2026 Excellence in Environmental Engineering and Science® Awards Competition Winner

Honor Award - University Research

Mainstream Deammonification by Ion Exchange and Bioregeneration via Partial Nitritation/Anammox

Entrant: University of South Florida, Penn State University, Technion Israel
Engineer in Charge: Sarina Ergas, Ph.D., P.E., BCEE
Location: Florida, Pennsylvania, Haifa Israel

Entrant Profile

The following table describes the entrants and their role(s) in the project:

Project Description

One of the most remarkable advances in wastewater treatment in the past three decades is the use of partial nitritation/anammox (PN/A) for nitrogen removal. However, PN/A has mainly been used to treat high ammonia strength wastewaters, such as anaerobic digestion sidestreams. It is not typically applied to remove nitrogen from mainstream municipal wastewater (MMW) because the high COD and low ammonia concentrations in MMW do not favor selection and retention of slow growing ammonia oxidizing microorganisms (AOM) and anammox and suppression of undesirable nitrite oxidizing bacteria (NOB) and heterotrophic denitrifiers.

Innovation

To overcome these challenges, research teams at the University of South Florida (USF), Penn State University,and the Technion Israel Institute of Technology developed a novel process that combines ion exchange (IX) on natural zeolite minerals and PN/A. In this process (Fig. 1):

1) MMW was pretreated using either high-rate contact stabilization or chemically enhanced primary treatment (CEPT). This redirects organic carbon to bioenergy production and reduces the COD/N ratio to inhibit denitrifiers.

2) Pretreated MWW was passed through columns containing natural zeolite to separate and concentrate NH₄⁺.Natural zeolites, such as chabazite, are low-cost aluminosilicate minerals with a high affinity and selectivity for NH₄⁺.

3) Once breakthrough occurred, NH₄⁺ saturated columns were switched to bioregeneration mode, which we accomplished using different approaches:

• USF and Penn State: PN/A biofilms were grown directly on the zeolite surfaces. Low dissolved oxygen(DO) conditions were applied to promote oxidation of NH₄⁺ by AOM and anammox (Fig. 1a).
• Technion Israel: A high strength brine solution was passed through the packed column to desorb NH₄⁺.The NH₄⁺-rich brine was treated in a separate halophilic PN/A biofilm reactor, where NH₄⁺ was converted to nitrogen gas (Fig. 1b).

4) Once zeolite was regenerated, adsorption and bioregeneration steps were repeated for many cycles. Little or nochemical regenerant was added to the process, and no contaminated waste brines were produced.

Quality

Research was carried out in bench-scale reactors at three universities, resulting in eight (8) peer reviewed journal articles,four (4) PhD dissertations, two (2) MS theses, one (1) patent and seventeen (17) conference presentations. A summary of each team’s major findings is provided below:

USF Team: Anammox and AOM were enriched from wastewater seed and combined in a bench-scale IX-PN/A sequencing batch biofilm reactor (SBBR) (Fig. 2). Recirculation was used to provide aeration at the top of the SBBR, while DO consumption by AOM promoted anoxic conditions for anammox at the bottom. High total inorganic nitrogen (TIN) removal efficiency (81%) and ammonium removal rates (0.11 g N/L/day) were achieved at a recirculation velocity of 1.43 m/h (Fig. 3). The core microbiome of the SBBR (Fig. 4) contained a high abundance of bacteria of the phyla Pseudomonadota, Patescibacteria, Chloroflexota, and Planctomycetota, while qPCR showed the highest ammonia monooxygenase (amoA) and anammox (amx) in the top layers. The IX-PN/A SBBR achieved stable N removal for > two years without chemical inputs, media replacement or brine waste production. The USF team also developed novel hydrogel biofilm carriers with encapsulated zeolite and anammox (Fig. 5).

