Biomass-derived syngas often contains additional constituents such as CH4, some higher hydrocarbons (C2H2, C2H4 and C2H6), tar, ash, and char particles. Since most of the researchers use bottled synthetic gas mixtures for syngas fermentation studies, there are limited studies that examine the effects of impurities on syngas fermentation (Ahmed and Lewis, 2007). The authors reported the effects of NO on hydrogenase activity, cell growth, and product distribution using C. carboxydivorans. The authors further concluded that NO concentration below 40 ppm had no significant effect on syngas fermentation process. Ahmed et al. (2006) reported that tars could promote cell dormancy and product redistribution (etha­nol and acetic acid) during syngas fermentation. Kundiyana et al. (2010) examined the ability of Clostridium ragsdalei ((ATCC BAA-622), previously known as strain Pll) to grow and metabolize CO under microaerophilic condition (5% O2) in a pilot-scale fermentor. Further, the growth of acetogens such as M. thermoacetica and Clostridium magnum in a medium supplemented with 21% O2 was reported by Karnholz et al. (2002). These findings provide the prospects of scaling-up syngas fermentation for commercialization. Furthermore, the microbial catalysts used in syngas fermentation had higher tolerance to toxic gases and trace contaminants such as hydrogen sulfide (H2S) and carbonyl sulfide (COS) than that of bio­chemical pathway (Worden et al., 1991; Younesi et al., 2005).