Mechanism-driven nitrogen removal in aquaculture wastewater via Comamonas testosteroni: A novel metabolic pathway analysis

Nitrogen pollution in aquaculture wastewater poses significant environmental challenges, with traditional chemical and physical methods proving insufficient for comprehensive mitigation. This study investigates the potential of Comamonas testosteroni FJ17, a heterotrophic nitrogen-removing bacterium, to address nitrogen pollution through biological means. Optimization experiments revealed that strain FJ17 achieved maximum nitrogen removal efficiency (TN=91.5 %) under the following conditions: sodium lactate as the carbon source, a C/N radio of 15, an N/P radio of 20, an inoculum size of 3 %, unadjusted pH, a temperature of 30 °C, and a shaking speed of 150 rpm. Nitrogen balance analysis and RT-qPCR studies indicated that the cell primarily assimilates ammonia nitrogen into biomass, with a minor portion undergoing nitrification and denitrification to release gaseous nitrogen. Additionally, nitrogen content and morphological analysis of extracellular polymeric substances (EPS) highlighted their adsorption role in the removal of ammonia. Finally, a sequencing batch reactor (SBR) was established with a hydraulic retention time (HRT) of 12 h, an influent ammonia concentration of 100 mg/L, and an aeration volume of 15 L/h. Long-term operation demonstrated that the effluent ammonia and total nitrogen (TN) concentrations met China's primary municipal wastewater discharge standards. Highlighted in this study is the potential of C. testosteroni FJ17 to be an effective biological agent for nitrogen removal in aquaculture wastewater.