Penn State Team: IX-PN/A was carried out in upflow anaerobic sludge blanket (UASB) reactors (Fig. 6). The counter-diffusion mechanism created spatially separated redox zones, enabling efficient mass transfer and sustaining anammox activity. UASBs achieved NH₄⁺ removal efficiencies of 63.5-87.0% across varying nitrogen loading rates (100-50 mg/L/d) and temperatures (12-22 °C). FISH analysis revealed distinct biofilm architectures, with AOM in outer layers and anammox closely associated with NOB near the zeolite surface. The dominant anammox bacteria was Candidatus Brocadia fulgida, while Feammox played an important role at low temperature. Life cycle assessment (LCA) results indicated that high-rate contact stabilization combined with IX-PNA has a lower global warming impact than conventional BNR, driven by improved bioenergy recovery and reduced N₂Oemissions and aeration energy consumption (Fig. 7).

Technion Team: NH₄⁺ was removed from MMW by a zeolite column, which was regenerated with seawater (Fig. 8). The high NH₄⁺ strength brine solution was treated in a hypersaline PN/A reactor. The PN/A reactor initially treated recirculating brine from the IX column for 48 cycles of NH₄⁺ absorption and bioregeneration with minimal blowdown. Cations in the regenerant solution were stable except for Ca²⁺, which reached values > 3,000 mg/L and caused PN/A reactor failure due to mineral precipitation. The buildup of Ca²⁺ in the regenerant was addressed in two ways: 1) 20 % regenerant replacement per cycle and 2) precipitation of CaCO3 via sodium carbonate addition. Both methods were effective for 30 absorption and bioregeneration cycles, allowing for stable PN/A reactor operation (Fig. 9). Microbial community analysis of the PN/A reactor by next-generation sequencing (NGS) revealed an obligately halophilic Candidatus Scalindua anammox bacteria and halotolerant Nitrosomonas AOM. NOB were not observed as a result of low DO and nitrite scavenging by anammox.

Complexity

This project offers a low-cost, low-complexity approach to achieve the environmental conditions needed to combine AOM and anammox and suppress NOB for MMW treatment. The IX units are modular and compact and may be accommodated in existing treatment layouts with minimal disruption.

Social, Public, Environmental Health and Economic Advancements

PN/A implementation for MMW treatment has the potential to reduce energy costs for aeration by ~60%, eliminate supplemental organic carbon addition for denitrification, increase bioenergy production and reduce greenhouse gas emissions. This innovative process overcomes the main limitations of PN/A application to MWW by: 1) reducing the volume of wastewater to be treated via PN/A, 2) providing a favorable COD/N ratio, and 3) ensuring high stable NH₄⁺ concentrations and environmental conditions needed to select and retain AOM andanammox and suppress NOB and heterotrophic denitrifiers. Students working on the project increased their global competency through international collaboration and visits with Israeli researchers. The project also provided training for community college students in PA and FL to provide a diverse workforce for the water industry.

Acknowledgements: This material was based on work supported by the National Science Foundation-US-Israel Binational Science Foundation (NSF-BSF) under Grant Number 2000980.

Click images to enlarge in separate window.

Figure 1: Process flow diagrams showing how ion exchange (IX) was coupled with partial nitritation/anammox (PN/A): left) USF and PSU approach, right) Technion approach	Figure 2: Reactor photo and schematic for USF team.
Figure 3. Nitrogen species concentrations over 1,000 days of operation (USF team).	Figure 4: Microbiome of IX-PNA SBBR: (a) sampling locations, (b) heatmap each phylum, (c) percent abundance of anammox and non-anammox bacteria belonging to phylumPlanctomycetota, (d) heatmap of amx694Pf/amx960r anammox, (e) AOM and non-AOM belonging tophylum Pseudomonadota, NOB and non-NOB belonging to phylum Chloroflexota, (f) heatmap of amoA1f/amoA2r AOM and nspra675f/nspra746R NOB
Figure 5: Hydrogel biofilm carriers with encapsulated chabazite and anammox	Figure 6: Reactor photo and schematic for Penn State team.
Figure 7: Results of life cycle assessment (LCA) comparing High-Rate Contact Stabilization(HiCS) and IX-PN/A with other biological nitrogen removal technologies.	Figure 8: Reactor photo and schematic for Technion team.
Figure 9: Nitrogen species concentrations before and after PN/A reactor treatment.

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