Efficient nitrogen removal by heterotrophic nitrification-aerobic denitrification yeast Candida boidinii L21: Performance, pathway and application

Efficient nitrogen removal yeasts are rarely encountered. Here, a heterotrophic nitrification-aerobic denitrification strain of Candida boidinii L21 was isolated. The optimal removal conditions for strain L21 were glucose as carbon source, C/N of 15, salinity of 10 ppt, pH of 7, shaking speed of 120 rpm, and temperature of 30 degrees C. Strain L21 removed NH4+-N, NO2--N, NO3 --N (14---140 mg/L) and achieved nearly complete NO2--N, removal. Nitrogen balance and enzyme activity analysis indicated the nitrogen removal pathway of strain L21 through assimilation, nitrification, and denitrification pathways. When applied in wastewater and sludge, strain L21 reduced inorganic nitrogen levels within 4 days, with a 58-fold increase in nitrite removal compared to controls. These findings demonstrate that strain L21 holds great potential for enhancing nitrogen removal in wastewater treatment processes, providing valuable insights for improving environmental management practices.