Evaluation of Corn Steep Liquor as the Primary Fermentation Medium Constituent in Ethanol Production From Syngas 2

Wednesday, November 10, 2010: 2:40 PM
255 A Room (Salt Palace Convention Center)
Prasanth Maddipati, Hasan K. Atiyeh and Raymond L. Huhnke, Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK

Corn steep liquor (CSL) is rich in carbohydrates, vitamins, minerals, and trace metals. It is also a lower cost nutrient compared to yeast extract (YE), the primary media constituent currently being used in syngas fermentation. Syngas is primarily a mixture of CO, CO2, and H2. 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. The temperature and pressure in the bioreactor were controlled at 37C and 143 kPa (absolute). Modeled syngas composed of 20% CO, 15% CO2, 5% H2, and 60% N2 (by volume) was used.

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. However, 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 based on CO consumed. 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 based on CO consumed. These results demonstrate that corn steep liquor is a source of nutrients for strain P11 and can replace yeast extract as the primary medium component.

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