Anaerobic digestion is an effective technology for wastewater treatment and energy recovery. Lots of effort has been made to improve performance and stability of anaerobic digesters by modifying digester architecture or optimizing digester parameters. Deliberately modifying the microbial community offers an altemative approach for improving digester performance, and several bioaugmentation tests were successfully demonstrated for this purpose. Syntrophic association in methanogenesis has been emphasized because a number of trophic groups affect the end-point methanogens. We hypothesized that cellulose hydrolysis and subsequent fermentation of monomers to methanogen-compatible substrates is a rate and extent-limiting factor in wastes with a significant cellulose fraction. The hypothesis was tested in bench-scale fed-batch reactors with amendment of the mesophilic cellulose-degrading Clostridium cellulolyticum H10, which degrades cellulose into hydrogen, acetate, and ethanol, all of which are expected to directly or indirectly enhance methanogenesis. The tested waste materials included cattle manure and wastewater sludge. Amendment with C.cellulolyticum resulted in a significant enhancement of methane, 20-30% of average increase in a significant enhancement of methane, 20-30% of average increase in cattle manure digesters and 10-20% of average increase in sludge digesters during the openration time.