12.5.2 Biosorbent Material
Some microorganisms show very powerful biosorbent behaviour towards metallic
ions due to the chemical composition of the microbial cells. This kind of biosorbent
contains dead and metabolically non-active cells. Certain varieties of biosorbents
most likely have a wide range which bind and accumulate most of the heavy metals
without any special preference, while some of them are particular for specific metals.
Some of the labs use easily obtainable biomass, while others are separated particular
strains of microorganisms and some processed existing unprocessed biomass to a
certain level to increase its biosorption properties. Current biosorption research has
concentrated on waste products, which are derivatives or remnants of big-scale
industrial processes like mycelia waste obtained from fermentation procedure,
solid waste of olive oil-making plants (Pagnanelli et al. 2002), activated sludge of
sewage treatment plants (Hammaini 2003), biosolids (Norton et al. 2004) and
aquatic macrophytes (Keskinkan et al. 2003). The biosorption procedure is intricate
which consist of mainly ion exchange, chelation, adsorption through physical forces,
entrapment in intra- and interfibrillar capillaries as well as spaces of the structural
polysaccharide network due to the concentration gradient and diffusion by cell walls
and membranes. There are many chemical groups that are supposed to draw and
sequester metals in biomass like acetamido groups of chitin; structural
polysaccharides in fungi; amino and phosphate groups in nucleic acids; amido,
amino, sulphydryl and carboxyl groups in proteins; hydroxyls in polysaccharide
and basically carboxyls and sulphates in polysaccharides of marine algae of
divisions Phaeophyta, Rhodophyta and Chlorophyta. But, the occurrence of a
specific functional group never guarantees biosorption maybe because of steric,
conformational, and other barriers.
12.5.3 The Choice of Metal for Biosorption Process
Suitable metals for biosorption investigations are chosen on the basis of point of
interest and the effect of different metals. Thus, they can be categorized into four
major classes: (a) harmful heavy metals, (b) strategic metals, (c) valuable metals, and
(d) radionuclides. Of these, categories (a) and (d) are of prime consideration
environmentally with respect to their elimination from the environment as well as
from point source effluent discharges. Besides the toxicological point of view, the
attention to particular metals is dependent on the representation of its behaviour in
relation to ultimate generalization of outcome about their biosorbent uptake. Chromium, arsenic and selenium are suitable choices for studying the harmful effects as
well as attractive solution chemistry of elements. Strategic and valuable metals are
significantly considered because of their recovery value, although they are not
environmentally alarming. Studies on biosorption were started in the 1980s (Volesky
and Holan 1995; Volesky 2001). In the past, studies in this area employed bioremediation with microorganisms only, to decompose organic compounds (Lovley and
Coates 1997). A lot of work has been done since then, to explore the binding
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N. Srivastava
Some microorganisms show very powerful biosorbent behaviour towards metallic
ions due to the chemical composition of the microbial cells. This kind of biosorbent
contains dead and metabolically non-active cells. Certain varieties of biosorbents
most likely have a wide range which bind and accumulate most of the heavy metals
without any special preference, while some of them are particular for specific metals.
Some of the labs use easily obtainable biomass, while others are separated particular
strains of microorganisms and some processed existing unprocessed biomass to a
certain level to increase its biosorption properties. Current biosorption research has
concentrated on waste products, which are derivatives or remnants of big-scale
industrial processes like mycelia waste obtained from fermentation procedure,
solid waste of olive oil-making plants (Pagnanelli et al. 2002), activated sludge of
sewage treatment plants (Hammaini 2003), biosolids (Norton et al. 2004) and
aquatic macrophytes (Keskinkan et al. 2003). The biosorption procedure is intricate
which consist of mainly ion exchange, chelation, adsorption through physical forces,
entrapment in intra- and interfibrillar capillaries as well as spaces of the structural
polysaccharide network due to the concentration gradient and diffusion by cell walls
and membranes. There are many chemical groups that are supposed to draw and
sequester metals in biomass like acetamido groups of chitin; structural
polysaccharides in fungi; amino and phosphate groups in nucleic acids; amido,
amino, sulphydryl and carboxyl groups in proteins; hydroxyls in polysaccharide
and basically carboxyls and sulphates in polysaccharides of marine algae of
divisions Phaeophyta, Rhodophyta and Chlorophyta. But, the occurrence of a
specific functional group never guarantees biosorption maybe because of steric,
conformational, and other barriers.
12.5.3 The Choice of Metal for Biosorption Process
Suitable metals for biosorption investigations are chosen on the basis of point of
interest and the effect of different metals. Thus, they can be categorized into four
major classes: (a) harmful heavy metals, (b) strategic metals, (c) valuable metals, and
(d) radionuclides. Of these, categories (a) and (d) are of prime consideration
environmentally with respect to their elimination from the environment as well as
from point source effluent discharges. Besides the toxicological point of view, the
attention to particular metals is dependent on the representation of its behaviour in
relation to ultimate generalization of outcome about their biosorbent uptake. Chromium, arsenic and selenium are suitable choices for studying the harmful effects as
well as attractive solution chemistry of elements. Strategic and valuable metals are
significantly considered because of their recovery value, although they are not
environmentally alarming. Studies on biosorption were started in the 1980s (Volesky
and Holan 1995; Volesky 2001). In the past, studies in this area employed bioremediation with microorganisms only, to decompose organic compounds (Lovley and
Coates 1997). A lot of work has been done since then, to explore the binding
324
N. Srivastava