Floating Floc Goals

Spring 2009 Team members

Tiffany McClaskey
Ling Cheung
Tanya
Haley
Wenny Wu

Spring 2009 Goals

This semester it is imperative that we find a solution to the issue of flocs rising to the surface of the water in the sedimentation tank. The Marcala and Tamara plants are seeing a significant amount of particles rising to the surface. Last semester the theory was that the water is coming into the plant super-saturated with oxygen. Once the water enters the grit chamber and is under atmospheric pressure, bubbles of oxygen begin to form. Some of these air pockets then attach to the sediment particles in the water. Flocs form around the bubbles that have not left the water during the time the water is in the grit chamber. Since bubbles form faster when they are attached to something (you may have noticed that your glass of faucet water develops bubbles on the sides), the idea is to put things in the water for the bubbles to form on. Larger bubbles rise faster than smaller bubbles, so the goal is to create the largest bubbles possible in the shortest amount of time. This semester we are going to look at the problem from the view of flocculation. We want the bubbles to "floc" together.

Ideas:

• Add air bubbles using suction through a small hole in the side of a down-flowing pipe right before the water enters the grit chamber. The air introduced to the water will increase the size of the bubbles that form as it joins the preexisting air pockets.
• Add sand to the bottom of the grit chamber to simulate backwash in a sand filter. The idea is that the dissolved oxygen in the water will form bubbles on the sand particles. Once the buoyant force is greater than the connection between the bubble and the sand particle, the bubble will rise to the surface of the water.
• Add the equivalent of lamellas to the grit chamber. Bubbles will form on the underside of the lamella and eventually become large enough that they slide across the lamella surface and float to the surface of the water.

A contraption will be made that we will use to simulate different situations to help us determine the best course of action. This device will be made of clear PVC and have attached to it a dissolved oxygen probe, a pressure probe, suction outlet, a hole for influent water, air pump, aerator stone, a stir bar at the bottom, and a place for the water to leave. The stir bar will help us model a complete mix system. The pressure probe will allow us to know the actual pressure in the pipe as we decrease the pressure using the suction outlet. The DO probe will allow us to track the rate at which oxygen leaves the water.

Several different experiments will be conducted:

• Adding air using the air pump and aerator and waiting to see how the extra bubbles affect the rate of decrease in DO.
• Possibly adding sand to the bottom and seeing how that affects the influent water.
• Aerating the water as it flows through to a basin that is under atmospheric pressure, simulating the grit chamber.
• Once the contraption is built, other experiments will likely come to mind

Literature searches into aeration and the "flocculation" of air particles in water will be conducted. The team member that finds each article will type up a summary which will be reviewed by the team.