6 Wood Discoloration

244 9 Positive Effects of Wood-Inhabiting Microorganisms
9.3
Biological Pulping
Mechanical and chemical processes for pulp and paper production consume
energy and chemicals. Their wastes have to be controlled in view of environmental
aspects. Biotechnological processes have thus been successfully
implemented in the pulp and paper industry during the last decade driven
by the objective to reduce manufacturing costs using new delignification processes
and by environmental considerations (Messner et al. 2003). The application
of white-rot fungi, or their ligninolytic systems, was one option for
this. The aim was termed as biological pulping or briefly biopulping. In its
strict sense, biopulping was defined as the pretreatment of wood chips with
selectively delignifying white-rot fungi prior to mechanical or chemical pulping
(Messner 1998). In a broader sense, the term biopulping is also used for
any biochemical assistance to the pulping process such as the application of
blue-stain fungi for resin reduction or the use of enzymes for bleaching and
deinking.
Nilsson had found Sporotrichum pulverulentum (first termed Chrysosporium
lignorum) in chip piles in Sweden, where it caused serious damages (Bergman
and Nilsson 1966). In 1972, Henningsson et al. described the fungus as the
thermophilic white-rot basidiomycete Phanerochaete chrysosporium (teleomorph
of S. pulverulentum) causing defibration of wood. In the late 1960s,
Eriksson in Stockholm had already started research to decrease the lignin
content in the wood microbially by treatment of wood chips with white-rot
fungi (Eriksson 1985; Eriksson et al. 1990). Mechanical pulp was produced
from chips pretreated with P. chrysosporium by Ander and Ericksson (1975).
Because white-rot fungi of the “selective delignification type” would also attack
the carbohydrates sooner or later, cellulase-less mutants such as Cel 44 of S.
pulverulentum have been produced by UV irradiation of conidia (Ander and
Eriksson 1976) and later by crossing of Cel − -mutants with monokaryons of
high ligninolytic activity (Johnsrud 1988).
Phanerochaete chrysosporium has also been isolated in the USA in the Arizona
desert (Burdsall and Eslyn 1974). Also in the late 1960s, Kirk in Madison
began research on P. chrysosporium with the isolation of lignin peroxidase (Tien
and Kirk 1983; see Chap. 4.5), and since the 1980s, biopulping is investigated
in the USA (Kirk et al. 1993).
There were masses of investigations and publications on various aspects
of biopulping during the past four decades. They report on the successful reduction
of chemicals and manufacturing and energy costs as well as on the
application of further white-rot fungi such as Ceriporiopsis subvermispora,
Dichomitus squalens, Merulius tremellosus, and Phlebia brevispora. For example,
when biopulped chips are used to produce mechanical pulp, energy for
refining was reduced from 25 to 35% and the sheet strength properties are
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