## ABSTRACT

Biofuels are referred to gas, liquid, and solid fuels predominantly produced from biomass. A variety of fuels can be produced from biomass such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, hydrogen, and methane (Demirbas 2008). Renewable and carbonneutral biofuels are necessary for environmental and economic sustainability (Nigam and Singh 2011). Biofuels are important because they replace petroleum fuels. Between 1980 and 2005, worldwide production of biofuels increased by an order of magnitude from 4.4 to 50.1 billion liters with further dramatic increases in the future (Armbruster and Coyle 2006; Licht 2008; Murray 2005). Different countries have adopted different measures to introduce biofuels. The economics of each fuel vary with location, feedstock, and several other factors. Political agendas and environmental concerns also play a crucial role in the

7.1 Introduction ........................................................................................................................ 155 7.2 Microbial biofuels .............................................................................................................. 156

7.2.1 Bioalcohols .............................................................................................................. 157 7.2.2 Biodiesel .................................................................................................................. 158 7.2.3 Biohydrogen ............................................................................................................ 160

7.3 Conclusion .......................................................................................................................... 164 References ..................................................................................................................................... 164

production and utilization of biofuels. There are a number of technologies that exist and several that are under development for the production of biofuels such as fermentation of sugar substrates, catalytic technology to convert ethanol to mixed hydrocarbon, hydrolysis of cellulose, biobutanol by fermentation, transesterication of natural oils and fats to biodiesel, hydrocracking of natural oils and fats, pyrolysis and gasication of various biological materials, and others. This chapter is an effort to summarize the microbial biofuel production system.