Preliminary Treatment (Headworks)Intermediate 14 min read

Preliminary Treatment (Headworks): System Optimization

Class B headworks optimization: the settling-velocity physics behind grit separation, designing and operating flow equalization basins, estimating and legally disposing of screenings/grit quantities, and controlling headworks odor.

Every grit chamber on the planet is, at its core, exploiting one physical fact: sand falls out of water faster than sewage does. As a Class B operator, understanding why — and how that principle drives real design tradeoffs in equalization, disposal, and odor control — is what separates running the headworks from actually optimizing it.

The Physics of Grit Removal: Settling Velocity and Selective Separation

Grit removal works because grit and organic solids fall through water at very different rates, and every grit chamber design is really just a different way of exploiting that difference.

A particle's settling velocity (

v_s

) — how fast it sinks through still or slow-moving water — depends on its size, shape, and density (specific gravity) relative to water. Grit is traditionally defined as particles larger than 0.21 mm (a size referred to by its screen designation, 65 mes

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