Batch fermentations were run at varying agitation rates and were either pressurized to 1 bar (15.2 psig) or nonpressurized. Agitation and pressure both affect the level of dissolved hydrogen gas in the media, which in turn influences solvent production. In nonpressurized fermentations volumetric productivity of butanol increased as the agitation rate decreased. While agitation had no significant effect on butanol productivity under pressurized conditions, overall butanol productivity was increased over that obtained in the nonpressurized runs. Maximum butyric acid productivity, however, was found to occur earlier and increased as agitation increased. Peak hydrogen productivity occurred simultaneously with peak butyric acid productivity. The proporation of reducing equivalents used in forming the above products was determined using a redox balance based on the fermentation stoichiometry. An inverse relationship between the final concentrations of acetone and acetoin was found in all fermentations studied. The results show that agitation and pressure are important parameters for solvent productivity in acetone-butanol fermentation.
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"), and when hydrogen production was inhibited by increasing hydrogen partial pressure (Doremus et al., 1985; Yerushaimi and Volesky, 1985), applying carbon monoxide (Datta and Zeikus, 1985; Meyer et al., 1986), limiting iron concentration (Junelles et al., 1988; Peguin and Soucaille, 1995), or using artificial electron carriers that can divert the electrons for hydrogen generation to NADH accumulation (Girbal et al., 1995; Kim and Kim, 1988; Peguin et al., 1994; Peguin and Soucaille, 1995, 1996; Rao and Mutharasan, 1986, 1987). In particular, increasing NADH availability through the use of artificial electron carriers, such as methyl viologen (MV), is relatively simple and effective to implement. "
"When 60 g/L resin was initially added to the culture, acetoin production was as high as 3.8 g/L, whereas acetone production was only 1.9 g/L. Interestingly, an inverse relationship between acetoin and acetone production was also observed in the study by Doremus et al., who investigated the effects of pressure and agitation on ABE fermentation . Thus, it appears that acetoin can be overproduced at the expense of acetone without negatively affecting butanol production. "
[Show abstract][Hide abstract] ABSTRACT: Clostridium acetobutylicum can propagate on fibrous matrices and form biofilms that have improved butanol tolerance and a high fermentation rate and can be repeatedly used. Previously, a novel macroporous resin, KA-I, was synthesized in our laboratory and was demonstrated to be a good adsorbent with high selectivity and capacity for butanol recovery from a model solution. Based on these results, we aimed to develop a process integrating a biofilm reactor with simultaneous product recovery using the KA-I resin to maximize the production efficiency of biobutanol.
KA-I showed great affinity for butanol and butyrate and could selectively enhance acetoin production at the expense of acetone during the fermentation. The biofilm reactor exhibited high productivity with considerably low broth turbidity during repeated batch fermentations. By maintaining the butanol level above 6.5 g/L in the biofilm reactor, butyrate adsorption by the KA-I resin was effectively reduced. Co-adsorption of acetone by the resin improved the fermentation performance. By redox modulation with methyl viologen (MV), the butanol-acetone ratio and the total product yield increased. An equivalent solvent titer of 96.5 to 130.7 g/L was achieved with a productivity of 1.0 to 1.5 g . L-1 . h-1. The solvent concentration and productivity increased by 4 to 6-fold and 3 to 5-fold, respectively, compared to traditional batch fermentation using planktonic culture.
Compared to the conventional process, the integrated process dramatically improved the productivity and reduced the energy consumption as well as water usage in biobutanol production. While genetic engineering focuses on strain improvement to enhance butanol production, process development can fully exploit the productivity of a strain and maximize the production efficiency.
Full-text · Article · Jan 2014 · Biotechnology for Biofuels
"Like any microbiological process performance parameters including pH, temperature, hydraulic retention time, seed sludge, nutrients, inhibitors, reactor design, and the means used for lowering hydrogen partial pressure are very important (Chen et al., 2001; Fang & Liu, 2002; Khanal et al., 2004; Lay et al., 2000; Lay, 2001). As for example, for the optimizing the cultivation of the non-sulfur purple bacteria over accumulation of dissolved hydrogen in the liquid and high hydrogen partial pressures are thought to inhibit the process of hydrogen production (Chenlin & Herbert, 2007; Doremus et al., 1985; Fennell & Gossett, 1998; Pauss et al., 1990). Infact, various factors have been studied in relation to bacterial hydrogen production including enzymes, of the process and inhibitory effects of NH 4 on gas production (Kim et al., 1980; Koku et al., 2003; Yoch & Gotto, 1982; Zhu et al., 2001). "