6 Wood Discoloration

9.3 Biological Pulping 245
typically improved 20 to 40% (Hunt et al. 2004). A 20% reduction was obtained
in the total pulping time necessary for achieving pulp and paper properties
comparable to those from controls (Chen et al. 1999). Körner et al. (2001)
showed that non-sterile incubation of wood chips with Coniophora puteana
yielded energy savings of about 40% during refining of wood chips, a three
times higher bending strength and more than half reduced water absorption
and swelling of fiber boards. The topic of biological treatment of chips of was
reviewed by Messner (1998).
Despitethemassiveamountofmoneyandworkdevotedtobiopulping,
a sweeping success seems however vague. The difficulties involved are mainly
microbiological problems: It is generally difficult to scale-up small-sized laboratory
experiments with fungal pure cultures via medium-sized rotating fermentors
with controlled aeration and temperature to the final aim of obtaining
the same result in chip silos or even in large-sized chip piles under natural outdoor
conditions. During controlled biopulping, the different white-rot fungi
may be grown on wood chips for 10 to 15 days. In a wood chip pile, available
nutrients, humidity, and temperature are, however, favorable to contamination
by many fungi. Most common are Trichoderma species, of which some
excrete antibiotics against other fungi. Uneven distribution of the inoculum,
unsuitable or uneven oxygen and carbon dioxide amounts, unfavorable or uneven
wood moisture content, and increase of the temperature to 50 ◦ Coreven
to the incineration point are common problems of large-sized outdoor bioconversions
in piled substrates. An example with respect to brown-rot fungi
is the successful laboratory and pilot-scale experiments by Leithoff (1997) to
bio-leach chromium, copper and other elements from treated waste wood by
means of Antrodia vaillantii (Chap. 7.4) and the failure of the method using
larger chip piles under practical conditions. Nevertheless, it has been stated
that development of the biopulping process has reached the pilot scale as far as
the use of white-rot fungi for mechanical and sulphite pulping is concerned, has
already been tested on a commercial scale with Ophiostoma piliferum for craft
pulping (Messner 1998) and that “biopulping ... is close to mill application”
(Messner et al. 2003).
As a “by-product”, the biotechnological attempts of using fungi or their
enzymes in the pulp and paper industry in processes as biopulping, biobleaching,
and fiber modification have spurred the understanding of the mechanisms
of wood decay (Chap. 4). It may however be mentioned that the most often
investigated fungus with respect to enzyme mechanisms, P. chrysosporium,has
beside chip piles no relevance for wood, neither for trees nor for constructional
timber.
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