Enrichment of comammox bacteria in anammox-dominated low-strength wastewater treatment system within microaerobic conditions: Cooperative effect driving enhanced nitrogen removal

In practical anammox systems, ammonia-oxidizing microbes (AOM) inevitably coexisted with anammox bacteria (AnAOB) due to residue oxygen in influent, but the diversity and impact of AOM in the system remain unclear. In this study, a practical anammox-dominated system with high relative abundance (15.15-19.07 %) of AnAOB (including Ca. Brocadia and Ca. Kuenenia) was studied, which treated low-strength wastewater with dissolved oxygen of 0.24-0.27 mg/L. Results demonstrated that complete ammonia-oxidizing (comammox) bacteria was the most abundant AOM and dominant over other canonical nitrifying bacteria, wherein comammox amoA gene was 8.3-fold more abundant than ammonia-oxidizing bacteria (AOB) amoA gene. Phylogenetic results indicated that the comammox bacteria in this study belonged to comammox Nitrospira clade A. Notably, when treating real nitritation municipal wastewater, cooperative effect of anammox bacteria, comammox bacteria and heterotro-phic denitrifiers enhanced nitrogen removal efficiency to 92.9 +/- 1.1 %. Hence, these results show that the functional significance of comammox bacteria in engineered ecosystems was previously overlooked. Our findings highlight that comammox bacteria could be an essential functional group in mainstream anammox systems and possess a high potential for energy-efficient nitrogen removal.

Automated summary

This study found that comammox bacteria, which were previously overlooked, are the most important ammonia-oxidizing microbes in Anammox systems, and play a significant role in nitrogen removal.