Process optimization for butanol production from developed rice straw hydrolysate using Clostridium acetobutylicum MTCC 481 strain

In this study, an attempt is made to optimize the effect of various physical and cultural parameters on butanol production by microbial strain Clostridium acetobutylicum MTCC 481 by employing L₁₈ orthogonal array design of experiments. A set of five parameters, viz., temperature, pH, inoculum size, inoculum age, and agitation have been studied. Utilizing a pre-optimized rice straw hydrolysate medium, the clostridial strain produced maximum amount of butanol at optimum conditions of temperature 37 °C, pH 4.0 ± 0.5, inoculum size 5 % (v/v), inoculum age 18 h, and agitation 150 rpm. Among these parameters, pH, temperature, and agitation were found to be the most significant factors affecting solvent production. The optimized physical and cultural parameters were further verified at shake flask and bioreactor scale (2 L and 5 L bioreactor). Experiments using 2 and 5 L bioreactor under the optimized process condition showed nearly complete utilization of soluble sugars with the production of 15.84 g L⁻¹ of total solvents with 12.17 g L⁻¹ of butanol in 2 L bioreactor and 16.91 g L⁻¹ of total solvents with 12.22 g L⁻¹ of butanol in a 5 L of bioreactor, respectively. The experimental data were further validated by fitting it to a kinetic model reported in literature to determine the kinetic parameters of the fermentation process.