Residual materials from currently unused plant matter are available locally in abundance and serve as a valuable substrate for biogas production via anaerobic digestion. However, in most cases, a pretreatment is necessary to overcome their recalcitrant behavior. Against this background, earlier ground biomass from Phragmites australis, better known as common reed, is pretreated in a vapothermal atmosphere at temperatures between 122 and 178 °C and residence times between 18 and 102 min. Herein, the influence of such a pretreatment on the specific biogas and methane yield is aimed to be evaluated. In addition, the main causes for changes in degradability are identified by means of accompanying analytics. It is found that vapothermal pretreatment is able to significantly enhance degradation velocity during anaerobic digestion. However, under severe conditions, the biogas and methane yields decrease, which is traced back to an increase in cellulose crystallinity, inaccessibility of pores due to precipitated reaction products, as well as the formation of inhibiting substances and proportional increase in nondegradable lignin.
