Environmental Engineering Reference
In-Depth Information
nature result in reversible adsorption. Electro-
static interactions have been demonstrated to be
responsible for copper biosorption by bacterium
Zoogloea ramigera and alga Chlorella vulgaris
(Aksu et al. 1992 ), and for chromium biosorption
by fungi Ganoderma lucidum and Aspergillus
niger (Srivastava and Thakur 2006 ).
b. Factors Affecting Biosorption
The following factors affect the biosorption
process:
1. Temperature seems not to influence the
biosorption performances in the range of
20-35 ᄚC (Aksu et al. 1992 ).
2. pH seems to be the most important param-
eter in the biosorptive process: it affects the
solution chemistry of the metals, the activ-
ity of the functional groups in the biomass
(Galun et al. 1987 ).
3. Biomass concentration in solution seems
to influence the specific uptake: for lower
values of biomass concentrations there is
an increase in the specific uptake. Interfer-
ence in between the binding sites due to
increased biomass was suggested as a pos-
sible reason (Gadd et al. 1988 ).
c. Biosorption Equilibrium Models
Chemical Adsorption If the attraction forces are
due to chemical bonding, the adsorption process
is called chemisorption. In view of the higher
strength of the bonding in chemisorption, it is
difficult to remove chemisorbed species from the
solid surface. Aksu et al. ( 1992 ) hypothesized
that biosorption of copper by C. vulgaris and Z.
ramigera takes place through both adsorption
and formation of coordination bonds between
metals and amino and carboxyl groups of cell
wall polysaccharides. Microorganisms may also
produce organic acids (e.g., citric, oxalic, glu-
onic, fumaric, lactic, and malic acids), which may
chelate toxic metals resulting in the formation of
metalloorganic molecules. These organic acids
help in the solubilization of metal compounds
and their leaching from the surfaces.
One of the most important characteristics of
an adsorbent is the quantity of adsorbate it can
accumulate which is usually calculated from
the adsorption isotherms. The adsorption iso-
therms are constant-temperature equilibrium
relationship between the quantity of adsorbate
per unit of adsorbent (q e ) and its equilibrium
solution concentration (C e ). Several equa-
tions or models are available that describe this
function like the Freundlich and the Langmuir
equations.
Ion Exchange Ion exchange is basically a
reversible chemical process wherein an ion from
solution is exchanged for a similarly charged
ion attached to an immobile solid particle. Ion
exchange shares various common features along
with adsorption, in regard to application in
batch and fixed-bed processes and they can be
grouped together as ''sorption processes'' for a
unified treatment to have high water quality. Ion
exchange has been fruitfully used too for the
removal of colors. By far the largest application
of ion exchange (Clifford 1999 ) to drinking water
treatment is in the area of softening that is the
removal of calcium, magnesium, and other poly-
valent cations in exchange for sodium. Various
studies have been carried out using ion exchange
for the removal of dyes (Liu et al. 2007 ; Wu et al.
2008 ). Delval et al. ( 2005 ) prepared starch-based
polymers by a crosslinking reaction of starch-
enriched flour using epichlorohydrin as a cross-
linking agent in the presence of NH 4 OH.
2.8
Future Prospects
The present status described in the chapter has al-
lowed important information on the types of spe-
cies involved in decolorization and degradation
of distillery spent wash in the various lab scale to
pilot scale studies but their interaction with the
native microbial communities is still being ques-
tioned. Future studies should, therefore, focus
not only on identification of other communities
as observed in denaturing gradient gel electro-
phoresis (DGGE) band pattern but also their
quantification using reliable quantitative meth-
ods. Assessment of activity and the interactions
between the introduced organisms will also be
 
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