What does a TSS level above 100 mg/L in gravity thickener effluent indicate?

A Total Suspended Solids (TSS) level above 100 mg/L in the effluent from a gravity thickener indicates that sludge is leaving the thickener through the effluent weir. In a properly functioning gravity thickener, the objective is to concentrate the solids by allowing the heavier particles to settle, while the liquid (supernatant) containing lighter particles is drawn off. When the TSS concentration in the effluent is high, it suggests that some of the settled solids are being carried over with the liquid, which often occurs when the sludge blanket is too thick or if the thickening process is not effectively capturing all the solids.

This situation arises typically when there are operational issues within the gravity thickener, such as inadequate retention time, poor settling characteristics of the sludge, or overloaded conditions. Monitoring TSS levels can provide critical feedback to operators about the performance of the thickening process and guide necessary adjustments.