Effects of settling time on the flocculation progress and treatment performance in the co-culture of microalgae-activated sludge photobioreactor

The application of microalgae-based wastewater treatment systems using wastewater as a source of nutrients has been success-fully developed in recent years and has brought about positive results in wastewater treatment and microalgal biomass recovery while producing valuable products. This study presents the application of a microalgae and activated sludge (AS) co-culture in a low agitation photobioreactor (aPBR), which could reduce energy usage. In addition, the results demonstrate the role of settling time on co-culture flocculation progress and wastewater treatment performance. The average Chemical Oxygen Demand (COD) removal was up to 76.1% of co-culture and was achieved using a PBR system with a low agitation speed of 80 rpm. Moreover, a high biomass growth was observed to be coupled with high nutrient removal. After 63 days of operation, heavy flocs with excel-lent settling ability were dominant in the photobioreactor. This would be a preliminary step for activated algae granulation in a co-culture system.