Optimization of cultural conditions for conversion of glycerol to ethanol by Enterobacter aerogenes S012

Abstract

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.

Biohydrogen production by co-fermentation of crude glycerol and apple pomace hydrolysate using co-culture of Enterobacter aerogenes and Clostridium butyricum

“…Maximum hydrogen was produced by these microorganisms using glucose as carbon source. But during crude glycerol fermentation, both E. aerogenes and C. butyricum mainly produced ethanol and 1,3-PD (Zeng, 1996;Gonzalez-Pajuelo et al, 2005;Ito et al, 2005;Nwachukwu et al, 2013). By using these microorganisms at higher concentration of crude glycerol, the yield of 1,3-PD and ethanol was maximum, but by using co-substrate, the contrasting results were obtained.…”

“…The reason of using ethanol and 1,3-PD data was to monitor the utilization of crude glycerol in presence of APH for increased H 2 production with minimum end-product formation. Ethanol and 1,3-PD are the most common metabolites of glycerol metabolism by E. aerogenes (Ito et al, 2005;Jitrwung and Yargeau, 2011;Nwachukwu et al, 2012Nwachukwu et al, , 2013 and C. butyricum (Zeng, 1996 Szymanowska-Powałowska, 2014). Ito et al (2005), indicated that a higher initial concentration of crude glycerol decreased the yield of H 2 and ethanol.…”

“…The higher reduction state of glycerol needs excess of reducing equivalents, which can be accomplished by diverting NADH consuming pathway towards reduced or neutral end-products (ethanol or 1,3-PD) or via H 2 production (Heyndrickx et al, 1991). Research carried out using the Enterobacter and Clostridium with crude glycerol as substrate either produced ethanol (Ito et al, 2005;Jitrwung and Yargeau, 2011;Nwachukwu et al, 2012;Nwachukwu et al, 2013) or 1,3-propanediol (Zeng, 1996;Gonzalez-Pajuelo et al, 2004;Gonzalez-Pajuelo et al, 2005;Chatzifragkou et al, 2011;Szymanowska-Powałowska, 2014), which needs to be produced at higher concentration at the expense of media cost (Jitrwung and Yargeau, 2011). Additionally a co-culture of facultative (Enterobacter aerogenes) and strict anaerobe (Clostridium butyricum) can ensure high H 2 yield by using glucose as carbon source in the absence of expensive reducing agent (Yokoi et al, 1998;Phowan et al, 2010).…”

Fermentation of glycerol by Anaerobium acetethylicum and its potential use in biofuel production

“…Glycerol (1,2,3‐propanetriol) is a simple trivalent alcohol that results from the natural degradation of the glyceride component of plant cell wall phospholipids or reserve lipids of plant seeds (Roger et al ., ; Nwachukwu et al ., ). It is produced in major amounts during transesterification of vegetable oils and animal fats (Solomon et al ., ; Barbirato et al ., ,b, ; Colin et al ., ) and has wide applications in different industries such as food and drinks, toothpaste, cosmetics, toiletries, plastics, tobacco, pulp and paper, paint, leather and textile, pharmaceuticals and automotive (Choi, ; Nicol et al ., ; Rossi et al ., ).…”

“…The economic value of industrial glycerol has decreased due to the surplus crude glycerol generated during biodiesel production, and it cannot be utilized directly in any industrial applications due to the presence of impurities. Furthermore, it cannot be directly released into the environment without treatment as the cost of such treatment is not economical (Nwachukwu et al ., ). Recently, fermentative conversion of crude glycerol into valuable products such as, e.g., bioethanol has gained interest for the development of biodiesel‐producing industries, and also for replacing conventional carbohydrate sugars used in industrial microbial fermentation processes to convert it into a broad range of value‐added organic products such as bioethanol (Dharmadi et al ., ; Rossi et al ., ).…”