CrypticLifestyle, I will find that answer out for you tomorrow night in my Chemlab class, I will take one piece of Matrix and one BBq scrubber into lab class with me and examine it and hopefully photograph it adnd I will post the findings here, I might be able to get some grad students to chem analize it for us too.
I'll be waiting for mass spectrometry results then. But seriously, I don't think you'll find many helpful graduate students, trust me, I know from experience. I was one of them
I think, and I'm not an expert by any means, the actual process in denitrification involves bacteria reducing nitrates to nitrites, and then reducing that to two things; nitrogen gas and ammonia. The part that's converted back to ammonia will get used again by the bb, but the part turned into nitrogen gas is not usable and is lost to the atmosphere.
Neither am I, my research had nothing to do with soil bacteria
A quick search on Pubmed reveals that denitrification generally involves bacteria reducing nitrates to nitrogen through the nitrite intermediary. There are some bacteria that just leave it at the nitrite step (meaning it would be available for beneficial bacteria), while some take it all the way to nitrogen gas.
While direct reduction to ammonium from nitrates is possible, apparently it is rarer than going through the nitrite intermediate.
I still find it hard to believe that an anaerobic environment could exist in a canister filter with good flow and porous media. Now, if it were a plenum, I could see it happening.