Treatment of wood chips with lignin-degrading fungi prior to pulping has been shown to have great potential for mechanical as well as chemical pulping on a laboratory scale. Ceriporiopsis subvermispora, when grown on aspen or loblolly pine for 4 weeks, was found to be superior to other fungi. On aspen there was an energy savings of 47%, and an increase in burst and tear indices of 22% and 119%, respectively. With loblolly pine, energy savings amounted to 37%, while burst and tear indices increased by 41% and 54%, respectively. The weight loss was only 6%, but a decrease in optical properties had to be accepted. After sulfite cooking of wood chips pretreated for 2 weeks, the Kappa number decreased by 30% with hard- and softwood. Tensile and tear indices decreased by only 10%, while the brightness of unbleached pulp increased by 4% with birch. Information obtained by immunoelectron microscopy and differential staining led to the conclusion that the biopulping effect obtained after 2 weeks of incubation cannot be explained by the direct action of enzymes on lignin or polysaccharides. Instead, a low molecular mass agent is considered to be responsible for the biopulping effect. These results have changed the aims of biopulping from an emphasis on removing the bulk of lignin to an emphasis on a short-term process, lasting 2 weeks and yielding a low mass loss. Data on these kinetics of fungal development and the degree of asepsis will help to scale-up the process. An advanced chip pile is assumed to be the most feasible process design, rather than a controlled enclosed reactor.

Biopulping : an overview of developments in an environmentally safe paper-making technology

Lignin is the most abundant aromatic polymer in nature. It is synthesized by higher plants, reaching levels of 20–30% of the dry weight of woody tissue. Although white-rot fungi were long recognized as efficient lignin-degrading microbes, research on their enzymology and genetics was somewhat neglected until the past decade. The impetus for increased research interest can be traced to the discovery of “ligninases” and potential commerical applications in the pulp and paper industry and in the degradation of xenobiotics. In this chapter, we briefly summarize several decades of research on white-rot fungi, and readers are referred to several comprehensive reviews for additional background information. Recent developments in molecular biology and enzymology are emphasized. Areas where knowledge is incomplete are highlighted.

https://www.fpl.fs.fed.us/documnts/pdf2004/fpl_2004_cullen002.pdf

Enzymology and Molecular Biology of Lignin Degradation

This review article summarizes the results on microstructural changes and delignificantion, lignin-degrading enzyme systems, and biopulping of wood with lignin-degrading fungi. Biopulping, defined as the treatment of wood chips with lignin-degrading fungi prior to pulping, saves substantial amount of electrical energy during mechanical pulping, results in stronger paper, and lowers the environmental impact of pulping. Optical properties are diminished; however, brightness can be restored readily with peroxide bleaching. The economics of the process look attractive if the process can be performed in a chip-pile based system. Past work on biopulping had been minimal, however a comprehensive evaluation of biopulping at the Forest Products Laboratory suggests that biopulping has a good chance of commercial success.

Fungal delignification and biomechanical pulping of wood

The presence of lignin in lignocellulosic biomass leads to a protective barrier which prevents enzymes from being accessible to cellulose and hemicellulose for hydrolysis. As a result, pre-treatment is a 'must' step for subse- quent enzymatic hydrolysis. Bio pre-treatment is normally conducted at low temperatures and low pressures without using expensive equipment, chemical agents, reactors, and additional energy for lignin removal and biomass struc- ture destruction. Therefore, it is a green, safe, and inexpensive method. White-rot fungi (WRF), a group of fungi (more than 1500 different species) are successfully applied in bioconversion processes such as sewage treatment, biopulp- ing, conversion of forest and agricultural residues to animal feeds, and the production of edible or medicinal mush- rooms. In the bio pre-treatment process, WRF are mostly used for secreting ligninolytic enzymes, a variety of donor substrates and selective degradation of lignin. Current research related to WRF bio pre-treatment is mainly focusing on the following four aspects: (i) selection of candidate strains for certain biomass materials; (ii) optimization of cul- tivation methods; (iii) characterization of fungal treated materials; and (iv) evaluation of combining bio pre-treatment with chemical or physicochemical approaches. Future prospects and recommended research work on applying WRF in bio pre-treatment are also briefl y introduced and summarized in this review. These include (i) integrated methods (i.e. co-treatment with organic solvents, diluted acids, supercritical CO2 and ionic liquids) to resolve problems exist- ing in fungal pre-treatment applications; (ii) mutation breeding and crossbreeding of fungal mycelia to obtain engi- neering strains; and (iii) integration of fungal pre-treatment with simultaneous saccharifi cation and fermentation to produce biofuels and value-added products. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

Impact and prospective of fungal pre-treatment of lignocellulosic biomass for enzymatic hydrolysis

Fungal pretreatment of unsterilized yard trimmings for enhanced methane production by solid-state anaerobic digestion

Fresh wood chips destined and stored for pulp production are rapidly colonized by a variety of microorganisms, including many species of fungi. These organisms compete vigorously while easily assimilable foodstuffs last, and then their populations decrease. They are replaced by fungi that are able to degrade and gain nourishment from the cell wall structural polymers: cellulose, hemicelluloses, and lignin. Left unchecked, these last colonizers, mostly “white-rot fungi,” eventually decompose the wood to carbon dioxide and water. Some of them selectively degrade the lignin component, which is what chemical pulping processes accomplish. Biopulping is the concept of deliberately harnessing white-rot fungi for pulping.

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Use of Fungi in Pulping Wood: An Overview of Biopulping Research

A method of making a wood pulp is disclosed. Wood is first chipped into wood chips. The wood chips are treated with an amount of sulfite salt sufficient to inhibit indigenous microorganism growth. The treated wood chips are introduced into a bioreactor and inoculated with a culture of white-rot fungus. The wood chips are incubated under conditions favoring the propagation of white-rot fungus and then mechanically pulped.

John W. Koning

Papers

Use of Fungi in Pulping Wood: An Overview of Biopulping Research

Method of pulping wood chips with a fungi using sulfite salt-treated wood chips