Acidogenic fermentation of pretreated food waste under psychrophilic conditions for volatile fatty acids production

Abstract

Mixed‐culture fermentation generally produces volatile fatty acids (VFAs) as a mixture of C2–C6 acids. Among operational parameters, temperature has a distinct effect on the microorganisms' metabolic activity, which can shift the composition of the metabolites. Performing food‐waste fermentation at mesophilic or thermophilic temperatures results in a rich mixture of metabolites where further extraction of targeted VFAs can be challenging. Moreover, in colder countries, it is energy‐intensive when the average temperatures remain under psychrophilic ranges for most of the year. This study evaluated the production of VFAs under the psychrophilic temperature of 17 °C in comparison to the mesophilic temperature of 37 °C after thermal–alkaline pretreatment of the substrate to enhance hydrolysis. With pretreatment at 120 °C and pH 9, total VFA production reached 1 g/L under psychrophilic temperature. This also resulted in a less complex VFA mixture with acetic acid as the major constituent. This enhanced acetic acid production was due to the increased abundance of Hafnia and Fonticella species, responsible for acetic acid production. The higher accumulation of acetic acid indicates a shift towards simpler VFA profiles under psychrophilic conditions. The estimated power consumption also highlighted the mesophilic operation to be more than twice as intensive as the psychrophilic operation. The use of psychrophilic temperature and substrate pretreatment selectively promotes the activity of microorganisms towards a more tailored generation of VFAs.