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Pre-treatment of beech wood by the erosive strain of Phanerochaete chrysosporium and lignin-selective strain of Ceriporiopsis subvermispora and its effect on the course of organosolv and Magnefite pulping. (Part 1: pre-treatment of normal wood)
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Pre-treatment of beech wood by the erosive strain of Phanerochaetechrysosporium and lignin-selective strain of Ceriporiopsis subvermispora and its effect on the course of organosolv and Magnefite pulping. • (Part 1: pre-treatment of normal wood) • Rastislav Solár, Ladislav Reinprecht and František Kačík
Introduction • in recent decades much work has been done to modify the conventio- • nal pulping processes. The aim was to reduce the consumption of • energy and chemicals in pulping and bleaching of pulp, • possible means to achieve this goal may be the biotechnologies, espe- • cially the fungal pre-treatment of raw materials and application of • enzymes and bio-mimetic systems in the pre-bleaching of crude pulps. • The aim of presented contribution was to estimate the influence of medium-term fungal pre-treatment of beech wood on its chemical composition and the course of its chemical pulping.
Materials and methods For biodegradation of sound beech wood the erosive (P.chrys.) and lignin-selective (C. subv.) white-rot fungi were used. The conditions of cultivation have been described in the contribution. Sound and bio-pretreated chips of beech wood were submitted to acid catalysed organosolv pulping at a temperature of 170 oC for 10, 20, 30, 60 and 90 min. The Magnefite method (acid sulphite process) of pulping was also tested. The cooks were carried at 140 oC during 15, 30, 45, 60 and 120 min. Analyses of wood and pulp are thoroughly described in the correspon- ding contribution (CD ROM).
Results and discussion • General data: • biotic pre-treatments of normal beech wood resulted in its weight loss • ( 6.24 % P. chrys. and 3.1 % C. subv.) due to biotic degradation of its • components (Tab. 1), • analyses confirmed a lignin-selective effect of the applied strain of C. • subvermispora, givenby doubled amount of removed lignin as com- • pared to that removed by erosive fungus P. chrysosporium (Tab. 1), • the amount of degraded cellulose was negligible, especially if lignin- • selective fungus was applied (Tab. 1).
Tab. 1: Weight loss of beech wood and its components resulting from 28-day degradation by the erosive strain of P. chrysospori- um and the lignin-selective strain of C. subvermispora (%) The yields of organosolv pulp from sound and pretreated normal beech wood versus time of pulping are plotted in Fig. 1.
As it can be seen in Fig.1, the biodegradation of beech wood did not influence a drop in the yield of pulp positively in the first phase of of organosolv delignification. • At the end of the second phase of pulping the effect of biodegradati- • on became more apparent, and the final yield of pulps from biodegra- • ded material was reduced by approximately 5 %. • In Fig. 2, the kinetic plotts of organosolv delignification are presented, including the relative rate constants of the first phase of this process.
As seen in the Fig.2, increase in the rate constants of organosolv • delignification of both biodegraded samples was only moderate • (approx. by 7.5 %), however the contents of residual lignin in pulps • from bio-degraded chips after 90 minutes of pulping were apparent- • ly reduced. • More effective pre-treatment in this regard seems to be the pretreat- • ment by erosive strain of P. chrysosporium. • The effect of fungal pre-treatment of beech wood on the course of • its delignification was not as high as expected.
For example, the pre-treatment of hornbeam wood by the same strain of P.chryso- sporiumunder similar conditions biodegradation and the same conditions of pulp- ing doubled the kinetics of its delignification (Fig. 3). • Fig. 3: Kinetic plots of acid catalysed organosolv delignification of sound and biode- • graded hornbeam wood by erosive strain of P. chrysosporium (t = 170 oC) • (Solár, et al. 2001 a)
A marked difference in the course of organosolv delignification of • hornbeam wood is most probably given by a different degree of bio- • degradation of the compared substrates. • The different axial permeabilty of beech and hornbeam wood in sound • and bio-degraded state possibly influences the rate of organosolv de- • lignification significantly. • Magnefite pulping • In Fig. 4, the plots expressing the yield- time dependence of Magnefite • pulping of sound and biodegraded beech wood samples are presented.
Fig. 4: Yield of pulps from sound and degraded beech wood chips prepared by the Magnefite method (t = 140 oC)
As seen in Fig. 4, biotic pre-treatment of beech wood by the tested white rot fungi did not influencethe yield of Magnefite pulp marked- ly, and the dependence of yield on the time of pulping were almost identical, regardless the sound or pre-treated chips of beech wood were processed. Similarly, the effect of fungal pre-treatment on the course of Magne- fite delignification was not any remarkable (Fig. 5).
Fig. 5: Kinetic plots of acid sulphite (Magnefite) delignification of sound and biodegraded chips (t = 140 oC)
The increase in the relative rate constants of beech wood Magnefite de- lignification due to biotic pre-treatment, illustrated in Fig. 5, was only only very moderate - by 4.3 %, regardless to the species of fungus used. Also, the final contents of residual lignin in the compared pulps from sound and degraded wood were almost identical (Fig. 4). The results concerning the Magnefite pulping showed only a slight influence of fungal pre-treatment of normal beech wood on the pulp yield and kinetics of pulping.
Conclusions • The experimental data allow to draw the following conclusions: • biodegradation of beech wood specimens by the selected white-rot fungi led to their apparent delignification, this was however deeper when the lignin-selective fungus C. subvermispora was applied, • fungal pre-treatment by erosive strain of P. chrysosporium caused mo- derate degradation of hemicelluloses, and removal of cellulose did not exceed 1.5 %, • degradation of hemicelluloses by lignin-selective fungus C. subvermi- spora was negligible, while the cellulose content remained unchanged,
both white-rot fungi influenced positively yield of organosolv pulps and content of residual lignin in them, • biodegradations of a substrate influenced neither the final yield of Magnefite pulps, nor the contents of residual lignin in them, • pre-treatment of beech wood by the applied white-rot fungi moderate- ly increased the rate of both fast and slow phases of organosolv de- delignification, • pre-treatment of beech wood by the applied white-rot fungi accelera- ted to a minor degree only the fast phase of Magnefite delignificati- on,
pre-treatment of beech wood by selected white-rot fungi did not influence properties of K-H cellulose and pulps significantly; da- ta are a subject of the contribution recorded on CD ROM. Address of the authors: Faculty of Wood Sciences and Technology, Technical University of Zvolen, SR.