Effect of Short-Chain Fatty Acid Production on Biogas Generation

Abstract

The short-chain fatty acids (SCFAs) are generated in the acidogenesis step of the anaerobic digestion, and their production is very important for the global process and efficient biogas production. SCFA production takes place inside the cells of fermentative microorganisms, which are the first ones to start the complex soluble carbon degradation. The SCFA reactions are the most energetic among the anaerobic digestion steps, which means that this step will hardly be limiting for biogas production in normal conditions—except if the previous hydrolysis is rough or impaired. The SCFAs produced are subsequently converted to acetic acid, which is effectively converted to methane by methanogenic acetoclastic archeas. Nevertheless, acetic acid production from SCFA releases a large amount of hydrogen in the medium, and in some situations, it will reduce the process pH to inhibitory levels for methanogenic archeas and consequently suppress biogas production. This chapter will focus on these events, approaching SCFA formation, the functional microorganisms involved, and their importance for the global process.