Coagulation and flocculation are the two decisive steps that transform murky, unstable raw water into clear, treatable water ready for filtration and disinfection. They neutralize the electrical charges (typically −15 to −30 mV zeta potential) that keep colloidal particles — often 0.01 to 1 µm in size — in permanent suspension, then bind them into settleable floc of 0.5 to 2 mm. What nature would take days, or even decades, to achieve through gravity alone is accomplished in just 10 to 45 minutes of controlled treatment.
Success depends on two tightly coupled variables: hydraulic mixing energy and precise chemical dosing.
- Rapid mix must deliver a velocity gradient (G value) of roughly 600–1,000 s⁻¹ over 30–60 seconds to disperse coagulant instantly.
- Flocculation then requires a gentler G of 20–70 s⁻¹ sustained for 15–30 minutes to grow strong, settleable floc without shearing it apart.
- Coagulant dosing — whether aluminum sulfate (10–80 mg/L), PACl (5–50 mg/L), or ferric chloride (10–100 mg/L) — must be controlled within tight tolerances, often ± 2–3 %, to stay within the optimal charge-neutralization window.
- Polymer flocculants are dosed at far lower rates (0.05–1.0 mg/L), where even a 0.1 mg/L deviation can shift floc strength, settling velocity, and filter run time.
Underdose, and turbidity breaks through — filter runs shorten, disinfection demand rises, and finished water risks exceeding the < 0.3 NTU target. Overdose, and chemical costs climb by 15–30 %, sludge volume increases, residual aluminum or iron rises, and floc becomes fragile and shear-sensitive. The margin between optimal and inefficient is often just a few ppm — and it shifts continuously with raw water turbidity, temperature, pH, and TOC.
That is exactly where LMI metering pumps make the difference: delivering ±1 % steady-state dosing accuracy, 10,000:1 turndown on advanced models, and stable, repeatable, jar-test-validated chemical addition — hour after hour, across every shift in raw water quality. From 0.1 GPH lab-scale trials to 300+ GPH municipal feed lines, LMI pumps give operators the precision coagulation and flocculation demand, so the chemistry behind clarification always performs exactly as designed.
