Hydrogen is foreseen as a viable CO2-neutral alternative to fossil fuels for generation of energy. Production of H2 from wastes/wastewaters is possible as this is one of the main products resulting from anaerobic fermentation of organic compounds. If hydrogenotrophic methanogens are suppressed, H2-rich biogas can be recovered from anaerobic reactors. In order to optimize and improve H2 production, it is essential to get more insight into the composition and structure of the microbial communities involved in the process. In this study microbial community shifts in expanded granular sludge ...