Abstract
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•Palm kernel expeller (PKE) as a substrate for converting into microalgal hydrogen.•Low thermal pre-treatments could release soluble carbohydrates from PKE.•Highest hydrogen yield (638 mL H2/g microalgae) was attained at 90 °C for 4 h.•Longer pre-treatment duration had released more inhibitory compounds from PKE.
The production of hydrogen from microalgae has inevitably intrigued considerable interests off late. However, the commercial production of microalgal hydrogen is not yet feasible due to the intricate production processes and expensive procedures. Therefore, this research work intended to streamline the microalgal hydrogen generation by utilizing the organic solid waste, palm kernel expeller (PKE), for converting into microalgal hydrogen. Accordingly, the impacts of low thermal pre-treatment method using hydrolysis process was studied at 50 °C, 70 °C, and 90 °C to overcome the recalcitrance of lignocellulosic PKE in associating with the rate of microalgal hydrogen production. The results evidenced that the maximum hydrogen yield was attained at 638 mL H2/g microalgae under the dark anaerobic environment whilst using PKE that was pre-treated at 90 °C for 4 h. In comparison with untreated PKE, this microalgal hydrogen yield had increased by two folds. The release of inhibitory compounds had increased significantly at 50 °C. Thereafter, the zeroth order model was employed to quantify the kinetics of microalgal hydrogen production. The highest rate was successfully achieved at 128 mL H2/g microalgae-d while subsisting on 90 °C pre-treated PKE for 4 h.