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Commercial Success of ECLAIR Programme
AGRE-0047: Biopulping and biobleaching |
AGRE-0047: Biopulping and biobleaching
Science Background
In the pulping process cellulosic fibres are released from the plant material, by destruction or removal of most of the hemicellulose and lignin components. Residual lignin has to be bleached. In conventional processes pulping and bleaching are achieved using chemicals, such as strong alkali solutions, chlorine compounds or peroxides. A number of different types of filamentous fungi which grow on dead plant material produce enzymes that are capable of breaking down hemicellulose and lignin without adversely affecting the cellulose fibres. This raises the possibility of developing biological pulping methods.
Objectives
The aim of this project, coordinated by INETI (Portugal), was to investigate the feasibility of producing paper pulp from various raw materials, including eucalypt chips and straw, using biological methods as substitutes for the alkali and chemical (chlorine) bleaches used at present. This would be achieved by identifying and isolating suitable microorganisms; producing mutants or strains with enhanced ability to degrade lignin; and then characterizing the enzyme complex involved in lignin degradation. Enzymatic and non-enzymatic methods of generating hydrogen peroxide as a bleaching agent would also be compared. Further objectives included the design of a reactor in which the biological systems for pulping (biopulping) of wood chips and straw could be carried out. The project also aimed to investigate appropriate enzymatic solutions for the biobleaching of Eucalyptus Kraft pulp and then characterize the bleached pulp. This was to be followed by pilot scale studies to enable technical and economical evaluation of an integrated biobleaching process.
Significant changes and results since end of ECLAIR
Research has continued under AIR, confirming and extending the results of this project. Adoption of processes arising from this work would require significant changes in well-established industrial procedures, within an industry that has considerable capital investment. A clear demonstration of significant cost-benefits would be required.
Results
At end of this ECLAIR project
The project enabled comparison between the, then, best known fungus capable of degrading lignin (Phanerochaete chrysosporium) and other fungi such as Aspergillus, Penicillium and Pleurotus, with the latter shown to be a selective degrader of straw lignin. In contrast the Ascomycetes, such as Aspergillus, were shown not to degrade lignin, but have xylanase activity, and hence could degrade hemicellulose. Several enzymes involved in lignin degradation (lignin peroxidase, manganese peroxidase, laccase) hydrogen peroxide generation (phenyl oxidase, aryl alcohol oxidase, glucose oxidase) as well as others involved in oxidation/reduction reactions (cellobiose dehydrogenase and cellobiose:quinone oxidoreductase) were isolated and characterized. An electrochemical cell was also designed, as an alternative to the biological route of peroxide generation. Attempts to increase the levels of enzymes available included expression of the heterologous P. chrysosporium LiP gene in A. niger and over production of LiP by P. chrysosporium, as well as over production of xylanase by A. niger. Another fungus, Pycnoporus cinnabarinus was shown effective in biopulping of eucalypt chips, while species of Pleurotus were shown to be effective in straw delignification and xylanases from A. niger were shown to be effective in biobleaching of eucalypt pulp - both with significant energy savings.
New reactors were developed as prototypes for solid state microbial pulping and non-enzymatic continuous hydrogen peroxide delivery to air-lift reactors for peroxidase production. It was concluded that bioprocessing for use in the paper and pulp industries must be developed as part of a fully integrated process that takes account of the economics of its introduction and the environmental impact of the whole process. Adoption of the actual processes has to be decided on a case by case analysis into aspects related to the use of peroxidases and auxiliary systems, scaling up, molecular biology and reactor technology in discussion with the industry.
Current position
Some participants from this project, including the coordinator, participated in AIR2-CT93-1291: Biological delignification in paper manufacture: optimisation of enzyme mixtures for treating cereal straw and other non-wood materials. This extended and confirmed the results of the ECLAIR project as follows. The refining, cooking and papermaking features of straw substrates treated with enzymes or fungal cultures were evaluated. A decrease in the energy necessary to produce biomechanical pulps gave test sheets with properties similar to those from mechanical pulps obtained with higher energy consumption. Combining biological pretreatment was with soda cooking gave higher quality paper. Other results suggested that some process improvement could be obtained using laccase/ABTS as a pretreatment before soda cooking of wheat straw while the most promising result was attained with the MnP/Mn2+ system as a post-treatment to improve characteristics of crude or refined pulp. This gave better mechanical properties, including increased tensile indices, and again resulted in a significant energy saving.
Impact
Commercial
Results do not appear to have been extensively applied on a commercial basis.
Associated
An alternative biological approach has been to use genetic engineering as a means of reducing lignin content, ( AGRE-0021) enabling a less chemical-intensive conventional pulping process to be used. This approach is more attractive to the industry, since it does not necessitate adoption of new factory processes.
Further Information
Duarte, J.C. (1997) Biopulping and biobleaching. In: Proceedings of the European Conference on Pulp and Paper Research: The present and the future (Eds: A. Arabatzis, L. Eriksson, I. Seone) pp354-361
Contacts
Author
CSIC
INETI
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by CPL Press:
03/07/2007
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