Utilization of wood-decay fungi for biokraft pulping of softwood

English: The forest products industry is one of the most important earners of foreign exchange for South Africa. The major focus of the industry is the production of pulp with an annual capacity of 2,4 million tons. Wood from plantations of exotic trees is the most important source of fibre, but other fibre sources are also used. Biotechnology can play a significant role in the industry to produce high value products at lower cost and could reduce the environmental impact of conventional processes. Biopulping is potentially the most important of these biotechnological processes, because it can influence all downstream operations. The aim of this study was, therefore, to develop a biopulping process for the treatment of softwood at the Sappi Ngodwana kraft mill in Mpumalanga. Initially, 278 strains of wood-decay fungi were collected from various natural habitats. This collection represents a diversity of fungal families and included species that have not previously been recorded from South Africa. The first step in selecting suitable fungal strains for biopulping was to characterize different groups on the basis of the enzymes that they produce and their oxidase reactions. The suitability of these strains for the pre-treatment of softwood chips prior to kraft pulping was subsequently assessed by evaluating their influence on kappa number, yield and strength properties of pulp. Seven of the strains tested were able to reduce the kappa number of pulp significantly, without having a significant influence on the pulp yield. These strains were more efficient than strains of Phanerochaete chrysosporium and Ceriporiopsis subvermispora that have been patented for other biopulping applications. Treatment of wood with strains of Peniophora sp., an unidentified specie as well as two strains of Stereum hirsutum resulted in pulp with improved strength properties. The envisaged biopulping process aimed at treating wood chips in outside chip storage with a biopulping fungus. The aim of one study was to investigate conditions such as temperature, moisture, CO2 and microbial populations that develop in a chip pile, and to determine the suitability of the chip pile for colonization by biopulping fungi. High temperatures and high moisture levels were observed in some areas of the chip pile, which suggested that part of the pile was unsuitable for colonization by mesophilic fungi. It will, therefore, be necessary to manage the chip pile to maintain a suitable environment for biopulping. Problems were experienced with poor colonization of freshly chipped softwood by biopulping fungi. The effect of contaminating microbes and inhibitory compounds present in wood was, therefore, studied. It was found that the inhibition of biopulping fungi by α-pinene and by contaminating microbes were both very important. The inhibition by microbes, as well as by extractives, was mitigated by a short steam treatment of wood chips. Steaming for ten minutes under atmospheric pressure could be an economical method to improve colonization by biopulping fungi. Alternatively biopulping fungi with good competitive ability and tolerance to monoterpenes could be selected. Pinus patula wood chips were pre-treated with a selected strain of Stereum hirsutum to determine the optimal conditions for the kraft pulping of pre-treated softwood and to do an economic evaluation of the process. Chips were pulped on a small scale under various pulping conditions. Lignin content, yield, and viscosity of the pulp as well as alkali consumption were evaluated. The results were used to develop models for biokraft pulping. This study showed that biopulping can reduce the kappa number of pulp or reduce the pulping time. Pulp yield losses were relatively small when pulps with low kappa number were produced. Increased alkali consumption was, however, an important factor in the economic evaluation.