3 Organic Pollutants of Distillery Waste
The origin of high COD, BOD, and color in distillery effluent is due to the existence
of tannin- and lignin-like structural compounds, for example, melanoidins, crosslinked polyphenols, and EDCs which are resistant to physical, chemical, and biological degradation. These recalcitrant organic compounds present in distillery
effluent are generated during the distillation process of fermented molasses slurry
and the subsequent methanogenesis of the SW.
3.1 Melanoidins
Melanoidins, the major nitrogenous color imparting organic compounds in distillery
effluent, formed through the Maillard reaction (MR) or nonenzymatic browning
reaction occur between amino acids and carbohydrates at temperatures above 50
C
and pH 4.0 to 7.0 (Hayase 2000). Melanoidins with an MW distribution between
5 and 40 kDa consist of polymeric, acidic, negatively charged, and highly dispersed
colloids. The negative charge of melanoidins is due to the dissociation of carboxylic
and phenolic groups (Moreira et al. 2012).
The MR is a complex series of reactions; the first stage involves the initial
condensation of the sugar with amino acid and the isomerization of the resulting
products to form Heyns or Amadori products. Amadori product and its dicarbonyl
derivatives can undergo concurrently retro-aldol reactions producing more reactive
C 2 -C 5 sugar fragments, such as diketones, glyceraldehydes, and hydroxyacetone
derivatives. This chemical reaction is called as Strecker degradation, and it is
characterized by the production of CO 2 (Arimi et al. 2015). The aldehydes formed
may be important as auxiliary flavor compounds, and they also contribute to
melanoidin formation. The formation of melanoidins from sugar and amino acid
reactions is illustrated in Fig. 20.2a. Due to the recalcitrant antioxidant nature of
melanoidins, it inhibits microbial growth used in biological treatment processes of
distillery effluent. Consequently, distillery effluent is a major source of aquatic and
terrestrial pollution in the environment.
Since, melanoidins are generally regarded to be heterogenous, negatively
charged, and highly dispersed polymer with similar chemical properties to humic
substances (Migo et al. 1993). It has been reported that due to their net negative
charge, various HMs such as Cu
2+ , Cr
3+ , Fe
3+ , Zn
2+ , Pb
2+ , etc. bind with
melanoidins to form an organometallic complex (Hatano et al. 2016; Migo et al.
1997). Consequently, the high HM-binding tendency of melanoidins also enhances
the vulnerability of organometallic complex toward its toxicity in the ecosystem. In
sugar processing, melanoidins are formed during purification and evaporation steps.
The elemental and chemical structure of melanoidins depends heavily on the nature
and molecular concentration of reactant and reaction conditions such as pH, heating
time temperature, and solvent. Cammerer et al. (2002) have proposed the
20 Bioremediation of Melanoidins Containing Distillery Waste for. . .
501
The origin of high COD, BOD, and color in distillery effluent is due to the existence
of tannin- and lignin-like structural compounds, for example, melanoidins, crosslinked polyphenols, and EDCs which are resistant to physical, chemical, and biological degradation. These recalcitrant organic compounds present in distillery
effluent are generated during the distillation process of fermented molasses slurry
and the subsequent methanogenesis of the SW.
3.1 Melanoidins
Melanoidins, the major nitrogenous color imparting organic compounds in distillery
effluent, formed through the Maillard reaction (MR) or nonenzymatic browning
reaction occur between amino acids and carbohydrates at temperatures above 50
C
and pH 4.0 to 7.0 (Hayase 2000). Melanoidins with an MW distribution between
5 and 40 kDa consist of polymeric, acidic, negatively charged, and highly dispersed
colloids. The negative charge of melanoidins is due to the dissociation of carboxylic
and phenolic groups (Moreira et al. 2012).
The MR is a complex series of reactions; the first stage involves the initial
condensation of the sugar with amino acid and the isomerization of the resulting
products to form Heyns or Amadori products. Amadori product and its dicarbonyl
derivatives can undergo concurrently retro-aldol reactions producing more reactive
C 2 -C 5 sugar fragments, such as diketones, glyceraldehydes, and hydroxyacetone
derivatives. This chemical reaction is called as Strecker degradation, and it is
characterized by the production of CO 2 (Arimi et al. 2015). The aldehydes formed
may be important as auxiliary flavor compounds, and they also contribute to
melanoidin formation. The formation of melanoidins from sugar and amino acid
reactions is illustrated in Fig. 20.2a. Due to the recalcitrant antioxidant nature of
melanoidins, it inhibits microbial growth used in biological treatment processes of
distillery effluent. Consequently, distillery effluent is a major source of aquatic and
terrestrial pollution in the environment.
Since, melanoidins are generally regarded to be heterogenous, negatively
charged, and highly dispersed polymer with similar chemical properties to humic
substances (Migo et al. 1993). It has been reported that due to their net negative
charge, various HMs such as Cu
2+ , Cr
3+ , Fe
3+ , Zn
2+ , Pb
2+ , etc. bind with
melanoidins to form an organometallic complex (Hatano et al. 2016; Migo et al.
1997). Consequently, the high HM-binding tendency of melanoidins also enhances
the vulnerability of organometallic complex toward its toxicity in the ecosystem. In
sugar processing, melanoidins are formed during purification and evaporation steps.
The elemental and chemical structure of melanoidins depends heavily on the nature
and molecular concentration of reactant and reaction conditions such as pH, heating
time temperature, and solvent. Cammerer et al. (2002) have proposed the
20 Bioremediation of Melanoidins Containing Distillery Waste for. . .
501