I've been using a wet-dry sump type filter for the last year as part of
a well rounded approach to denitrification
For denitrifacation, you need anaerobic bacteria(low oxygen). wet dry filters
produce aerobic bacteria because of the oxygen rich water passing over the
filter media. aerobic bacteria is great (much better than anaerobic) for
converting ammonia to nitrite, then to nitrate, but thats where it stops, and
the nitrates will continue to build. You would get better denitrifacation by
removing the filtermedia, so the aerobic bacterai wont compete with the
anaerobic bacteria. Let the anaerobic bacteria grow, so it can perform
denitrifacation to its full potential.