Managing High Ammonia and Phosphorus in Wastewater Treatment: Practical Operator Solutions

Solving High Ammonia And Phosphorus In Wastewater Treatment Plants

Operator‑focused guide • Practical diagnostics, fast fixes, and prevention

Elevated ammonia and phosphorus in effluent often signal biological imbalance, chemical under‑dosing, or hydraulic stress. This guide gives operators a field‑ready framework to diagnose causes, implement quick wins, and lock in stable compliance with nutrient limits.

Understanding Ammonia And Phosphorus Targets

Ammonia (NH₃‑N): Indicates nitrification performance; high values show poor conversion to nitrate.
Phosphorus (TP/Ortho‑P): Indicates biological or chemical removal efficiency; high values risk eutrophication.
Goal: Maintain stable nitrification and phosphorus removal to meet permit limits and protect receiving waters.

Common Root Causes

High Ammonia

Low DO: Nitrifiers require >2 mg/L DO; insufficient aeration stalls conversion.
Cold temperatures: Nitrification slows in winter; sludge age must be increased.
Toxic shocks: High load of solvents, metals, or pH swings inhibit nitrifiers.
Sludge age: Too low MCRT; nitrifiers wash out.

High Phosphorus

Biological P removal upset: Poor anaerobic/anoxic selector function; insufficient volatile fatty acids (VFAs).
Chemical dosing issues: Alum/FeCl₃/polymer under‑dosed or poorly mixed.
Hydraulic short‑circuiting: Clarifier bypass or poor solids capture lets P‑rich biomass escape.
Sludge handling: Return liquors (centrate/filtrate) recycle phosphorus back to headworks.

Quick Diagnostics

Symptom	Likely cause	Fast check	Immediate action
High ammonia in final effluent	Low DO, short sludge age, cold temps	DO profile, MCRT calc, temperature	Raise DO, increase sludge age, adjust wasting
Ammonia spikes after toxic load	Industrial discharge shock	Influent monitoring, pH, toxicity screen	Isolate source, divert flow, add alkalinity
High phosphorus despite good solids capture	Chemical dose too low or poor mixing	Jar test, dose check, mixer inspection	Optimize alum/FeCl₃/polymer dose and contact
Biological P removal failing	Selector zones not anaerobic; low VFAs	DO in selector, VFA test	Restore anaerobic conditions; add carbon source if permitted
Phosphorus recycle from sludge dewatering	Return liquors high in P	Sample centrate/filtrate	Side‑stream treatment or dose chemicals at return

Fast Fixes

For Ammonia

Increase DO: Raise aeration setpoints; check diffuser condition.
Extend sludge age: Reduce wasting; target MCRT > 8–10 days in cold weather.
Add alkalinity: Ensure sufficient alkalinity for nitrification (7.1 mg/L alkalinity per mg NH₃‑N oxidized).
Protect nitrifiers: Monitor industrial inputs; isolate toxic loads.

For Phosphorus

Optimize chemical dose: Run jar tests; adjust alum/FeCl₃/polymer feed.
Improve mixing: Verify rapid mix and flocculation stages; repair mixers.
Enhance biological removal: Maintain anaerobic selectors; ensure VFAs available.
Manage recycle streams: Treat or chemically dose return liquors from sludge handling.

Control Targets

DO: ≥2 mg/L in aeration for nitrification.
MCRT: 8–12 days in cold weather; 5–8 days in warm.
Alkalinity: ≥50 mg/L residual in aeration effluent.
Phosphorus: <1 mg/L effluent (typical permit); optimize chemical/biological removal.

Action Plans

First 24 Hours

Check DO, MLSS, MCRT, alkalinity, and temperature.
Run jar tests for phosphorus removal chemicals.
Adjust wasting to extend sludge age.
Increase aeration intensity if DO low.

Next 7 Days

Trend ammonia, nitrate, phosphorus daily.
Microscopy for nitrifiers and PAOs (polyphosphate‑accumulating organisms).
Optimize chemical feed pumps and mixers.
Evaluate return liquors; consider side‑stream treatment.

Frequently Asked Questions

Does more air always fix ammonia?
Not if sludge age is too low or nitrifiers are inhibited. Air helps only if DO is limiting.

Can I rely only on chemicals for phosphorus?
Chemicals work but cost more; biological removal reduces chemical demand if selectors are healthy.

What’s the best quick test?
For ammonia: DO and MCRT check. For phosphorus: jar test with alum/FeCl₃.

Conclusion

Stable ammonia and phosphorus removal comes from balanced biology, adequate DO and sludge age, and optimized chemical dosing. Diagnose quickly, adjust aeration and wasting, and fine‑tune chemical feeds. Lock improvements with routine trending and side‑stream management.

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