**2.3. Biomass types and characteristic**

Biomass is usually derived from trees, forest residues, grasses, aquatic plants and crops. They are very important feedstock to produce valuable chemicals and fuel. These plants undergo photosynthesis process to convert carbon dioxide and water to primary and secondary metabolites. Primary metabolites include carbohydrates and lignin which presents in large concentration in biomass. The carbohydrates are simple sugar, cellulose and hemicellulose which take up more than 50% of the content of the biomass. However, some researchers divided the biomass in different moisture contents [36]. The high moisture content biomass includes aquatic plants and manures which have to undergo 'wet' processing techniques to convert it to energy. For example, conversion of these materials to biofuel commonly involves degradation of the materials using microorganisms or fermentation. Meanwhile, woody plants or dry biomass involves physical techniques such as gasification, pyrolysis or physical combustion.
