Enhanced methanogenesis of waste activated sludge by bioaugmentation with metal-reducing bacteria

Anaerobic digestion (AD) has been getting increasing attention due to its ability of stabilizing organic pollutants along with biogas generation. AD has therefore been widely used to treat high-strength organic wastes including waste activated sludge (WAS). This study investigates the potential to enhance the AD efficiency of WAS by bioaugmentation with metal-reducing bacteria (MRBs). A mesophilic continuously-stirred tank reactor was anaerobically operated to treat WAS for over 7 months. After the stabilization of the reactor at a hydraulic retention time (HRT) of 20 days (Phase 1), FeO(OH) was fed to the reactor (final concentration, 20mM) through the feed WAS while no operating condition was changed (Phase 2). The reactor was then further augmented with enriched MRB culture from anaerobic sludge and monitored for performance changes. Methane production rate and yield increased significantly over phases (18.2–48.0%). Denaturing gradient gel electrophoresis (DGGE) analysis showed that there was no visible change in archaeal community structure, but marked changes in bacterial community structure, induced by the addition of FeO(OH) or MRBs