally) insignificant amounts of water are actually bound up in the
commodities produced. The large amount of water used by
agriculture are released through evaporation, which is eventually
recycled as rainfall. Agricultural use of water is, therefore, usually much
more environmentally clean than domestic or industrial uses, where degradation
of the water quality makes its reuse difficult without expensive treatment. It
should be noted that the preceding estimates of global water resources and their
consumption by agriculture are at best educated guesses (3) and will remain so until more consistent schemes are adopted
for the collection, quality control and interpretation of hydrological data.
Even with the uncertainties in global water use, agriculture remains by
far the largest user of freshwater. It has been estimated that global demand
for food, fuel and fibre provided by agricultural crops will increase by a
factor of between two and six during the next two generations (4). Currently, one sixth of the human
population goes hungry on a regular basis and 1 billion people do not have
access to clean water (5). Two
hundred and thirty million people are living in some 26 countries considered to
be water scarce. Countries are normally considered to be water scarce when
annual internal renewable water resources are less than 1000 m3 per
capita per year. By 2020, the number of water scarce countries is likely to
approach 35. Where scarcities loom, competition between industrial, domestic
and agricultural water users intensifies and, typically when supplies tighten,
agricultural users lose out.
Moreover, the longer term threat of climate change, as a result of the
build up of greenhouse gases, casts ominous shadows over future water budgets (6).
The global statistics on water resources and forecasts of future needs
have prompted many predictions of a crisis in the availability of water
resources. It is argued in this paper, however, that this crisis can be averted
by managing water resources more efficiently and that this is best achieved
within a framework of integrated catchment management
(ICM). It is also argued that adopting programmes of ICM can be a key step towards sustainable agricultural
development, particularly in semi-arid areas.
Unfortunately, there is little consensus on the definitions of ICM and sustainable agricultural development (SAD). ICM can be defined as the co-ordinated planning and
management of land, water and other environmental resources for their
equitable, efficient and sustainable use at the catchment
scale. There have been many attempts to define sustainability in absolute terms
and, since the Brundtland Commission's definition of
sustainability in 1987, at least 70 more definitions have been constructed,
each different in subtle ways, each emphasising different values, priorities
and goals (7). This said, a
definition of SAD that has gained a reasonable level of acceptance is the one
proposed by the FAO (1990), whereby SAD is defined as
the management and conservation of the natural resource base and orientation of
technological and institutional change in such a manner as to ensure the
attainment and continued satisfaction of human needs for present and future
generations. Such sustainable development conserves land, water, plant and
animal genetic resources, is environmentally sound, technically appropriate,
economically viable and socially acceptable.''
To many institutions and agencies, ICM is
solely an improvement in catchment planning, whereby
relevant central institutions work constructively and in collaboration.
However, for sustainable agricultural development in a given catchment to be achieved, other stakeholders must
participate in the decision-making and implementation processes.
Major features of ICM programmes, that are
beginning to show positive results, include: an overall natural resource
management strategy that clearly defines the management objectives, a range of
delivery mechanisms that enable these objectives to be achieved and a
monitoring schedule that evaluates programme performance; decision-making and
action take place at the basin-wide, regional and local levels.
Wherever possible, local communities are involved both in decision
making and in resulting activities; mechanisms and policies are established
that enable long-term support to programmes of environmental recovery.
To protect our groundwater and rivers from impurities, waste water has
to be cleaned properly. Our modern sewage treatment plants are expensive,
inefficient, and not very effective.
Natural waste water treatment features small decentralized sewage
treatment facilities which use the natural purifying characteristics of marsh
plants. These facilities are operating successfully in
The use of wetlands for treatment can significantly lower the cost of
wastewater treatment because the systems rely on plant and animal growth
instead of the addition of power or chemicals. Also, the plant communities
present in the wetlands naturally adjust to changing water levels and water
quality conditions by shifting dominance to those species best adapted to
growing under the new conditions.
Wetlands mean different things to different people. All wetlands are
highly productive systems and support high biodiversity. Like other ecosystems,
wetlands perform
many ecological functions. The hydrological, biological and biogeochemical
functions impart them various values. However, it is important to recognize
that not all wetlands are similar in their function.
Nutrient transformation is one of the major wetland functions which is translated into their value for improving the quality of
wastewater. Wetlands are now constructed worldwide, designed especially for
secondary and tertiary treatment (8).
They offers many advantages over the traditional
oxidation pods.
Aquatic plant are an essential component of
constructed wetlands, and contribute to the nutrient transformation by abetting
in the physical, chemical, and microbial process besides removing nutrients for
their own growth (9). They offer
mechanical resistance to the flow, increase the retention time and facilitate
settling of suspended particulates. They improve conductance of the water
through the soil as the roots grow and create spaces after their death. The plant add organic matter into the water as well as providing
a large surface area for microbial growth. Many aquatic plants actively
transport oxygen to the anaerobic layers of the soil and thus help in oxidation
and precipitation of heavy metals in the root.
One of the main considerations in promoting the use of constructed
wetlands is their relatively low cost for construction, operation and
maintenance, relative to the conventional treatment systems.
Estimates of the land requirement for treating per capita domestic waste
based on the nutrient loading rates vary from 10 to 20 person
per hectare. The land prices is one of the major deterrent.
It is often argued that the wetland systems are more suitable for the
tropical/subtropical regions, because of high temperature permitting growth
throughout the year. The source and quality of the wastewater are also
important factors which should be seriously considered when recommending
constructed wetlands in developing country.
References
1. Maidment,
D.R., 1992. Handbook of Hydrology,
2. Shiklamanov,
I.A., 1991. The world's water
resources. In: Proc. Int. Symp. to commemorate 25 years of IHP.
UNESCO/IHP, pp. 93±126.
3. Rodda,
J.C., 1995. Guessing or assessing the world's water resources. J. IWEM 9, 360-368.
4. Penning de Vries,
F.W.T., Rabbinge, R., 1997.
Potential and attainable food production in different regions.
Phil. Trans. Roy. Soc. London, B.
5. Serageldin,
Environment Conf, IFPRI,
6. Postel,
S.L., 1993. Water and agriculture.
In: Gleick, P.H. (Ed.),
Water in Crisis: A Guide To The World's Fresh
Water Resources,
7. Pretty, J.N.,
1995. Regenerating agriculture: policies and practice for sustainability and
self-reliance, Earthscan,
8. Kadlec,
R . and Brix,
H. ,1995. Wetland Systems for water pollution control. Wat. Sci.
Tech., 32
9. Brix,
H. 1997.Do macrophytes play role in constructed
treatment wetlands. Wat. Sci. Tech., 35