I have a bunch of anchors to spec for a wastewater treatment plant to secure FRP grating and sections to concrete. What is the best material to use? 316 Stainless or a duplex alloy threaded rod epoxied in place?
If there are real loads then you need to use real anchors (Hilti or such).
If you are just trying to hold things in place then using epoxy and duplex SS makes sense.
Don't use a threaded rod, the part that is potted should not be threaded. All of the crevices can lead to corrosion issues.
Make sure that water cannot pool at the anchors, assure that the epoxy does not settle and form a pocket.