Butanol production using non-defined microbial cultures

For a smoother transition towards a bio-based society, no longer dependent on current liquid fossil fuels, sustainable alternatives to energy sources like gasoline and diesel need to be implemented. Due to their similarities, butanol can already today be used as direct replacement for gasoline. Industrial production of biobutanol is a well-established process. However, it relies on pure culture batch fermentation and expensive pure substrates (e.g. glucose), which carries some challenges such as culture contamination, competition with the food segment, and low adaptability to variations in substrate composition. Due to their microbial diversity, mixed microbial cultures (MMC) can overcome such limitations and become the predominant bio-based production platform for biobutanol. Previous studies have shown that butanol formation was feasible using only butyrate as carbon source and hydrogen (H2) as electron donor during batch cultivation of an anaerobic mixed culture (Steinbusch et al., 2008). Both substrates are common intermediates during the decomposition of organic residues, as is the case for industrial waste streams, offering a cheap feedstock alternative that avoids competition with food production. Moreover, MMCs are less susceptible to contaminations rendering biobutanol production by continuous fermentation a possibility.
In this work, we investigate the feasibility of butanol formation by anaerobic MMCs in a continuous production process. To ensure process consistency, batch fermentations were first conducted to determine possible limitations of the selected MMCs. Elevated H2 partial pressures and acidic conditions (pH 5.5) were applied to suppress competing side reactions such as anaerobic butyrate conversion and methanogenesis. It was found that anaerobic butyrate conversion was selectively inhibited. The obtained butanol concentration was about three times larger than previously reported by Steinbusch et al. (2008), hinting at future applications of MMC for continuous butanol production from waste streams.