Hydrothermal pretreatment of date palm (Phoenix dactylifera L.) residues to improve enzymatic convertability and ethanol production

Date palm is one of the most economically important woody crops cultivated in the Middle East and North Africa, providing abundant lignocellulosic biomass. Investigation of using date palm lignocellulosic waste for bioethanol production has not been reported previously. In our study, date palm leaflets and rachis were harvested and subjected to hydrothermal pretreatment to overcome the recalcitrance of the biomass to biological conversion. Composition analysis revealed high carbohydrates content (38.34% of glucan and 20.07% of xylan) in rachis while high lignin accumulation (30.54%) in leaflets. Evident morphological, structural and chemical group changes were observed and analyzed by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier transform infrared (FTIR) after pretreatment. High glucan (>90% for both leaflets and rachis) and xylan (>75% for leaflets and >79% for rachis) recovery were achieved. Enzymatic hydrolysis and Simultaneous Saccharification and Fermentation (SSF) of solids fraction showed hydrothermal pretreatment was capable of significantly enhancing enzymatic digestibility and ethanol production for both leaflets and rachis. Fermentability test of the liquids fraction proved that no considerable fermentation inhibitors were produced during hydrothermal pretreatment. The high sugar recovery, low production of fermentation inhibitors as well as increase of cellulose convertability and subsequent ethanol production, shows that hydrothermal pretreatment is a promising pretreatment method in the conversion of date palm residues to bioethanol.