A sulfur-autotrophic bacterial-algal synergistic system for enhanced nitrogen and phosphorus removal

To address the limitations of traditional bacteria–algae symbiotic systems in treating low C/N wastewater—specifically, the high demand for external carbon sources and stringent aerobic conditions. This study constructed and investigated a novel sulfur-based autotrophic bacteria–algae synergistic system (BAS) aimed at achieving efficient and low-energy nitrogen and phosphorus removal. By optimizing operational parameters, the study systematically evaluated pollutant removal performance and operational stability and further elucidated the underlying mechanisms through microbial community structure analysis. The results showed that under conditions without external organic carbon input and aeration, the BAS system achieved NO 3 − -N and TP removal efficiencies of 92 %–98.6 % and 60 %–65 %, respectively. The extracellular polymeric substances (EPS) content significantly increased; Chlorella exhibited robust growth with minimal biomass loss, and sludge flocculation performance was enhanced, enabling effective adsorption of byproducts such as SO 4 2− . Dominant genera such as Thiobacillus , Sulfurimonas , and Ferritrophicum were further enriched during the stable operation of the system. Driven by light-dark cycle regulation, the system achieved temporally coupled, high-efficiency nitrogen and phosphorus removal through bacteria–algae cooperation, effectively overcoming the carbon limitation bottleneck of traditional systems under low C/N conditions. This provides a novel approach for developing energy-efficient biological wastewater treatment technologies. • A novel BAS system enables efficient nitrogen and phosphorus removal. • BAS outperforms single systems in N/P removal, settleability, and Chlorella growth. • BAS reduces effluent SO 4 2− , minimizing secondary pollution. • Bacteria-algae synergy stabilizes pH, DO, and enhances operational stability.