How to read these design cases
Mainstream deammonification and anammox are still highly site-dependent. The examples below are documented pilot studies or a conceptual design model, not customer testimonials, vendor guarantees, or universal design values. The page separates measured application evidence from model assumptions so that engineers can use the cases as reference points without treating them as direct performance promises.
Design principle: transfer the process logic, monitoring strategy, and risk controls—not a published setpoint—into the project’s own wastewater, climate, effluent, and regulatory context.
Case portfolio at a glance
| Case | Evidence type | Design relevance | Important boundary |
|---|---|---|---|
| IFAS mainstream anammox | One-year pilot-scale operation | Shows how anammox retention, low DO, FNA treatment, and residual-ammonium control can be combined. | Performance was achieved in a controlled pilot receiving HRAS-pretreated wastewater; it is not a full-scale design guarantee. |
| Cold-climate PDA | 50 m3/d pilot treating actual municipal wastewater | Shows a partial-denitrification/anammox route for seasonal cooling and nitrite supply resilience. | It is PDA coupled with anammox, not a simple one-stage PN/A train; reported values are study-specific. |
| Temperate 30,000-PE concept | Conceptual model with laboratory-supported assumptions | Shows how carbon removal, reactor volume, energy demand, and energy recovery can be assessed together. | Model outputs depend on assumed nitrogen-removal rates and upstream carbon capture; they are not measured plant results. |
Case 1 — One-year IFAS mainstream anammox pilot
Zheng and colleagues reported a one-year pilot-scale mainstream anammox process using integrated fixed-film activated sludge (IFAS). The continuous-flow configuration included an anoxic zone and an oxic zone, with anammox-containing carriers retained in both zones. The feed was domestic wastewater pretreated by a high-rate activated sludge (HRAS) process that captured approximately 60% of COD. The reported design parameters included a 12-day solids-retention time, a 3.2-hour hydraulic-retention time in the anoxic zone, and a 6.7-hour hydraulic-retention time in the oxic zone. [1]
The control strategy combined low dissolved oxygen of 0.4 ± 0.2 mg O2/L, regular free-nitrous-acid (FNA) sludge treatment at approximately 2 mg HNO2-N/L, and residual-ammonium control near 8 mg N/L. The study reported effluent total nitrogen mostly below 10 mg N/L and average total-nitrogen and ammonium-removal efficiencies above 80% over the one-year period. A temporary rise in NOB activity required operational adjustment, illustrating that robust performance came from integrated control rather than one universal setpoint. [1]
| Observed design lesson | How it translates into a project review |
|---|---|
| Retain anammox biomass on carriers in multiple zones. | Confirm carrier inventory, biofilm protection, detachment risk, mass transfer, and how biomass is retained during hydraulic and toxicant shocks. |
| Use low DO together with residual-ammonium control. | Define the nitrogen-species balance and test the effect of DO changes on AOB, NOB, anammox, and effluent ammonia rather than copying a single target. |
| Apply FNA treatment as part of NOB management. | Assess chemical handling, contact strategy, safety, sludge impacts, permit implications, and whether the approach is suitable for the site. |
Case 2 — Cold-climate partial-denitrification/anammox pilot
Zhao and colleagues established a 50 m3/d pilot plant in northern China treating actual municipal wastewater. The process combined anaerobic, anoxic, and oxic zones with biological contact oxidation and used partial denitrification to supply nitrite for anammox. The pilot operated for 210 days while the operating temperature fell from 27.8 °C to 7.5 °C. [2]
Reported total-inorganic-nitrogen removal efficiency was 75.0 ± 4.6% at 27.8–20.0 °C, 72.5 ± 4.8% at 20.0–10.0 °C, and 70.4 ± 4.5% at 10.0–7.5 °C. Ammonium removal remained approximately 99% across the phases, while effluent total inorganic nitrogen was approximately 8.2, 12.1, and 12.6 mg N/L in the three temperature phases. At 10.0–7.5 °C, the study reported an in-situ anammox rate of 32.7 ± 4.7 g-N/(m3·d), contributing up to 39.7 ± 6.7% of nitrogen removal. [2]
The engineering significance is not that cold-weather PN/A can simply use the same controls as a warm plant. Instead, the case shows how a partial-denitrification route can provide nitrite when low temperature makes partial nitritation and NOB suppression more difficult. The additional nitrate-reduction step also changes the carbon, alkalinity, anoxic-volume, and greenhouse-gas balance that must be assessed.
