Flocculation and Settling Rates

The rate of particle settling in a water column, representing a lake, pond, or any other water impoundment, can be described by Stokes Law  

Equation 9.13 shows that nonphysically and nonchemically interacting particles of a given density and relatively large diameter settle faster than particles with similar composition but relatively smaller size. Additionally, particles with a given diameter and a relatively large density settle faster than particles with the same diameter but a relatively smaller density. The rate of settling (Sr) in meters per hour (m s 1) can be described by 

Equation 9.15 points out that a small increase in particle diameter due to colloid agglomeration has a large impact on the rate of particle settling (Sr). 

Perikinetic agglomeration applies to a monodisperse suspension and can be represented by a second-order rate law  

If you need to decrease the double-layer thickness by half in order to induce colloid flocculation, calculate the change in salt concentration you would need to introduce. Explain whether this is a realistic approach for cleaning up water. 

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