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1. Ion exchange and bioregeneration by partial nitritation/anammox for mainstream municipal wastewater treatment

   Chero-Osorio, Sheyla; Steele, Lanica; Carson, Valerie; Bhattacharjee, Ananda S; Wang, Meng; Kuhn, John; Ergas, Sarina J (July 2025, Bioresource technology)

   Conventional biological nitrogen removal (BNR) processes for mainstream municipal wastewater (MMW) treatment have high energy and chemical costs. Partial nitritation/anammox (PN/A) has the potential to reduce the carbon footprint of BNR; however, its implementation for MMW treatment has been limited by the low ammonium and high organic matter concentrations in MMW, which prevent suppression nitrite oxidizing bacteria (NOB) and heterotrophic denitrifiers. In this study, after organic carbon diversion, ammonium was separated from MMW in a novel bench-scale sequencing batch biofilm reactor (SBBR) containing chabazite, a natural zeolite mineral with a high ammonium ion exchange (IX) capacity. After breakthrough, chabazite was bioregenerated by PN/A biofilms. Recirculation was applied from the bottom to the top of the column to create an aerobic zone (top) for ammonia-oxidizing microorganisms (AOM) and an anoxic zone (bottom) for anammox bacteria. Rapid IX-PN/A SBBR startup was observed after inoculation with PN/A enrichments. The time required for bioregeneration decreased with increasing recirculation rate, with high total inorganic nitrogen (TIN) removal efficiency (81 %) and ammonium removal rate (0.11 g N/L/day) achieved at recirculation velocity of 1.43 m/h. The core microbiome of the IX-PN/A SBBR contained a high abundance of bacteria of the phylum Pseudomonadota (15.27–20.62 %), Patescibacteria (12.38–20.05 %), Chloroflexota (9.36–14.23 %), and Planctomycetota (7.55–12.82 %), while quantitative PCR showed the highest ammonia monooxygenase (amoA, 2.0 × 102) and anammox copy numbers (amx, 1.0 × 104) in the top layers. The single-stage IX-PN/A SBBR achieved stable BNR for >two years without chemical inputs, media replacement or brine waste production. 

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2. Microbiomes and Planctomycete diversity in large-scale aquaria habitats

   https://doi.org/10.1371/journal.pone.0267881  

   Elbon, Claire E.; LeCleir, Gary R.; Tuttle, Matthew J.; Jurgensen, Sophie K.; Demas, Thomas G.; Keller, Christian J.; Stewart, Tina; Buchan, Alison (May 2022, PLOS ONE)

   Senko, John M. (Ed.)

   In commercial large-scale aquaria, controlling levels of nitrogenous compounds is essential for macrofauna health. Naturally occurring bacteria are capable of transforming toxic nitrogen species into their more benign counterparts and play important roles in maintaining aquaria health. Nitrification, the microbially-mediated transformation of ammonium and nitrite to nitrate, is a common and encouraged process for management of both commercial and home aquaria. A potentially competing microbial process that transforms ammonium and nitrite to dinitrogen gas (anaerobic ammonium oxidation [anammox]) is mediated by some bacteria within the phylum Planctomycetes. Anammox has been harnessed for nitrogen removal during wastewater treatment, as the nitrogenous end product is released into the atmosphere rather than in aqueous discharge. Whether anammox bacteria could be similarly utilized in commercial aquaria is an open question. As a first step in assessing the viability of this practice, we (i) characterized microbial communities from water and sand filtration systems for four habitats at the Tennessee Aquarium and (ii) examined the abundance and anammox potential of Planctomycetes using culture-independent approaches. 16S rRNA gene amplicon sequencing revealed distinct, yet stable, microbial communities and the presence of Planctomycetes (~1–15% of library reads) in all sampled habitats. Preliminary metagenomic analyses identified the genetic potential for multiple complete nitrogen metabolism pathways. However, no known genes diagnostic for the anammox reaction were found in this survey. To better understand the diversity of this group of bacteria in these systems, a targeted Planctomycete-specific 16S rRNA gene-based PCR approach was used. This effort recovered amplicons that share <95% 16S rRNA gene sequence identity to previously characterized Planctomycetes, suggesting novel strains within this phylum reside within aquaria. 

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3. Response of mixed community anammox biomass against sulfide, nitrite and recalcitrant carbon in terms of inhibition coefficients and functional gene expressions

   Hong, S; Clippeleir, H; Goel, R (July 2022, Chemosphere)

