Effect of N -methylmorpholine- N -oxide Pretreatment on Biogas Production from Rice Straw, Cocoa Shell, and Hazelnut Skin

This study investigated effects of chemical pretreatment with N -methylmorpholine- N -oxide (NMMO) on methane yields of rice straw, cocoa bean shell, and hazelnut skin. Three lignocellulosic materials were separately pretreated with NMMO at 120°C for 3 h. Subsequently, batch biomethane production tests were performed under mesophilic (37°C ± 2°C) conditions, also with the untreated feedstocks, to provide methane production baseline data. Pretreatment was particularly effective for rice straw, with an 82% increased biomethane production yield from 206 mL CH 4 /g volatile solids (VS) obtained with the untreated substrate. A lower enhancement of the biomethane yield from 199 to 226 mL CH 4 /g VS (i.e., 14% increase) was observed for cocoa shell. For hazelnut skin, NMMO pretreatment resulted in a faster digestion rate in the initial 7 days, increasing the biomethane yield from 17 to 27 mL CH 4 /g VS·day. However, the cumulative biomethane yield after 40 days was not affected by NMMO pretreatment.