Ethanol Production from Syngas by Clostridium Strain P11 Using Corn Steep Liquor as a Nutrient Replacement

Abstract

The objective of this research is to evaluate corn steep liquor (CSL) as an inexpensive nutrient and substitute to yeast extract (YE) used in the conversion of synthesis gas (syngas) to ethanol. Syngas is primarily a mixture of CO, CO2, and H2. CSL is rich in carbohydrates, vitamins, minerals, and trace metals and is much lower in cost compared to YE. Yeast extract was employed at a concentration of 1 g/L, while two CSL concentrations (10 g/L and 20 g/L) were investigated. Initially, growth and product profiles of Clostridium strain P11 in YE and CSL media were followed during fermentation in 250-mL serum bottles fed with syngas every 24 h at 239 kPa (absolute). In subsequent runs, the syngas fermentation was scaled-up to 7.5-L fermentor, in which growth, product profile and redox potential were closely monitored during the fermentation process. After 600 h of fermentation, ethanol concentrations in 250-mL serum bottles with 1 g/L YE, 10 g/L and 20 g/L CSL were 1.3 g/L, 1.5 g/L, and 2.7 g/L, respectively. Ethanol yields in these media after 336 h were 72%, 79% and 142% of the theoretical values based on CO consumed, respectively. The maximum ethanol concentrations after 360 h of fermentation in 7.5-L fermentor with 10 g/L and 20 g/L CSL media were 8.6 g/L and 9.6 g/L, respectively, which represent 57% and 60% of the theoretical ethanol yields. Only about 6.1 g/L of ethanol was obtained in the medium with 1 g/L YE after 360 h, which represents 53% of the theoretical ethanol yield. These results showed that CSL can be used as a substitute for YE in syngas fermentation. In addition, CSL can enhance ethanol production and provide substantial savings by reducing the cost of the medium, which is an important factor in large scale ethanol production.