I have built numerous denitrifiers from coils to sand in the bucket methods of all types. To understand how they work you need to understand the bacteria. Anerobic bacteria do not consume nitrates as a food, but as an oxygen source. These bacteria evolved in a low oxygen envoriment, so through time they devoloped the means to extract oxygen from nitrates and producing the by-product of nitrogen gas. Even tho they need nitrate to lived they also need a food source, some type of carbon fuel. Thats my I always had better results with the bucket method if you could at least have a drip trickle coming out the bottom. I understand about over complicating, but even tho the nitrates will diffuse through the sand over time, organic carbons don't diffuse as easy and need some a little push through the sand. And btw the trickle will not effect anything as the areobic bacteria always are in the top couple inches and as they consume food they will consume all oxygen. Thats also why you need a little trickle because the anerobic will also comsume all the carbon food too, before the anerobic can. I am not saying the simply flow over method will not work, just a way to make it work better.
Even tho I have not tried it yet, vodka dosing at very small amounts over the rdsb should kick it into high gear also, since vodka is a high carbon food source.
Even tho I have not tried it yet, vodka dosing at very small amounts over the rdsb should kick it into high gear also, since vodka is a high carbon food source.