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Biochemical Pulping

Gary M. Scott, Ph.D. Faculty of Paper and Bioprocess Engineering Empire State Paper Research Institute State University of New York, College of Environmental Science and Forestry gscott@esf.edu

Summary

Biopulping is defined as the pretreatment of wood chips with a lignin-degrading fungus prior to pulping. Previous work has established the efficacy of biopulping for mechanical pulping, resulting in energy savings of over 30%. This research transfers that technology to kraft pulping. We hypothesize that the biological action of the white-rot fungi cause a swelling and softening of wood cell walls as a result of the modification and depolymerization of the lignin. This action should result in better liquor penetration thus improving the kraft process.

Approximately 85% of the pulp produced in the United States is manufactured with the kraft pulping process. Thus, the research has a high interest in the industry due to its potential to save energy, reduce chemical needs (both pulping and bleaching), and have less impact on the environment. The biotreatment process is designed to produce a uniform treatment. Thus, the uniformity of the chips being sent to the digesters can potentially improve, since random degradation by other organisms is eliminated through the use of biopulping. Promising results have been seen with the kraft pulping of both eucalyptus and kenaf. For these two substrates, we found significant reductions in the bleaching needs after kraft pulping.

Biopulping with the white-rot fungus Ceriporiopsis subvermispora has been shown to be highly effective for sulfite pulping. Focus was on the kappa number and yield, effluent quality, and pulp bleachability after pulping. During sodium bisulfite pulping, the fungal pretreatment reduced the kappa number by 27%, with slightly lower yield compared to the control. During calcium-based pulping, the two strains of the fungus reduced the kappa number by 48% and 21%, respectively, compared to the control. No loss in yield was noted. A simple kinetic model of the reactions which helped in the interpretation of the results. Cooking liquor consumption was not appreciably affected by the fungal treatment. Environmentally, BOD and COD (Biological and Chemical Oxygen Demand) remained essentially unaffected, while the effluent toxicity was substantially lowered with the treatment. Although a slight loss in brightness was seen with the treatment, additional bleaching was not needed to bring the pulp up to 80 brightness. Thus, the fungal pretreatment was shown to be advantageous for sulfite pulping.

On an annual basis, large quantities of agricultural plants and their residues are available in the United States and throughout the world. Most of these resources would make an excellent alternative source of fiber for paper manufacturing, particularly in light of the increasing pressure being placed on the nation's forests, both from diminishing return and environmental legislation. The fungal treatment of wood chips can reduce pollution, reduce pulping chemicals, and improve paper properties. An environmentally sound approach for pulp production would be to use nonwood fibers together with biological treatments. The results indicated that biotreatment is very effective for both the mechanical and kraft pulping of kenaf. For mechanical pulping, the energy savings and property improvements that are seen in wood are also seen with kenaf. For the kraft pulping of kenaf, a more easily bleached pulp with improved strength properties results.

Current Work

The overall goal of this research is to reduce the consumption of chemicals and energy during the kraft pulping process and reducing the amount of odor-producing chemicals involved in the process. The specific objectives of this research are:

1. to study the effects of pretreatment on the kraft pulping process;
2. to correlate the fungus induced changes in wood with the pulping process and optimize the fungus pretreatment/kraft pulping systems;
3. to design and engineer a process that produces uniformly treated chips with a minimum disruption of a mill's wood yard operation.

The pertinent questions that will be answered by this work will be:

1. How are the pulping kinetics and initial lignin content changed by fungal pretreatment?
2. How does the pretreatment affect the spent liquor both from an environmental standpoint and the recovery system?
3. What are the economic (and social) benefits of incorporating biopulping into a kraft pulp mill?

Co-Workers

Key Publications

1. Scott, Gary M.; Akhtar, Masood; Lentz, Michael, Sykes, Marguerite; and Abubakr, Said (1995). "Environmental Aspects of Biosulfite Pulping," In Proceedings of the 1995 Tappi Environmental Conference , Atlanta, GA: Tappi Press. pp. 1155-1161. (PDF)
2. Scott, Gary M.; Akhtar, Masood; Lentz, Michael, Sykes, Marguerite; and Abubakr, Said (1995), "Biosulfite Pulping using Ceriporiopsis Subvermispora ," In Proceedings of the Sixth International Conference on Biotechnology in the Pulp and Paper Industry: Advances in Applied and Fundamental Research , pp. 217-220.
3. Scott, Gary M.; Akhtar, Masood; and Lentz, Michael (1995), "Fungal Pretreatment of Wood Chips for Sulfite Pulping," In Proceedings of the 1995 Tappi Pulping Conference , Atlanta GA: Tappi Press. pp. 355-361. (PDF)
4. Messner, Kurt; Koller, K.; Wall, Mary Beth; Akhtar, Masood; and Scott, Gary M. (1998). "Fungal Pretreatment of Wood Chips for Chemical Pulping," In: Environmentally Friendly Technologies for the Pulp and Paper Industry , John Wiley & Sons, New York. pp.385-419.
5. Ahmed, Aziz; Scott, Gary M.; Akhtar, Masood; and Myers, Gary C. (1998). "Biokraft pulping of kenaf and its bleachability," In: 1998 North American nonwood fiber symposium , Tappi Press, Atlanta, GA, pp. 231-238. (PDF)
6. Ahmed, Aziz; Akhtar, Masood; Myers, Gary C.; and Scott, Gary M. (1998) "Kraft pulping of industrial wood waste," In: Proceedings of the 1998 Pulping Conference , Tappi Press, Atlanta, pp. 993-1000. (PDF)
7. Scott, Gary M. and Akhtar, Masood (2001). "Biotechnological Applications of Lignin-Degrading Fungi (White-Rot Fungi)," In: Biopolymers: Lignin, Humic Substances and Coal (Alexander Steinb\"uchel, Ed.), Wiley-VCH, Weinheim, Germany, pp. 181-207.

Copyright 2001, Gary M. Scott. All rights reserved.