Comparative Evaluation of Ammonium Removal Activity and Microbial Community Structure in Field-Derived Nitrifying Inocula

Abstract

This study evaluated ammonium removal activity and microbial community structure in three field-derived nitrifying inocula with different origins and cultivation histories. Batch NH3-N removal tests were conducted, and the specific nitrification rate (SNR) was calculated based on mixed liquor volatile suspended solids (MLVSS). Microbial community composition was analyzed using 16S rRNA gene sequencing. The average NH3-N removal rates of inocula A, B, and C were 19.05, 21.32, and 26.23 mg NH3-N/L/hr, respectively. The corresponding SNR values were 1.99, 2.51, and 2.62 mg NH3-N/g MLVSS/hr. Inoculum A showed the highest OTU richness, Shannon diversity, and combined relative abundance of Nitrosomonas and Nitrospira (3.46%), but exhibited the lowest SNR. In contrast, inoculum C showed the highest NH3-N removal activity despite a low abundance of nitrification related microorganisms (0.60%). These results indicate that 16S rRNA-based relative abundance alone does not directly represent actual ammonium removal activity. Therefore, microbial community analysis should be combined with batch activity tests and SNR assessment when evaluating field-derived nitrifying inocula.