Feasibility of rice straw as alternate substrate for biobutanol production

Biobutanol has recently emerged as a potential alternate liquid fuel for gasoline and diesel. In this work, we have studied clostridial fermentation of stress assisted-acid hydrolyzed rice straw that exhibited a typical trend of acidogenesis followed by solventogenesis. Acid hydrolysis of 5% (w/v) mixture of rice straw in water with simultaneous application of shearing stress resulted in release of 3.9% (w/v) total sugar out of which 3.1% (w/v) was reducing sugar. Glucose formed major fraction (75%) of the reducing sugar (or 2.3% w/v total sugar). Thus, essentially, 5% (w/v) of rice straw solution released nearly 46% (w/w) (i.e. 23 g L−1 glucose for 50 g L−1 rice straw solution) glucose. Anaerobic fermentation of rice straw hydrolyzate using Clostridium acetobutylicum NCIM 2337 resulted in production of 6.24 g L−1 of acetone, 13.5 g L−1 of butanol and only 0.82 g L−1 of ethanol. The net consumption of substrates was as follows: glucose 12.86 g L−1 (i.e. ∼55%), total reducing sugar 18.32 g L−1 (∼57%) and total sugar 24.5 g L−1 (∼61%). Thus, higher solvents yield and significant sugar utilization makes rice straw a potential feedstock for biofuels production.