6 Wood Discoloration

250 9 Positive Effects of Wood-Inhabiting Microorganisms
waste paper in a deinking plant consisted of 41% newspapers, 39% magazines,
9% wood-free paper, 6% unusable paper and board, 4% other bright papers,
and 1% non-paper components (Hager 2003). More than 70% of mixed office
waste paper consists of uncoated papers that are printed with copy or
laser printer toners, which may be difficult to remove by conventional, alkaline
deinking (Kenealy and Jeffries 2003). Fibers may be treated by hydrolyzing
enzymes to remove print (deinking). Cellulases are particularly effective in
the removal of toners from office waste papers. It was concluded that the primary
role of cellulases in deinking involves separating ink-fiber agglomerates
and dislodging or separating ink particles and fibrous material in response
to mechanical action during disintegration (Kenealy and Jeffries 2003). Few
experiments have used oxidative enzymes for deinking. The missing potential
for the reduction of specks that derive from residual ink and the observed
lignin modification rendered laccase either alone or combined with the mediator
1-hydroybenzotriazole unsuitable for practical ink elimination of wood
containing waste paper (Hager et al. 2002). Recycled paper sludge generated
during repulping was simultaneously hydrolyzed with fungal cellulase and fermented
with the yeast Kluyveromyces marxianus to convert cellulose fibers to
ethanol (Lark et al. 1997).
Papers made from secondary fibers often show a higher microbial load
which is of disadvantage for some applications, e.g., as hygienic papers (Cerny
and Betz 1999).
Anaerobic treatment of pulp mill effluents was reviewed by Guiot and Frigon
(1998).PhanerochaetechrysosporiumandTrametes versicolor havebeenusedto
degrade the chlorolignins in the effluents produced during chlorine bleaching
(Eriksson et al. 1990). The ligninolytic systems of white-rot fungi, particularly
P. chrysosporium, was used to degrade several persistent environmental
pollutants such as benzo(a)pyrene, DDT, and dioxin. Bacteria metabolized
dibenzo-p-dioxin (Wittich et al. 1992). Aerobic bioremediation techniques
for the cleanup of creosote and PCP-contaminated soils were reviewed by
Borazjani and Diehl (1998) (also Prewitt et al. 2003). Aerobic PCP transformation
initially produced small amounts of pentachloroanisole; however more
than 75% of both chemicals disappeared in 30 days from the test soil. Under
methanogenic conditions, PCP was reductively dechlorinated to tetra-, tri-,
and dichlorophenols (D’Angelo and Reddy 2000). Bioremediation of wood
treated with preservatives using white-rot fungi was treated by Majcherczyk
and Hüttermann (1998). The peroxidases of white-rot fungi unspecifically oxidize
aromatic compounds by generating such a high redox-potential that they
“burn down” all available aromatics present in the proximity of the mycelia.
Phanerochaete laevis transformed polycyclic aromatic hydrocarbons (Bogan
and Lamar 1996). Tubular bio-filters filled with straw, which were previously
colonized with Pleurotus ostreatus mycelium was used to filter out ammonia
from the waste air of cattle sheds (Majcherczyk et al. 1990). Experiments on the
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