A Yeast <i>Candida Palmioleophila</i> W1 Enables Effective Nitrogen Removal from Wastewater through Heterotrophic Nitrification and Aerobic Denitrification

Yeasts capable of nitrogen removal from wastewater have rarely been identified. In this study, a novel yeast strain, Candida palmioleophila W1, isolated from Shenzhen Bay, demonstrated remarkable nitrogen removal efficiency via heterotrophic nitrification-aerobic denitrification (HN-AD). Single-factor experiments and response surface methodology (RSM) optimization revealed that the optimal conditions for nitrogen removal were a C/N ratio of 15.95, salinity of 15.78 ppt, and pH of 6.40. Furthermore, strain W1 exhibited superior nitrogen removal performance (the inorganic nitrogen removal efficiencies of 97.33%–99.98%) when supplied with ammonium, nitrite, nitrate, or their mixtures as nitrogen sources. Nitrogen balance analysis and enzyme activity assays indicated that nitrification and denitrification pathways predominated in the metabolism of inorganic nitrogen, with partial nitrogen assimilation. The addition of strain W1 into semisynthetic wastewater improved nitrogen removal by more than 2-fold compared to the control group without strain W1. These findings provide valuable insights into wastewater treatment processes and may inform future predictions regarding nitrogen removal by yeast.