Direct development of microalgae-bacterial granular sludge system by seeding pre-made microalgae-dewatered sludge granules: Performance and mechanism analysis

Microalgae-bacterial granular sludge (MBGS) process has great potential in achieving carbon neutrality and energy neutrality, but rapidly cultivating MBGS remains challenging. To address this challenge, this study proposes a new strategy to develop MBGS systems using pre-made granules from microalgae and dewatered sludge. The results indicate that using pre-made microalgae-dewatered sludge granules (M-DSG) as inoculants can directly develop MBGS system, with M-DSG maintaining a relatively stable granular structure, and ultimately achieving pollutant removal efficiencies of 94.0% for chemical oxygen demand (COD), 99.7% for ammonium nitrogen (NH₄⁺-N), and 86.0% for total inorganic nitrogen (TIN). Extracellular polymeric substances (EPS) play a dominant role in maintaining the structure of granules, while filamentous bacteria/algae provide additional reinforcement. The adhesion of microalgae to granules possibly relies on polysaccharides in tightly bound extracellular polymeric substances (TB-EPS) and proteins in loosely bound extracellular polymeric substances (LB-EPS). Microbial community analysis reveals that the target algae (Chlorella) remain the primary algae, and heterotrophic nitrifying bacteria (HNB) and denitrifying bacteria are enriched.