Polymer / Flocculant Dosing & Make-Down Equation
Polymers (polyelectrolytes) are sold as dry powder, emulsion or liquid, but always made down to a 0.1–0.5% working solution before dosing. Neat dose is typically 0.5–10 mg/L of feed flow for clarification, or 3–15 kg active per dry tonne of sludge for dewatering. The make-down step is critical — under-aged or over-mixed polymer loses 30–60% of its activity.
Where:
- Flow = Main flow rate in m³/hr
- Dose_PPM = Target concentration in mg/L or ppm
- Strength_% = Percentage active ingredient of the stock chemical
- SG = Specific Gravity (density relative to water) of the stock
Related dosing calculators
Other chemical-specific dosing calculators in the same series — same formula, different defaults:
- Chemical Dosing Calculator (generic) — the universal seed page
- Coagulant Dosing Calculator — Coagulation · PAC · FeCl₃
- Alum Dosing Calculator — Coagulation · Jar Test Scale-Up
- RO Antiscalant Dosing Calculator — RO · Desalination · Membrane Protection
- All Chemical Engineering Calculators →
Frequently Asked Questions
3–8 kg active polymer per dry tonne of sludge for belt presses; 5–12 kg/dt for centrifuges; 8–15 kg/dt for screw presses. For a 100 kg/hr dry-solids feed at 8 kg/dt: 0.8 kg/hr active polymer. From a 0.3% working solution that is 267 L/hr of dosing solution.
Polymer chains take 30–60 minutes to fully hydrate and uncoil after dilution. Without ageing, only 40–60% of the molecular activity is available. Standard practice: 2-tank make-down with 30 min retention, transfer pump to dosing tank, slow agitation, dose from there.
Cationic (positive charge): for organic / biological / municipal sludge. Anionic (negative charge): for inorganic / mineral sludge or alum-floc thickening. Non-ionic: for low-charge waters as a coagulant aid. Use a beaker or jar test to confirm — wrong charge polymer gives zero performance.
No — neat polymer (35% emulsion or 100% powder) is too viscous to disperse evenly in the process stream. It will form 'fish-eyes' (gel balls) that pass through unmixed and waste 50%+ of the chemical. Always dilute to 0.1–0.5% working strength first.
Working-strength polymer (0.1–0.5%) keeps activity for 8–24 hours; stronger solutions (>1%) degrade in 4–8 hours. Always make down only what you can dose in one shift. Do not store overnight without antimicrobial preservative.