Anaerobic digestion of waste activated sludge using dynamic membrane at varying substrate concentration reveals new insight towards methanogenic pathway and biofilm formation

Biomass retention through the dynamic membrane (DM) proved beneficial to the stable performance of AnDMBR treating waste activated sludge without prior pretreatment. The highest average methane production rate of 1.04 L-CH₄/L/d was achieved at a feed concentration of 100 g-COD/L and an organic loading rate of 6.25 g-COD/L-d. Increasing substrate concentration resulted in archaeal population shift from a mixed acetate/H₂ utilizing methanogens (Methanosarcinales) to strict H₂ utilizing methanogens (Methanobacteriales). Predicted functional gene analysis also confirmed hydrogenotrophic encoding genes became dominant in methanogenic pathways at higher feed concentration. The occurrence of glycosyltransferase encoding genes has substantiated the role of EPS towards DM layer (biofilm) formation which could retain essential microorganisms and achieve steady sludge treatment performance at the high organic loading rate. Moreover, increase in average particle size distribution may suggest the presence of microbial aggregates which also helped in establishing the DM layer. This study shows a promising potential of high-rate treatment of WAS using an AnDMBR system and provides new insights regarding biofilm (DM layer) development.