Effect of stepwise or one-time illumination strategy on the development of algal-bacterial aerobic granular sludge in sequencing batch reactor

Abstract

Algal-bacterial aerobic granular sludge (AGS) as a promising wastewater treatment biotechnology has attracted more attention in recent years. Still, limited information is available on the effect of stepwise illumination on algal-bacterial AGS. In this study, two illumination strategies, i.e., stepwise (R1) and one-time (R2) daily, were applied to cultivate algal-bacterial AGS from bacterial AGS. Results indicated that R1 holds more advantages over R2 in terms of algal-bacterial AGS formation, biomass growth, extracellular polymeric substances excretion and phosphorus (P) accumulation. Specifically, algal-bacterial AGS in R1 contained higher chlorophyll a content of 5.84 mg/g-MLVSS with the biomass yield of 0.50 g-MLVSS/g-COD in comparison to 5.04 mg/g-MLVSS and 0.43 g-MLVSS/g-COD in R2. Moreover, stepwise illumination effectively alleviated the negative effects of microalgae on anaerobic P release and P accumulation. However, no significant difference was detected between R1 and R2 regarding granule diameter and morphology in addition to organics and nutrients removal.