Insights into the resistance of different extracellular polymeric substance (EPS) layers to the fermentation environment in sludge anaerobic digestion

• EPS layer delamination had great promotion for the methane production. • The semi-rigid structure of sludge flocs was damaged after EPS layer delamination. • EPS layer delamination reduced metal contents and the apparent activation energy. Extracellular polymeric substance (EPS) is key in maintaining microbial cell stability and agglomeration in sludge, which may play as a protective layer for cells. This study tried to assess the digestive performances of sludge after delamination of different EPS layers, aiming to understand the resistance of different EPS layers to the external environment. Results indicated that, after EPS layer delamination, the cumulative methane yield in anaerobic digestion (AD) was improved from 148.8 to 199.9 mL/g COD. The total methane yield for the EPS layers and EPS extracted sludge increased by 32.2% compared to the raw sludge. Moreover, with the delamination of EPS layers, the apparent activation energy (AAE) of the sludge samples decreased, and the interactions between metals and organic substances were destroyed, resulting in lower energy barrier in organic solubilization. Additionally, the treatment changed the distribution of organic substances in sludge, and the residual organic substances presented higher theoretical methane production (TMP). Therefore, both the hydrolytic efficiency and the conversion efficiency of organic substances to methane in AD were improved. By understanding the resistance effects of different EPS layers to the fermentation environment, this study will help us develop more targeted methods in sludge pretreatment for improving its digestive performance.