Use of extracellular polymer substances as additives for improving biogas yield and digestion performance

To understand how extracellular polymer substances (EPS) as additives promotes methanogenesis, batch tests of methane production potential in anaerobic reactors with the addition of EPS or not were conducted. Research showed that EPS increased remarkably methane production during anaerobic digestion (36.5% increase compared with the control). EPS enriched functional microorganisms such as Firmicutes, Actinobacteria, Synergistetes, and Chloroflexi. Among them, 8.86% OTUs from the important hydrolysis and acidification phyla, which may be an important reason for the enhanced methanogenic capacity of anaerobic granular sludge. Additionally, EPS also improved the abundance of cytochrome c (c-Cyts), accelerating the direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens, thus enhancing the methane production. Interestingly, the average particle size, volatile suspended solids/total suspended solids (VSS/TSS) and EPS content of anaerobic granular sludge (AnGS) in the EPS reactor were approximately equal to that of the control reactor during the anaerobic digestion, illustrating that EPS could not affect the physicochemical properties of AnGS. Therefore, these results suggested that EPS mainly played a role in the form of conductive materials in the anaerobic digestion process. Compared with conductive materials, EPS as biomass conductive materials was not only environmentally friendly and economical but also no secondary pollution.\n\nImportanceCompared with the reported conductive materials, EPS has the potential of biodegradation, electron transfer and no significant secondary pollution. Besides, there are few studies on the utilization of EPS resources, especially the effect of EPS as an additive on anaerobic digestion performance. To clarify whether EPS as conductive materials or carbon source promotes methanogenesis. Therefore, in this study, we investigated the influence of EPS as an additive on the methanogenic capacity, physical-chemical properties, microbial community structure and metabolic function of anaerobic granular sludge (AnGS), and preliminarily expatiate the influence mechanism of EPS as an additive on methanogenesis. At the meantime, the research is expected to provide new solutions for the improvement of anaerobic digestion performance and disposal of waste mud.