Efficient Pretreatment for Bioethanol Production from Water Hyacinth (Eichhornia crassipes) Involving Naturally Isolated and Recombinant Enzymes and Its Recovery

摘要

Simultaneous saccharification and fermentation (SSF) experiments involving water hyacinth (Eichhornia crassipes), an abundantly available renewable bioresource, using hydrolytic enzymes, and fermentative microbes were investigated. Water hyacinth containing 30.01 (%, w/w) cellulose, 44.49 (%, w/w) hemicellulose, and 20.04 (%, w/w) lignin was subjected to three different pretreatments, namely, wet oxidation, phosphoric acid (H_3PO_4)-acetone, and ammonia fiber explosion (AFEX). Hydrolytic enzymes, namely, recombinant Clostridium thermocellum cellulase (GH5) and hemicellulase (GH43), Tri-choderma reesei and Bacillus subtilis AS3 cellulases were employed separately for saccharification. Saccharomyces cerevi-siae and Candida shehatae were used for fermentation. The AFEX pretreated 1% (w/v) water hyacinth along with recombinant cellulase (GH5)-hemicellulase (GH43) consortium gave the highest ethanol titer of 1.52g/L as compared with wet oxidation (1.23 g/L) and phosphoric acid-acetone pretreatments (1.31 g/L). The best SSF combination with 5% (w/v) substrate at shake flask contributed an ethanol titer and yield of 7.83 g/L, 0.266 (g of ethanol/g of substrate) and its scale up at bioreactor level resulted in significantly higher ethanol titer and yield of 14.39 g/L and 0.489 (g/g), respectively. 93.0 (%, v/v) ethanol from bioreactor was recovered by rotary evaporator with 20.4% purification efficiency.