Algae-to-Sludge Inoculation Ratio Regulates Organic Matter and Nitrogen Removal in Algal-Bacterial Symbiosis Systems...

This study evaluated the influence of algae-to-sludge inoculation ratio on biomass development and pollutant removal in an algal-bacterial symbiotic system (ABSS) treating shrimp farming wastewater. Batch reactors operated at ratios of 1:2-1:6, along with monoculture controls, were assessed for biomass characteristics, organic matter removal, and nitrogen transformation. The 1:3 ratio achieved the most balanced biomass growth (MLSS: +54.9%; MLVSS: +57.8%) and the highest removal efficiencies, reaching 60.5% ± 7.3%, 89.4% ± 2.9%, and 55.2% ± 15.2% for chemical oxygen demand (COD), ammonium (NH₄ ⁺-N), and total nitrogen (TN), respectively. Co-culture reactors consistently outperformed monocultures, suggesting the benefits of coupling algal photosynthesis with bacterial metabolism. The results indicate that biomass balance is a key operational factor governing system performance, likely through its influence on oxygen availability, substrate utilization, and internal mass transfer. Optimizing the algae-to-sludge ratio provides a simple and effective strategy to enhance ABSS performance without increasing aeration demand, offering practical implications for sustainable aquaculture wastewater treatment.