Comparison of marine and rushton impeller in high solid loading of two-step pretreated oil palm trunk using simultaneous saccharification and fermentation for ethanol production

Abstract

Substrate loading enhancement in fermenter generates difficulty in mixing that results in low ethanol yield owing to insufficient mass transfer. Thus, this study evaluated the efficiency of a six-blade Rushton turbine and a three-blade marine type propeller in a 3 L stirred tank bioreactor (STBR) by using steam exploded and alkaline pretreated oil palm trunk (OPT) fibers in a unique batch and fed-batch strategy. The fed-batch began with 5% (w/v) solid loading and after 12 h of simultaneous saccharification and fermentation (SSF) reaction, 2.5% (w/v) solid was added in the bioreactor with 6 h interval. The marine and Rushton impellers were compared at 5% (w/v) batch and 20% (w/v) fed-batch SSF, using agitation rate of 100 rpm. At 5% (w/v) solid loading, the highest ethanol concentration and theoretical yield were 15.66 ± 1.71 g/L and 61.69 ± 2.34%, and 12.10 ± 0.98 g/L and 54.01 ± 3.52%, respectively for marine and Rushton impeller. At high solid loading (20% w/v), the marine impeller achieved maximum ethanol concentration of 41.33 ± 2.02 g/L at 72 h of fermentation, with a low power consumption of 54.73 kW. The Rushton impeller resulted in ethanol concentration of 39.08 ± 1.47 g/L at 96 h of fermentation with relatively higher power consumption of 83.62 kW. The marine impeller is therefore efficient with the fed-batch strategy.

Keywords

• Ethanol production
• Fed-batch
• Impeller type
• SSF
• High solids loading
• Power consumption