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1. Successful Implementation of Biofilm Anammox in IFAS A2O Process for Simultaneous N and P Removal in Mainstream Treatment Train

   Hong, S; Winkler, MKH; Wang, Z; Goel, R (October 2023, WEFTEC PRoceedings)

   WEF (Ed.)

   This research studied integrated fixed film activated sludge (IFAS) technology to simultaneously remove N and P in real municipal wastewater by combining anammox biofilms with flocculent activated sludge for enhanced biological P removal (EBPR). The study was conducted in a sequencing batch reactor (SBR) operated as a conventional A2O (anaerobic-anoxic-oxic) process with an 8.8 h hydraulic retention time. After achieving steady-state operation, the reactor showed robust performance, with average removal efficiencies of 91.3±4.1% for total inorganic nitrogen (TIN) and 98.4±2.4% for phosphorus (P). Denitrifying polyphosphate accumulating organisms (DPAOs) were responsible for 15.9% of P uptake during the anoxic phase, while biofilms showed anammox activity in the aerobic step. The IFAS configuration with a low solid retention time (SRT) of 5 days prevented the washout of biofilm anammox bacteria and allowed selective washout of unwanted organisms. The results demonstrated the successful coexistence of anammox bacteria with other bacteria for efficient nutrient removal in real wastewater conditions. 

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2. Successful Implementation of Biofilm Anammox in IFAS A2O Process for Simultaneous N and P Removal in Main Stream Treatment Train

   Hong, S; Winkler, MKH; Wang, Zhiwu; Goel, R (October 2023, WEFTEC Proceedings)

   Soklida, Hong; Mari-KH, Winkler; Zhiwu, Wang; Goel, Ramesh (Ed.)

   This research studied integrated fixed film activated sludge (IFAS) technology to simultaneously remove N and P in real municipal wastewater by combining anammox biofilms with flocculent activated sludge for enhanced biological P removal (EBPR). The study was conducted in a sequencing batch reactor (SBR) operated as a conventional A2O (anaerobic-anoxic-oxic) process with an 8.8 h hydraulic retention time. After achieving steady-state operation, the reactor showed robust performance, with average removal efficiencies of 91.3±4.1% for total inorganic nitrogen (TIN) and 98.4±2.4% for phosphorus (P). Denitrifying polyphosphate accumulating organisms (DPAOs) were responsible for 15.9% of P uptake during the anoxic phase, while biofilms showed anammox activity in the aerobic step. The IFAS configuration with a low solid retention time (SRT) of 5 days prevented the washout of biofilm anammox bacteria and allowed selective washout of unwanted organisms. The results demonstrated the successful coexistence of anammox bacteria with other bacteria for efficient nutrient removal in real wastewater conditions. 

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3. Process intensification and emerging contaminant management in wastewater treatment using reactive migrating carriers

   Qureshi, A; Goswam, Ai; Murthy, S; Giraldo, E; Goel, R (October 2025, WEFTEC Proceedings)

   Results of an innovative use of GAC for process intensification carbon efficient nutrient and micropollutant removal are presented. GAC is used as a reactive migrating carrier enabling SRT uncoupling and GAC bioregeneration furthering the use of migrating carriers for process intensification in existing wastewater treatment plants. Two model micropollutants were used, short and long-chain per- and polyfluoroalkyl substances (PFAS), and one synthetic estrogen, 17α-ethynylestradiol (EE2). Two sequencing batch reactors were operated in classical A2O mode, with one serving as a control (RC) and the other was supplemented with granular activated carbon, and was designated as reactive migrating carrier reactor (RAC). The nutrient removal efficacy in both RAC and RC was similar, with average ammonium nitrogen (NH₄⁺-N) at 95.2 ± 4.8%, total inorganic nitrogen (TIN) at 76.4 ± 17.6%, phosphate (PO₄³⁻-P) at 89.7 ± 10.3%, and soluble chemical oxygen demand (sCOD) at 97.1 ± 1.4% achieved in both reactors. However, the removal efficiencies of long hanin PFAS compounds and the estrogen in the RAC was mush higher than in the RC reactor in which case, both physical sorption to biomass and potential biodegadation contributed to the fate of these micropollutants. The average EE2 removal efficiencies were 72 ± 9% in RAC, attributed to high localized EE2 concentrations, and 35.2 ± 13.9% in RC. A physical selective pressure of passing the waste sludge through a 500 micron sieve promoted significant granulation in both reactors, where the extent of granulation in the RAC reactor was higher than in the RC reactor. 

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4. 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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5. 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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