Open loop vs Closed Loop

[Canoe]

It's still foam fractionation then no ? ... has to actually enter the gas phase. You pass water over beads or other packing material and blow air the other way. ...

Horizontal air stripper: no beads or other media, air bubbled into water in chambers, water flows from chamber to chamber, both DOS foam fractionation & VOC phase change.
Not optimal for either, but you get both cheaply. Much cheaper to run than media based stripping - can be optimized (well, not optimized, but biased really) for one versus the other, but not as good as VOC stripping with media providing tons of surface area for phase change, nor for DOS foam fractionation as water flow is cross-flow to the bubbles and therefore does not maximize bubble-to-water dwell time like a counter-flow system does.

To really optimize it for our requirement of foam fractionation of DOS, water flow modified from cross-flow (horizontal from chamber to chamber), to counter-flow within each chamber by the use of what we call a bubble trap in our sumps. Most (all?) skimmers I've seen are counter-flow, with the bubbles in the bottom and the water introduced in the top and taken out the bottom. A commercial dual foam-phase stripper could be cheaply modified by simply alternately closing-off the upper divider holes then the lower holes in the next chamber, but that effectively halves the number of working chambers. Our bubble traps to channel down-flow water out the bottom of one chamber and up and into the top of the next chamber would be way more efficient.

And as stated before: And there's the issue as to the bubble source, and a pump capable of supplying that much air... and at what cost to run and the noise...