rate of flow thru carbom

[astroboy]

Does anyone have any thoughts on what the optimal rate of water flow thru activated carbon might be?

 

I was reading this article:

www.pets-warehouse.com/carbon.htm,

 

where someone does some actual tests on how much carbon should be used in a tank. There's one interesting paragraph on the second page:

 

A popular canister filter for carbon use has a flow rate of 250 gallons per hour. Evidence suggests that adsorption rates decline when water moves past the carbon faster than 65 milliliters per minute, roughly one gallon per hour. Spotte recommends that no more than one tank volume be circulated through the carbon per day. Using Thiel

[Origami]

I'm not sure if the 65 milliliters per minute is supposed to be 65 millimeters per minute or not....

 

 

My current set up has a Rio 600 (200 gph) sending water thru a three inch diameter container filled with carbon.

The velocity of the flow works out to about 50 mm/sec. The volume of the flow works out to about 5 ml/sec.

 

They probably mean 65 milliliters (not millimeters) per minute. That's the flow rate (volume per unit time).

 

200 gph equates to 12,617 ml / minute or 210 ml / second.

 

I've not read the article but I will. Off hand, though, it would seem to me that rate of adsorbtion should be mediated by contact time with the media and concentration of the compound to be adsorbed (not absorbed). If that were the case, I have difficulty understanding why a low flow is better than a high flow in a recirculating system (such is the case in our tanks).

 

I neither flow fast nor slow through my reactor, though I do throttle back the flow enough so that the media is not tumbling so aggessively as to abrade but enough that it stays open to flow.

Edited February 6, 2009 by Origami2547

[astroboy]

They probably mean 65 milliliters (not millimeters) per minute. That's the flow rate (volume per unit time).

 

200 gph equates to 12,617 ml / minute or 210 ml / second.

 

Oops. Typo. I got 200 gph as 210 ml/second also...

 

I guess I'm not clear on this: I could have 65 ml going thru a pound of carbon each second, or a few grams. That's sort of comparing apples and oranges, isn't it?

[Origami]

The way I read the study, the author used a powerhead supplying 1500 ml/min (or 23 gph) thru 20 grams (0.7 ounces) of GAC (granular activated carbon) in his experiment (which recirculated 4 liters of sea water containing yellowing organics) over 12 hours. From this, he concluded that GAC from lignite offered the best price / performance ratio.

 

While he mentions the lower flow rate in other, different, experiments, he does not indicate how these other tests were set up. That is crucial information to have before you can compare what the author has done with what others have done.

 

However, you can, from reading the author's paper, gather that a lignite GAC can remove nearly 90% of yellowing gelbstoff under comparatively high-flow conditions.