Dual Effects of Starter Inoculum and Thermal Pretreatment on Oil Palm Mesocarp Fiber for Methane Production in Solid-State Anaerobic Digestion

Palm oil is the world’s largest used in vegetable oil. During the processes of crude oil production, oil palm mesocarp fiber (OPMF) is one of the significant solid waste generations. OPMF is the lignocellulosic solid residue from processes of palm fruit cooking and pressing during extraction of crude palm oil. Although OPMF contains high amounts of cellulose (33%), hemicellulose (22%), and lignin (21%), its utilization as feedstock for biomethane production is hampered by its recalcitrant to degrade this complex structure. This study evaluated dual effects on how active various sources of seed inoculums from anaerobic treatment of palm oil mill effluent (POME), cow manure (CM), and swine manure (SM) as well as OPMF hydro-pretreatment using heat or thermal energy as from crude palm oil industry. The thermal pretreatment of OPMF with sterilized hot water (SHW) and boiling hot water (BHW) were conducted to examine the enhancement of methane production and compared to non-pretreatment. A biochemical methane potential (BMP) assay was performed in both effects using OPMF as the feedstock. Within 30 d of incubation, the potential methane yield produced at 355, 168, and 162 mL/gVS using CM, POME, and SM inoculum, respectively. BMP of CM showed 2 times higher potential than POME and SM. The methane production rate for CM, POME, and SM was 18.8; 6.8, 5.8 mL/d, respectively. Whereas the SHW and BHW pretreatment of OPMF showed slight effect on methane production. Furthermore, CM inoculum was used in modified solid inclined (MSI) reactor for anaerobic digestion fed with raw OPMF (62% TS). The methane production rate and yields from OPMF were 9.2 L/d and 266 L/KgVS, respectively, within 30 days digestion period.  This high solid-state MSI reactor shows the high capability to degrade the solid waste of OPMF for methane production.