Biological pretreatment of organic waste for short-chain fatty acids production: State-of-the-art, advances, challenges and prospectives

Acidogenic fermentation is an emerging technology that has gained significant attention for producing short-chain fatty acids (SCFA), but its efficiency is often constrained by the lower hydrolysis of organic substrates. To overcome this challenge, biological pretreatment such as enzymatic, fungi, and bacterial are an attractive alternative due to their ability to target specific substrate structures, lower energy consumption, and the absence of inhibitory compounds. This review provides comprehensive overview of the current status of biological pretreatments used in acidogenic fermentation, with a particular emphasis on their impact on substrate hydrolysis, SCFA production and composition, and microbial community structure. It was found that enzymatic pretreatment is particularly effective for food and kitchen wastes, while fungi and bacterial pretreatments are more suitable for lignocellulosic biomass and algae, respectively, for SCFA production. These pretreatments influence SCFA composition, with enzymatic and bacterial pretreatments promoting acetic and butyric acids, while fungi pretreatment favors acetic and propionic acids. Furthermore, all these pretreatment methods significantly impact microbial composition by enriching functional hydrolytic and acidogenic bacteria. This review also presents the challenges of biological pretreatment assisted acidogenic fermentation and discusses strategies to address them. The insights presented in this review will help identify existing challenges and guide future research directions to facilitate the industrial implementation of this technology for SCFA production.