Cloudy clarifier overflow, floc carrying over the weir or sludge floating to the surface are signs the plant is heading for a failed discharge sample. Most causes are simple to check. Work through this list before changing chemicals or suppliers.
1. pH has drifted
Every coagulant has a pH window: alum works best in a narrow band around neutral, while PAC and ferric chloride tolerate a wider range. A change in production upstream can shift effluent pH overnight. Check pH at the flash mixer before anything else.
2. Coagulant underdosed or overdosed
Too little coagulant leaves fine particles suspended. Too much can restabilise them and make the water cloudy again, and always wastes money. Run a fresh jar test on today's effluent to reset the dose.
3. Polymer not prepared properly
Polyelectrolyte that is lumpy, too concentrated or not given time to age performs poorly. Check the make-up concentration, mixing and ageing time. See Choosing a Polymer for preparation tips.
4. Wrong polymer or wrong dosing point
Polymer added too early is sheared apart in the rapid mixer; added too late, it doesn't mix in. It should go in where mixing is gentle but thorough. If floc stays small, the polymer charge or molecular weight may not suit your effluent.
5. Hydraulic overload
Flow above the clarifier's design rate gives particles too little time to settle. Check whether production has increased, or whether a pump is cycling and sending surges.
6. Sludge blanket too high
If sludge isn't withdrawn often enough, the blanket rises and solids escape over the weir. Measure the blanket depth and increase desludging.
7. Septic or rising sludge
Sludge left too long at the bottom goes septic, produces gas and floats up in clumps. In biological plants, denitrification in the clarifier causes similar floating sludge. Shorter sludge retention usually fixes it.
8. The effluent itself has changed
New products, cleaning chemicals, oils or detergents in the effluent can upset coagulation. Talk to production about what changed, and re-test the coagulant and polymer combination.
Need a different chemical?
If the problem is the chemical itself, compare alternatives with a jar test. We supply PAC, alum, ferric chloride, Poly DADMAC and SNF polyelectrolytes, with documentation, across South India.