Nitrogen and phosphorus removal and interactions between algae and bacteria during algal-bacterial granular sludge formation and stabilization

Algal-bacterial granular sludge (ABGS) was studied in a 10 L sequencing batch reactor (SBR) for treating synthetic municipal wastewater. ABGS was rapidly achieved within approximately 15 days. Algae provided the filamentous framework and promoted extracellular polymeric substance (EPS) production, which benefited ABGS formation.The removal rates of NH4+-N, COD, PO43--P, and TN were 99 %, 92 %, 95 %, and 78 %, respectively. Compared to aerobic granular sludge (AGS), TN removal rate in ABGS increased by 18 %. During ABGS formation and stabilization, major functional bacteria, such as glycogen accumulating organisms (GAOs) and phosphate accumulating organisms (PAOs), were enriched, while algae underwent succession. Nitzschia and norank_f_norank_o_Chloroplast replaced Scenedesmus and Auxenochlorella as the predominant algae. Furthermore, there were various mutual relationships including cooperation and competition between bacteria and algae. Bacillariophyta positively correlated with major functional bacteria, while Chlorophyta negatively correlated with most functional bacteria in ABGS. The interaction between bacteria and algae was crucial in ABGS construction and regulation.