Page History

...

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

...

1. Measure the oxygen concentration in the water after the supersaturator using a dissolved oxygen probe. Take a sample (install a manual sample valve if necessary) and then measure the dissolved oxygen concentration. Compare this with theoretical values.
2. Measure the oxygen concentration after the bubble collector. You can use the MathCAD file I sent to calculate the resulting equilibrium concentration of oxygen. Note that the oxygen concentration will not be the same as the concentration we would get from equilibrium with the atmosphere.

Comments

The theoretical bubble formation potential is about 18 mL/L for water that was exposed to 1 atm gage pressure at 25 C. We are only removing about 5 mL/L. We need to determine if the supersaturator is producing water that is in equilibrium with 1 atm gage pressure by measuring the dissolved oxygen concentration.

...

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.

In order to better understand what is happening in the system in term of gas removal, we plan to measure the oxygen concentration in the water before and after the pressurized aerator using a dissolved oxygen probe. Additionally, the oxygen concentration will be measured before and after the sand filter and the bubble collector. The values collected will be compared to the theoretical model to better assess the functionality and efficiency of the system.