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Research performed last semester focused on studying the effects of sand grain size on gas removal. We found that smaller sand grains provide more surface area per unit volume than larger grains, but grains that are too small are carried to the surface with bubbles and are washed away. Grain size also affects porosity �porosity- pore size of the sand bed, which affects the distance a gas molecule must diffuse to reach a surface. This also may affect aggregation of gas molecules to form larger bubbles. Further study of optimum grain size will be explored through MathCAD modeling, or through experimentation, if that is deemed necessary.

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Our hypothesis is that the behavior of gas removal over time will change. The current relationship between the volume of gas removed over time considering sand grain size or bed depth is found to be fairly linear at a constant rate. When the dissolved air concentration of the water is adjusted, the gas removal rate probably will be the same initially, then will decrease or level off as the gas concentration in the water reaches saturation at atmospheric pressure. This hypothesis is based on the notion that water that is not supersaturated with respect to atmospheric pressure will not form bubbles. We believe that as the concentration of gases decreases, fewer bubbles will form and fewer will grow large enough to float away from the sand filter.