Case 3 — Temperate 30,000-population-equivalent concept
Cheenakula and colleagues developed a conceptual mainstream deammonification plant model for 30,000 population equivalents under German mainstream conditions. Their approach evaluated chemical precipitation and ultrafine screening before deammonification to reduce COD by 80% and lower the COD:N ratio from 12 to 2.5. Laboratory testing across 8–20 °C, pH 6–9, and COD:N ratios of 1–6 reported a volumetric nitrogen-removal rate of at least 50 g N/(m3·d) for the tested deammonifying sludges. [3]
Using an assumed 50 g N/(m3·d) rate, the concept used 0.115 m3 of reactor volume per population equivalent. Its model estimated total plant electricity demand of 21.5 kWh/(PE·a) and energy-recovery potential of 24 kWh/(PE·a), compared with 35 and 15.8 kWh/(PE·a), respectively, for its conventional reference model. These figures are model outputs, not measured full-scale results, and they depend on carbon-capture performance, biological rate, sludge handling, and energy-recovery assumptions. [3]
| Model assumption | Design question before reuse |
|---|---|
| Upstream COD reduction | Can the plant capture carbon without compromising downstream polishing, phosphorus removal, or resilience to wet-weather loads? |
| Volumetric nitrogen-removal rate | Has the rate been demonstrated with the project’s actual wastewater, winter temperature, toxicity, and solids inventory? |
| Energy recovery | Are digestion, dewatering, aeration, pumping, chemical preparation, heating, and residual treatment included in the plant-wide balance? |
Warm-climate full-scale context
The conceptual-study review identifies stable full-scale mainstream deammonification at the Changi Water Reclamation Plant in Singapore at approximately 30 °C, while noting that temperate and cold climates present a more difficult operating envelope. The same review discusses pilot and full-scale work in Europe, including MBBR/IFAS approaches and enhanced carbon removal, but also emphasizes that low-strength mainstream stability and long-term NOB suppression remain significant challenges. [3]
This contrast is useful during option screening. A warm-climate full-scale reference can demonstrate that mainstream anammox is technically possible at plant scale, but it should not be used as a direct proxy for a colder plant with lower ammonium, different carbon availability, and different seasonal dynamics.
Cross-case design translation
| Design workstream | Questions to answer | Evidence to collect |
|---|---|---|
| Feed characterization | What are the seasonal ammonium, nitrate, COD fractions, alkalinity, temperature, salinity, toxicants, and wet-weather loads? | Load-resolved sampling, temperature history, toxicity screening, and a nitrogen/carbon mass balance. |
| Carbon management | Should primary carbon be captured for digestion, retained for polishing, or divided between autotrophic and heterotrophic pathways? | COD fractionation, capture efficiency, methane potential, and effluent-polishing trials. |
| Biomass retention | How will slow-growing anammox organisms be retained through low-load, toxicant, washout, and maintenance events? | Carrier or granule tests, solids inventory, activity testing, and restart plans. |
| NOB control | Which combination of DO, residual ammonium, SRT, intermittent aeration, biofilm selection, FNA/FA treatment, or partial denitrification is appropriate? | Long-term nitrite/nitrate trends, respirometry, microbial surveillance, and upset-response testing. |
| Effluent polishing | How will residual ammonium, nitrite, nitrate, phosphorus, suspended solids, and trace contaminants meet permit requirements? | Seasonal polishing envelope, redundancy analysis, and bypass/contingency strategy. |
| Emissions and energy | Do lower aeration and carbon demand remain beneficial after pumping, chemicals, sludge, heating, and N2O are included? | Whole-plant energy balance, dissolved/off-gas N2O measurement, and lifecycle assumptions. |
Recommended design-case workflow
A defensible project workflow begins with an eight-to-twelve-week characterization campaign across representative seasons, followed by bench or pilot testing with the actual wastewater. The test plan should deliberately include low temperature, low ammonium, high and low COD:N, wet-weather dilution, expected toxicants, and restart conditions. The preferred configuration should then be compared with conventional nitrification–denitrification and hybrid alternatives using the same effluent, resilience, energy, carbon, sludge, emissions, and capital-cost boundaries.
For the next design gate, document the assumed nitrogen-removal rate, minimum temperature, required biomass-retention strategy, NOB-control response, final-polishing duty, measured N2O factor, and fallback operating mode. The decision should be based on the complete treatment train rather than on the anammox reaction alone.
Related engineering resources
Read the parent Mainstream Deammonification and Anammox technology overview, and compare it with aerobic granular sludge, MABR, and AnMBR process pathways.
References
- Zheng, M. et al., “One-year stable pilot-scale operation demonstrates high flexibility of mainstream anammox application,” Water Research X (2023)
- Zhao, Q. et al., “Pilot-scale implementation of mainstream anammox for municipal wastewater treatment against cold temperature,” Nature Communications (2024)
- Cheenakula, D. et al., “Concept development of a mainstream deammonification and comparison with conventional process in terms of energy, performance and economical construction perspectives,” Frontiers in Microbiology (2023)