Revolutionizing comammox enrichment: Novel approaches for comammox enrichment through reactor configuration and ammonia concentration mediation

Abstract

The identification of comammox Nitrospira as a complete ammonia oxidizer marked a significant milestone in the field of ammonia oxidation. Nonetheless, the slow growth rate of comammox bacteria poses a challenge in differentiating them from conventional ammonia-oxidizers. In this study, different reactor configurations (SBR and SBBR) were used to explore the enrichment effect of comammox Nitrospira. The operation process of both reactors was organized into three distinct phases according to the concentration of NH4+ in the influent. With the increase in running time, the abundances of comammox bacteria in R1 (SBR) and R2 (SBBR) increased. The relative abundances of comammox amoA in Phase III of R2 were 27.9 times that of R1. After 240 days of enrichment, the abundances of Nitrospira in R1 and R2 increased from 0.03 % to 3.33 % and 22.79 %, respectively. The enrichment in R2 was about 6.8-fold of R1. The results showed that comammox Nitrospira is more competitive in an oligotrophic environment, and they are more favorable to grow in biofilms. This study shed new light on the impact of reactor configurations and provides a novel strategy for enriching comammox bacteria, highlighting the potential for optimizing wastewater treatment processes and advancing our understanding of microbial ecology.