Three-Stage Anaerobic Co-Digestion of Food Waste and Waste Activated Sludge: Identifying Bacterial and Methanogenic Archaeal Communities and Their Correlations with Performance Parameters

Food waste (FW) and waste activated sludge (WAS) are critical global issues currently. To combine the benefits of high-solids anaerobic digestion (AD) and wet AD of FW and WAS to improve digester performance and methane production, a three-stage anaerobic digester was developed in this study. Three-stage anaerobic co-digestion of FW and WAS was conducted while corresponding bacterial and methanogen communities were characterized. Results showed that the average methane yield in the three-stage digester was 13-52% higher than that of one- and two-stage digester. An increase of 12-47% in volatile solids reduction was achieved in the three-stage digester, compared to the controls. Bacterial phyla Proteobacteria, Firmicutes and Bacteroidetes dominated in one-, two- and three-stage digester while genera Pseudomonas, Tissierella, and Petrimonas were selectively enriched in the three-stage digester due to functional segregation. Taxonomic analysis identified 8 dominant methanogen genera, of which Methanosarcina, Methanosaeta, Methanobacterium and Methanolinea collectively accounted for 80%. With increasing organic loading rate and digester stage number, the dominant methanogenic pathway shifted from hydrogenotrophic pattern to acetoclastic pattern and reached a final synergy of these two. Methanosarcina was enriched by 1.5-1.7 times in the three-stage digester, contributed to the enhanced methane production. The three-stage digester is promising to be applied to the industrial biogas plants after scale-up and further optimization.