Efficient bioenergy recovery from different date palm industrial wastes

The potential of date palm residues as abundant lignocelluloses in arid regions for biomethane and bioethanol production was investigated. Main palm residues, including trunk, leaf sheath, leaves, pedicels, and seeds, underwent a concentrated phosphoric acid pretreatment at 50 °C for 45 min, producing a cellulose-rich solid fraction and a hemicellulose-rich liquor. Two scenarios, i.e., (I) biomethane production from the pretreated solid and liquor and (II) bioethanol production from the pretreated solid (via non-isothermal simultaneous saccharification and fermentation) and biomethane production from liquor and ethanol production residues, were followed. The first scenario increased methane production from all residues except leaves and seeds, and considering 1 kg of each residue, yielded 1153.6 L total methane, containing 1301.2 mL gasoline equivalent energy. The second scenario was effective for all residues except seeds and yielded 862.5 mL ethanol and 1513.4 L methane, containing the energy of 2278.7 mL gasoline. The highest ethanol yield of 97.7% and methane yield of 669.7 mL/g VS were obtained from the pretreated leaves and ethanol production residues of untreated seeds, respectively. Generally, the second scenario without seeds pretreatment was recommended for the biorefining of date palm residues.