The performance and microbial community characteristics of a novel multilayer high-light energy utilization rate...

The algal-bacterial symbiotic system is a promising sustainable technology for wastewater treatment. This study conducted a comparative analysis of a novel multilayer high-light energy utilization rate algal-bacterial symbiotic system and a conventional activated sludge system, focusing on pollutant removal efficiency, energy consumption, and microbial community structure under temperature variation. Experiments were performed over two 48-day periods at 20 °C and 30 °C. Results indicated that at 30 °C, the symbiotic system achieved removal efficiencies of 96.84 ± 1.20% for COD, 99.87 ± 0.12% for NH₄⁺-N, and 93.00 ± 1.80% for PO₄^3--P, was all significantly better than the treatment efficiency under 20 °C conditions (p < 0.05). However, total nitrogen removal was somewhat limited, likely due to elevated dissolved oxygen levels (averaging 6.7 ± 0.45 mg/L). The symbiotic system consumed 0.364 kWh per day, representing a 46% reduction in energy use compared to the activated sludge system. The aeration energy consumption of the algal-bacterial symbiotic system is only 0.096 kWh/day, which is 20% of that of the activated sludge system. At 30 °C, the microbial-algal symbiosis system supported a more diverse microbial community, and the beneficial bacterial genera and microalgae flourished, while algivorous microorganisms were suppressed. Overall, the algal-bacterial symbiotic system operated at 30 °C demonstrated superior performance in efficient pollutant removal, energy savings, and carbon emission reduction, which can be attributed to a stable and synergistic microbial ecosystem promoted by optimal temperature regulation. This study provides theoretical support for optimizing and advancing resource-oriented applications of algal-bacterial symbiotic systems.