## 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?