CHAPTER 7 – Gravity Separation: Gravity separation is a unit process in which gravity removes suspended solids and attached pollutants, floatables, and dispersed petroleum products. Removal is downward for solids denser than water (sedimentation) and upward for solids lighter than water, such as petroleum byproducts and litter (flotation). Vortex or hydrodynamic separation is another form of gravity separation. Laminar or coalescing plates take advantage of a special aspect of settling.

Some of the questions considered in Chapter 7

• What is Stokes Law and how may it be used incorrectly?
• Why is detention time not the appropriate criterion for sizing wet pool systems?
• What are the various types of vortex separators and how might they differ in performance?
• What are laminar plates and how might they be used in stormwater treatment systems?
• What is the significance of inlet and outlet design to the performance of wet pool systems?
• What are the alternative methods to size settling basins?
• Why is drawdown rate, not time, the correct criterion for extended detention basins, and why it matters?
• What are the special considerations in cold and semi-arid climatic region?

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