 Needle Wheel Skimmer Theory
Some of the theory with a needle wheel is that the recirculated water is already relatively 'clean', so the bubbles you're adding flow upward through the water that has yet to be cleaned, absorbing DOCs as they rise, and the water falls. (concentrating the dirtier water near the inlet/riser tube) If designed properly, no bubbles will be inhaled by the needle wheel, and so the concern about "chopping up" bubbles that have already been loaded with DOCs is somewhat of a bunk concern.
I'm in the process of designing such a skimmer right now, and I've read that the most time consuming DOCs can take 2 minutes to fully attach to an air bubble, so that's a good target for your flow through rate if you want to make sure your skimmer is being as effective as is possible. |