C/N Ratio Shifted Autotrophic Partial Nitrification to Heterotrophic Nitrification and Aerobic Denitrification in High-Strength Ammonium Wastewater Treatment

Abstract

Partial nitrification (PN) is an effective process for treating high-strength ammonium wastewater with a low C/N ratio, because the cooperative interaction with denitrification or anammox can result in a reduction of approximately 25% in aeration costs and 40% in the use of organic sources during biological nitrogen removal. However, the key functional microorganism in the partial nitrification (PN) process is ammonia-oxidation bacteria (AOB), an autotrophic microorganism that is influenced by carbon sources. Therefore, C/N ratio affected the performance of PN process when treating high-strength ammonium wastewater. In this study, five sequence batch reactors were constructed and operated for 42 days, which were fed with synthetic high-strength ammonium wastewater (500 mg/L) with various C/N ratios (at 0, 0.5, 1, 2, 4). The results suggested that PN process could be accomplished at C/N ratios of 0 and 0.5, but its performance decreased significantly when C/N ratio increased to 1 due to the occurrence of simultaneous nitrification and denitrification occurred. Since AOB could not compete with the heterotrophic bacteria, as the C/N ratios increased, the abundance of Nitrosomonas (a genus of autotrophic AOB) decreased, and it was not detected C/N ratios of 2 and 4. Instead, the heterotrophic nitrification and heterotrophic denitrification (HNAD) bacteria were appeared and their relative abundance increased when C/N ratios increase from 1 to 4.

Keywords: partial nitrification, High-strength ammonium wastewater, C/N ratio, Microbial community, Heterotrophic nitrification and aerobic denitrification