Ironically anoxic bacteria[ab] are the main work horse in very large waste water treatment plant in reducing nitrates very effectively.I suggest that a few hours spent on searching this forum for "denitrification" would answer a lot of the questions. It has been explored ad nauseum. Dentrification can be done (I've done it) in a FW aquarium. However, it can only shave a relatively small amount of NO3 and, as someone mentioned, water changes dwarf denitrifiers in their ability to reduce nitrates (if that's what you really want to do in a planted tank). It's simply not worth the effort.
If you have nitrates so high that you need to reduce them, anoxic bacteria are not going to make much of a dent. You would be far better off looking at the source of the problem, which is likely organics issues and, if this is the source, the organics are going to contain a lot more problematic things than just nitrates.
I think they use ab floc held in supension.[?] And after a period the whole section is moved foreward in the line, by the system flow.
At the moment more tweaks are done to turn the 'dwarf'' into giants denitrifiers in FW aquarium. lol