Different susceptibilities of wheat straw and corn stover to mechanical pretreatment for biomethane production

The effects of milling on the anaerobic degradability of wheat straw and corn stover were investigated. Pretreatment was carried out by an industrial-scale device, able to process over one ton per hour. After 28 days of digestion under mesophilic conditions, the cumulative methane production from the pretreated straw (250 Nm3 t−1 of volatile solids) was 49.2% greater than that from the raw material. Pretreated stover reached a cumulative methane yield of 219.8 Nm3 t−1 of volatile solids, gaining 10.1% as compared to the feedstock. The specific electrical energy requirements for pretreatment were 66.6 kWh t−1 for processed straw and 64.8 kWh t−1 for stover; these consumptions were not significantly different. With reference to biomethane production, the impact of raw material on the production cost decreased from EUR 0.418 Nm−3 to EUR 0.328 Nm−3 for pretreated straw, whereas it increased by 5.8% for corn stover, whose pretreatment, therefore, was not economically feasible.