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The fermentation processes using molasses as carbon and energy source for alcohol
production generate wastewater (vinasse) with a high organic load. For each liter of ethanol
produced, 10-15 L of vinasse is generated. There are around 295 distilleries in India,
producing approximately 2.75 billion liters of alcohol, which generate around 45 billion liters
of wastewater annually. The environmental pollution impact of vinasse is very high due to
its organic matter content and dark brown color. The color is due to the presence of
recalcitrant polymers, such as melanoidin, caramel and alkaline degradation products.
The untreated distillery effluent is acidic in nature with a pH of 3.5 to 4.0. It does not
have any toxic hazardous chemicals but has potential as a liquid fertilizer after reduction in
color and chemical oxygen demand (COD), as it contains high levels of organic carbon, N, K, S,
Ca and Mg, apart from small amounts of micronutrients, viz., Zn, Fe, Cu and Mn (Sweeney
and Graetz, 1991). Biomethanation and biologically activated sludge reduce considerably
the levels of COD and BOD, but the color of the effluent still remains. The presence of
brown color in effluent is mainly due to the presence of coloring compounds such as
caramel, melanoidin, alkaline degradation products and polyphenols formed during the
manufacture of sugar from sugarcane juice (Dhamankar and Patil, 2001). Microbial decolorization is
an environment-friendly technique for removing color from distillery spent wash (Ghosh et al., 2003). Fungi are found to decolorize it via adsorption of coloring compounds by mycelia
and/or via production of active oxygen from hydrogen peroxide (Sirianuntapiboon et al., 1988a). Decolorization of molasses pigment could be seen with Mycelia sterilia D-90 around 93% (Sirianuntapiboon et al., 1988b) and with Aspergillus fumigatus
G-2-6 around 75% (Ohmomo et al., 1987). Phanerochaete chrysosporium was found to decolorize the molasses spent
wash around 59%, when the cells were immobilized in calcium alginate (Fahy et al., 1997). Coriolus versicolor showed 75% decolorization yield in only 20 h by continuous decolorization
in bubbling column reactor at a dilution rate of 0.03/h (Aoshima et al., 1985; and Ohmomo et al., 1985). A thermophilic strain of Aspergillus oryzae Y-2-32 showed around 75%
decolorization activity of melanoidin solution by adsorption of melanoidin to mycelia. The degree
of adsorption was found to be influenced by the kind of sugars utilized for growth and it
was found to be repressed by a high concentration of salt (Ohmomo et al., 1988). |
