Thermo- and mesophilic anaerobic digestion of wheat straw by the upflow anaerobic solid-state (UASS) process

► Anaerobic digestion of wheat straw in UASS reactors was examined. ► The emphasis was to observe process behavior at different temperature levels. ► Thermophilic temperature showed faster degradation and methane yields. ► Lignocellulosic substrate is degraded within a short hydraulic retention time. ► A significant difference in nutrient demand at different temperature levels was observed. In this experimental work, the feasibility of wheat straw as a feedstock for biogas production is investigated using the newly developed upflow anaerobic solid-state (UASS) process. With the analytical emphasis placed on methane and metabolite production, both mesophilic and thermophilic 39L UASS reactors were operated for 218days at an organic loading rate of 2.5gVSL−1d−1 using wheat straw as sole substrate. For improved methanization of soluble metabolites, each UASS reactor was connected to an individual 30L anaerobic filter (AF). During steady state thermophilic straw digestion was found to have a 36% higher methane yield (0.165LgVS−1) whereas the hydrolysis rate constant increased by 106% (0.066d−1).