Effect of temperature conversion on continuous operation and microbial community of anaerobic digestion system

Through 210 days of continuous anaerobic digestion experiment in the same anaerobic digestion system with food waste as fermentation substrate, the conversion of fermentation temperature from medium temperature to high temperature was achieved. In medium temperature fermentation stage, the maximum organic loading rates (OLR) was 6.5kg COD/(m3·d), the average biogas production rate was 658L/(kg COD·d); Methanosaeta (57.0%)、Methanospirillum (10.0%)、Methanomethylovorans (9.2%) and Methanobacterium (19.7%), which formed a symbiotic relationship with hydrolytic acidifying bacteria and homoacetogenesis to achieve efficient methanogenic process, were included in the dominant methanogens. After 35 days’ heating process, the medium temperature fermentation system smoothly converted into high temperature system. In high temperature fermentation stage, the maxium OLR was 5.0kg COD/(m3·d), and the average biogas production rate was 480L/(kg COD·d); Methanoculleus (96.2%) became dominant methanogenic bacteria, and formed an interacting relationship with syntrophic hydrogen-producing bacteria and syntrophic acetate oxidation bacteria, which jointly promoted H2utilization and methanogenic process. However, obvious acidification trend and reduced gas production efficiency appeared in later stage of high-temperatures system. It was inferred that the activity of methanogens was inhibited with highly enriching of hydrolytic acid-producing bacteria, resulting the imbalance of organic acids production and utilization and the system collapse. Therefore, online temperature conversion of anaerobic fermentation system was technically feasible, but the performance and stability of high temperature fermentation system were lower than that of medium temperature fermentation system. © 2024 Chinese Society for Environmental Sciences. All rights reserved.