Diluted swine and aquaculture wastewater enhance carbon sequestration and nutrient removal by the red seaweed Agardhiella subulata

Swine wastewater poses significant environmental challenges, and conventional microalgae treatments often leave high residual nutrients while consuming substantial freshwater. This study explored the potential of the saltwater macroalgae Agardhiella subulata for nutrient removal and carbon assimilation under varying salinity and ammonium concentrations. Using diluted swine and aquaculture wastewater, A. subulata achieved ammonium and phosphorus removal efficiencies of up to 93 % and 68 %, respectively, within 24 h. It also removed CO₂ at rates five times higher than the global forest average and enhanced dissolved oxygen levels, reducing the environmental impact of nutrient-rich wastewater while minimizing freshwater demand. Notably, A. subulata effectively utilized swine wastewater with ammonia concentrations up to 600 μM under salinity conditions of 27-34 ppt. These results demonstrate the potential of A. subulata for large-scale nutrient removal and CO₂ reduction, providing a sustainable solution to the environmental impacts of the livestock industry.