Removal mechanisms of phosphorus in non-aerated microalgal-bacterial granular sludge process

Microalgal-bacterial granular sludge processes are attracting increasing research interest in fields of biological municipal wastewater treatment. However, these processes currently suffer from inefficient phosphorus removal and long hydraulic reaction time. As such, a self-sustaining synergetic microalgal-bacterial granular sludge process was explored for improving phosphorus removal. Results showed that about 86% of influent phosphorus could be removed within 6 h comprising 2-hr dark phase and 4-hr light phase. Slight phosphorus release was observed in dark phase, followed by a significant phosphorus uptake in light phase together with the accumulation of poly-phosphorus in microalgal cells. The analyses by PacBio's sequencing and fluorescence in situ hybridization revealed that microalgal genus of Pantanalinema were the major phosphorus-accumulating organisms. Based on these experimental observations, the removal mechanisms of phosphorus by microalgal-bacterial granular sludge process were identified. It is expected that this study may shed lights on the pathways of biological phosphorus removal in microalgal-bacterial granular sludge process.