Clostridium cellulolyticum is capable of producing glycosyl hydrolase enzymes as well as fermentation products including ethanol and acetate. In this study, the potential of using C. cellulolyticum for ethanol and volatile fatty acid production from straw and grape pomace was examined. For rice straw, the effects of alkaline pretreatment and substrate sterilization prior to fermentation on products yields were also investigated. Effects of alkaline pretreatment and necessity for subsequent washing were tested for two types of grape pomace. For rice straw, the highest ethanol yield was 0.16？g/gVS from the straw pretreated with 10% sodium hydroxide loading at 1 2 1 ° C for 1 hour. Sterilization of the straw prior to fermentation was found to be not significant for ethanol production. Sterilization appeared to decrease native acetogen populations in the rice straw, resulting in lower acetic acid yields. The highest ethanol yield from grape pomace was of 0.09？g/gVS from the pretreated pomace. Pomace type (red or white) and washing were found to be not significant. Ethanol yields by C. cellulolyticum were lower than those from yeast in a simultaneous saccharification and fermentation system, but overall conversion of cellulose and hemicellulose was high, between 68 and 79%. 1. Introduction Lignocellulosic biomass, including crop and forestry residues, grasses, and other plant materials, is currently the primary focus feedstock for bioethanol and biochemical production research. This study focused on two lignocellulosic substrates that are common in California: rice straw and grape pomace. In California, there are around 200,000 hectares of rice planted resulting in around 1.1 million tons of rice straw per year [1]. The rice straw is usually burned or tilled into the soil. Tilling can be cost intensive, and burning causes significant air pollution, which is highly regulated in California. An environmentally friendly and economic use for this agricultural residue is needed. The rice straw used in this study was composed of 16.8% lignin, 38.8% cellulose, 24.1% hemicellulose, and 20.4% ash on a dry basis with a moisture content of 5.8%. The hemicellulose fraction was made up of 83.3% xylose, 1.3% galactose, and 15.4% arabinose. Grape pomace is also abundant in California with around 150,000 dry tons of grape pomace produced each year in California [2]. There are two types of grape pomace: white (produced from grape crushing prior to fermentation) and red (resulted after fermentation). The white pomace used in this study contained 16% lignin, 8.9% cellulose,
References
[1]
L. Terry, B. Fletcher, B. Effa et al., Recommendations for Rice Straw Supply, Board CAR, 2001.
[2]
G. C. Matteson and B. M. Jenkins, “Food and processing residues in California: resource assessment and potential for power generation,” Bioresource Technology, vol. 98, no. 16, pp. 3098–3105, 2007.
[3]
X. Chen, R. Zhang, Y. Zheng, S. Shoemaker, and E. Hughes, Alkaline Pretreatment of Winery Industry Waste for Enhancing Bioenergy Yield, Clearwater Beach, Fla, USA, 2010.
[4]
M. C. Y. Chang, “Harnessing energy from plant biomass,” Current Opinion in Chemical Biology, vol. 11, no. 6, pp. 677–684, 2007.
[5]
L. D. Gomez, C. G. Steele-King, and S. J. McQueen-Mason, “Sustainable liquid biofuels from biomass: the writing's on the walls,” New Phytologist, vol. 178, no. 3, pp. 473–485, 2008.
[6]
C. A. Cardona and O. J. Sanchez, “Fuel ethanol production: process design trends and integration opportunities,” Bioresource Technology, vol. 98, no. 12, pp. 2415–2457, 2007.
[7]
C. Weber, A. Farwick, F. Benisch et al., “Trends and challenges in the microbial production of lignocellulosic bioalcohol fuels,” Applied Microbiology and Biotechnology, vol. 87, no. 4, pp. 1303–1315, 2010.
[8]
L. R. Lynd, P. J. Weimer, W. H. van Zyl, and I. S. Pretorius, “Microbial cellulose utilization: fundamentals and biotechnology,” Microbiology and Molecular Biology Reviews, vol. 66, no. 3, pp. 506–577, 2002.
[9]
M. Maki, K. T. Leung, and W. S. Qin, “The prospects of cellulase-producing bacteria for the bioconversion of lignocellulosic biomass,” International Journal of Biological Sciences, vol. 5, no. 5, pp. 500–516, 2009.
[10]
Y. H. P. Zhang, “What is vital (and not vital) to advance economically-competitive biofuels production,” Process Biochemistry, vol. 46, no. 11, pp. 2091–2110, 2011.
[11]
M. Galbe, P. Sassner, A. Wingren, and G. Zacchi, “Process engineering economics of bioethanol production,” Biofuels, vol. 108, pp. 303–327, 2007.
[12]
M. Desvaux, E. Guedon, and H. Petitdemange, “Cellulose catabolism by Clostridium cellulolyticum growing in batch culture on defined medium,” Applied and Environmental Microbiology, vol. 66, no. 6, pp. 2461–2470, 2000.
[13]
M. Desvaux, “Clostridium cellulolyticum: model organism of mesophilic cellulolytic clostridia,” FEMS Microbiology Reviews, vol. 29, no. 4, pp. 741–764, 2005.
[14]
E. Guedon, S. Payot, M. Desvaux, and H. Petitdemange, “Carbon and electron flow in Clostridium cellulolyticum grown in chemostat culture on synthetic medium,” Journal of Bacteriology, vol. 181, no. 10, pp. 3262–3269, 1999.
