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Periodically the filter becomes clogged with dirt and needs to be cleaned. At that time, the plant operator, will shut off the flow entering the filter and open a back wash drain and let the water drain out. Next, the clear well is opened and the water reenters the filter from the direction it left the filter. This water elevates the sand particles in the filter, loosening the dirt particles that were caught in the sand. The water carries away the dirt particles into the backwash pipe, but not the sand particles because those are heavier. The sand bed will expand 30-50% for optimal cleaning. To achieve this, there is an optimal height of water in the clear well and an optimal height of the clear well above the filter that we have to achieve. Once finished, the operator will close the back wash pipe and begin filtration again.
Our immediate goal is to determine the flow rate needed to sufficiently expand and clean the sand filter bed. This will help us determine how high the clear well needs to be above the filter, how large the flow pipes should be, and how much water should be in the clear well.
Figure 1: Clear Well Basic Concept
Method
Our attempt to validate our clear well design consisted of three stages. During the first stage, we conducted a literature and online review of existing filtration technology and research. We then developed a MATHCAD file to generate filtration design parameters given state inputs. We then conducted bench scale experimentation of design parameters produced from the MATHCAD file.
Click here for the Synopsis of literature and online review of existing filtration technology and research.
Click here for the description of the MATHCAD file and description.
Click here for the Fluidization Velocity Experiment.
Click here for the Expanded Bed Headloss Experiment.
Results and Discussion
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Plan of Action for Remainder of Spring 2010 Semester
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