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.

Automated summary

The study demonstrated the benefits of biomass retention through dynamic membrane (DM) for stable performance of AnDMBR treating waste activated sludge, with an observed shift in archaeal population and functional gene expression at higher substrate concentrations. The presence of glycosyltransferase encoding genes in the biofilm formation process and the increase in average particle size distribution suggests the potential for high-rate treatment of waste activated sludge using an AnDMBR system.