pH spurring microalgal cells to subsist onto palm kernel expeller for growing into biodiesel feedstock

Abstract

The potentiality of microalgae as a feedstock for biodiesel production is actively being explored to resolve the inadequacy of biomass and lipid indexes conundrum, and economic infeasibility associated to the conventional cultivation system. Current study is an extension of a pre-optimized cultivation condition which has further elaborated the impact of pH on attached microalgal cultivation onto nutritional lignocellulosic waste; palm kernel expeller (PKE) by employing a novel periphytic growth and harvesting technique. The highest microalgal density was achieved at 10.9 ± 0.8 g/g-PKE in pH 5 cultivation medium with highest carbon-PKE assimilation. In fact, the microalgal growths under mixotrophic condition demonstrated a positive correlation between pH of cultivation medium and carbon-PKE assimilation by microalgae. The maximum lipid productivity was obtained at 33.1 ± 3.3 mg/L day from the attached microalgae of pH 11 medium. However, the lowest microalgal density was likewise attained at similar pH due to the trigger by which the carbon metabolic activity shifted towards lipid production instead of growth. Owing to the highest microalgal density attained at pH 5 medium, the gap of lipid productivities with pH 11 was narrowed down to merely 7.0 mg/L day. The attached microalgal feedstock harvested from this study was eventually found satiating most of the essential biodiesel properties in compliance with the international standards decreed by ASTM D6751-03 and EN 14214.