Hydrothermal and wet disk milling pretreatment for high conversion of biosugars from oil palm mesocarp fiber

• Combined pretreatment using hydrothermal and WDM was performed on OPMF.
• Maximal H2O contact and hemicellulose removal were favored under HCW than SHS.
• Defibrillation of OPMF is key factor for higher glucose conversion.
• Optimal combined pretreatment of HCW–WDM was 180 °C, 20 min after 9 cycles of WDM.
• Glucose yield (98%) obtained from HCW–WDM with power requirement 9.6 MJ/kg OPMF.

Eco-friendly pretreatment methods for lignocellulosic biomass are being developed as alternatives to chemical based methods. Superheated steam (SHS), hot compressed water (HCW) and wet disk milling (WDM) were used individually and with combination to partially remove hemicellulose and alter the lignin composition of recalcitrant structure of oil palm mesocarp fiber (OPMF). The efficiency of the pretreatment methods was evaluated based on the chemical compositions altered, SEM analysis, power consumption and degree of enzymatic digestibility. Hemicellulose removal (94.8%) was more pronounced under HCW compared to SHS, due to maximal contact of water and production of acetic acid which enhanced further degradation of hemicellulose. Subsequent treatment with WDM resulted in defibrillation of OPMF and expansion of the specific surface area thus increasing the conversion of cellulose to glucose. The highest glucose yield was 98.1% (g/g-substrate) when pretreated with HCW (200 °C, 20 min) and WDM which only consumed 9.6 MJ/kg of OPMF.