it is easy to think of a sulphur denitrator as a miniature DSB...but instead of relying on a large and deep sand bed to encorage the growth of denitrifying bacteria, Sulfur media is used to create the oxygen deprived space. Water is then passed thru this ''reactor'' and the bacteria consume it. releasing CO2 as a byproduct. This in turn is removed by placing crushed coral as a buffer. These type of reactors are popular in europe where they are mostly used in FOWLR type systems...or to control the initial nitrate spyke that comes from cycling a new tank.