Simultaneous nitrification and aerobic denitrification by Agrobacterium sp. KG3 and Stutzerimonas sp. KA4: Isolation,...

Semiconductor wastewater contains nitrogen and recalcitrant organic pollutants, making it challenging industrial effluents to treat. This study proposed two novel heterotrophic nitrification-aerobic denitrification (HNAD) bacterial strains, KG3 and KA4. Both HNAD strains had capability to completely remove ammonia, nitrate, and nitrite under aerobic conditions. They effectively removed ammonia under diverse conditions and exhibited alkali resistance even at pH 11. KA4 showed higher nitrogen removal rates under high carbon-to-nitrogen ratio and high dissolved oxygen concentration. In batch tests with the semiconductor wastewater, both strains completely removed ammonia, nitrate, and nitrite, and also showed potential to degrade some recalcitrant organic compounds. In continuous tests, both strains achieved ammonia removal rates of 431 mg-NH₄⁺-N/L/d, reaching specific removal rates of 225-460 mg-NH₄⁺-N/g-MLVSS/d, which is 3-15 times faster than typical autotrophic nitrification, suggesting their potential for high-rate nitrogen removal for semiconductor wastewater treatment. Whole-genome sequencing revealed that both strains lack classical nitrification genes, a feature commonly observed in previously reported HNAD strains, but possess genes for denitrification and ammonia assimilation pathways. These results highlight the metabolic versatility and treatment potential of the HNAD strains for industrial nitrogenous wastewater containing diverse microcontaminants, supporting their application in advanced semiconductor wastewater treatment.