This standard provides guidelines for the design and selection of rapid mixing devices used in the coagulation stage of water treatment plants. It details the purpose of rapid mixing, outlines various types of devices (mechanical, hydraulic), and establishes key design criteria like velocity gradient (G), detention time (t), and the Gt value.
Guidelines for rapid mixing devices
Quick Reference Values
Recommended Velocity Gradient (G)700 to 1000 s⁻¹
Recommended Detention Time (t)20 to 60 seconds
Recommended Gt Value (Camp Number)20,000 to 60,000
Minimum Velocity Gradient (G)300 s⁻¹
Typical Baffle Spacing in Baffled ChannelNot less than 450 mm
Key Formulas
G = sqrt(P / (μ * V)) — Velocity Gradient (Camp and Stein equation)
Practical Notes
The primary goal is the near-instantaneous dispersion of coagulant; achieving a precise Gt value is secondary to preventing short-circuiting and ensuring uniform chemical distribution.
For mechanical mixers, the impeller type (e.g., radial flow turbine) and its position within the tank are critical to creating the correct flow patterns and avoiding dead zones.
Hydraulic methods like baffled channels or hydraulic jumps are effective but offer less operational flexibility compared to mechanical mixers, as mixing energy is dependent on flow rate.