Poor Settling
Solids Not Settling as Designed
When solids simply will not settle, the problem lies in the particle characteristics or the conditions they are given — chemistry, temperature and loading.
Understanding the Problem
Settling depends on particles being large and dense enough to fall faster than the upflow velocity. Fine, colloidal or low-density particles resist settling unless conditioned.
The usual levers are coagulation/flocculation (to build settleable floc), pH (to make the coagulant work) and temperature (which changes viscosity and settling velocity).
Confirm the influent has actually changed — a new upstream process or product can shift particle characteristics and defeat a previously adequate design.
Common Symptoms
- ›Persistent haze in effluent
- ›Slow or no floc formation
- ›Sludge blanket not consolidating
- ›Poor results despite correct sizing
Causes & Corrective Actions
Cause
Colloidal / non-flocculating particles
Corrective Action
Introduce or optimise coagulation and flocculation.
Cause
pH away from coagulant optimum
Corrective Action
Adjust pH into the effective range.
Cause
Cold water raising viscosity
Corrective Action
Derate loading; allow more settling margin.
Cause
Changed influent characteristics
Corrective Action
Re-characterise the water; re-tune chemistry and loading.
Prevention
Still seeing the problem?
Send us your operating data and effluent results. Our process engineers will diagnose the issue and recommend a corrective plan.