Long solids retention times and attached growth phase favor prevalence of comammox bacteria in nitrogen removal systems

High functional diversity among Nitrospira populations that dominate rotating biological contactor microbial communities in a municipal wastewater treatment plant

“…The dominance of comammox Nitrospira in biofilm samples collected from RBCs treating municipal wastewater of Guelph, Ontario, Canada is in contrast to several previous studies of full-scale activated sludge WWTPs that report comammox Nitrospira at lower relative abundances than AOA and other AOB [7,[18][19][20][21], albeit for systems with ammonium concentrations and operational parameters distinct from those in the RBCs. This current study, along with other recent studies [12,15,17,18,22], shows that comammox Nitrospira can dominate municipal wastewater treatment systems. Although previous analyses of the Guelph WWTP did not test for these newly discovered ammonia oxidizers [29,30], the presence of comammox Nitrospira was predicted previously from activity data and an abundance of Nitrospira cells that actively assimilated labeled bicarbonate when incubated with ammonium [30].…”

“…For example, on the day of sampling in 2016, the ammonium concentration in aeration basin influents averaged 2.5 mM NH 3 -N, which is typical of aerobic secondary aeration basin conditions reported elsewhere [e.g., [20][21][22]62]. A large surface area for attached growth may be an important factor explaining the dominance of comammox bacteria, given their high prevalence in wastewater treatment systems with attached growth components [18]. The predicted low ammonium niche and biofilm-specific growth of comammox Nitrospira [4,5] may help explain the dominance of these nitrifiers in the tertiary treatment system RBCs in Guelph, Ontario.…”

“…Consistent with a low ammonium niche, comammox Nitrospira have been detected in drinking water systems [7][8][9][10][11][12][13][14]. First identified from water treatment system metagenome sequences [5,6], most wastewater-associated comammox Nitrospira belong to clade A [5,7,12,[14][15][16][17][18], albeit with abundances generally lower than those reported for AOA and AOB [7,[18][19][20][21]. Nonetheless, amoA gene abundances of comammox Nitrospira may outnumber those of AOB in activated sludge samples from several WWTPs [12,18,22], and comammox Nitrospira have been enriched in wastewater treatment reactors with low dissolved oxygen conditions [15,17].…”

“…First identified from water treatment system metagenome sequences [5,6], most wastewater-associated comammox Nitrospira belong to clade A [5,7,12,[14][15][16][17][18], albeit with abundances generally lower than those reported for AOA and AOB [7,[18][19][20][21]. Nonetheless, amoA gene abundances of comammox Nitrospira may outnumber those of AOB in activated sludge samples from several WWTPs [12,18,22], and comammox Nitrospira have been enriched in wastewater treatment reactors with low dissolved oxygen conditions [15,17]. In addition, the high abundance of amoA transcripts from comammox Nitrospira detected in activated sludge suggests an active role in nitrification [23,24].…”

“…In addition, the high abundance of amoA transcripts from comammox Nitrospira detected in activated sludge suggests an active role in nitrification [23,24]. Previous studies examining comammox Nitrospira in WWTPs focused primarily on activated sludge secondary treatment systems and sequencing batch reactors [12,[15][16][17][18][19][20][21][22][23][25][26][27][28]. To our knowledge, no studies have investigated comammox Nitrospira in biofilm-based tertiary wastewater treatment systems.…”