   Anaerobic ammonium oxidation (anammox) has evolved as a carbon and energy-efficient nitrogen management bioprocess. However, factors such as inhibitory chemicals still challenge the easy operation of this powerful bioprocess. This research systematically evaluated the inhibition kinetics of sulfide, nitrite, and recalcitrant carbon under a genomic framework. The inhibition at the substrate and genetic levels of sulfide, nitrite and recalcitrant carbon on anammox activity was studied using batch tests. Nitrite inhibition of anammox followed substrate inhibition and was best described by the Aiba model with an inhibition coefficient KI,NO􀀀2 of 324.04 mg N/L. Hydrazine synthase (hzsB) gene (anammox biomarker) expression was increased over time when incubated with nitrite up to 400 mg N/L. However, despite having the highest specific nitrite removal (SNR), the expression of hzsB at 100 and 200 mg N/L of nitrite was more muted than in most other samples with lower SNRs. Sulfide severely inhibited anammox activities. The inhibition was fitted with a Monod-based model with a KI,S2􀀀 of 4.39 mg S/L. At a sulfide concentration of 5 mg/L, the hzsB expression decreased throughout the experiment from its original value at he beginning. Recalcitrant carbon of filtrate from thermal hydrolysis process pretreated anaerobic digester had a minimal effect on maximum specific anammox activity (MSAA), and thus the value of the inhibition coefficient could not be calculated. At the same time, its hzsB expression profile was similar to that in the control. Resiliency and recovery tests indicated that the inhibition of nitrite (up to 400 mg N/L) and recalcitrant carbon (in 100% filtrate) were reversible. About 32% of MSAA was recovered after repeated exposures to sulfide at 2.5 mg/L, while at 5 mg/L, the inhibition was irreversible. Findings from this study will be helpful for the successful design and implementation of anammox in full-scale applications. 

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4. Nitrite accumulation and anammox bacterial niche partitioning in Arctic Mid-Ocean Ridge sediments

   https://doi.org/10.1038/s43705-023-00230-y  

   Zhao, Rui; Babbin, Andrew R.; Roerdink, Desiree L.; Thorseth, Ingunn H.; Jørgensen, Steffen L. (December 2023, ISME Communications)

   Abstract By consuming ammonium and nitrite, anammox bacteria form an important functional guild in nitrogen cycling in many environments, including marine sediments. However, their distribution and impact on the important substrate nitrite has not been well characterized. Here we combined biogeochemical, microbiological, and genomic approaches to study anammox bacteria and other nitrogen cycling groups in two sediment cores retrieved from the Arctic Mid-Ocean Ridge (AMOR). We observed nitrite accumulation in these cores, a phenomenon also recorded at 28 other marine sediment sites and in analogous aquatic environments. The nitrite maximum coincides with reduced abundance of anammox bacteria. Anammox bacterial abundances were at least one order of magnitude higher than those of nitrite reducers and the anammox abundance maxima were detected in the layers above and below the nitrite maximum. Nitrite accumulation in the two AMOR cores co-occurs with a niche partitioning between two anammox bacterial families ( Candidatus Bathyanammoxibiaceae and Candidatus Scalinduaceae), likely dependent on ammonium availability. Through reconstructing and comparing the dominant anammox genomes ( Ca . Bathyanammoxibius amoris and Ca . Scalindua sediminis), we revealed that Ca . B. amoris has fewer high-affinity ammonium transporters than Ca . S. sediminis and lacks the capacity to access alternative substrates and/or energy sources such as urea and cyanate. These features may restrict Ca . Bathyanammoxibiaceae to conditions of higher ammonium concentrations. These findings improve our understanding about nitrogen cycling in marine sediments by revealing coincident nitrite accumulation and niche partitioning of anammox bacteria. 

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5. Fate and Transport of the Biologically Treated Landfill Leachate Induced Dissolved Organic Nitrogen (DON)

   Md Ashik Ahmed*, Md Redowan (June 2023, AEESP Research and Education Conference, Northeastern University, June 20-23, 2023)

   This study evaluated the performance of sequencing batch reactors (SBR) in the fate and transport of dissolved organic nitrogen (DON) using a blend of wastewater and landfill leachate. Most nitrogen removal methods concentrate on inorganic nitrogen, whereas some biological processes add DON to the effluent. Two reactors were introduced with wastewater and landfill leachate of high and low organic carbon and compared them to a reactor without leachate. DON transformation, characterization, and microbial community dispersion were examined to understand the effects of leachate-induced effluent DON on the biological nitrogen removal process. The ammonium removal efficiencies were found 96, 97, and 98%; COD removal efficiencies were 75, 59, and 63%; and total nitrogen (TN) removal efficiencies were 83, 86, and 88%, for R1, R2, and R3, respectively. The effluent nitrate concentrations were found 1.67 ± 0.89 (R1), 3.05 ± 2.08 (R2), and 1.31 ± 1.30 (R3) mg/L and DON went down from 9.67 ± 2.5 to 6.02 ± 2.8 mg/L (R1), 9.29 ± 3.4 to 7.49 ± 3.6 mg/L (R2), and 3.59 ± 1.6 to 2.08 ± 1.1 mg/L (R3). Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and excitation-emission matrices (EEMs) with parallel factor (PARAFAC) analysis were used to characterize DON. Microbial community analysis was also conducted. Leachate-induced DON discharge's environmental effects were assessed using in-situ aquatic ecosystem algal bioassay. SBR system removed most inorganic nitrogen species and a small amount of leachate-induced DON. The study emphasizes the need for independent investigations to assess their effects on receiving water bodies. 

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