Influence of Inoculum Type on Volatile Fatty Acid and Methane Production in Short-Term Anaerobic Food Waste Digestion Tests

The anaerobic digestion of food waste can yield valuable volatile fatty acids (VFAs), especially when methane (CH4) production is inhibited. Selecting an inoculum with lower methanogenic populations may help reduce CH4 production and improve VFA accumulation. In this study, we investigated VFA and CH4 production in short-term anaerobic batch bioreactors as a function of three inocula compositions derived from a full-scale wastewater treatment facility: (1) anaerobic sludge (AnS), (2) thickened waste activated sludge (TWAS), and (3) TWAS with AnS. The highest VFA concentration (6.62 ± 0.08 g/L) and the lowest total CH4 volume (296 mL) were measured with TWAS only. In contrast, the highest CH4 volume (625 ± 3 mL) was measured in the TWAS + AnS, likely because the AnS was well adapted to digesting TWAS. 16S rDNA sequencing showed that TWAS alone had the lowest relative abundance of methanogens at the start and end of the incubations. The addition of TWAS significantly changed the initial community diversity. These insights suggest that TWAS improves VFA accumulation by providing a microbial community that is more diverse and lower in methanogen abundance relative to AnS. These findings will help guide the selection of inoculation strategies that promote VFA accumulation in anaerobic digesters.