High-Efficiency Ammonia Nitrogen Removal from Aqueous Solution Using Marine Cyanobacteria: A Comparative study of Anabaena spp. and Oscillatoria acuta

Objective: This study aimed to comparatively evaluate the growth performance and total ammonia nitrogen (TAN) removal efficiency of two indigenous marine cyanobacterial isolates, Anabaena spp. and Oscillatoria acuta, under different initial ammonia concentrations, and to identify the most effective isolate for potential application in biological treatment of ammonia-contaminated saline waters. Methods: The cyanobacterial isolates were cultivated in sterilized F/2 medium supplemented with four initial TAN concentrations (0.1, 0.5, 1.0, and 1.5 mg L⁻¹) under controlled laboratory conditions for 20 days. Algal growth was monitored by chlorophyll-a content, while TAN concentration was determined using the indophenol blue method. Ammonia removal efficiency was calculated throughout the experimental period. Results: Both cyanobacterial isolates efficiently assimilated ammonia at low and moderate TAN concentrations. Anabaena spp. exhibited significantly higher growth and ammonia removal efficiency than Oscillatoria acuta. The maximum TAN removal efficiency reached approximately 99% after 10 days at an initial concentration of 1.0 mg L⁻¹ using Anabaena spp., whereas O. acuta achieved approximately 96% removal after 12 days under the same conditions. Chlorophyll-a accumulation followed a trend similar to TAN removal, indicating that enhanced photosynthetic activity was closely associated with nitrogen assimilation. In contrast, exposure to 1.5 mg L⁻¹ TAN markedly inhibited algal growth and reduced ammonia removal efficiency in both isolates, reflecting the inhibitory effects of elevated ammonia concentrations. Conclusion: The findings demonstrate that marine cyanobacteria are effective biological agents for ammonia removal under controlled laboratory conditions, with Anabaena spp. showing superior performance compared with Oscillatoria acuta. This comparative evaluation provides baseline information for selecting suitable marine cyanobacteria for future applications in sustainable aquaculture water management and saline wastewater treatment. Further investigations using real wastewater, molecular characterization, biomass productivity assessment, nitrogen mass balance analysis, and pilot-scale validation are recommended to support practical implementation.