Biodegradation of lignin by the white rot fungus Polyporus varius and its promising potential for biopulping

Abstract

Much attention has currently been drawn toward development of new environmentally-friendly technologies for pulp and paper manufacture. 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, paper pulps are usually produced from wood fibres using chemical and mechanical methods. Mechanical pulping characterized by its high yield, is considered as an appropriate 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 cellulose. A second drawback to chemical pulping is the large amount of potentially hazardous chemicals which pose a threat 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. 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 in biopulping. In this study, ten strains of 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 Poplar chips. During 14-day liquid culture, the enzymatic activity of LiP reached 213 IU/mL, Lac 546 IU/mL and MnP 1009 IU/mL, respectively. The degradation rate of lignin was 24.16% at 37°C, pH 4.5 and 10% of inoculum concentration and electrical energy consumption was reduced by 19.60% during refining after treating the chips for 20 days. The experiment indicated that it will be a potential lignin degrader with application in biopulping.