Understanding diurnal variability in organic matter processing by microalgal-bacterial granular sludge in lake water...

This study investigates the diurnal variability of organic matter removal by microalgal-bacterial granular sludge (MBGS) in lake water remediation. Results showed that daytime removal efficiencies for NH₄⁺-N, NO₃^--N, NO₂^--N, TN, and TP reached 72.1%, 73.2%, 91.5%, 60.5%, and 52.8%, respectively, exceeding nighttime values of 52.7%, 55.8%, 88.4%, 37.9%, and 39.9%. However, chemical oxygen demand (COD) exhibited a net release during daytime, contrasting with removal during night conditions. Significant microbial community shifts, notably increased Bacteroidota abundance, were driven by fluctuations in dissolved oxygen and organic carbon levels. Additionally, the upregulation of fatty acid metabolism-related genes like paaF and ACSL provided mechanistic support COD removal efficiency. These findings suggest that optimizing MBGS operation through diurnal parameter regulation can enhance lake restoration efficacy and provide a theoretical foundation for developing sustainable engineering strategies in aquatic ecosystem management.