2.2 Classification of Biofuels
Biofuels can be classified into four categories, and these categories are named as
first, second, third, and fourth generations. The classification is mainly based on the
materials used for production purpose. The generation of biofuels and their sources
have been shown in Fig. 2.2.
Fig. 2.1 Microbial aspects of biofuel production
Fig. 2.2 First-generation biofuels are produced from edible biomass, while second-generation
biofuels are produced from non-edible biomass. Third-generation biofuels are produced from
several species of macro- and microalgae. Modifications in metabolic pathways and genetic
materials are the major source of fourth-generation biofuels
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