Effect of temperature, pH and buffer presence on ethanol production from synthesis gas by ‘‘Clostridium ragsdalei’’ Dimple K. Kundiyana, Mark R. Wilkins ⇑ , Prasanth Maddipati, Raymond L. Huhnke Department of Biosystems and Agricultural Engineering, Oklahoma State University, 224 Ag Hall, Stillwater, OK 74078, USA article info Article history: Received 21 October 2010 Received in revised form 4 February 2011 Accepted 5 February 2011 Available online 4 March 2011 Keywords: Biofuels Anaerobic Biomass Syngas Acetogens abstract Fermentation pH, incubation temperature, and presence or absence of media buffer can alter the activity of microorganisms. For instance, carbon monoxide and hydrogen components of syngas show decreased solubility with increasing temperature, Clostridium species preferentially switch from acetogenesis to sol- ventogenesis phase at pH below 5.0, and morpholinoethanesulfonic acid (MES) added as media buffer has been shown to increase lag time for ethanol production. The objective of the present study was to deter- mine the effects of temperature, pH and MES buffer on ethanol production by ‘‘Clostridium ragsdalei’’. This study showed syngas fermentation using ‘‘Clostridium ragsdalei’’ at 32 °C with media without buffer was associated with higher ethanol concentration and reduced lag time in switching to solventogenesis. Tem- perature above 40 °C and pH below 5.0 were outside the optimal range for growth and metabolism of the bacteria. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Biologically, ethanol can be produced either by direct fermenta- tion of fermentable sugars in sugar crops, by enzymatic and phys- ico-chemical degradation of cellulosic biomass to sugar followed by fermentation by yeast or bacteria, or by biomass gasification- syngas fermentation. One of the major disadvantages with the uti- lization of straw, wood and other cellulosic biomass is the presence of a large proportion of non-degradable components such as lignin. Gasification of cellulosic biomass is one approach of overcoming this major hurdle. Gasification produces synthesis gas (syngas) in which CO and H 2 are the essential components for subsequent eth- anol production. Syngas fermentation offers several advantages to chemical catalytic conversion of syngas such as the higher sub- strate specificity of biocatalysts, lower energy costs, greater resis- tance to catalyst poisoning and the lack of a requirement for a fixed CO:H 2 ratio (Bredwell et al., 1999). Biological fermentation of syngas is irreversible in nature as it ensures complete conversion of cellulosic feedstock. Production of acetate by utilizing CO, CO 2 and H 2 can be summarized by the following reactions (Ljungdahl, 1986): 4COþ2H 2 O !CH 3 COOHþ2CO 2 ðDG  ¼37:8 kJ=g mol CH 3 COOHÞ ð1Þ 2CO 2 þ 4H 2 !CH 3 COOH þ2H 2 OðDG  ¼18:6 kJ=g mol CH 3 COOHÞ ð2Þ Based on the similarity with respect to Eqs. (1) and (2) above, the following stoichiometry for ethanol production in autotrophic acetogens has been proposed (Vega et al., 1989). 6CO þ 3H 2 O ! C 2 H 5 OH þ 4CO 2 ðDG  ¼59:9 kJ=g mol C 2 H 5 OHÞ ð3Þ 2CO 2 þ 6H 2 ! C 2 H 5 OH þ 3H 2 O ðDG  ¼23:2 kJ=g mol C 2 H 5 OHÞ ð4Þ Microorganisms that can reduce CO 2 to acetate via the Wood- Ljungdahl pathway (acetyl-CoA pathway), are termed acetogens. These bacteria are strictly anaerobic and produce acetate as the major fermentation end product (Muller, 2003). Production of ethanol by acetogens follows a path similar to the Wood-Ljungdahl pathway for acetate production by acetogens such as Clostridium acetobutylicum (Jones and Woods, 1986). Oxi- dation of H 2 to 2[H + ] or of CO with H 2 O to CO 2 and 2[H + ] produces the reducing equivalents needed for the conversion of CO 2 and CO to acetate or alcohols (Henstra et al., 2007). Ethanol is a non- growth related product formed during syngas fermentation. Sev- eral acetogenic bacteria have been shown to produce ethanol. Prominent among these are Clostridium ljungdahlii (continuous 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.02.032 ⇑ Corresponding author. Tel.: +1 405 744 8416; fax: +1 405 744 6069. E-mail address: mark.wilkins@okstate.edu (M.R. Wilkins). Bioresource Technology 102 (2011) 5794–5799 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech