STUDIES ON PRODUCTION OF MICROBIAL ENZYMES AND THEIR USE IN BIODELIGNIFICATION OF BAGASSE

Abstract

The pulp and paper industry is intensive in terms of consumption of raw materials, chemicals, energy, water and capital requirements besides environmental emissions. The energy cost as a percentage of manufacturing cost has increased from 15% in 1979-80 to about 33% in 2007-08. The current need in the pulp and paper industry is the energy conservation i.e. reduction of the net energy per unit of product. Therefore, use of energy-efficient equipments, processes and productivity are few of the immediate steps which should be given due thoughts. The benefits of the above mentioned options include lower production cost, a more competitive edge, an improved ability to withstand future fluctuations in energy cost and an improvement in productivity and environmental benefits. Therefore, the global concerns about energy, preservation of forests and elimination of pollution from pulping and bleaching processes has led us to explore alternate fibrous resources other than wood and new pulping and bleaching processes that are environmentally benevolent without sacrificing product quality. The pulp and paper industry is also under constant pressure to reduce and modify environmental emissions to air and water due to stringent rules of the governments. So the present investigation aims at developing an environmental benign technology for production of pulp and paper using a cheap agricultural residue i.e. sugarcane bagasse. The objective of the study is to evaluate and estimate the viability of reducing chemical consumption with preserving mechanical strength properties of sugarcane bagasse soda-AQ pulp through enzymatic treatment. ii Sugarcane bagasse has been given mechanical treatments i.e. dry and wet depithing followed by intensive screening to remove most of the non-fibrous pith cells. The detailed morphological and anatomical features of sugarcane bagasse are determined and chemical characterization of depithed sugarcane bagasse is carried out to assess its suitability for pulp and papermaking. The studies indicate that depithed sugarcane bagasse can satisfactorily be used for pulp and paper production and will be proved as a good raw material for papermaking process. Dry and wet depithed sugarcane bagasse is delignified by soda pulping process. It requires milder cooking conditions due to its open and looser structure and low specific gravity. The various operating process variables for soda pulping like, maximum cooking temperature, cooking time and active alkali dose are optimized for soda process and effect of anthraquinone (AQ) is also observed. An active alkali dose of 12% (as Na2O), maximum cooking temperature 150 °C and cooking time of 60 min are found optimum for soda pulping of sugarcane bagasse. A small dose of 0.1% AQ accelerates the delignification rate with improvement in screened pulp yield. The mechanical strength properties are also optimized at different alkali doses as well as beating levels and are optimum at active alkali dose 12% (as Na2O) and beating level of 45 °SR. The spent liquor generated during soda-AQ pulping is analyzed for various characteristics. Fiber length distribution of sugarcane bagasse soda-AQ pulp using Bauer-McNett fiber classifier shows the abundance of medium sized fibers in sugarcane bagasse soda-AQ pulp, therefore the sugarcane bagasse soda-AQ pulp obtained will be of good quality for paper making. The scanning iii electron microscopic (SEM) study is carried out to understand the procedure of alkaline pulping and its affect on the fibers of sugarcane bagasse. An investigation has been undertaken to isolate, screen and identify a potent microorganism having the potential ability to secrete xylanase. A thorough survey of various sites leads to isolation of two persuasive xylanase producing fungal strains. The strains are having notably higher xylanase activity along with lower cellulase contamination and identified to be the two different strains of white rot basidiomycete Coprinellus disseminatus from Forest Research Institute, Dehradun (India). Both of the strains have been designated as SW-1 and SW-2 respectively. The detailed morphological study of both of the test strains has been carried out using SEM which shows that the hyphae,of fungal strain SW-1 are thin and elongated whereas, the hyphae of the fungal strain SW-2 are thick and compact. Xylanase production from SW-1 and .SW-2 is evaluated under submerged and solid-state fermentation conditions;, of these, the level of xylanase production observed is higher in solid-state fermentation (SSF) conditions. SSF is carried out for the optimization of various operating parameters i.e. incubation period, temperature, pH, carbon source, nitrogen source and moisture content using hyper-xylanase producing C. disseminatus SW-1 and SW-2 to achieve the maximum levels of xylanase secretion by both of the test strains. The biochemical characterization of crude xylanase produced by both of the isolates shows that the xylanase produced by C. disseminatus SW-1 is more alkali and thermotolerant in comparison to that produced by C. disseminatus SW-2. Therefore the test strain C. disseminatus SW-1 has been chosen for the further biobleaching studies of sugarcane bagasse soda-AQ pulp. iv The xylanase produced by C. disseminatus SW-1 is analyzed and evaluated for its application in biobleaching of sugarcane bagasse pulp and to reduce the toxicity of effluents generated during various bleaching sequences, in terms of AOX. The various parameters for xylanase prebleaching i.e. xylanase dose, reaction time and pulp consistency are optimized and the pulp filtrates have been checked for the release of reducing sugars and chromophores from the sugarcane bagasse pulp. The xylanase preparation has been used in the biobleaching of sugarcane bagasse soda-AQ pulp during the conventional (CEHH, CEHHP and OCEHH), ECF (ODED and OD(Eop)DP) and TCF (0(Eop)P) bleaching sequences. The xylanase pretreatment reduces the total chlorine demand by 29.70% for CEHH and CEHHP and 36.53% for OCEHH bleaching sequence, while still achieving high degree of brightness and preserving mechanical strength properties of sugarcane bagasse soda-AQ pulp in comparison to control. Xylanase pretreatment also reduces the AOX formation by 28.16% for CEHH, 27.6% for CEHHP and 34.65% for OCEHH bleaching sequences. For ECF (ODED and OD(Eop)DP) and TCF (O(Eop)P) bleaching sequences; xylanase pretreatment increases the overall brightness ceiling of the pulp at the same chemical charge with a decrease in all the mechanical strength properties except tear index of sugarcane bagasse pulp. Xylanase pretreatment results in small gain in viscosity over control for all the bleaching sequences. ODED and OD(Eop)DP bleaching sequences reduce the AOX formation by 84.84 and 87.36%, COD by 23.8 and 21.16% and color by 33.11 and 22.2% respectively in combined bleach effluent compared to that of CEHH bleaching sequence. The introduction of xylanase stage before ODED and OD(Eop)DP bleaching sequences reduces the AOX formation by 41.43 and 40% respectively. The reduction in copper number after xylanase pretreatment of all bleaching sequences shows that there is no brightness reversion with time while a small increase is noticed in effluent COD and color values after xylanase pretreatment of conventional (CEHH, CEHHP and OCEHH), ECF (ODED and OD(Eop)DP) and TCF (O(Eop)P) bleaching sequences. SEM study has been carded out in order to attain a better understanding of the effect of xylanase pretreatment on bagasse pulp bleachability which reveals that xylanase pretreatment helps in fiber surface modifications. So the xylanase pretreatment renders the fibers more susceptible for chemical bleaching, hence saving a fair amount of chemicals and reducing the effluent toxicity in terms of AOX. Additionally it improves the mechanical and optical properties of paper along with reduction in chlorine consumption which in turn mitigate the pollution load, therefore, denoting it to be an ecofriendly and environment benign ;bleaching technology. v