Coagulant Dosing Calculator

The calculator applies a coagulant-specific alkalinity consumption factor — 0.92 mg/L alkalinity per mg/L of ferric chloride versus 0.44 for alum — reflecting the real chemistry difference between ferric and aluminum salts reacting with water's natural bicarbonate buffering. At the same mg/L dose, ferric chloride will therefore show roughly double the alkalinity draw and a correspondingly larger estimated pH drop.

Coagulant Feed Rate (lbs/day) is the dry-chemical-equivalent dose from the standard flow × dose × 8.34 formula. Liquid Feed Rate divides that by the coagulant's specific concentration and specific gravity, since coagulants are delivered as liquid solutions of varying strength — for example, PACl's low 10% concentration means its liquid feed rate in gallons/day is much higher than alum's 48% solution for the same dry-chemical dose.

It's explicitly a rough approximation — alkalinity consumption divided by 50 — not a real acid-base equilibrium calculation. It's meant as a flag that a meaningful alkalinity or pH shift is likely, prompting you to verify with actual jar-test or online monitoring data rather than relying on this number for dosing decisions.

The calculator treats polymer as a separate flocculant aid priced independently from whichever primary coagulant (alum, ferric chloride, ferric sulfate, or PACl) you select, since polymer type and pricing don't correlate with the coagulant choice. If your actual polymer contract differs from $2.50/lb, the reported daily and annual polymer costs will be proportionally off even though the feed-rate calculation itself is unaffected.

Those two volumes are sized purely from flow rate and fixed detention-time assumptions — 30 seconds for rapid mix and 25 minutes for flocculation — not from dose, turbidity, or coagulant type. They're meant as a starting point for basin sizing based on hydraulic residence time, not a dose-responsive result, so use them alongside your own G-value and basin geometry checks.