Enhanced bioethanol production from water hyacinth (Eichhornia crassipes) by statistical optimization of fermentation process parameters using Taguchi orthogonal array design

• Temperature, pH, enzyme volume, inoculum volume were optimized for SSF trials.
• GH43 volume, pH and temperature were the Taguchi optimized significant factors.
• Optimized SSF with 1% (w v−1) E. crassipes gave ∼2-fold upturn in ethanol titre.
• 5% (w v−1) substrate in shake flask offered 5.3-fold rise in ethanol concentration.
• Bioreactor gave 1.4-fold rise as compared to shake flask with 5% (w v−1) substrate.

Water hyacinth (Eichhornia crassipes), a fast growing aquatic weed and a potential lignocellulosic substrate with high hemicellulosic (44.68 ± 0.39%, w w−1) content was used for bioethanol production. The commercial fungal enzymes are expensive in nature. Taguchi orthogonal array design was employed for optimization of simultaneous saccharification and fermentation (SSF) process parameters involving recombinant Clostridium thermocellum hydrolytic enzymes and fermentative microbes for enhanced bioethanol production from mixed, microwave-assisted alkali and organosolv pretreated substrate. The factors optimized in 100 mL SSF medium were (%, v v−1): GH5 cellulase (5.6 U mg−1, 0.44 mg mL−1), 0.5; GH43 hemicellulase (3.8 U mg−1, 0.33 mg mL−1), 2.0; Saccharomyces cerevisiae (∼3.8 × 109 cells mL−1), 0.5; Candida shehatae (∼2.9 × 108 cells mL−1), 2.0; pH, 5.4 and 35 °C, temperature. GH43 hemicellulase volume, pH and temperature were the three significant factors. The optimized flask SSF with 1% (w v−1) substrate contributed ∼2-fold upturn in ethanol titre and yield (1.84 g L−1, 0.310 g of ethanol g of substrate−1) as compared with unoptimized conditions (1.0 g L−1, 0.160 gg-1). 5% (w v−1) substrate in shake flask and bioreactor contributed ethanol titre and yield of 9.78 g L−1, 0.329 gg-1 and 13.7 g L−1, 0.462 gg-1 respectively.