Chapter I: Introduction
CHAPTER I
INTRODUCTION
1.1 Background:
Heavy metals may be classified as essential and non-essential metals. Heavy metals such
as zinc and copper are essential metals as they serve biological functions. Indeed essential
metals have been very well studied, for example in their role as enzymatic cofactors or as
a part of metalloenzymes. However, the biochemical mechanisms involved in
homeostasis, metal metabolism and regulation are still not fully understood. Some of these
metals, e.g. copper, nickel and zinc, are essential at low concentrations for the normal
functioning of living organisms, but are toxic at high concentrations. Other heavy metals,
such as lead, mercury and cadmium, do not serve any known biological function and
hence termed as non-essential and can be very harmful to the organism, including human,
even at low concentrations. Heavy metals are elements and hence cannot be degraded or
destroyed. They tend to be accumulated in soils, plants and animals, with increasing
concentrations in the top predators of the food chains. The effect of these heavy metals on
human health include different types of cancer, renal dysfunction, alteration of the nervous
system, decrease of learning capacity, etc. The effect of heavy metals on the environment
depends on their concentration and mobility within the atmosphere, hydrosphere and
lithosphere. The polluting heavy metals may be mobilized and transported in solubilized
form through air. This includes solid phase (particles and aerosols), liquid (fogs) and
gaseous (steams) transfer. Dispersion and dilution lead to contamination of new regions,
thus affecting the environment in areas far away from the original pollution. Over the
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Chapter I: Introduction
years, there has been significant increase in the utilization and release of chemicals
including heavy metals, due to rapid industrialization and population increase. Industries
such as metallurgical, electroplating, metal finishing, tanneries, chemical manufacturing,
mine drainage and battery manufacturing are the main sources of heavy metal pollution.
Heavy metals, due to their high toxicity, pose a serious threat to biota and environment. In
many parts of the world, strict regulations exist that regulate the concentration of metals
discharged in the effluent.
Conventional techniques for removing dissolved heavy metals include chemical
precipitation, chemical reduction, carbon adsorption (Namasivayam and Yamuna, 1995;
Lotfi and Adhoum, 2002; Bai and Abraham, 2003), ion exchange (Sengupta and
Clifford,1986; Rengaraj et al., 2003), solvent extraction (Mauri et al., 2001), reverse
osmosis (Padilla and Tavani, 1999), filtration, membrane process, evaporation and several
other electrolytic and chemical methods. However, these techniques are ineffective when
applied to low strength waste with heavy metal ion concentration and have certain
disadvantages as listed below:
There is production and accumulation of secondary waste products during the
series of treatments involved in treating heavy metals (including Cr (VI), Cu
sludge).
Some of the treatment methods involve high operating and maintenance cost
(Tewari et al., 2005)
There is low efficiency and operational complexity.
These methods involve high energy requirements and often incomplete metal
removal (Ucun et al., 2002)
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Chapter I: Introduction
Phytoremediation i.e. the use of plants for the treatment of heavy metal contamination is a
cost effective method but is considered extremely time consuming. Due to the
disadvantages of these methods, there is need for other methodologies that would be
efficient at low concentration of pollutants.
The use of sorbents of biological origin (Bailey et al., 1999; Babel and Kurniawan, 2003)
for the removal of heavy metals has gained interest among researchers due to its several
valuable advantages. The biological methods are generally cost effective and
biodegrades/detoxify the hazardous contaminants. There is also a possibility of recovery
of the metal in the case of biological origin remediation methods.
1.2 Objectives and Scope of the project:
The project aims at the following objectives:
Isolation of chromium-tolerant microorganism from effluent as well as solid waste
from the electroplating industry.
Basic biochemical characterization and genus identification of the obtained
isolates.
A study on the toxicity effects of chromium on these isolates.
Indentifying the morphological and biochemical changes of isolates that occur
upon exposure to chromium.
Determining the chromium binding sites over the functional groups of the
microorganisms.
Indentifying the behavior of the cells after intracellular transport of chromium.
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Chapter I: Introduction
Surface morphological changes after chromium bioaccumulation and its
quantification.
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... (Namasivayam and Yamuna, 19 95; Lotfi and Adhoum, 2002; Bai and Abraham, 2003), ion exchange (Sengupta and Clifford ,19 86; Rengaraj et al., 2003), solvent extraction (Mauri et al., 20 01) , reverse... study on the toxicity effects of chromium on these isolates Indentifying the morphological and biochemical changes of isolates that occur upon exposure to chromium Determining the chromium binding... extraction (Mauri et al., 20 01) , reverse osmosis (Padilla and Tavani, 19 99), filtration, membrane process, evaporation and several other electrolytic and chemical methods However, these techniques are