SCREENING OF LIGNIN-DEGRADING FUNGUS AND ITS POTENTIAL USE IN BIOPULPING

摘要

Pulp and paper manufacturing constitutes one of the largest industry segments in the world in term of water and energy usage and total discharges to the environment. Traditionally, pulps are usually produced from wood fibres using chemical and mechanical methods. Mechanical pulping characterized by its high yield, is considered as a way to extend the resources used as raw materials, but it is extremely energy intensive. The primary chemical pulping process employed today is the kraft process, in which wood chips are cooked in a solution containing sodium hydroxide and sodium sulfide. The yield from chemical processes is generally lower than mechanical pulping due to some degradation of lignin and carbohydrates. A second drawback to chemical pulping is the large amounts of potentially hazardous chemicals which pose a danger to both mill workers and the environment. Nowadays, biopulping is being considered a suitable or complementary alternative to traditional methods due to its ability to reduce the environmental impact of paper-mill industries and to save energy and chemical costs. Biopulping is defined as the treatment of lignocellulosic materials with lignin-degrading fungi prior to pulping. Biopulping uses fungi that are known to be able to degrade wood as well as lignin constituent of wood. Amongst these white rot fungi are the most proficient biodegrader. The fungus is non-sporulating and is a selective lignin degrader. It colonizes either on living or dead wood and decomposes all wood polymers including lignin and extractives making it to be extremely potential to be used during biopulping. In this study, the mechanism of lignin biodegradation was investigated. At the same time, ten strains of the white-rot fungi that can produce lignin peroxidase (LiP), laccase(Lac) and manganese peroxidase(MnP) were screened and then one strain of them, which has the most excellent enzymatic activity, was selected to grow on Broussonetia papyrifera chips. During the period of 14-day liquid culture, the enzymatic activity of LiP reached 213 IU/mL, Lac 546 IU/mL and MnP 1009 IU/mL, respectively. The lignin degradation rate of Broussonetia papyrifera chips reached 23.07% and it caused reduction of electrical energy by 19.81% at 37°C, pH 5.0 and 10% of inoculum concentration after treating the chips for 20 days. The experiment showed that it will be a potential lignin degrader with application in biopulping.