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Abstract
Microbial nitrogen removal mediated by anaerobic ammonium oxidation (anammox) are
cost-effective, yet it is time-consuming to accumulate the slow-growing anammox bacteria
in conventional wastewater treatment plants (WWTPs). Inoculation of anammox enriched
pellets is an effective way to establish anammox and achieve shortcut nitrogen removal
in full-scale WWTPs. However, little is known about the complex microbial nitrogen-cycling
networks in these anammox-inoculated WWTPs. Here, we applied metagenomic and metatranscriptomic
tools to study the microbial nitrogen removal in three conventional WWTPs, which have
been inoculated exogenous anammox pellets, representing partial-nitrification anammox
(PNA) and nitrification-denitrification nitrogen removal processes. In the PNA system
of Bali (BL), ammonia was partially oxidized by ammonia-oxidizing bacteria (AOB) Nitrosomonas
and the oxidized nitrite and the remaining ammonium were directly converted to N2
by anammox bacteria Ca. Brocadia and Ca. Kuenenia. In the nitrification-denitrification
system of Wenshan (WS), ammonia-oxidizing archaea (AOA) Thaumarchaeota unexpectedly
dominated the nitrifying community in the presence of AOB Nitrosomonas. Meanwhile,
the biomass yield of Ca. Brocadia was likely inhibited by the high biodegradable organic
compound input and limited by substrate competitions from AOA, AOB, complete ammonia
oxidizers (comammox) Nitrospira, nitrite-oxidizing bacteria (NOB) Nitrospira, and
heterotrophic denitrifiers. Unexpectedly, comammox Nitrospira was the predominant
nitrifier in the presence of AOB Nitrosomonas in the organic carbon-rich nitrification-denitrification
system of Linkou (LK). These results clearly showed that distinct active groups were
working in concert for an effective nitrogen removal in different WWTPs. This study
confirmed the feasibility of anammox application in ammonium-rich systems by direct
inoculation of the exogenous anammox pellets and improved our understanding of microbial
nitrogen cycling in anammox-driven conventional WWTPs from both physiochemical and
omics perspectives.