Widespread but Overlooked DNRA Process in a Full-Scale Simultaneous Partial Nitrification, Anammox, and Denitrification Plant

Similar
to denitrification and anaerobic ammonium oxidation (anammox)
processes, dissimilatory nitrate reduction to ammonium (DNRA) is widely
distributed in natural ecosystems. However, DNRA in wastewater treatment
plants (WWTPs) is usually underestimated or fully ignored. Here, a
full-scale simultaneous partial nitrification, anammox, and denitrification
(SNAD) WWTP was studied, and the composition of nitrogen metabolism
microorganisms in each compartment of the WWTP was analyzed. Ammonia
oxidizing bacteria, anammox bacteria, nitrite oxidizing bacteria,
denitrifying bacteria, and DNRA organisms coexisted in this full-scale
WWTP. The relative abundance of the DNRA functional gene (nrfA) was significantly higher (150–301 reads per
million reads (RPMR)) than that of the denitrification functional
gene (nosZ, 68–97 RPMR). The SNAD process
dealing with high NH4+-N and high organic wastewater
provided suitable conditions for the growth of DNRA. However, the
unintended selection of DNRA in the SNAD process created an engineering
inefficiency of nitrogen removal by utilizing carbon that should be
otherwise allocated for denitrification. Our results demonstrate a
need to innovate and improve low energy nitrogen removal processes,
such as SNAD, to better understand the ecology and function of DNRA
organisms in engineered systems.