Environmental Engineering Reference
In-Depth Information
sole phenoloxidase (Pointing et al.
2000
). Lac-
case purified from
Trametes hirsuta
, was able to
degrade triarylmethane, indigoid, azo, and athra-
quinonic dyes used in dyeing textiles (Abadulla
et al.
2000
) as well as 23 industrial dyes (Rodri-
guez et al.
1999
).
2003
), and
Corynebacterium glutamicum
(Won
et al.
2004
).
a.
Mechanism of Biosorption
According to the dependence on the cell's
metabolism, biosorption mechanisms can be
divided into:
1. Metabolism-dependent
2. Nonmetabolism-dependent
According to the location where the sorbate
removed from solution is found, biosorption
can be classified as
1. Extracellular accumulation/precipitation
2. Cell surface sorption/precipitation and
3. Intracellular accumulation
Microbial biomass consists of small particles
with low density, poor mechanical strength, and
little rigidity. This phenomenon is generally
based on a set of chemical and physical mecha-
nisms (involving physicochemical interactions
such as electrostatic interactions, ion exchange,
complexation, chelation, and precipitation) lead-
ing to the immobilization of a solute component
on the microbial cell wall components. The com-
plexity of the microbial structure implies that
there are many ways for the pollutant to be cap-
tured by the cells. Biosorption mechanisms are
therefore various (physical adsorption, chemical
binding of ionic groups, ion exchange, etc.) and
in some cases they are still not very well under-
stood (Veglio and Beolchini
1997
). Cell surface
sorption is a physicochemical interaction, which
is not dependent on metabolism. Cell walls of
microbial biomass mainly composed of poly-
saccharides, proteins, and lipids, offer abundant
functional groups such as carboxyl, hydroxyl,
phosphate, and amino groups, as well as hydro-
phobic adsorption sites such as aliphatic carbon
chains and aromatic rings (Ringot et al.
2005
).
This physicochemical phenomenon is quick and
can be reversible.
2.7
Adsorption-Assisted
Decolorization
Several methods for the treatment of colored
wastewaters have been proposed in the literature.
These include physicochemical treatment pro-
cesses, chemical oxidation, and biological deg-
radation. Among various physicochemical treat-
ment processes, adsorption has been found to be
an attractive technique for the removal of most
organic compounds in wastewaters, especially at
lower concentrations. Activated carbon has been
the most commonly used adsorbent. However,
high cost of activation, regeneration, and the dis-
posal of the concentrate from the cleaning cycles
pose problems in the use of activated carbon.
Hence, the search of new low cost adsorbents
has attracted a number of investigators. Several
low cost adsorbents like wood, coir pith, coal fly
ash, bagasse fly ash (BFA), and coal-fired boiler
bottom ash have been used for the treatment of a
wide variety of wastewaters.
An efficient, cost-effective, and environmen-
tally friendly technique; biosorption is mainly
a physicochemical process involving the use of
biological material-live or nonviable, can be used
to concentrate and recover or eliminate the pol-
lutants from aqueous solutions. Various work-
ers have investigated the biosorption of various
organic pollutants and color from wastewaters
(Tsezos and Bell
1989
; Fu and Viraraghavan
2001
). Biomass of some natural microbial spe-
cies, including bacteria, fungi, and algae, is ca-
pable of removing the different textile dyes by
biosorption, biodegradation, or mineralization
(Carliell et al.
1995
). Some low-cost fungal bio-
mass has been used as biosorbent for the removal
of dye and metal ions from or wastewater, which
included
Trametes versicolor
(Bayramoglu et al.
Physical Adsorption
If the attraction between
the solid surface and the adsorbed molecules is
physical in nature, the adsorption is referred to
as physical adsorption (physiosorption). Gener-
ally, in physical adsorption the attractive forces
between adsorbed molecules and the solid surface
are van der Waals forces and they being weak in
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