Getting selenium to ppb is usually less about «stronger mixing» and more about selenium speciation + a polishing step. AVS (vortex layer) can intensify redox/precipitation and improve reagent contact, so it may help as a reaction accelerator in a chemical treatment train (similar to how GlobeCore describes AVS intensifying heavy-metal reduction/precipitation processes). But on its own, AVS is not a selective Se separator. In mining waters, iron co-precipitation works well for selenite, but removes very little selenate, and ppb targets typically require downstream clarification/filtration and often a final «polishing» technology (anion exchange, membranes, etc.). So: Yes, ppb is achievable, but usually with a multi-stage scheme (convert selenate ? selenite, co-precip/filtration, then polishing). AVS can be a useful intensifier in the reaction step-just don’t expect it to be the single device that guarantees ppb by itself.