Depth vs. Surface Sand Filtration

Depth vs. Surface Sand Filtration

The big goal of this research is to understand the difference between surface and depth filtration and the parameters that determine which regime is operative. We suspect that subsurface injection of the water to be filtered shifts the regime to depth filtration. Begin by conducting a literature search to find discussions of depth and surface filtration.

Current Research

Depth filtration likely occurs when the fluid forces on the flocs that bridge across a pore in the filter bed exceed the strength of the flocs.  Thus the dimensionless parameter that determines whether depth or surface filtration occurs must include both floc strength and pressure drop through a thin layer of flocs. Pressure drop through a thin layer of flocs is influenced by the porosity of the flocs which is a function of their fractal dimension. Small flocs are less porous than large flocs and thus small flocs are less likely to produce surface filtration.

The laboratory research goals of this research are to determine the difference in head loss and particle capture efficiency between conventional rapid sand filtration where raw water is added above the filter bed and SRSF where the water is injected into the filter bed through slotted pipes.

Set up two filters in parallel that both receive the same raw water but with one filter operating as a conventional rapid sand filter and the other filter having the raw water injected below the surface of the sand.