Differences in Bleaching Responses from Fungal versus Bacterial Derived Enzymes, 2011 International Pulp Bleaching Conference
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Several mills within North America have been successfully employing xylanase enzymes expressed from tricaderma reesei, (a fungus) as part of their bleaching sequence for many years. These mills encompass hardwood and softwood species with and without oxygen delignification. These mills also include three, four, and five stage bleaching sequences. The North American mills tend to report increased pulp brightness ceilings and decreased bleaching costs as benefits associated with the application of enzymes in the bleaching process. Laboratory testing suggests that eucalyptus pulp is highly susceptible to both fungal and bacterial derived enzyme bleaching and should result in significant levels of cost savings in South American mills. At least four different mills in South America have attempted to perform enzyme bleaching trials using bacterial derived enzymes. Each of these mill trials have resulted in significantly increased operating costs and/or unsustainable operating conditions. More recently, one of these South American mills has performed a short trial employing a commercially available fungal derived enzyme. This trial was technically successful. The current work attempts to determine why the South American mill experiences with bacterial derived enzymes have been poor while North American mills and the one South American mill trial have good results with fungal derived enzymes. Operating conditions and trial goals for both North and South American mills will be examined and discussed.