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The current relationship between the volume of gas removed over time considering sand grain size or bed depth is found to be fairly constant. 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 the local absolute pressure and the gas composition of potential bubbles will not form bubbles. We predict that, as the concentration of gases decreases, fewer bubbles will form and fewer will grow large enough to float away from the sand filter.
Additional Tasks
A mathematical model of the system suggests that 18 ml of gas should be able to be removed by the sand filter system. However, experiments performed last semester indicated a removal of 5.09 ml/L with Sand 40 (grain size 0.42 mm - 0.59 mm) and even lower removal with larger sand grains. While it is likely that the conditions of the sand filter may not be suitable to remove 18 ml/L, it is also likely that other components of the system are not functioning ideally. It was assumed that the dissolved gas concentration in the aerator had enough time to equilibrate with the 2 atm of absolute pressure in the apparatus; however, that may not be a completely valid assumption. Additionally, the bubble collector may not be collecting all the bubbles that leave the sand filter.
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