Effect of dark/light periods on the polyhydroxyalkanoate production of a photosynthetic mixed culture

Abstract

This work studied the possibility of operating a viable polyhydroxyalkanoate (PHA) producing photosynthetic mixed culture (PMC) under dark/light periods without aeration. The culture was subjected to a feast and famine regime, being fed in the dark phase and entering into famine during the light phase. Throughout consecutive feast and famine dark/light periods, the PMC became enriched in PHA accumulating organisms, where non-PHA producing algae that can grow under continuous illumination were out-competed. The very low algae levels enabled greater light and carbon source availability for PHA accumulating bacteria, leading to higher metabolic rates and PHA levels. The PMC reached a PHA content of 30% PHA/VSS, and doubled its specific PHA production rate in relation to PMCs operated previously under continuous illumination. This new process takes a further step towards operating a more cost effective PMC system for PHA production, opening up the possibility for direct sunlight utilization in the future.

Keywords: Anaerobic culture selection; Dark/light cycles; Feast and famine; Photosynthetic mixed cultures; Polyhydroxyalkanoates (PHA).