Different Categories of Pretreatment Methods
Pretreatment technologies can be basically classified into the following four categories:
1. Physical pretreatment
2. Physicochemical pretreatment
3. Chemical pretreatment
4. Biological pretreatment
Physical pretreatment is often called size reduction to reduce biomass physical size; it is also the first step in many other pretreatment processes as raw biomass comes in the form of larger pieces in most situations, except in a case like sawdust from a mill. Chemical pretreatment utilizes chemical transformations to overcome the recalcitrance so that the enzymes can have access to cellulose for microbial depolymerization. Biological pretreatment uses enzymes to achieve the accessibility for the hydrolysis step and is not as widely used as other methods. Then there are multiple techniques within some of these classifications. In this chapter various pretreatment techniques are presented in detail under these four categories; however some of the techniques may have features of more than one category.