Problems with bacteriophage infections emerged in almost all historical industrial ABE fermentation processes, no matter how good hygiene and plant practices were applied (Hastings, 1971; Jones et al., 1986). While most bacteriophage infections manifest in similar symptoms such as decreased growth rates and poor solvent production, bacteriophages seem to be very strain specific. The most successful method to overcome the effects of bacteriophage infections proved to be strain immunization (Jones et al., 1986).

10.5 Future trends

As already stated in the introduction, a problem that every biofuel candidate must face is the question of substrate. Competition between nutritional and transportational needs represents a major ethical problem. Although new plants have been built and existing ones reopened in Brazil and China (see Section 10.3), these are still based on sugar cane or starchy materials. In future, the possibility of converting other compounds into butanol will be becoming more and more important. One interesting resource is lignocellulosic hydrolysates. Processes using such substrates are already used for ethanol formation (Durre, 2007). Currently, a large number of research projects focus on this topic. Another exciting possibility is the use of synthesis gas. This mixture of mostly carbon monoxide and hydrogen can easily be obtained from biomass, thus avoiding costly pretreatments. As syngas is a common bulk material in the chemical industry, technical experience in operation of the respective equipment already exists. The proof of principle of biological butanol formation from syngas has been demonstrated (Kopke, 2009). An additional argument in favor of such a process is the direct consumption of gaseous CO and CO2, thus helping to reduce the global greenhouse effect. It is envisaged that therefore such processes will become important industrial applications in future.