Biopulping and Biobleaching:

An Energy and envioronment Saving Technology

for Indian Pulp and Paper Industry

Pulp and paper industry in India is the sixth largest energy consumer in the industrial sector and it’s energy costs account for about 24.5% of the total manufacturing cost. Paper can be made from wood, agricultural residues or from waste paper, having a share of 43%, 28% and 29%, respectively. The use of wood based technology is gradually on the decline because of capital and raw material availability constraints. The share of waste paper (secondary fiber) based technology, which is less energy intensive, is expected to increase in future. The production of pulp and paper involves three major processing steps – pulping, bleaching, and paper production. The type of pulping, and amount of bleaching used, depends on the nature of feedstock and the desired quality of the end product. The production of the chemical pulps has been dramatically altered over the past decade in response to new environmental regulations and consumer activism. Although current pulp manufacturing technologies address required environmental performance regulations, new challenges and opportunities are developing. The need for improved manufacturing efficiencies, enhanced wood utilization practices and continuing environmental concerns has become one of the central research themes of the late 1990’s. Recently, significant interest has developed in the production of bleached kraft pulp originating from high lignin content pulps. The primary factor contributing to this research is the well known loss of pulping selectivity when attempting to remove the last vestiges of lignin in pulps by kraft delignification. Several recent publications have examined the improved yield benefits of utilizing a single or double oxygen stage to delignify high lignin content pulps.

Unfortunately, chemical consumption and environmental considerations severely limit the types of delignification technologies that can be employed with high kappa pulps. To date, the two most promising delignification technologies for high lignin content pulps consist of using oxygen delignification or modifying the pulping process. The use of fungus prior to pulping offers an attractive opportunity for mechanical wood pulp facilities. This technology could save an estimated 30% of the energy consumed in refining the mechanical pulp. The technology also improves paper strength, reduces pith content, and could reduce the emissions of volatile organic compounds.

Biopulping is the treatment of wood chips and other lignocellulosic materials with natural wood decay fungi prior to thermomechanical pulping. The technical and economic feasibility of biopulping was established through two industry sponsored consortia and 22 pulp and paper and related companies of U.S.A.

The fungal treatment process fits well into a mill’s woodyard operations. Wood is debarked, chipped and screened according to normal mill operations. Then chips are briefly steamed to reduce natural chip microorganisms, cooled with forced air, and inoculated with the biopulping fungus. The inoculated chips are piled and ventilated with filtered and humidified air for 1 to 4 weeks prior to processing.

While engineering analysis indicates that the biopulping process is technologically feasible, economic analysis indicates that the biopulping process is also economically beneficial. The use of biopulping as a pretreatment for the kraft process is still an open research issue. Finally, the use of this technology for other substrate – non woody plants such as kenaf, straw, and corn stalks will have to be investigated.

Reduced electrical energy consumption (at least 30%) during mechanical pulping; potential 30% increase in mill through put for mechanical pulping; Improved paper strength properties; Reduced pitch content and Reduced environmental impact.

The biobleaching of kraft with laccase/mediator continues to receive strong interest, in part due to the discovery of new mediators for laccase. Therefore, new environmentally benign elemental chlorine free (ECF) and totally chlorine free (TCF) bleaching technologies are necessary for minimizing the hemi-cellulose content in dissolving pulp, adjusting the brightness at a high level and improving simultaneously, the quality of the effluents in terms of toxicity and adsorbable organic halogen (AOX). Biological methods of pulp prebleaching using xylanases provide the possibility of selectively removing upto 20% of xylan from pulp and saving up to 25% of chlorine containing bleaching chemicals. Alternatively, pulp can be bleached with white-rot fungi and their lignolytic enzymes, enabling chemical savings to be achieved and a chlorine free bleaching process to be established.

Reduced consumption of bleaching chemical; reduced adsorbable organic halogen; improved pulp and paper quality; improved brightness; reduced effluent toxicity and pollution load.

The paper industry has been investigating biological replacements for some of the chemicals used in the paper making process in the hope of reducing capital and operating costs and minimizing its environmental impact. One use of biological treatments, which has been of recent interest, is for reducing refining energy consumption in mechanical pulping processes. It has been shown that certain fungal treatments can achieve this end without damage to the resulting fiber and possibly with better quality fiber in the end. There has also been some success in pretreating wood chips for chemical pulping processes. In this type of application more uniform delignification, improved yield, or decreased chemical usage are the goals. Research into chip treatment with cellulose and hemicellulose enzymes is just beginning. Pretreatment of hard wood chips with Pseudomonas chrysosporium shows an improvement in kraft pulp yield after 20 days, but is more pronounced after a period of 30 days. The resulting pulp compared at the same kappa number has a higher tensile strength and a corresponding lower tear strength. The pulps also refine faster, thus saving refining energy to achieve the same pulp properties.

White rot fungi produce extracellular oxidative enzymes, which initiate oxidation of lignin. Due to their lignin degrading capacity, whole cultures of various white rot fungi cause extensive brightness gains and delignification of kraft pulp. MnP is considered to be the most important enzyme involved in kraft biobleaching. Pretreatment of sulphite pulp with Aureobasidium pullulans xylanases could improve alkali volubility and brightness, important parameters of dissolving pulp for producing viscose rayon. The major effect caused by xylanases is a selective reduction of the hemicellulose content of dissolving pulp. On the other hand, biobleaching with the white rot fungus Ceriporiopsis subvermispora could enhance significantly the brightness affecting the cellulose content of the dissolving pulp.

The use of environment friendly processes is becoming more popular in the pulp and paper industry and therefore biotechnological processes are coming to the forefront of research. An application of biotechnology in Indian pulp and paper industry is the xylanase pre-bleaching of pulp. Extensive R & D work on enzymatic prebleaching of pulp from raw materials is widely prevalent in India. Due to pressure on reducing organochlorine compounds in the effluent, more and more paper mills are getting interested in this process and have also started taking mill trials. The commercialization of freeness control and biomechanical pulping will serve to continue the optimization of these processes and reduce the costs associated with the enzymes and fungi. Enzyme technology offers great potential for reducing capital and energy costs, improving properties of degraded fiber furnishes, and reducing the environmental impact of paper making processes.