Grassland is ubiquitous in Ireland, covering over 91% of agricultural land. Grass biomethane has shown to be a sustainable biofuel with a very strong energy balance. Anaerobic digestion is a mature technology, particularly wet continuous digestion. However, the retention periods for grass digestion are relatively long, typically over 60 days. Recently, dry batch digestion has become quiet prevalent; retention times are lower, at about 30 days, but because half of the feedstock is left in the digester for a second cycle as an innoculum, the actual retention time is of the order of 45 days. A methodology that is at the development stage is a two-stage system. The first stage is a dry batch leaching stage (hydrolysis and acidogenesis). The leachate produced is treated in an upflow anaerobic sludge blanket (UASB), where methanogenisis occurs. This should allow for the shorter retention times of the dry batch process because there is no need to leave half of the feedstock in the digester as an innoculum for a ...