260345 Bio-Pulping Assisted Steam Pretreatment of Bagasse by Solid State Cultivation of White Rot Fungi

Thursday, November 1, 2012: 8:30 AM
303 (Convention Center )
Jian Liu, Chuannan Long, Hailong Li, Xiaobing Wu and Minnan Long, School of Energy Research, Xiamen University, Xiamen, China

Pretreatment is an important processing step to increase the accessibility of cellulosic material in plant biomass, impacting efficiency of subsequent hydrolysis and fermentation. White rot fungi degrade lignin and have biotechnological applications in conversion of lignocellulose to valuable products. Steam pretreatment is considered to be one of the most practical and versatile pretreatment methods, but to be cost-effective it must produce more accessible fiber for enzymes and prevent the formation of by-products in lower temperature. This study investigated steam pretreatment assisted by bio-pulping of bagasse by solid state fermentation (SSF) using Ceripriopsis sp. to facilitate the conversion into fermentable sugar. The effects of substrate moisture content (68%, 75% and 82%), nutritional addition with metal ions and culture time (040 days) on ligninolytic activity, lignin degradation, total weight loss, pulp yield, sugar yield and sugars in soluble fraction were examined. Moisture content significantly affected lignin degradation, with 75% moisture content degrading approximately 2.9-3.7% more lignin than 68% and 82% moisture content after 40 days. Within the same moisture content, fermentations supplemented with metal ions nutrition were statistically better than those without nutrition for lignin degradation and sugar yield from both pulp and soluble fraction, but all 3 ligninolytic activities significantly decreased. Beyond the 21 days pretreatment, additional time resulted in greater lignin degradation, but indicated a decrease in pulp yield and sugar yield. Considering cost, solid state fermentation at 75% moisture content with nutrition was the most preferable pretreatment resulting in 19.1% lignin degradation, 68.2% pulp yield and 25.1% sugar yield over a period of 21 days. It was proved that microbial pretreatment by solid state fermentation has the potential to be a low cost, environmentally friendly alternative to chemical approaches. Moisture relationships will be significant to the design of an effective microbial pretreatment process using SSF technology. Microbial pretreatment employs microorganisms and their enzyme systems to breakdown lignin present in lignocellulosic biomass. This environmentally friendly approach has recently received increased attention and has potential advantages over the prevailing physicochemical pretreatment technologies due to reduced energy and material costs, simplified processes and equipment, and use of biologically based catalysts. Several basidiomycetes such as Phellinus sp., Ceriporiopsis subvermispora, Phlebia subserialis and Pleurotus ostreatus are capable of efficiently metabolizing lignin in a variety of lignocellulosic materials. Ceriporiopsis subvermispora, is a white rot fungus implicated in many diseases of broad-leaved and coniferous trees, causing heart rot, canker and root diseases, and also esca disease of grapevines. It produces oxidative enzymes that degrade lignin. Reducing the lignin content of biomass helps to expose the highly-ordered crystalline structure of cellulose and facilitates substrate access by hydrolytic enzymes. White rot fungi can decompose lignin effectively by excreting unique extra-cellular peroxidases (MnP) as secondary metabolites under nutrient starvation. It has been widely investigated because of its non-specific nature and exceptional oxidation potential for lignin degradation. The degradation efficiency and minimal use of cellulosic polymers relative to other white rot fungi make it a suitable candidate for pretreatment and lignin degradation. However, the efficiency of biodegradation varies with fermentation methods and environmental conditions. Solid state fermentation (SSF) is defined as the growth of microorganisms on solid materials in the absence of free liquid and the technology has been investigated for the development of bioprocesses. Compared to liquid fermentation, where microorganisms are submerged in free liquid, SSF possesses advantages such as simpler operation, lower raw material and input costs and reduced environmental impact from waste water. Moreover, solid state fermentation provides environmental conditions under which white rot fungi grow in nature, thus making it ideal for growth. Considering these merits, applying SSF technology to pretreat lignocellulosic biomass and biopulping may lead to better efficiency and reduce pretreatment costs. However, very limited resources report the application of SSF of Phellinus. sp. for pretreatment of lignocellulosic materials, especially to meet the need for generation of a sugar platform for ethanol production. In the present study, bio-pulping assisted steam pretreatment were applied to determine the efficiency in bagasse. This study examines the microbial pretreatment of wood powder by solid state fermentation. The natural compositions in the wood are not sufficient to meet critical nutrient requirements of fungi. The supplementation of extra nutrients(wheat bran and inorganic salt) is necessary in this study. Moisture content was assumed as a key factor that affected the lignin degrading performance. Moisture content, substrate characteristics, nutrient supplements, aeration and culture duration are important variables for performance of fungi in SSF, impacting growth and metabolite formation, but these processing parameters have not been fully explored. It is reported that moisture content is significant to microbial performance in SSF systems and affects growth as well as product formation. Water in SSF systems functions as a solvent for transport of nutrients, metabolites and other solutes as well as helps maintain stable cellular and molecular structures. Some research have found the quantity and kinetic properties of free water to be more influential to the diffusion of nutrients and metabolites and overall microbial activity. It is reported that the effectiveness of fermentation without nutrition addition on fungal growth and lignin degradation supports the recognized advantages of SSF systems in using wood substrates that provide necessary nutrients in medium preparation. Therefore, the effects of initial substrate moisture content (68%, 75% and 82% wet-basis), nutrition and culture time (040 days) on lignin degradation, pulp yield and sugar yield were investigated to evaluate process effectiveness.

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