Filtration Rate

As a surface water operator, one of the commonly used math equations is for calculating the filtration rate of their conventional plant. There are two parts of the equation: flow in gallon per minute (gpm) and surface area (sqft) of the plant’s filters. Sounds easy enough? So let’s try a practice problem.

What is the filtration rate of a conventional plant that has two filters that measure 8 ft long by 12 ft wide and the flow of the plant is 800 gpm?

To find the filtration rate, its best to write out the formula:

FR= Flow (gpm) ÷ Surface Area (sq ft)

Now we plug in the numbers we have been given. While also using the area formula of a rectangle which is width x length. You must also remember to read the question twice. This plant has two filters so we must take our surface area and multiply it by two.

FR= 800 gpm ÷ ((8×12) x 2)

Once we have solved for both numbers in our formula we now just divide and find the filtration rate.

FR= 800 gpm ÷ 192 sqft

FR= 4.2 gpm/sqft

Now that we worked out the example, try this practice problem:

The treatment facility has four filters, each one measuring twenty five feet square.  The flow rate at the plant is 7000 gpm.  What is the filtration rate?

To check your answer, click here.

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