Process Control · Hydraulic & Organic Loading
Solids Loading Rate (Clarifier)
Mass of solids applied per unit clarifier area per day, a check independent of hydraulic (flow-based) loading.
Solids Loading Rate = (MLSS, mg/L × Flow, MGD × 8.34) ÷ Clarifier Surface Area (sq ft), typically kept under roughly 20–30 lbs/sq ft/day for secondary clarifiers.
A clarifier can pass a hydraulic loading check (SOR) while still failing a solids loading check if MLSS is running unusually high, so both need to be verified separately.
Solids loading, not just flow, is often the true limiting factor when a plant considers raising MLSS to extend SRT during colder months.
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