Ammonia Breakthrough / Poor Nitrification
Effluent ammonia rises unexpectedly even though the system has nitrified reliably before.
Symptoms: effluent ammonia concentration climbing above permit limits or historical baseline, sometimes with nitrite also rising.
Probable Causes: dropping mixed liquor temperature, insufficient DO, low alkalinity/pH suppression, SRT too short for nitrifier growth, or a toxic/inhibitory industrial discharge.
Troubleshooting Steps: 1) Check mixed liquor temperature trend — cold weather may require extending SRT. 2) Confirm DO is consistently above 2.0 mg/L in the nitrifying zone. 3) Test alkalinity — supplement with bicarbonate or caustic if it's been depleted. 4) Rule out a toxic slug load by checking for unusual industrial discharges or spill reports. 5) If SRT has been trimmed for energy savings, consider extending it — nitrifiers need more time to reestablish than heterotrophs.
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