FAIR-CT98-5009 Methods to improve the selectivity of lignin degradation in biopulping processes

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FAIR Area 1.3 - Forestry-Wood Chain : FAIR Marie Curie Research Training Grants : Paper/Pulp

Objectives:

The goal of this research was to develop new methods to improve the selectivity of biopulping processes. The strategies considered were based on removing nitrogen from wood chips by both incubation with sap-staining fungi and pre-treatment with proteases. The investigation was based on three major research tasks:

• Wood pre-treatment with sap-staining fungi that reduce the nitrogen availability for subsequent biopulping.
• Wood pre-treatment with proteases and washing of liberated amino acids to reduce the nitrogen availability in subsequent biopulping.
• Optimisation of biopulping with nitrogen depleted wood chips.

Activities and Results:

The effectiveness of reducing the N content in lignocellulosic materials as a means to enhance the selectivity of lignin degradation in biopulping processes was evaluated. Pre-inoculation with a sap-stain fungus (Ophiostoma piliferum), as well as solvent extraction and enzymatic pre-treatment with proteases, were used to remove the N from woody materials. The best results were obtained with the protease treatment that reduced up to 68% of the original N in hemp stems and by water extraction that decreased the N content by 39%. A rapid screening method to assess wood delignification selectivity by different white-rot fungal strains was developed and optimised. Bjerkandera sp. showed the highest selectivity in the degradation of Klason lignin in both hemp stem and poplar wood. Hemp stem containing varying levels of N (from 32% to 500% of the initial N content in fresh material) was inoculated with Bjerkandera sp. The results obtained showed a strong positive correlation between the level of N in hemp and the selectivity of lignin degradation. The highest selectivity index (i.e. ratio of percent lignin removal to percent holocellulose removal by the fungus) was found in the treatment corresponding to the lowest N content in the substrate (hemp pre-treated with the protease). A sharp decrease in the selectivity of Klason lignin degradation was observed with increasing N content in hemp. High N contents also contributed to enhance the overall degradation of the lignocellulosic material. Significant differences were also found in the ligninolytic (MnP, LiP, MIP) as well as the cellulolytic activities, reflecting the different N levels in the substrate tested. The highest ligninolytic enzyme activity was detected after the water extraction treatment. The lowest cellulose activity was found for the treatment with the lowest level of N. |In addition, several experiments were carried out in order to confirm the key role played by N in the biopulping of other lignocellulosic feedstocks commonly in the pulp and paper industry. The same tendency found for hemp was observed for a range of species, with the exception of Miscanthus.

Conclusion:

The results indicated the relative potential of wood pre-treatment methods ussed to reduce the nitrogen content in wood chips as a means to enhance the selectivity of lignin degradation in biopulping.

Keywords: biopulping, hemp

Contacts

Scientific Supervisor

• Reyes SIERRA-ALVAREZ / University of Agriculture Wageningen Division of Wood Science / NETHERLANDS