When dissolved oxygen (DO) falls or the clarifier starts to carry solids, first verify the reading. Then read the air, incoming load, and sludge trends together. A single number rarely identifies the cause.
See what changed
- Air and demand. Verify the DO probe, air delivery and distribution, and recent changes in incoming load. At ET-01, DO drops from 2.2 to 1.0 mg/L while indicated airflow stays steady and COD load increases. Both real air delivery and increased demand deserve a check.
- Settling and separation. Look at the settling curve, blanket depth, influent flow, return and waste sludge, and the outlet solids. Slow settling, fine floc, hydraulic carryover, and sludge that settles and later floats leave different clues.
Read two cylinders
SV30 is settled sludge volume after 30 minutes. Divide it by mixed liquor suspended solids (MLSS) in g/L to estimate the sludge volume index (SVI). ET-01 changes from 280 ÷ 2.8 = 100 mL/g to 480 ÷ 2.9 ≈ 166 mL/g. The larger value and a rising blanket support a solids-separation problem. Compare similar samples and investigate the cause before changing settings. For a discharge at risk, use the authorized response and verify that any available holding capacity is adequate.
Further reading · Ohio EPA activated sludge troubleshooting guide
Leave a Reply