## Friday, August 04, 2006

### What is an Empty Bed Contact Time (EBCT)?

We receive many questions on calculating the Empty Bed Contact Time as follows: "How do I calculate the "Empty Bed Contact Time" for sizing my carbon bed?"

Calculating the Empty Bed Contact Time, EBCT, is fairly easy to do once you know that the EBCT has the units of time, and usually presented in minutes. You need to know the volume of the carbon bed in your vessel and the flow rate. Just watch to be certain your units are consistent.

For the units commonly used in the United States:
V = Carbon Bed Volume (cubic feet)
Q = Flow Rate (gpm)
C = Conversion Factor (7.48 gallons/cubic foot)

EBCT= (V x C )/ Q

The EBCT for some common contaminants are:

Chlorine = 2 minutes
VOC's = 7 minutes
Hydrogen Sulfide = 4 minutes

Anonymous said...

Wow...this is almost like rocket science! Thanks for the info.

Anonymous said...

thxs for posting EBCT

But how did you get conversion factor, which you shown 7.48 gal/cubic ft.

Because, 7.48 gal/cubic ft = 1.0001=1

so whts meaning of conversionj factor to consider, and if, in which case?

thxs

Anonymous said...

Actually, 7.48gal/cubic ft = 7.48 and the the reason for C is that V is in cubic feet and Q is in gallons. Because these are two different measurements for volume, the conversion factor is needed for an EBCT in minutes.

Anonymous said...

Ahh the joys of using the metric system....

Anonymous said...

how about if we want to calculate in SI unit? do we still need C conversion? Thanks

T Dupnik said...

Since I posted this definition of Empty Bed Contact Time for carbon filters, I have been receiving many comments on how to calculate. From my engineering courses (too many years ago for my liking), all you need is to get the units right and the answer is correct. In this case we want to end up with minutes as the EBCT.

So,
EBCT=V x C/Q where:
V is volume of carbon generally cubic feet or cubic meters

Q is flow rate of system generally gallons/minute, cubic meters/hr, or liters/minute

C is conversion factor. It is only needed to make the answer come out to minutes.

The metric system does not help too much. More than likely you will still need a conversion factor. For example, if you have a carbon volume of 3 cubic meters and a flow of 30 cubic meters/hr your EBCT=0.1 hour. In order to make the EBCT to be in minutes, you need a conversion factor of 60 minutes=1 hour. Therefore, the EBCT=6 minutes.

Doug said...

I wasn't sure if I should use the entire vessel volume or the bed volume, but you cleared it up. Thanks!

Anonymous said...

how to calculate define area of carbon or sand filters, is this formula compatible for all type of filters

Anonymous said...

Okay I understand the math. So are we saying that if my water flow is 1.5 GPM, does that volume of water moving have to touch the medium for the calculated time to be efficient?