Effect of the feeding strategy on aerobic granular sludge formation and microbial selection in the treatment of real brewery wastewater

Although aerobic granular sludge (AGS) technology presents a promising alternative to conventional wastewater treatment methods, its application to real industrial wastewater is often limited by complexity and variability of influent wastewater. In this study, slow feeding (SF) and fast feeding (FF) reactors were operated under different feeding configurations. Both reactors achieved successful granulation under the anaerobic/aerobic (An/A) operational strategy, resulting in high pollutant removal efficiencies (total organic carbon (TOC), chemical oxygen demand (COD), and total nitrogen (TN) > 90%) and enhanced sludge settleability (sludge volume index (SVI) < 50 mL/g). The An/A operation effectively suppressed filamentous bacteria (<1% relative abundance) and promoted the selective enrichment of the glycogen-accumulating organisms (Candidatus_Competibacter), reaching 8.4% in SF and 7.8% in FF. In contrast, aerobic/aerobic feeding led to the proliferation of filamentous bacteria growth (Sphaerotilus and Thiothrix), resulting in poor sludge settleability. Moreover, a constant organic loading rate and prolonged anaerobic period significantly promoted the enrichment of phosphorus-accumulating organisms (PAOs), with their relative abundance in FF increasing to 0.84% by Week 33, correlating with enhanced phosphorus removal performance. Overall, this study shows that AGS can be developed through microbial selection solely, independent of substrate accumulation, offering a practical guidance for treating real industrial brewery wastewater.