Unraveling Anaerobic Digestion Foaming via Association between Bacterial Metabolism and Variations in Microbiota

Foaming in anaerobic digesters is considered to be a global concern because of its significant impact on process efficiency and operational costs. Although the importance of organic loading rate on anaerobic foaming is widely recognized, there is little information on key bacteria among the hundreds of species that induce foaming, especially the metabolite–microbiota correlation that influences foaming in anaerobic digesters. This study demonstrated that the organic loading rate promoted foaming and decreased the performance of bench-scale batch digesters. Metabolomic analysis revealed distinct changes in the metabolic phenotype, including short-chain fatty acids and amino acids, decreasing surface tension and inducing foaming. Furthermore, correlation analysis revealed that Clostridium clusters, Sporolactobacillus, and Bacteroides were the primary microbes that contributed to the metabolite foaming incidents. Thus, the findings of this study elucidate the complex formation of foaming in anaerobic digestion and provide an effective early warning to control foaming in full-scale digesters.