[15]
E. Guedon, S. Payot, M. Desvaux, and H. Petitdemange, “Relationships between cellobiose catabolism, enzyme levels, and metabolic intermediates in Clostridium cellulolyticum grown in a synthetic medium,” Biotechnology and Bioengineering, vol. 67, no. 3, pp. 327–335, 2000.
[16]
B. Suresh, Chemical Economics Handbook, SRI International, 2003.
[17]
Z. Ren, T. E. Ward, B. E. Logan, and J. M. Regan, “Characterization of the cellulolytic and hydrogen-producing activities of six mesophilic Clostridium species,” Journal of Applied Microbiology, vol. 103, no. 6, pp. 2258–2266, 2007.
[18]
Y. H. P. Zhang, “Reviving the carbohydrate economy via multi-product lignocellulose biorefineries,” Journal of Industrial Microbiology & Biotechnology, vol. 35, no. 5, pp. 367–375, 2008.
[19]
X. L. Chen, J. K. Wang, Y. M. Wu, and J. X. Liu, “Effects of chemical treatments of rice straw on rumen fermentation characteristics, fibrolytic enzyme activities and populations of liquid- and solid-associated ruminal microbes in vitro,” Animal Feed Science and Technology, vol. 141, no. 1-2, pp. 1–14, 2008.
[20]
M. Galbe and G. Zacchi, “Pretreatment of lignocellulosic materials for efficient bioethanol production,” Advances in Biochemical Engineering/Biotechnology, vol. 108, pp. 41–65, 2007.
[21]
Y. S. Lin and W. C. Lee, “Bioethanol production from alkali-pretreated rice straw by simultaneous saccharification and fermentation,” Journal of Biobased Materials and Bioenergy, vol. 5, no. 3, pp. 396–402, 2011.
[22]
H. S. Oberoi, N. Babbar, S. K. Sandhu et al., “Ethanol production from alkali-treated rice straw via simultaneous saccharification and fermentation using newly isolated thermotolerant pichia kudriavzevii hop-1,” Journal of Industrial Microbiology & Biotechnology, vol. 39, no. 4, pp. 557–566, 2012.
[23]
S. D. Zhu, Y. X. Wu, Z. N. Yu et al., “Simultaneous saccharification and fermentation of microwave/alkali pre-treated rice straw to ethanol,” Biosystems Engineering, vol. 92, no. 2, pp. 229–235, 2005.
[24]
M. Lever and G. Ho, “Reducing energy for cellulose ethanol production by the use of sterilising agents in lieu of steam,” Renewable Energy, vol. 43, pp. 403–406, 2012.
[25]
M. F. Temudo, R. Kleerebezem, and M. van Loosdrecht, “Influence of the pH on (Open) mixed culture fermentation of glucose: a chemostat study,” Biotechnology and Bioengineering, vol. 98, no. 1, pp. 69–79, 2007.
[26]
M. Vancanneyt, P. De Vos, and J. De Ley, “Ethanol production from glucose by Clostridiumthermosaccharolyticum strains: effect of pH and temperature,” Biotechnology Letters, vol. 9, no. 8, pp. 567–572, 1987.
[27]
M. Desvaux, E. Guedon, and H. Petitdemange, “Kinetics and metabolism of cellulose degradation at high substrate concentrations in steady-state continuous cultures of Clostridium cellulolyticum on a chemically defined medium,” Applied and Environmental Microbiology, vol. 67, no. 9, pp. 3837–3845, 2001.
[28]
K. Williams, Y. Zheng, J. McGarvey, Z. Fan, and R. Zhang, Characterization of Several Clostridia for Production of Ethanol and Volatile Fatty Acids from Plant-Based Substrates, San Francisco, Calif, USA, 2008.
[29]
E. K. Papadimitriou, “Hydrolysis of organic matter during autoclaving of commingled household waste,” Waste Management, vol. 30, no. 4, pp. 572–582, 2010.
[30]
S. Asakawa and M. Kimura, “Comparison of bacterial community structures at main habitats in paddy field ecosystem based on DGGE analysis,” Soil Biology & Biochemistry, vol. 40, no. 6, pp. 1322–1329, 2008.
[31]
L. A. Rodríguez, M. E. Toro, F. Vazquez, M. L. Correa-Daneri, S. C. Gouiric, and M. D. Vallejo, “Bioethanol production from grape and sugar beet pomaces by solid-state fermentation,” International Journal of Hydrogen Energy, vol. 35, no. 11, pp. 5914–5917, 2010.
[32]
A. Singh and N. R. Bishnoi, “Optimization of ethanol production from microwave alkali pretreated rice straw using statistical experimental designs by saccharomyces cerevisiae,” Industrial Crops and Products, vol. 37, no. 1, pp. 334–341, 2012.
[33]
R. K. Sukumaran, R. R. Singhania, G. M. Mathew, and A. Pandey, “Cellulase production using biomass feed stock and its application in lignocellulose saccharification for bio-ethanol production,” Renewable Energy, vol. 34, no. 2, pp. 421–424, 2009.
[34]
H. N. Chang, N. J. Kim, J. Kang, and C. M. Jeong, “Biomass-derived volatile fatty acid platform for fuels and chemicals,” Biotechnology and Bioprocess Engineering, vol. 15, no. 1, pp. 1–10, 2010.
