STUDIES ON DEVELOPMENT OF BIO-BLEACH PROCESSES FOR CYMBOPOGON MARTINI AND CYMBOPOGON CITRATUS

Abstract

The path of progress of paper industry has ever since been associated with pollution; a fact that often mars the reputation of the industry. The industry is hence looked upon as a notorious pollution maker and unfortunately the truth can't be denied. The global concerns about energy, preservation of forests and elimination of pollution from pulping and bleaching processes have led us towards exploration of alternate fibrous resources other than wood and new pulping and bleaching processes that are compassionate with the environment 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 aimed at developing an environmental benign technology for production of pulp and paper using the left over waste (bagasse) of two aromatic, fibrous raw materials; lemon grass and sofia grass (after extraction of their essential oils by steam distillation). The prior objective of the study was to evaluate and estimate the feasibility regarding reductions in chemical consumption, while preserving mechanical strength properties of the lemon and sofia grass soda-AQ pulps through enzymatic treatment. The detailed morphological and anatomical features of lemon and sofia grasses were determined and thermo-chemical characterization of the two raw materials was carried out in order to assess their suitability for pulp and papermaking. The studies indicated that the steam distilled, left over lignocellulosic biomass of lemon and sofia grasses could satisfactorily be used for pulp and paper production thereby reducing the environmental load and also seizing the tree logging. Soda pulping process was used to pulp the dried bagasse of steam distilled lemon and sofia grasses. Owing to their open and loosened anatomy, they required milder cooking conditions. The various operating process variables for soda pulping like, maximum cooking temperature, cooking time and active alkali dose were optimized for soda process and effect of anthraquinone (AQ) was then observed. An active alkali dose of 14% (as Na20), and cooking time of 90 min at a maximum cooking temperature 150 and 160 °C respectively for lemon and sofia grasses were found optimum for soda pulping. AQ (0.1%) as a pulping additive accelerated the delignification rates along with improvement in screened pulp yields. The mechanical strength properties were also ii optimized at different beating levels and beating level of 40±1 °SR. Fiber length distribution of soda-AQ pulps using Bauer-McNett fiber classifier confirmed that sofia grass soda-AQ pulp had maximum percentage of fibers in middle and bottom fractions, while lemon grass in top fraction. The soda-AQ pulps thus obtained were of good quality for paper making. The scanning electron microscopic (SEM) study was carried out to understand the procedure of alkaline pulping and its effect on the fibers of lemon and sofia grasses. An investigation was undertaken to isolate, screen and identify a potent microorganism having the potential ability to secrete xylanase. A thorough survey of various sites led to isolation of two credible xylanase producing fungal strains. The strains had notably higher xylanase activity along with a minor cellulase contamination and were identified as two different strains of white rot basidiomycete Coprinopsis cinerea from Forest Research Institute, Dehradun (India). The test fungi were also tested as per Bavendamm plate assay for their ability to produce phenoloxidases, which hence confirmed that the two strains were white rotters. The two strains were designated as HK-1 and HK-2 respectively. Further the strain HK-1, with a higher xylanase activity was sent to Agharkar Research Institute, Pune (India) for confirmation of its identity on the basis of internally transcribed sequences (ITS). The detailed morphological study of both of the test strains was carried out using SEM which showed that the hyphae of fungal strain HK-1 were thick and compact whereas, the hyphae of the fungal strain HK-2 were thin and ribbon like. Occurrence of clamp connections and club shaped basidiospores further confirmed their identity under basidiomycetes. Xylanase production from HK-1 and HK-2 was evaluated under submerged and solid-state fermentation conditions; of these, the level of xylanase production observed was higher under solid-state fermentation (SSF) conditions. Various operating parameters, such as, incubation period, temperature, pH, carbon source, nitrogen source and moisture content were optimized under SSF for the hyper-xylanase producing C. cinerea strains HK-1 and HK-2 to achieve their maximum levels of xylanase secretion. The biochemical characterization of crude xylanases produced by the two fungal isolates confirmed that the xylanase produced by C. cinerea HK-1 was more thermo-alkali-tolerant in comparison to that produced by HK-2. Therefore the test strain C. cinerea HK-1 was chosen for the further biobleaching studies of lemon and sofia grass soda-AQ pulps. iii The xylanase produced by C. cinerea HK-1 was analyzed and evaluated for its application in biobleaching of lemon and sofia grass soda-AQ pulps and reduction of toxicity in effluents generated during various bleaching sequences, in terms of AOX. Various operating parameters for xylanase prebleaching i.e. xylanase dose, retention time and pulp consistency were optimized and the pulp filtrates were checked for the release of reducing sugars and chromophores from the pulp samples. The xylanase preparation was used in biobleaching of the soda-AQ pulps of lemon and sofia grasses during the conventional (CEHH and OCEHH), ECF (ODED and ODEDP) and TCF (O(Eop)P) bleaching sequences. The xylanase pretreatment of lemon and sofia grass soda AQ pulps depreciated the total chlorine demand by 22.67 and 29.73% for CEHH and 11.60 and 16.92% for OCEHH bleaching sequence, while still achieving high degree of brightness and preserving mechanical strength properties of the two soda-AQ pulp samples in comparison to their respective controls. Xylanase pretreatment also reduced the AOX formation in lemon and sofia grasses bleach effluents by 26.64 and 29.96% for CEHH while 35.11 and 30.73% for OCEHH bleaching sequences. For ECF (ODED and ODEDP) and TCF (O(Eop)P) bleaching sequences; xylanase pretreatment increased the overall brightness ceiling of the pulps at the same chemical charge with decrease in all the mechanical strength properties except tear index. Xylanase pretreatment resulted in small gains in viscosity over controls for all the bleach sequences. AOX formation reduced by 84.84 and 82.67% respectively, from lemon and sofia grass combined bleach effluents following investigated ECF bleaching sequences when compared to CEHH bleaching sequence. For lemon grass, after ODED and ODEDP, COD decreased by 14.71 and 18.15% respectively while colour decreased by 28.08 and 43.46% when compared to CEHH sequence, whereas for sofia grass, the respective decreases in COD were 15.06 and 19.71% and decrease in colour were 33.02 and 17.85%. The introduction of xylanase stage before ODED and ODEDP sequences reduced the AOX formation by 35.68 and 46.88% in lemon and sofia grasses respectively. The reduction in copper number after xylanase pretreatment for all bleaching sequences showed that there was no brightness reversion with time; whereas an increase was noticed in effluent COD and color values after xylanase pretreatment. SEM studies were carried out in order to attain a better understanding regarding the effect of xylanase pretreatment on lemon and sofia grass pulp bleachabilities which revealed that xylanase iv pretreatment brought about fiber surface modifications and rendered 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 improved the mechanical as well as optical properties of paper along with reduction in chlorine consumption which in turn mitigated the pollution load, thereby, signifying it as an ecofriendly and environmentally benign bleaching technology. v