Anaerobic Thermophilic Digestion of Maotai-Flavored Distiller's Grains: Process Performance and Microbial Community Dynamics

Improperly disposed Maotai-flavored distiller's grains (MDGs) cause environmental pollution. However, the high organic matter and moisture contents in MDG make this byproduct suitable for anaerobic digestion. The performance and stability of thermophilic anaerobic digestion were evaluated at an organic loading rate of 3 g VS/(L.d) and a working volume of 55 L. The microbial community dynamics were analyzed by high-throughput illumina pyrosequencing. A volumetric biogas production rate of 1.30 L/(L.d) was obtained upon reaching stability by diluting the feed without effluent recirculation. Defluviitoga, Candidatus Caldatribacterium, Hydrogenispora, Acetomicrobium, Methanosarcina, and Methanothermobacter were the dominant acidogenic and methanogenic genera. Recirculating the effluent without dilution caused acidification and instability due to its high levels of lactic (74 g/kg), acetic (31 g/kg), and succinic (24 g/kg) acids originally present in MDGs. Once acidified, the digester failed to recover using control measures such as halting effluent recirculation, adding trace elements, stopping feeding, and adding inoculum.