•The impact of bioaugmentation on methane production from spent grain was examined.•Methane production elevated for 17.8% with P. xylanivorans Mz5T bioaugmentation.•Bioaugmentation enhances the hydrolysis of brewery spent grain.•Changes in bacterial and archaeal communities were detected during biogas process.•Bioaugmentation enables successful biogas production from brewery spent grain. Lignocellulosic substrates are widely available but not easily applied in biogas production due to their poor anaerobic degradation. The effect of bioaugmentation by anaerobic hydrolytic bacteria on biogas production was determined by the biochemical methane potential assay. Microbial biomass from full scale upflow anaerobic sludge blanket reactor treating brewery wastewater was a source of active microorganisms and brewery spent grain a model lignocellulosic substrate. Ruminococcus flavefaciens 007C, Pseudobutyrivibrio xylanivorans Mz5T, Fibrobacter succinogenes S85 and Clostridium cellulovorans as pure and mixed cultures were used to enhance the lignocellulose degradation and elevate the biogas production. P. xylanivorans Mz5T was the most successful in elevating methane production (+17.8%), followed by the coculture of P. xylanivorans Mz5T and F. succinogenes S85 (+6.9%) and the coculture of C. cellulovorans and F. succinogenes S85 (+4.9%). Changes in microbial community structure were detected by fingerprinting techniques.