Comammox Nitrospira Species Dominate in an Efficient Partial Nitrification–Anammox Bioreactor for Treating Ammonium at Low Loadings

Abstract

Bacteria capable of complete ammonia oxidation (comammox) are widespread and contribute to nitrification in wastewater treatment facilities. However, their roles in partial nitrification–anaerobic ammonium oxidation (anammox) systems remain unclear. In this study, a bench-scale bioreactor with continuous stirring was operated for more than 1000 days with limited oxygen supply to achieve efficient nitrogen removal (70.1 ± 2.7%) at a low ammonium loading of 35.2 mg-N/L/day. High-throughput amplicon sequencing analysis of the comammox ammonia monooxygenase subunit A (amoA) gene revealed seven sequence types from two clusters in clade A of comammox Nitrospira. Quantitative polymerase chain reaction analyses suggested that the comammox species dominated the ammonia-oxidizing community, with an abundance as high as 89.2 ± 7.9% in total prokaryotic amoA copies. Multiple linear regression further revealed the substantial contribution of the comammox Nitrospira to ammonia oxidation in the bioreactor. The investigation with bioreactor and batch experiments consistently showed that activities of comammox Nitrospira were inhibited by free ammonia far more severely than other ammonia-oxidizing microbes. Overall, this study provided new insight into the ecology of comammox Nitrospira under hypoxic conditions and suggested comammox-associated partial nitrification–anammox as a potential method for treating low-strength ammonium-containing wastewater.

Role of air scouring in anaerobic/anoxic tanks providing nitrogen removal by mainstream anammox conversion in a hybrid biofilm/suspended growth full‐scale WWTP in China

“…As one of the well‐known NOB genera, Nitrospira has been widely reported as a complete aerobic ammonia‐oxidizing bacteria (comammox) (Gonzalez‐Martinez et al, 2016; Lawson & Lücker, 2018), and some Nitrospira , such as Nitrospira inopinata , have a relatively low affinity for nitrite, making the symbiotic association with anammox bacteria possible. Sustained nitrogen loss has been observed in a combination of Comammox Nitrospira and anammox bacteria, especially in low ammonia condition and sometimes in low DO condition (Gottshall et al, 2020; Roots et al, 2019; Shao & Wu, 2021). The dominant NOB genus in this case, as shown in the reference (Yuan et al, 2020), was Nitrospira , and its relative abundance in the suspended solids was 2 times higher in summer and 7 times higher in winter than the biofilm.…”

“…It is possible that Nitrospira in the suspended solids in this case acts as Comammox and cooperated with anammox bacteria attached on the carriers. Cooperation between Comammox and anammox bacteria were found both in a sequencing batch reactor for sludge digester liquor treatment (Wu et al, 2019) and in a continuous reactor for low‐strength ammonia‐containing wastewater treatment (Shao & Wu, 2021). van Kessel et al, (2015) reported that Comammox bacteria are capable to produce nitrite and cooperate with anammox for nitrogen removal.…”

Comammox Nitrospira bacteria outnumber canonical nitrifiers irrespective of nitrogen source and availability

“…Soil microcosms amended with high ammonia concentrations were enriched in AOB compared to those with lower ammonia concentrations where clade B comammox bacteria proliferated , He et al, 2021. Interestingly, in a lab-scale partial nitrification-anammox reactor operating with incrementally increased ammonia loadings, comammox bacteria initially dominated over strict AOB but its abundance significantly declined as loadings were further increased (Shao & Wu, 2021).…”

“…This suggests that clade-specific comammox bacterial niche, if applicable, may be arise from a combination of factors ranging from affinity to inhibition. Beyond clade specific traits, identifying the potential environmental and physiological factors driving the coexistence of comammox bacteria with canonical nitrifiers is also important to better understand comammox bacteria role in complex nitrifying communities (21)(22)(23)(24)(25)(26)(27)(28)(29). Comammox bacteria have been detected along with their canonical nitrifying counterparts in wastewater treatment plants (18,25,(30)(31)(32), drinking water systems (6,9,15,33,34) and soils (22,28,35,36) at varying abundances over a wide range of ammonium concentrations.…”

“…This suggests that clade-specific comammox bacterial niche, if applicable, may be arise from a combination of factors ranging from affinity to inhibition. Beyond clade specific traits, identifying the potential environmental and physiological factors driving the coexistence of comammox bacteria with canonical nitrifiers is also important to better understand comammox bacteria role in complex nitrifying communities (Gulay et al, 2019, Zheng et al, 2019, Gottshall et al, 2020, Wang et al, 2020, He et al, 2021, Shao & Wu, 2021. Comammox bacteria have been detected along with their canonical nitrifying counterparts in wastewater treatment plants (Gonzalez-Martinez et al, 2016, Roots et al, 2019, Zheng et al, 2019, Cotto et al, 2020, Yang et al, 2020, drinking water systems (Pinto et al, 2016, Tatari et al, 2017, Poghosyan et al, 2020 and soils (Prosser & Nicol, 2012, Shi et al, 2018, He et al, 2021 at varying abundances over a wide range of ammonium concentrations.…”