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Post-industrialization, and particularly post-globalization, air pollution—
introduction of chemicals, particulate matter, or biological materials into
the atmosphere—has become a matter of grave concern for all, for it
causes harm to human beings, and other living organisms. Stratospheric ozone
depletion caused by air pollution has become the greatest threat to the Earth's
ecosystems. One of the common air pollutants is Volatile Organic Compounds (VOCs).
They are of two types: methane and non-methane VOCs. Methane is the real culprit
in causing enhanced global warming. There are also other hydrocarbons—VOCs
that are known to be significant greenhouse gases, but their effect varies
depending on local air quality. Among the NMVOCs, the aromatic
compounds—benzene, toluene and xylene—are suspected to be carcinogens, causing leukemia
through prolonged exposure.
As the world is becoming more and more critical of air pollution and its
side effects, many countries, including developing countries, have introduced
various regulations directing industries to minimize the emission of VOCs into
the atmosphere. As a result, biofiltration—a pollution-control technology—is
being increasingly resorted to for the elimination of malodorous gas emissions and
of low concentrations of VOCs emitted by industries such as chemical
and petrochemical, oil and gas, synthetic resins, paint and ink and
pharmaceutical. Biofilteration has become more popular because: one, the VOCs are
biodegradable; and two, it is the cheapest.
A critical requirement for effective functioning of biofilter is a
well-established community of aerobic microorganisms that can well adapt to the bed
conditions and the nature of the VOCs present in the waste gases being treated. The
bed packing material should therefore be of such nature that it enables biofilter
function for an extended period, while at the same time being of low cost. Against
this backdrop, the authors, Y Nitipavachon, P Chetpattananondh, M A Connor and
K Prasertsit of the first article, "The Suitability of Peanut Shells and Palm
Shells for Use as Bed Packing Media in Biofilters", have studied the characteristic
features of peanut and palm shells as packing media in biofilters and evaluated their
ability to treat the contaminated air with methanol, toluene and mixtures of
methanol and toluene for over 200 days. The findings revealed that although
the characteristics of peanut shell and palm shells differed from each other, both
of them were found to be suitable as packing material in biofilters to treat
gases contaminated with methanol or toluene or their mixture. The elimination
capacities of these two materials were comparable with those obtained using the
existing media. The ECmax values obtained with peanut shells were, however, found to
be higher than those of the palm shells; but palm shells could retain their
structural integrity better than peanut shells, which means warranty replacement
less frequently. The authors, therefore, opine that usage of either peanut shells
or palm shells for installing biofilters to remove VOCs would benefit Thai
industries more vis-à-vis the usage of conventional packing material.
Next to air pollution, water pollution due to discharge of contaminated
water with dye stuffs, such as methylene blue, malachite green and crystal violet,
is found to be mutagenic and carcinogenic for living beings. In the past three
decades, numerous techniques of dye removal from the water released by textile,
paper and plastic industries are in practice. Amongst them, biosorption has become
the procedure of choice for treatment of waste water for the removal of dyes.
Earlier studies have indicated that many biosorbants present in the nature have
great capacity for the removal of dyes. The authors, D Appala Naidu, P Vijay, P
King and V S R K Prasad of the next article, "Biosorption of Congo Red from
Aqueous Solution Using Guava (Psidium
guajava) Leaf Powder: Equilibrium and Kinetic Studies", have evaluated the biosorption capacity of guava leaf powder for
Congo red from aqueous solution. Their study reveals that guava leaf powder is
an effective and cheap biosorbant for the removal of Congo. Its biosorbant
performance is, however, strongly affected by parameters such as pH, initial
concentration, biosorbant dosage, biosorbant average particle size and temperature.
Maximum biosorption was found to take place at pH 1. The authors have also analyzed
the kinetics of biosorption data and opined that the pseudo-second-order
kinetics describes it better.
In the next article, "Role of Illumination and Dissolved Oxygen
Concentration on Purple Membrane Production by Halobacterium
halobium", the authors,
Prasanna B D, Dinesh Goudar, Chetan Shetty, Gurunath Katagi and Shivraj
Ghatge have studied the role of illumination and dissolved oxygen concentration on
the production of purple membrane by batch culture of Halobacterium halobium and found that continuous illumination was deleterious for the biomass growth.
The authors conclude that higher PM production per liter could be achieved either
by providing dissolved oxygen of 60% and above with continuous illumination
of 30,000 lumins per sq. m for 96 h or by building biomass for 72 h in fully
aerobic conditions with no illumination, and then incubating this culture in
microaerophilic conditions for 72 h under illumination. However, higher production of PM
could be obtained by culturing the organism at moderate aeration under
continuous illumination.
In the last article, "Parameter Analysis of a 500 W PEM Fuel Cell Stack
Using Design of Experiments", the authors, A Leela Manohar, S V Naidu, V Dharma
Rao and B Sreenivasulu have evaluated the influence of gas pressure and flow
rate parameters on fuel cell performance, using four types of control
factors—pressures of the fuel and oxidant, and the flow rates of the fuel and oxidant. The
statistical analysis of the data indicates that hydrogen flow rate and oxygen flow rate
have a major influence on the performance of the fuel cell stack. The authors are also
of the opinion that their fractional factorial experiments can be extended to
other ranges and factors with various levels for minimizing the variation caused
by various factors that influence the fuel cell performance with less number of
trails, compared to full factorial experiments.
-- GRK Murty
Consulting Editor |
