PAC Dosing Problems | Overdose, Residual Al, Seasonal Drift

Underdose: pin floc, cloudy supernatant, colour still in the weir, polymer “does nothing.” Raise PAC in small steps after you confirm flash-mix energy and that powder is fully dissolved. Do not dump extra polymer first.

Overdose: fluffy or sticky sludge, clarifier blanket rising, filters blinding, residual aluminium high on the outlet. Cut PAC 10–20% and re-check pH. PAC that is not dissolved (lumps in the day tank) behaves like underdose even when the pump setpoint looks high.

Dissolve powder PAC as a 2–5% stock with agitation; dose into the flash-mix zone, then polyelectrolyte on slow mix. Reverse order or dosing dry powder into a pipe wastes product. Liquid PAC (10–18% Al₂O₃) is not interchangeable kg-for-kg with 28–30% powder — convert on Al₂O₃ from the COA.

If floc forms in the flash mixer and then shears, the problem is energy or retention, not “weak PAC.” Fix mixing before you change grade.

Monsoon and campaign dye loads in Gujarat raise turbidity and colour overnight. Re-jar; do not copy last April’s dose. Winter can slow floc on alum more than on PAC, but PAC still needs a fresh ladder if temperature and alkalinity moved.

Keep a log: inlet NTU/colour, PAC kg/day, polymer kg/day, outlet clarity, sludge comments. That log is what a Vadodara supplier can use to suggest a trial grade — not a generic “PAC 30%” email.

If PAC dose keeps climbing and colour/phosphate still fail, the next trial is often ferric chloride as an assist — see PAC vs Ferric Chloride. If sludge volume is the complaint on alum, the comparison is PAC vs Alum, not a higher PAC pump setting.

Drashti Chemicals stocks PAC 28–30% from Vadsar with batch COA. Share your last jar-test ladder and current kg/day for a documented bulk quote — no list prices.