Efficiency studies of biobutanol production from pretreated lemongrass leaves using clostridium beijerinckii sr1

Abstract

The increase in energy consumption and the limited supply of petroleum fuels has raised interest toward development of biobutanol production from cellulosic materials. This research performed the production of biobutanol using hydrolysate from pretreated lemongrass leaves in addressing the petroleum depletion issue and serves as an efficient process for green fuel technology. Chemical composition analysis shows that lemongrass leaves are made up of cellulose, hemicellulose and lignin with solid fraction of 47.21%, 32.41% and 13.17% (w/v), respectively. Screening for suitable pretreatment methods resulted in the highest reducing sugar production of 61.05 g/L employing physico-chemical pretreatment method (autoclaving at 121°C for 15 minutes in 2% (v/v) of sulphuric acid) followed by enzyme saccharification using Celluclast and Novozyme enzyme cocktails at concentration of 3% (v/v) each using 7% (w/v) of lemongrass leaves. Application of central composite design (CCD) on enzyme saccharification further improved reducing sugar production to 80.1 g/L equivalent to 1.31 fold improvement compared to that before optimization. A total of 13 bacteria strains were isolated anaerobically from various sources using rolling tube technique and anaerobic chamber. Strain SR1 which was further identified as Clostridium beijerinckii SR1 using 16S rRNA technique exhibited ability to produce highest butanol of 0.71 g/L. Optimization of biobutanol production in batch culture using general factorial design (GFD) for screening of suitable nitrogen source and CCD for optimization of fermentation parameters resulted in improved biobutanol production of 1.40 g/L which was 1.97 fold higher compared to before optimization. Application of CCD further suggested that temperature, pH, reducing sugar concentration, nitrogen source (meat extract) concentration were fixed at 34.91°C, 6.48, 50.06 g/L and 47.72 mM respectively. An initial pH of 6.48 (without pH control at acidogenic phase) and controlled pH during solventogenic phase at 5.5 gave rise to biobutanol production to 1.52 g/L which was 1.09 fold before application of pH control strategy. Fix mode, constant variable mode and exponential mode of feeding were screened for optimum biobutanol production in fed batch culture. Exponential feeding mode with dilution rate of 0.04 h-1 resulted in highest biobutanol production of 1.91 g/L that was 1.26 fold higher compared to batch culture. Application of repeated fed batch system using 60% (v/v) of replacement ratio further improved biobutanol production to 2.46 g/L which was 1.28 fold and 1.62 fold higher compared to fed batch system and batch system respectively. Based on the research performed, pretreated lemongrass leaves have a great potential to be used as a substrate for biobutanol production.