Date Published: February 6, 2013
Author(s): Raymond E S Nwachukwu, Abolghasem Shahbazi, Lijun Wang, Mulumebet Worku, Salam Ibrahim, Keith Schimmel.
The aim of this research is to optimize the cultural conditions for the conversion of glycerol to ethanol by Enterobacter aerogenes S012. Taguchi method was used to screen the cultural conditions based on their signal to noise ratio (SN). Temperature (°C), agitation speed (rpm) and time (h) were found to have the highest influence on both glycerol utilization and ethanol production by the organism while pH had the lowest. Full factorial design, statistical analysis, and regression model equation were used to optimize the selected cultural parameters for maximum ethanol production. The result showed that fermentation at 38°C and 200 rpm for 48 h would be ideal for the bacteria to produce maximum amount of ethanol from glycerol. At these optimum conditions, ethanol production, yield and productivity were 25.4 g/l, 0.53 g/l/h, and 1.12 mol/mol-glycerol, repectively. Ethanol production increased to 26.5 g/l while yield and productivity decreased to 1.04 mol/mol-glycerol and 0.37 g/l/h, respectively, after 72 h. Analysis of the fermentation products was performed using HPLC, while anaerobic condition was created by purging the fermentation vessel with nitrogen gas.
Fossil fuels are the major sources of energy, and they account for about 80% of global energy demand (Sarma et al.
2012). But they are characterized with a lot of problems, which include non-renewability, erratic prices, global warming, ecosystem imbalance, health hazards, and other environmental/agricultural effects like pollution and food shortage. Therefore, there is need for a renewable, healthier, more environment friendly, abundant/secure, and sustainable alternatives. Biofuels potentially provide these advantages and are increasing in global demand (Sarma et al.
The screening of important cultural factors by Taguchi method shows that initial pH had the least effect on the production of ethanol from glycerol by E. aerogenes S012. The reason could be that the range of pH values tested was very close to the optimum value. Ito et al. (
2005) found pH 6.8 to be optimum for hydrogen and ethanol production by E. aerogenes HU-101, while Nakashimada et al. (
2002) found pH 7.0 and 6.3 best for growth and hydrogen production, respectively, by E. aerogenes AY-2 strain. Therefore, best pH for fermentation by E. aerogenes S012 is between 6.3 and 6.8.
The authors declare that they have no conflict of interests.