1Symptom
The blowers deliver more air than before for the same load and DO, or DO cannot be held even with high airflow. You may see large boils, uneven bubbling, or areas of no bubbles.
2Check first
- Walk the basin surface. Note boils (broken diffuser or pipe), dead areas and coarse bubbling.
- Trend blower discharge pressure over months. Fine bubble membrane fouling raises pressure and lowers efficiency.
- Check air header drain legs for water.
- Check for surfactants or grease that lower alpha.
- Confirm the air flow meters and DO probes read correctly.
3Possible causes
- Diffuser fouling or scaling (biological slime, calcium, iron).
- Membrane hardening or tearing.
- Broken pipe, loose diffuser, or failed gasket creating a boil.
- Surfactants, grease or high MLSS lowering alpha.
- Water in the air piping.
4Next investigation
- Run a dynamic wet pressure check or ask the manufacturer for a test.
- Compare air per pound of oxygen required against design.
- Inspect a grid when a basin is drained.
5Corrective actions
- Bump or flex membranes if the manufacturer allows (brief high air rate).
- Clean diffusers (acid gas cleaning, hosing, or replacement) on a planned schedule.
- Repair boils and drain water from headers.
- Control grease at the source.
6When to call for help
- The basin needs to be drained, which affects capacity.
- You need to estimate transfer efficiency for a budget or design decision.
Make one change at a time, record it, and follow your plant procedures and permit. If you suspect a toxic discharge, a safety hazard or a permit violation, notify your supervisor right away.
This guide also appears on ActivatedSludge.com, our consulting site. Results are for training and operator use; always follow your plant’s procedures.