Current Research
Procedure
The experimental setup consists of a vertical glass tube that is 63 cm long with a 2.5 cm diameter. The glass tube is partially filled with sand, and tap water is sent upward through this tube. The tap water cannot be guaranteed to be super-saturated with oxygen already, so the aeration apparatus previously used by the aeration method has been implemented to supersaturate the cold water before it is fed through the glass column. The aeration chamber is kept under 1 atmosphere of pressure while the water is bubbled by an aeration stone. Air is allowed to leave through a valve attached to the aeration apparatus and controlled by [Process Controller] and a rotameter, which restricts its flow to maintain pressure inside the chamber.
From the bubble chamber, the super-saturated cold water joins hot tap water and flows through 1/4" tubing into the flow accumulator, which uses a pressure sensor, temperature probe, and two valves controlled by [Process Controller] to regulate the flow rate of water, which is altered to achieve the desired level of suspension of the filter media in the glass column, and the temperature of the mixed water, which is set to 20°C.
The mixed water passes through the flow accumulator and into the glass column through 1/4" tubing, suspending the filter media in the glass column. After flowing through the suspended filter media, the water and any bubbles that formed in the process pass into the bubble collector.
The bubble collector is made of a 1.5"- diameter PVC pipe that is sealed at both ends. Water and bubbles from the glass filter column enter the chamber through 3/8" tubing that connects the top of the glass filter column to the bottom of the bubble collector. Inside the chamber (which is initially filled with water before each experiment), bubbles float to the surface while the water flows out through 3/8" tubing attached the bottom of the bubble collector. A 1/4" tube attached to the top of the bubble collector allows air to enter and leave. This tube as well as the water outflow tube at the bottom are both controlled by valves that are opened and closed by [Process Controller], which uses a pressure sensor to monitor the water level inside the chamber.
At the start of an experimental run, the bubble collector chamber is nearly filled with water, the air valve at the top of bubble collector is shut, and the water outflow valve at the bottom of the bubble collector is open. As bubbles enter the bubble chamber and gather at the top, the water level in the chamber slowly sinks. When enough bubbles have entered the chamber to lower the water level as far as possible, the outflowing water valve is shut and the air valve is opened, allowing the chamber to refill. When the water level in the chamber reaches the maximum level again, the air valve shuts and the water valve opens, and the process begins again. The chamber can be drained by opening both valves at the same time. The system continues running during all of these processes in order to keep conditions as constant as possible. The water level inside the chamber can be visually monitored through an additional 1/4" clear plastic tube that is attached to the top and bottom of the bubble collector.
The rate at which the water depth changes during a run is the same as the rate that air is being added to the collector, and so this is proportional to the rate that dissolved gases are being removed from the super-saturated water. Our data can be used to find the volume of dissolved gases removed per liter of water that flows through the system, allowing us to compare the relative effectiveness of each sand size, flow rate, and bed depth combination.