Biofuels: Types, Promises, Challenges, and Role of Fungi

Abstract

Liquid biofuels are known as suitable alternatives to fossil fuels whose growing utilization has already endangered both the environment and public health. Nevertheless, first-generation biofuels have been extensively criticized for their unfavorable impacts on sustainable supply of food and feed. In light of that, higher generations of biofuels have been at the center of attention over the last years. More specifically, second-generation biofuels such as lignocellulosic-based bioethanol and waste oil-oriented biodiesel have been considered promising in mitigating greenhouse gas emissions and combating climate change. However, since these kinds of biofuels require additional pretreatment and hydrolysis steps, rendering their production is economically inefficient in many cases. Therefore, research efforts have been diverted toward the development of more economically viable technologies to overcome these challenges. In this chapter, different types of biofuels, including solid (firewood, wood chips, and wood pallets), liquid (bioethanol, biodiesel, pyrolysis bio-oil, and drop-in biofuels), and gaseous biofuels (biogas and syngas) are first introduced, and subsequently, the obstacles faced in the production of these biofuels are reviewed. Finally, the potentials of fungi and yeasts in biofuels (bioethanol and biodiesel) production are presented and discussed. Overall, fungi could be used in biofuel production in three ways: (1) application as the source of cellulase for hydrolyzing lignocellulosic materials for bioethanol production, (2) application as the source of lipids for biodiesel production, and (3) application as the source of lipase for catalyzing the transesterification of lipids in biodiesel production.