Troubleshooting Center

Start from the symptom. Each guide walks through what to check, likely causes and what to do next.

Every guide follows the same order an experienced operator would: Symptom, Check first, Possible causes, Next investigation, Corrective actions, When to call for help. Prefer to start from what you see? Use the interactive Troubleshooting Matrix.

Settling and floc

High SVI

Sludge settles slowly and the blanket climbs. SVI above 150 mL/g and rising.

Pin Floc

Tiny, dense floc particles that settle fast but leave a hazy supernatant.

Straggler Floc

Large, fluffy, light floc particles floating in the supernatant and over the weirs.

Filamentous Bulking

Filaments extend from floc and bridge between particles. SVI high, blanket fluffy.

Rising Sludge (Denitrification in the Clarifier)

Clumps of sludge float to the clarifier surface with small gas bubbles.

Aeration and DO

Low DO in the Aeration Basin

DO below setpoint, especially at peak load or in the first zone.

Excessive DO and High Blower Demand

DO well above need and blower power higher than it should be.

Poor Oxygen Transfer

Lots of air, little DO. Coarse bubbling or rising header pressure.

Nitrification and chemistry

High Effluent Ammonia (Loss of Nitrification)

Effluent ammonia above normal or above the permit limit.

Low Alkalinity

Effluent alkalinity below about 50 to 70 mg/L, pH drifting down.

Temperature Effects

Seasonal changes in nitrification, settling, DO and foaming.

Toxic Upset Recognition

Sudden loss of treatment, dead protozoa, odd color or foam, OUR collapse.

Clarifiers and RAS

Increasing Clarifier Blanket

Blanket depth growing day by day or during peak flow.

Solids Washout and Hydraulic Overload

Storm flows carry blanket solids over the weirs.

RAS Problems

Thin RAS, plugged lines, uneven pump flows or flow meter errors.

Foam and effluent quality

Stable Brown Foam

Thick, greasy, chocolate brown foam that does not break down.

White Foam

Billowing, crisp white foam, often during startup or low MLSS.

Effluent TSS High

Effluent solids above normal or trending toward the limit.

These guides support, not replace, your plant's O&M manual, permit requirements, safety procedures and the judgment of your licensed operator in charge.

This guide also appears on ActivatedSludge.com, our consulting site. Results are for training and operator use; always follow your plant’s procedures.