Coupling mechanisms of community assembly and pollutant removal in algal-bacterial granular sludge systems

This study comparatively assessed algal-bacterial granular sludge (ABGS) decontamination performance and microbial community mechanisms under two cultivation modes: flocculated sludge transformed into ABGS (AS_ABGS) and aerobic granular sludge transformed into ABGS (AGS_ABGS). The results indicated that, AS_ABGS achieved superior pollutant removal (COD: 92.2 %, TN: 82.1 %, TP: 61.5 %) versus AGS_ABGS (COD: 96.3 %, TN: 75.1 %, TP: 53.3 %). Microbial community analysis revealed deterministic assembly dominated AS_ABGS, narrowing niches, and enhancing functional specialization of N/P-removing taxa. AS_ABGS exhibited higher modularity, robustness, and stronger positive algal-bacterial interactions (52.32 %). Conversely, stochastic assembly in AGS_ABGS yielded weaker interactions (50.45 %). Metagenomics confirmed AS_ABGS enriched N/P metabolic genes (amo, acc) may be driven by Thauera, Micavibrio, and Aquisediminimonas, while AGS_ABGS favored Amaricoccus and Rhodovulum but showed lower N/P gene abundance. This study highlights the effect of algal-bacterial ecological interactions mediated by functional genes on the decontamination efficiency of ABGS and provides valuable insights for advancing this method.