Molasses is a primary carbon source, especially in the microbial industry;
however, molasses includes many colored substances, like melanoidins, which become
concentrated by the Maillard reaction after sterilization [41]. Thus, these remain in the
Molasses Wastewater (MWW) after use. For effective treatment of MWW, biological
methods are attracting attention. Section 1-10, in the previous Chapter 3, showed
molasses to be available as a carbon source for the growth of Dec 1, and that partial
color removal of molasses by Dec 1 was possible. The enhanced color removal of
molasses by Dec 1 was conducted using a jar fermenter system consisting of fan-type
agitators and a pressure swing adsorption oxygen generator. The oxygen-enriched air
supply was effective not only in obtaining the highest decolorization degree of
molasses, but also the highest activity of peroxidase, DyP for the decolorization of
several dyes.
By simultaneous decolorization of molasses and an anthraquinone dye, RB5, the degree
of decolorization of molasses reached 87%, and thus, the maximum decolorization rate
of the dye, RB5, was achieved. However, the decolorizing activity of purufied DyP
toward molasses was significantly lower than that of culture broth of Dec 1 due to the
inhibitory effects of molasses on DyP, but the inhibition was reduced in the progress of
degradation of molasses by growing Dec 1 concentration. Dec 1 degraded molasses
containing substances with a wide range of molecular weights prepared by ultrafiltered
fractions of molasses. As Dec 1 was not able to utilize sucrose, sucrose in the molasses
was hydrolyzed with invertase to utilize all sugars in molasses. As a result, the
decolorization of molasses and rate of decolorization of the dye, RB5, by Dec 1
reached the highest level.
A long and stable decolorization of molasses was attempted using both suspended and
immobilized cells of Dec 1. In semi-batch cultivation using suspended cells of Dec 1,
80% decolorization of molasses and a stable DyP activity were maintained for
approximately four weeks. When repeated batch cultivation of Dec 1 cells immobilized
on polyurethane foam was applied, a longer and stable decolorization of molasses as
well as stable DyP activity lasted for more than eight weeks.
Dec 1 was applied for the decolorization of kraft pulp bleaching effluent, abbreviated
as E-effluent when glucose was supplemented. The color removal of E-effluent and the
reduced amount of Absorbable Organic Halogens (AOX) reached 78% and 43%,
respectively. The average molecular weight of colored substances in molasses was
reduced to less than 3000 from the original 5600. The contribution of extracellular enzymes, such as Peroxidase (DyP) and Manganese Peroxidase (MnP), to the
decolorization of the kraft pulp bleaching effluent was observed in the later stage of
decolorization.
Dec 1 decolorized up to 72% of Oxygen-delignified Bleaching Effluent (OBE).
Biobleaching of Oxygen-delignified Kraft Pulp (OKP) was conducted at 2% pulp
concentration. The brightness of OKP increased by 13% and the kappa value of OKP
decreased by 4 points only for 3 days. However, at 25% of pulp concentration, the
brightness of OKP increased only by 4% and the kappa value decreased by 3 points
during a 12-day incubation period mainly because of oxygen limitation. When the
culture after OBE decolorization was used for bleaching of OKP, the brightness of
OKP increased to 62.7% at 2% pulp concentration. In the decolorization and
biobleaching, the involvement of DyP and MnP was confirmed. From these results, the
potentiality of Dec 1 for the decolorization of kraft pulp wastewater and biobleaching
of kraft pulp in paper mills can be observed.
Keywords: Absorbable organic halogens, Immobilization on polyurethane foam, Kraft pulp bleaching effluent, Kappa value, Molasses, Oxygen-delignified bleaching effluent, Oxygen-delignified kraft pulp, Pressure swing adsorption oxygen generator, Repeated-batch cultivation, Ultrafiltered fractions of molasses.
