Meta-Omics Analysis of a Formate Sidestream-Mediated Partial Nitritation-Coupled Anammox Process

Abstract

A stable partial nitritation process that was achieved by treating activated sludge in sidestream with formate as a selective inhibitor has been previously described. However, little is known about the effect of formate on the microbial communities in both the partial nitritation and the subsequent anammox process. To this end, a formate sidestream-mediated partial nitritation-coupled anammox process was established and studied. The effluent ratio of nitrite/ammonia in the partial nitritation remained at 1.24 ± 0.19, and the total nitrogen removal efficiency of the anammox process was maintained at 80.0 ± 1.6%. Metagenomic and metatranscriptomic analysis showed that the nitrite oxidizing bacteria (NOB) was almost eliminated from the partial nitritation process, while Nitrosomonas europaea was the dominant ammonia-oxidizing bacteria (AOB) with an abundance of 30.8% of total reads. The high expression of nitrous oxide reductase genes in the partial nitritation process suggested a great potential for mitigating nitrous oxide release. Candidatus Kuenenia stuttgartiensis and Candidatus Brocadia sinica were identified as the main anammox bacteria, and their abundances were as high as 49.3 and 11.8%, respectively. There was a highly expressed gene encoding a formate tetrahydrofolate ligase in the Candidatus Kuenenia stuttgartiensis metagenome-assembled genomes (MAG), suggesting that formate-related metabolic activity may contribute to its enrichment in the anammox process.