Environmental Engineering Reference
In-Depth Information
19.13.1
Wastewater treatment
The decrease in fresh water due to global warming, drought, and various other factors has increased the need for waste-
water treatment especially in most of the underdeveloped countries. Most of the diseases that occur in children are mainly
due to the uptake of contaminated water having many harmful pathogenic microbes [110-114]. Wastewater treatment
follows a series of steps, among which one of the major steps is the destruction of bacteria and other pathogenic organisms
found in wastewater [115]. The commonly used technique for this step is the use of ultraviolet (Uv), light chlorine, and
other halogens [116]. There is a rising concern regarding toxicity associated with the use of chlorine in water treatment.
The ammonium ion is another major contaminant in drinking water. The presence of this ion decreases the dissolved
oxygen in water and reduces its toxicity as the ammonium ion is toxic to most fish species [117]. Water treatment also
involves the substitution of these ions by biologically suitable ions, for example, Na + , K + . Certain studies involve evalu-
ating the property of synthetically and naturally produced zeolite, metal ions like Ag + , and polymer films as effective anti-
bacterial agents [83, 118-124]. The larger surface area of NPs enables them to be more reactive, and hence they have the
ability to directly react with contaminants more effectively [125, 126]. Around the twentieth century nanofilters were
developed, which were very useful in eradicating the hardness and organic solutes that were in the range of 1000-3000 da
[127]. Synthesized MgO and magnesium NPs proved to be effective bactericidal agents against both Gram-negative and
Gram-positive bacteria like E. coli and Bacillus megaterium , respectively [126]. Jain and Pradeep extensively studied the
use of silver NPs for water treatment in Gram-negative, rod-shaped coliform bacteria due to its heavy presence in waste-
water [128]. Later, various other studies to detect the bactericidal property of silver NPs were undertaken for many other
Gram-positive and Gram-negative microbes like E. coli , Staphylococcus aureus , K. pneumoniae , and Pseudomonas aeru-
ginosa [128, 129]. Silver NPs have the ability to destroy bacterial cells by binding to their cell wall and proteins at multiple
sites and inhibiting their function. They also infiltrate the bacterial dNA and RNA at the precise site and cause cell lysis
[130, 131]. The coating of silver NPs on various materials began mainly in 1993 when silver ions were coated on sand fil-
ters [132]. This was further expanded to many other materials like zeolites [133] and more recently on fiberglass [134].
Thus the future of nanotechnology for water treatment would mainly be the use of combinations of NPs on filters like
ceramic and activated charcoal; this would result in enhanced bactericidal activity and efficient removal of other insoluble
impurities (Fig. 19.5).
19.13.2
nanobiotics
This term basically refers to the use of antibiotics conjugated to NPs. This complex enhanced the bactericidal activity of NPs.
Ping li and his fellow workers considered the effect of silver NP on E. coli using amoxicillin as a conjugate. This complex was
found to have a higher bactericidal activity than silver NPs when they were used alone. The chances for the development of
resistance were decreased considerably as either of the two was sufficient for destroying the bacteria. Other such antibiotics
used in combination were beta-lactam antibiotics [135] (Fig. 19.6).
FiGurE 19.5
Sewage water treatment using Ag NPs.
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