Velocity Gradient (Mixing)
Calculate the mean velocity gradient (G) in rapid-mix and flocculation chambers, G = √(P ÷ (μ × V)), from the dissipated power (W), the water dynamic viscosity (Pa·s) and the chamber volume (m³). The result, in s⁻¹, measures mixing intensity: rapid mixing needs high G (700–1000 s⁻¹) to disperse the coagulant, while flocculation uses low G (20–70 s⁻¹) to promote floc collision and growth without breaking them. Enter power, viscosity and volume.
Result
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Velocity gradient (mixing)
In coagulation-flocculation, the intensity of the agitation counts just as much as the chemical dose, and it is measured by the mean velocity gradient G, defined by Camp and Stein as G = √(P ÷ (μ × V)): the square root of the dissipated power P (W) divided by the dynamic viscosity of the water μ (Pa·s) times the chamber volume V (m³). The result, in s⁻¹, describes how much neighboring layers of water slide over one another. The two stages call for opposite regimes: rapid mixing needs a high G (700–1000 s⁻¹), a violent, short burst of agitation that instantly disperses the coagulant and destabilizes the colloidal particles; flocculation, by contrast, needs a low G (20–70 s⁻¹), gentle and prolonged agitation that promotes collision and growth of the flocs without breaking them apart — large, dense flocs settle far better. The product G·t (gradient × time) is used as a design criterion as well. Enter the power, the viscosity and the chamber volume.
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Calculate the coagulant consumption of a water treatment plant, consumption = flow × dose ÷ 1000, multiplying the treated flow (m³/day) by the coagulant dose (mg/L) set by jar test. The result, in kg/day, sizes the storage, dilution and dosing pumps for products such as aluminium sulphate, ferric chloride or PAC, ensuring efficient coagulation of colloidal particles. Enter the treated flow and the coagulant dose.
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Chlorine Demand
Calculate the chlorine demand of a water, demand = applied dose − chlorine residual, subtracting the measured chlorine residual (mg/L) from the applied chlorine dose (mg/L). The result, in mg/L, is the chlorine consumed by organic matter, ammonia, iron, manganese and other reducers before free chlorine remains for disinfection. Knowing the demand is essential to dose chlorine correctly and keep an adequate residual in the network without waste or underdosing. Enter the applied dose and the measured residual.
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