The Purification Efficiency and Synergistic Mechanism of the Algal-Bacteria System for Simulating Livestock Wastewater

As a sustainable biological approach for polluted water management, algal-bacterial systems are increasingly being explored because of their synergistic physiological and metabolic interactions. This study established an algal-bacterial consortium composed of Escherichia coli and Chlorella vulgaris to evaluate treatment performance of simulated livestock wastewater and elucidate the associated synergistic mechanisms. Compared with the pure algal system, the algal-bacterial consortium significantly enhanced algal growth, increasing chlorophyll concentration by 52.8% and achieving a maximum algal density of 16.46 × 106 cells mL−1. The biochemical composition of the biomass was improved, with total lipids, neutral lipids, and proteins increasing by 18.9%, 26.8%, and 16.4%, respectively. Pollutant removal efficiencies were markedly enhanced, as total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), and nitrite nitrogen (NO2−-N) increased by 19.1%, 9.5%, 26.0%, 13.5%, 17.2%, and 13.8%, respectively, compared with the monoculture. Mechanistic analysis was supported by monitoring chlorophyll content, algal density, dissolved oxygen, bacterial density, total inorganic carbon, and pH, which collectively suggested the involvement of a synergistic carbon–oxygen exchange process: oxygen produced by microalgae supported bacterial respiration, while carbon dioxide generated by bacteria enhanced algal photosynthesis and growth. Furthermore, the presence of E. coli markedly stimulated nitrogen metabolism-associated enzymatic functions in C. vulgaris, which may have facilitated their mutual growth. Overall, this study provides a conceptual and experimental basis for algal-bacterial consortium design for treating livestock wastewater, thereby enhancing pollutant removal efficiency and algal biomass accumulation, highlighting its potential as a sustainable and resource-efficient wastewater treatment strategy.