Ethanol from Sugar Cane Bagasse by a Simultaneous Saccharification and Fermentation Process (Ssf) with Candida Krusei Icm-Y-05
Keke Cheng, Division of Green Chemistry and Technology, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing, 100084, China and Jian-An Zhang, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing, 100084, China.
Ethanol has attracted worldwide attention because of its potential use as an alternative automotive fuel. There are numerous advantages related to the utilization of ethanol, especially improved quality of the urban air and its association with the reduction of CO2, heavy metals, nitrogen oxides and hydrocarbon emissions Abundant, renewable and less expensive raw material such as lignocellulosic residues could be utilized as a source of fermentable sugars for conversion into ethanol. Sugar cane bagasse is one such readily available raw material, which represents one of the most important Chinese agricultural residues, with an estimated annual surplus of 16 million tons. Most of it is currently used to burn directly for steam generation and heat, which not only use inefficient but also pollute the air. Sugar cane bagasse composition varies according to the influence of factors such as sugar cane cultivation and processing. It contains about 20-25% of lignin, 23-30% of hemicellulose and 45-50% of cellulose. In this paper, simultaneous saccharification and fermentation (SSF) process for ethanol production from sugar cane bagasse has been investigated using the thermotolerant yeast strain Candida krusei ICM-Y-05. Sugar cane bagasse was previously treated in a 1% NaOH and 0.6% H2O2 solution at 30 °C, 140 rpm for 24 h to provide pretreated biomass with increased cellulose content relative to untreated materials and to enhance cellulase accessibility. During this process, 27.1% hemicellulose and 77.6% of lignin are stripped down, but the cellulose is not removed. SSF experiments were performed in laboratory conditions at 10% (w/v) substrate concentration and 12 FPU/g substrate of commercial cellulase. In the first step of the SSF, The pH were maintained at 5 using citrate buffer. small amounts of cellulases were added at 50 °C, the optimal temperature of enzymes. After 48 h enzymatic hydrolysis, the concentration of glucose and cellobiose in the hydrolysate were 31 g/l and 9 g/l, respectively. In the second step more cellulases were added in combination with Candida krusei ICM-Y-05 at 40 °C. Based on the cellulose available in pretreated materials, 77% of the theoretical ethanol yield was obtained. After 72 h of SSF the highest ethanol concentration of 32 g/l was achieved in fermentation media. The SSF results showed that a further increase of substrate concentration reduced the ethanol yield significant as a result of insufficient mass transfer. The fermentation could be monitored by the weight loss of the produced CO2.