Effect of the Return Activated Sludge on the Start-Up of a Lab-Scale Continuous Flow EBPR Reactor

Abstract

Since it was difficult in the atmosphere to obtain a deeper anaerobic environment, most previous investigations for drawing conclusions to further study denitrification and phosphorous removal, especially biological P removal, were based on the operations of SBR or full-scale reactors. In this study, a 4 L/h of continuous flow enhanced biological phosphorus removal (EBPR) reactor was constructed and started up, and activated sludge and EBPR performances were monitored for 365 days. The analysis of suspended solids (SS) and flow velocity at different temperature stages, indicated that the poor return activated sludge (RAS) was caused by the large dynamic friction of sludge in the larger specific surface area flow field. The start-up time of the bio-reactor feeding 5 mg-P/L and the ≥88% removal efficiency was extended to 200~365 days, with the relative abundance of polyphosphate accumulating organisms (PAOs) + polyphosphate accumulating organisms (GAOs) above 12.2% at the genus level after its stabilization. The results of the start-up phase showed that the key to a lab-scale continuous flow reactor was smooth RAS. If the problem was better settled, it would provide a promising and practical alternative for further study on N and P removal.