Exploring anaerobic fermentation stability against a temperature perturbation: process indicators and recovery strategies

Anaerobic fermentation (AF) efficiency is highly influenced by temperature, and operational disruptions in industrial settings can lead to severe process failure. In this study, AF of food wastes (FWs) was subjected to a temperature drop from 25 °C to 15 °C to elucidate AF behaviour and proper recovery strategies. The temperature decrease caused a marked decline in volatile fatty acids (VFAs) production from 23.7 ± 0.2 to 6.1 ± 0.2 g/L, reducing the bioconversion yields from 42.8 ± 0.4 to 8.9 ± 0.3 %. VFAs-producing pathways shifted toward lactic (HLact, 13.3 ± 0.1 g/L) and succinic (HSu, 4.0 ± 0.2 g/L) acids, indicating partial inhibition of the acidogenesis step. This shift was correlated with the enrichment with HLact-producing bacteria (LAB), namely Enterococcus, Lactobacillus, and Lactococcus. To recover VFAs production levels, two strategies were applied: (i) natural recovery by re-establishing the original operational conditions to 25 °C and (ii) a combined approach of re-establishing the operational conditions plus partial re-inoculation of the fermentation broth. While both strategies restored VFAs production and metabolite distribution, the re-inoculation strategy halved the recovery period. These findings underscore the severity of temperature-induced stress in AF of FWs and highlight the importance of effective interventions to recover the performance of a bioprocess under stress. Adopting appropriate countermeasures can effectively mitigate perturbations and safeguard the stability of industrial AF processes.