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Bioconversion kinetics and valorisation of oil palm empty fruit bunches for biomethane production and lignin derived compounds
Irnia Nurika, Eka Nur Shabrina, Nurul Azizah, Sri Suhartini, Guy C. Barker, Timothy D.H. Bugg
This study assesses the facultative anaerobe Comamonas testosteroni as a mild, chemical-free pre-treatment for valorising oil palm empty fruit bunches (OPEFB) into biomethane and lignin-derived aromatics. Incubation with 2 % (v/v) C. testosteroni for 7 days at 30 °C, reduced lignin to 15.67 % (33.42 % removal), while retaining high cellulose (53.48–56.19 %) and hemicellulose (up to 16.21 %). Pre-treated OPEFB showed 20 % weight loss (vs 8 % in controls) and a 51 % rise in total soluble phenols, evidencing active lignin depolymerisation. GC–MS of liquor and solids qualitatively confirmed lignin breakdown and identified representative low-molecular-weight products (e.g., phenol, betulin, acetic acid and benzoxazole), supporting co-product potential. In biochemical methane potential tests, the pre-treated residue achieved a specific methane potential of 0.173 m³ CH4 kg⁻¹ VS, an 85 % increase over the abiotic residue and higher than non-treated OPEFB. Kinetic fitting with Transference, Modified Gompertz and Logistic models yielded good agreement (R2 up to 0.92), with Modified Gompertz best capturing cumulative methane production and the shortest lag phases. A simple energy check indicates a favourable margin: the incremental methane (ΔSMP ≈ 0.08 m³ CH₄ kg⁻¹ VS) equates ∼0.8 kWh kg⁻¹ VS, whereas estimated mixing for pre-treatment is ∼0.017–0.034 kWh kg⁻¹ VS. Overall C. testosteroni pre-treatment enables dual valorisation (biomethane plus aromatics) under mesophilic conditions, offering a practical route for integrated OPEFB biorefineries.