Except the chemical ways, butanol can also be obtained from biological ways with the re­newable resources by the microorganism through fermentation. The Clostridia genus is very common for butanol synthesis under anaerobic conditions, and the fermentation products are often the mixture of butanol, acetone and ethanol. A few kinds of Clostridium can utilize cellulose and hemicellulose with the ability of cellulolytic activities (Mitchell et al., 1997; Be­rezina et al. 2009).

Compared with the chemical ways for butanol production, biological ways has the dis­tinct advantages. For example, it can utilize the renewable resources such as wheat
straw, corn core, switch grass, etc. Furthermore, biological process has high product se­lectivity, high security, less by-products. Furthermore, the fermentation condition of buta­nol production is milder than that of chemical ways and the products are easier to separate. The process of biobutanol production with Lignocellulosic feedstocks is as fol­lowing (Fig. 1):

Figure 1. Butanol production process from lignocellulosic feedstocks

For the first step, biomass containing lignocellulosics should be pretreated before they were used as the substrate for the fermentation, except for a few high cellulase activity strains (Ezeji and Blaschek, 2008). The pretreatment methods are different according to the different types of biomass used. There often use dilute sulfuric acid pretreatment, alkaline peroxide pretreatment, steam explosion pretreatment, hydrothermal pretreatment, organic acid pre­treatment etc. Some inhibitors such as acetic acid, furfural, 5- hydroxymethyl furfural, phe­nols etc. that need to be further detoxified. The ordinary detoxification methods are using activated charcoal (Wang et al., 2011), overliming (Sun and Liu, 2012; Park et al., 2010), elec­trodialysis (Qureshi et al., 2008c), membrane extraction (Grzenia et al., 2012) to remove the inhibitors. This step is determined by different feed stock and different pretreatment meth­ods. After the fermentation, the desired product is recovered and purified in the down­stream process. Biological ways has been set up for many years while it was inhibited for industrial application for economic reasons. So, as an alternative fuel, biomass feedstock for biobutanol production must be widely available at low cost (Kent, 2009). Therefore, by using agricultural wastes for butanol production such as straw, leaves, grass, spoiled grain and fruits etc are much more profitable from an economic point of view. Recently, other sources
such as algae culture (Potts et al., 2012; Ellis et al., 2012) also is studied as one substrate for butanol production.