Effect of the Organic Loading Rates Increase on Process Stability and Microbial Community Composition during the Anaerobic Digestion of Fresh Vinegar Residue

Anaerobic digestion (AD) was employed to utilize fresh vinegar residue (FVR) in this study. The performance and microbial community structure at increasing organic loading rates (OLRs) were evaluated. The results showed that the mono-fermentation of FVR was unstable at high OLRs due to the high acidity and the high cellulose content of the raw material. The optimum OLR was 2.0 g VS/(L·d), with the maximum average methane yield at 216 mL /g VS. High OLRs (2.5 g VS/(L·d)) led to the irreversible inhibition of AD process, although digester ceased feeding during the recovering stage. The diversity of microbial community decreased at high OLRs. The relative abundance of major bacterial community at different OLRs also varied. The syntrophic volatile fatty acids (VFAs) oxidizing bacteria declined while the acid-producing bacteria became dominant. The close correlation between the AD process stability and the microbial community structure suggested that maintaining a rich and diverse microbial community was essential for the practical application of AD on vinegar residue (VR) utilization. Graphic Abstract