pretreatment of oil palm empty fruit bunch (opefb) by n-methylmorpholine-n-oxide (nmmo) for biogas production: structural changes and digestion improvement

pretreatment of opefb (oil palm empty fruit bunch) by nmmo (n-methylmorpholine-n-oxide) on its subsequent digestions was investigated. the pretreatments were carried out at 90 and 120 °c for 1, 3, and 5 h in three different modes of dissolution (by 85% nmmo solution), ballooning (79% nmmo solution), and swelling (73% nmmo solution). the total solid recovery after the pretreatment was 89–94%. the pretreatment process did not have a major impact on the composition of opefb, other than a reduction of ash from 5.4% up to 1.3%. the best improvement in biogas production was achieved by a dissolution mode pretreatment of opefb, using conditions of 85% nmmo, 3 h, and 120 °c. it resulted in 0.408 nm³/kg vs methane yield and 0.032 nm³ ch₄/kg vs/day initial methane production rate, which correspond in improving by 48% and 167% compared to the untreated opefb, respectively.