Stirring speed optimization for improved microalgal-bacterial granular sludge morphology and performance in complex...

This study investigated the morphology regulation and pollutant removal performance of microalgal-bacterial granular sludge (MBGS) under different organic carbon conditions, specifically comparing simple and complex organics. Results showed that MBGS proliferated faster under complex organics conditions due to filamentous cyanobacteria dominance, requiring a higher stirring speed (300 rpm, 0.128 Pa) to inhibit excessive growth and maintain stability. Optimizing the stirring speed improved granule morphology in the complex group, reducing size and increasing density, which significantly enhanced pollutant removal efficiencies to 90.2 % for chemical oxygen demand, 86.2 % for total nitrogen, and 82.9 % for total phosphorus. Microbial community analysis further revealed that dominant phyla (Bacteroidota, Planctomycetota, Actinobacteriota) contributed significantly to the abundance of key carbon, nitrogen, and phosphorus metabolic genes (mqo, GLT1, ppk) under complex organic conditions. This study highlights the need for a higher stirring speed to regulate MBGS in complex wastewater, providing practical strategies for optimizing treatment performance.