Environmental Engineering Reference
In-Depth Information
estimated that 88 % of the molasses constituents
end up as waste (Jain et al.
2002
).
The spent wash is the most polluting stream
and contains practically all unfermentable sol-
uble matter present in the molasses. Apart from
the extremely high chemical oxygen demand
(COD) and biochemical oxygen demand (BOD)
load, the dark color is also a key concern. This
dark color is mainly imparted by melanoidins
that are low and high molecular weight polymers
formed as one of the final products of Maillard
reaction, which is a nonenzymatic browning re-
action resulting from the reaction of reducing
sugars and amino compounds (Martins and van
Boekel
2004
). This reaction proceeds effectively
at temperatures above 50 ﾰC and pH 4-7. These
are complex organic compounds, when released
in environment without treatment, react with a
wide variety of other chemicals in presence of
light and heat to form highly toxic and recalci-
trant compounds (Kinae et al.
1981
; Zacharewski
et al.
1995
). Thus, it is obligatory to treat the ef-
fluent before disposal into the environment.
low cost and the variations of work progress, the
biological methods have been most widely used
all over the world.
2.4
Treatment of Distillery Spent
Wash
Biological treatment can be divided into aero-
bic and anaerobic depending on the availability
of oxygen. Aerobic treatment involves activated
sludge treatment, aerated lagoons, and aero-
bic biological reactors. Anaerobic filter, upflow
sludge blanket (UASB), fluidized bed, anaerobic
lagoon, and anaerobic contact reactors are anaer-
obic processes, that are commonly used to treat
distillery mill effluents. Among these treatments
one thing is common, use of microbes (Pokhrel
and Viraraghavan
2004
). A number of fungi, bac-
teria, yeast, and algae have been reported to have
effluent-treatment capabilities.
2.4.1
Decolorization of Effluent
by Fungi
2.3
Bioremediation
In recent years, several basidiomycetes and as-
comycetes type fungi have been used in the de-
colorization of wastewaters from distilleries.
Filamentous fungi have lower sensitivity to vari-
ations in temperature, pH, nutrients, and aera-
tion, and have lower nucleic acid content in the
biomass (Knapp et al.
2001
).
Coriolus
sp. no. 20,
in class basidiomycetes, was the first strain for
the application of its ability to remove melanoi-
dins from molasses wastewater (Watanabe et al.
1982
). Published papers report the use of wide
variety of fungi like
Aspergillus fumigatus
G-2-6
(Ohmomo et al.
1987
),
Emericella nidulans var.
lata
(Kaushik and Thakur
2009a
),
Geotrichum
candidum
(Kim and Shoda
1999
),
Trametes
sp.
(Gonz￡lez et al.
2000
),
Aspergillus niger
(Patil
et al.
2003
),
Citeromyces
sp. (Sirianuntapiboon
et al.
2003
),
Flavodon flavus
(Raghukumar et al.
2004
), and
Phanerochaete chrysosporium
(Thak-
kar et al.
2006
) for decolorization of distillery
mill effluent.
Generally, methods of treating wastewater in-
clude physical-chemical methods and biological
methods. Methods such as sedimentation, flota-
tion, screening, adsorption, coagulation, oxida-
tion, ozonation, electrolysis, reverse osmosis, ul-
trafiltration, and nanofiltration technologies have
been used for treatment of suspended solids, col-
loidal particles, floating matters, colors, and toxic
compounds (Pokhrel and Viraraghavan
2004
).
The drawbacks of the physical-chemical meth-
ods include high costs and the need to re-treat
the products, which further increases the cost
of treatment. Biological method produces rela-
tively little amount of product after treatment by
resolving a large amount of organism elements
into carbon dioxide to be stabilized, or by remov-
ing organic matters contained in wastewater with
the generation of methane gas. In the biological
treatment method, pollutants in wastewater can
be resolved, detoxified, and separated by using
mainly microorganisms. Due to the relatively
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