Enhancing microalgal hydrogen production via photo-fermentative modelling with alimentation derived from palm kernel expeller

Microalgal hydrogen (H2) production via photo-fermentative process is an environmentally friendly alternative to the fossil fuel-based energy. Palm kernel expeller (PKE), a low-cost biomass had presented a significant advantage as organic nutrients' source in this study to fuel the photo-fermentative process. However, the increase of PKE concentrations beyond a threshold of 15.0 g/L had led to the decrease in H2 production. As this metabolic photo-fermentative process was driven by light illumination, it was essential to investigate the impact exerted by various light intensities on microalgal H2 productions. Accordingly, the oxygen (O2) concentration evolutions stemming from increasing photosynthetic dissolved oxygen (DO) concentrations within the culture mediums were evaluated and remodelled with the Andrew's substrate inhibition model. The absolute inhibition of photo-fermentation was predicted at 29.6 g/L of PKE with 0.006 g/L. day of photosynthetic oxygenation rate under a specific light intensity ranging from 100 to 500 μmol/m2s. On the other hand, at the optimum 5–15 g/L of PKE, the maximum H2 production rate could be attained at about 46 mL-H2/g-biomass.day with 200 μmol/m2s of light intensity. Further increasing of light intensities had also increased the photosynthetic activities, leading to the increased DO accumulations that favoured the culture photorespirations over photo-fermentative H2 productions. The sustainability of producing microalgal H2 was finally verified from the recycled study using a similar PKE organic nutrients' source to continuously generate H2 that had steadily maintained after the second cycle onwards with merely 4% of a gradual decrease until fourth cycle.