Basin overflow rates are calculated in exactly the same way that filtration rates are calculated. To easily visualize this procedure, think of a long sedimentation basin that is feeding its settled water into a filter. The filtration rate of the filter is the number of gallons per square foot of filter surface area that flow downward through the filter per minute. The basin overflow rate is the number of gallons per square foot of basin surface area that flow upward and out of the basin per minute, as if the basin level were slowly rising up and overflowing.
Filters have much less surface area than the much larger sedimentation basins. Yet, the same number of gallons is flowing out of the sedimentation basin that is flowing into and through the filter. If two gallons per minute is flowing through each square foot of filter surface, only a fraction of that two gallons is flowing up and out of each square foot of basin surface.
Below is a set of problems. Both problems assume that the flow is 600 gpm. One problem calculates filtration rate by dividing the flow by the number of square feet on the filter surface. The other problem calculates basin overflow rate by dividing the flow by the number of square feet on the basin surface.
1. A filter is 10 feet by 15 feet. The flow through the filter is 600 gpm. What is the filtration rate?
Answer: First, multiply 10 x 15 to obtain a filter surface area of 150 square feet. Next, divide 600 by 150 to obtain a filtration rate of 4 gallons per square foot per minute.
2. A basin is 10 feet wide by 90 feet long. The flow through the basin is 600 gpm. What is the basin overflow rate?
Answer: First, multiply 10 x 90 to obtain a basin surface area of 900 square feet. Next, divide 600 by 900 to obtain a basin overflow rate of .67 gallons per square foot per minute.
Sunday, June 7, 2009
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