Coil Denitrator

[mwood]

I am considering building a coil denitrator. The issue is I have limited space, and plan to mod the design just a touch to make it fit. I would like to understand the principles of a coil denitrator before starting. I have a couple of questions. Why does running water through a coil of tube reduce the oxygen in the water? Is there a relationship between the length of the tube and the size of the boiball chamber? What causes it to smell like rotten eggs of it runs too slow? What would be a good water pump to use, I have a rio 600 laying around.

Thanks
Marcus

[rutledgek]

Why does running water through a coil of tube reduce the oxygen in the water?

Because any aerobic bacteria living in the tube will use the oxygen to break down the ammonia and nitrites in the water.

Is there a relationship between the length of the tube and the size of the boiball chamber?

Well the tube is usually coiled in the bioball chamber so you need at least a length long enough to hold at least 75ft of tubing.

What causes it to smell like rotten eggs of it runs too slow?

There is a sulfer compound that forms in the process of breaking down nitrates into nitrogen gas. This produces the rotten egg smell. On thing to do that I have seen in many plans is to aerate the water as it comes out.

What would be a good water pump to use, I have a rio 600 laying around.

Again, most of the planst that I have seen do not use a pump because the amount of water moved is actually a dripping. or a small trickle.

I hope this has been helpful and anyone else can comment on the accuracy. I was going to build one myself but I just dont have the space for one currently. Maybe in the future.

[mwood]

If you don't use a pump, what moves the water?

[Randy Holmes-Farley]

Actually, I think it is mostly oxidation of the carbon source added (often methanol) that reduces O2 and then nitrate. Ammonia conversion would be a fairly small contribution in most cases. That's why the carbon source is necessary.

The rotten egg smell happens when the anaerobic bateria that were converting the nitrate into N2 begin to use sulfate instead of nitrate, producing hydrogen sulfide instead of N2.

I am not an expert on the engineering of such systems, so can't help much with that, but I do discuss the chemistry involved in this article:

Nitrate Issues
http://www.advancedaquarist.com/issues/august2003/chem.htm

from it:

"6. Use a carbon-driven denitrator. There are a variety of different commercial systems available, none of which are especially popular in the United States at this time. However, they can do a good job of removing nitrate and some aquarists quite like them.

In one of these types of systems, a carbon source is added to a portion of tank water in a low oxygen environment. In many cases, the carbon source is methanol. The methanol is mixed with aquarium water in a controlled situation (such as fluid pumped through a coil) and the methanol is consumed by bacteria that use nitrate as an electron acceptor instead of oxygen:

12 NO3- + 10 CH3OH + 12 H+ ---> 10 CO2 + 6 N2 + 26 H2O

The end result is that nitrate is removed from the aquarium. The typical drawback to such a system is the need for careful control over the conditions, and the consequent complexity that often accompanies such a reactor. "