Algae‐to‐Sludge Inoculation Ratio Regulates Organic Matter and Nitrogen Removal in Algal‐Bacterial Symbiosis Systems Treating Shrimp Farming Wastewater

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 (NH 4 + ‐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.