17 ENERGY RESEARCH at the University of Oulu An anaerobic bioreactor system for biobutanol production Johanna M. Päkkilä*, Tomi Hillukkala, Liisa Myllykoski and Riitta L. Keiski University of Oulu, Department of Process and Environmental Engineering, FI-90014 University of Oulu, P.O.Box 7300 1 Introduction Concerns about the greenhouse effect, as well as legislation to reduce CO 2 emissions and to increase the use of renewable energy have been the main reasons for the increased produc- tion and use of biofuels. In addition to bioethanol and biodiesel production, the research on biobutanol production has also increased during the past years. Butanol can be produced by chemical or biochemical routes. Fuel properties of butanol are considered to be superior to ethanol because of higher energy content, and better air-to-fuel ratio (Gautam and Martin 2000). Butanol is also less volatile and explosive than ethanol, has higher flash point and lower vapour pressure which makes it safer to handle (Huang et al. 2004). (Cascone 2007) Biobutanol production is an anaerobic two-stage fermentation process where acetic and bu- tyric acids, carbon dioxide and hydrogen are first produced in the acidogenic phase. Then the culture undergoes metabolic shift to solventogenic phase and acids are converted into acetone, ethanol and butanol. At the end of the fermentation, products are recovered from the cell mass, other suspended solids, and by-products. (Ezeji et al. 2007) Several species of Clostridium bacteria are capable to metabolize different sugars, amino and organic acids, polyalcohols and other organic compounds to butanol and other solvents. Feedstock materials for biobutanol are diverse, including different kind of by-products, wastes and residues of agriculture and industry. Optimal fermentation conditions (pH, temperature, nutrients), products and their ratio vary with strains and substrates used. (Jones and Woods 1986, Qureshi and Blaschek 2005) Biobutanol production has still some limitations including butanol toxicity to culture leading to low butanol yields. The product inhibition hinders the yield of butanol and acids, making integrated product separation process highly favorable. Butanol recovery from fermentation broth is expensive because of the low butanol concentration and high boiling point (118°C) (Qureshi and Blaschek 2001). Several different recovery methods are available. Membrane- based methods such as membrane evaporation, perstraction, pervaporation and reverse os- mosis with high selectivity are the most promising product recovery techniques despite of the tendency for clogging and fouling (Ezeji et al. 2003, Izák et al. 2008). Process development to achieve an economical and efficient production process have been done also by genetic strain manipulation, regulation of substrate utilization and butanol production, by using cell immobilization or cell recycling, and by using different kinds of product recovery techniques. (Cascone 2007, Ezeji et al. 2007) * Corresponing author, E-mail: johanna.pakkila@oulu.fi