Large treatment systems rarely disinfect or settle water in a single basin — water moves through a whole train of basins before it reaches the point where compliance is actually measured, and each basin along the way contributes its own share of theoretical time and its own short-circuiting behavior. This companion guide covers how to combine those stages correctly, and introduces the gold-standard method for measuring real (not estimated) contact time: the on-site tracer study.
Multi-Stage / Multi-Basin Detention Time Trains
A treatment train — for example, flocculation basin → sedimentation basin → filter → clearwell, or a two-cell chlorine contact chamber — routes the same flow, Q, sequentially through multiple basins. As established in the System Optimization guide, basins in series share the same Q, so: - Theoretical detention times add: $t_{total} = t_1 + t_2 + t_