El Mito Del Estado

Bioresource Technology 102 (2011) 6494–6501

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Bioresource Technology
journal homepage: www.elsevier.com/locate/biortech

Ethanol production from syngas by Clostridium strain P11 using corn steep liquor as a nutrient replacement to yeast extract
Prasanth Maddipati, Hasan K. Atiyeh ⇑, Danielle D. Bellmer, Raymond L. Huhnke
Department of Biosystemsand Agricultural Engineering, Oklahoma State University, Stillwater, OK 74078, USA

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The feasibility of replacing yeast extract (YE) by corn steep liquor (CSL), a low cost nutrient source, for syngas fermentation to produce ethanol using Clostridium strain P11 was investigated. About 32% more ethanol (1.7 g LÀ1) was produced with 20 g LÀ1 CSL media in250-mL bottle fermentations compared to media with 1 g LÀ1 YE after 360 h. Maximum ethanol concentrations after 360 h of fermentation in a 7.5-L fermentor with 10 and 20 g LÀ1 CSL media were 8.6 and 9.6 g LÀ1, respectively, which represent 57% and 60% of the theoretical ethanol yields from CO. Only about 6.1 g LÀ1 of ethanol was obtained in the medium with 1 g LÀ1 YE after 360 h, which represents53% of the theoretical ethanol yield from CO. The use of CSL also enhanced butanol production by sevenfold compared to YE in bottle fermentations. These results demonstrate that CSL can replace YE as the primary medium component and significantly enhance ethanol production by Clostridium strain P11. Ó 2011 Elsevier Ltd. All rights reserved.

Article history: Received 20 December 2010 Received inrevised form 15 March 2011 Accepted 16 March 2011 Available online 21 March 2011 Keywords: Clostridium Corn steep liquor Ethanol Syngas fermentation Yeast extract

1. Introduction The dominant biofuel in the US is ethanol made via yeast-based fermentation of corn starch, which is a well-developed technology. Ethanol made via fermentation of synthesis gas (syngas) produced from gasification ofnon-edible feedstocks such as biomass and municipal solid wastes is relatively a new technology. Syngas, primarily containing CO, CO2, and H2, can be fermented to ethanol and acetic acid by acetogenic organisms such as Clostridium ljungdahlii (Klasson et al., 1992; Phillips et al., 1994; Younesi et al., 2005), Clostridium autoethanogenum (Abrini et al., 1994), Clostridium carboxidivorans P7 (Ahmedand Lewis, 2007; Rajagopalan et al., 2002), and Clostridium strain P11 (Huhnke et al., 2010; Saxena, 2008). These microorganisms utilize the reductive acetylCoA pathway, also known as the ‘‘Wood–Ljungdahl’’ pathway, for the synthesis of acetyl-CoA, conservation of energy and growth and production of acetic acid and ethanol (Wood et al., 1986). The overall reactions for ethanol and acetic acidproduction from H2 and CO are (Vega et al., 1989):

4CO þ 2H2 O ! CH3 COOH þ 2CO2 2CO2 þ 4H2 ! CH3 COOH þ 2H2 O

ð3Þ ð4Þ

6CO þ 3H2 O ! C2 H5 OH þ 4CO2 6H2 þ 2CO2 ! C2 H5 OH þ 3H2 O

ð1Þ ð2Þ

When equal moles of CO and H2 are supplied, theoretically twothirds of the carbon from CO can be converted to ethanol and the remaining carbon is accounted for in CO2 production as seen by combining Eqs.(1) and (2). However, all the carbon supplied in the form of CO theoretically can be converted to acetic acid by combining Eqs. (3) and (4). Butanol production has also been reported from CO (Shen et al., 1999; Worden et al., 1991) or a mixture of CO, CO2 and H2 (Babu et al., 2010; Datar et al., 2004; Liou et al., 2005; Rajagopalan et al., 2002) by only three bacteria. Butyribacteriummethylotrophicum was reported to produce between 0.3 and 1.4 g LÀ1 butanol from pure CO (Shen et al., 1999; Worden et al., 1991). However, Clostridium strain P11 produced 0.3 g LÀ1 butanol from a simulated syngas mixture (Babu et al., 2010) and C. carboxidivorans produced 1.3 g LÀ1 butanol from syngas derived from cellulosic feedstock (Rajagopalan et al., 2002). The overall reactions for butanol production...