Biomethane Production as an Alternative for the Valorization of Agricultural Residues: A Review on Main Substrates Used as Renewable Energy Sources

Biomethane is one of the most promising gases among renewable energy sources. It is a fuel that can be applied to turbines, boilers, domestic stoves, and internal combustion engines to generate heat or electricity. One of the ways to obtain this gas is through biological technologies, such as anaerobic digestion reactors, that can convert agricultural residues like vinasse, swine effluent, and animal manure into biomethane, preventing their inappropriate disposal in the environment. Several studies show that co-digestion, the association of more than one type of waste, can be advantageous for obtaining this gas due to the greater availability of nutrients and diversification of microbial communities. However, obtaining biomethane and using it as a sustainable energy source still has challenges that range from improving the biological process to choosing the most efficient conversion technology. This chapter aims to present the main types and characteristics of agricultural wastes used as substrates and highlight some important factors that can influence the efficiency of biomethane production in anaerobic reactors.