Unit Filter Run Volume

Why to Use UFRV not Filter Run Time

Why to Use UFRV not Filter Run Time

July 24, 2018 – Filter run time does not tell the entire story for conventional granular media filters–here’s why.  Of course, treatment plant operators want long filter runs to stretch out the time between backwashes.  However, if hydraulically lightly-loaded, are the filters really performing well?

Filter Run Time

Instead, what should be looked at is throughput per unit area before backwash or Unit Filter Run Volume (UFRV):
UFRV = [(Filter Rate) x (Run Length)] / Filter Area

UFRV also provides a metric so filters of a different total area may be compared.

UFRV Chart

Source: AWWA ACE17 SUN01 Workshop, 06/11/17
At this month’s KY/TN WPC18, I helped present a paper on Nashville’s Omohundro WTP, which is in the  National Register of Historic Places. The nozzle-based, monolithic filters built back in 1929 are consistently running at UFRVs of 10,000 gal/sf —  Talk about long-term performance! The calculation is provided here.
If you’re an operator at a plant with conventional granular filters, I encourage you to calculate the UFRV of all the filters on a regular basis. If the values are closer to 5,000 than 10,000 gal/sf, you should investigate for potential improvements. Further, through trending, you can identify any concerning changes you may have over time.

Call us at ORTHOS if you have any questions!  (843) 987-7200


Remember Orthos’ HUGE life cycle cost benefits – At the end of the filter’s life cycle (~25 years), in contrast to a complete plastic block or folded sheet metal underdrain overhaul, nozzles are simply replaced, potentially saving $Millions.
“No need to replace the chandelier when all you must do is change out the light bulbs!”

Centurion Monolithic Filter Underdrain

ORTHOS is celebrating our 2018 platinum anniversary of ZERO monolithic filter underdrain failures

Traditionally, the 20-year anniversary gift is breakable china, but that would be like the multitude of plastic block or folded sheet metal underdrain failures –not ORTHOS!  We’re going platinum!

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