Environmental Engineering Reference
In-Depth Information
opening the loop would be felt decades later. One wonders what further unpleasant effects
of overexploitation of other resources are going to manifest. Unless, of course, we turn
around and see things in an interconnected manner as they are in reality.
The focus is then directed to the use of modern water puriication techniques like the
use of nanoparticles, or nanoparticle-impregnated membranes for reverse osmosis, or
nanoilms for capture of fog to condense water in arid regions, or for capture of fertilizers
that enter water ways causing immense environmental problems. The simple questions
that need to be asked is what materials are used to make these nanoparticles, how much
energy is required to make these nanoparticles, and what happens to the nanoparticles
during and after use? Let us take the example of silver nanoparticles that are used in water
ilters (Sumesh et al. 2011). Wet chemistry is one of the methods used for making silver
nanoparticles. In this process, a silver salt is reduced by using a reducing agent along with
a colloidal stabilizer. The wet process itself may not involve any energy consumption but a
large amount of energy is required to make the silver salts, the reducing agent, and the col-
loidal stabilizer. And the purity of these salts has to be high! This adds to a higher level of
energy consumption, and as mentioned earlier, most of the power produced in this world
is from unsustainable sources. The other issue is the dificulty in extracting the silver
nanoparticles after use. This is, without a doubt, going to be dificult and energy intensive.
The extraction of silver nanoparticles would be essential as silver is something that cannot
be regenerated and one has to follow the closed cycle when using silver nanoparticles. The
use of nanoparticles in membranes that attract water molecules and repel dissolved salts
and other contaminants is something that is gaining importance (Lind et al. 2010), and
such membranes are reported to more than halve the energy consumed in reverse osmo-
sis. The very making of these membranes involves considerable steps that consume energy
during the process and for making the raw materials used for making these membranes.
The reverse osmosis process itself still involves signiicant energy, making this process
an open one and thus not sustainable. This is even without considering the disposal and
loss of materials used in making these membranes that cannot be replenished. Thus, it is
essential that even if we develop technologies that purify water, it is essential that they are
themselves closed cycle, where the recovery or materials that cannot be replenished and
use of energy sources that are sustainable are essential. This philosophy is valid for any
product to make it sustainable. We would like to close the chapter by making the state-
ments “Science without sustainability and sustainability without science are both mean-
ingless” and “sustainability is of primary importance; eficiency and power output is of
secondary importance.”
References
Fukuoka, M. (1978),
One Straw Revolution
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Gilbert, N. (2009), The disappearing nutrient.
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Kailas, S.V., Mani, M., Dravid, Y., Umarji, V. (2011), Closing the cycle—Sustainability in natural
water systems and agriculture.
Ground Report India
, special issue on
Water & Agriculture
1(2),
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Kumarappa, J.C. (1957),
Economy of Permanence
. Bhargava Bhushan Press, Varanasi.
Lind, M.L., Suk, D.E., Nguyen, T.-V., Hoek, E.M.V. (2010), Tailoring the structure of thin ilm nano-
composite membranes to achieve seawater RO membrane performance.
Environmental Science
and Technology
44(21), pp. 8230-8235.
