Aeration Method
Abstract
Introduction and Objectives
One method used in the lab to get gases out of water is to aerate the water before it enters the system. This process requires a large amount of air to be pumped into the system, causing many little bubbles. The addition of more small bubbles to the system increases the rate of gas transfer. The gas in the water will then rise to the surface more rapidly. The contact time between the air and the water required to allow all or most of the gas to rise out of the water would thus be decreased.
The method of aeration for gas removal would require a high flow rate of air to be injected into the water. Pumps for getting air into the water are impractical to use in the Honduras towns that have AguaClara designed water treatment are not sustainable. Instead, the properties of gases and liquids can be used to create a sustainable method for infusing the water with small bubbles.
Henry's Law states:
At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Henry's Law can be utilized to pump air into the beginning of the system. A small hole in the pipe headed to the grit chamber at a point where the water is in free fall would create a pressure difference between the inside of the pipe and the atmosphere thus causing an influx of air. Henry's Law can then be applied to calculate the flow rate of air into the water. The density and velocity of the water after passing this hole can then be calculated. A time estimate for the amount of contact time between the atmosphere and water that is needed for all or most of the gas to leave the water can be calculated from those values.
A model of this process is being derived for the AguaClara systems.