Looking for a DIY denitrator (organic, alcohol fed) plan or how to...

[BigShot]

All of the DYI denitrator plans I've seen are based on the coil inside the denitrater. I've read that the ones where bacteris each organic balls and are fed with alcohol are much more efficient (like the Aqua Medic NitrateReductor1000).
Anyone have a how-to-do something like that at home? :-)

Thanks,
Luke

[ButterfyBoy]

They're actually not very complicated. Think of something very much like a calcium reactor -- basically a sealed chamber with a built-in recirculating pump. Instead of aragonite you have bioballs or whatever as a media (something with a fairly open structure, so you get even mixing and no dead zones). Really, the only major difference is that instead of a CO2 tank, you have a redox controller operating a dosing pump hooked up to the alcohol supply.

[BigShot]

butterfyBoy, thank for the info. I'm not sure about the dosing pump controlled with ORP controller, dosing alcohol. I though if I set the dosing pump (without a controller) to under 4 gph (I could just measure coming out water for nitrates) it would be fine. From what I understand, the dosing pump, 'rotates' the water from the tank to denitrator and back, and the feeding is done manually? Or do I have it wrong? Or do I need 2 pumps, one for the water and one for the alcohol?

thank you,
Luke

[ButterfyBoy]

Yes, it is also possible to feed manually (or continuously, via a slow drip) and use the dosing pump to control water throughput; a different methodology, but with the same basic effect. Either way, I personally would recommend using a controller. You don't have to use it, but it will make the system operate at its full efficiency. Let me see if I can explain a bit of the theory behind denitrification so you can see why.

People tend to assume that denitrifying bacteria "eat" nitrate, but it is really more correct to say that they "breathe" nitrate. Nitrate, NO3, is not the food source but the oxygen source; the bacteria remove the attached oxygens and thus reduce the NO3 to NO or N. This oxygen is then used to "burn" the carbon (from the alcohol) in a similar way to how we use oxygen to "burn" the carbon in our food.

Unfortunately, breathing nitrate isn't easy. A substantial amount of the energy produced by reacting those oxygens with that carbon is used simply to seperate the oxygens from the nitrate in the first place. It's not an efficient process, so in nature it doesn't happen unless it has to -- i.e. there is no other way to get oxygen. That's why denitrification only happens in an anaerobic environment, because if there is any free oxygen around the process isn't competetive.

Effectively, it's the redox value that determines what type of breathing reaction dominates. There is a fairly narrow range in which denitrification occurs.

If the redox value is too high, nitrate breathing isn't worth the energy it requires, because there is likely some free oxygen around to grab. Often, under these conditions, nitrate is reduced, but only partially, back into nitrite, NO2. This is why nitrate reactors often show a drop in nitrate but a rise in nitrite.

On the other hand, if the redox value is too low, it becomes more efficient to breath sulphate, SO4, which results in hydrogen sulphide as a byproduct -- that lovely rotten egg smell we're all so familiar with.

Basically, the principle behind a denitrator -- any denitrator -- is to create an environment within that redox range. The beauty of the carbon-fed closed reactors is that they give us the ability, with the aid of a controller, to actually regulate that range rather than relying on trial and error or guesswork.

There are two ways that the redox within the reactor can be controlled. I suggested one, you thought of the other. Lets look at the approach you were thinking of first.

In this method, the food level within the reactor is kept basically constant. There is always alcohol available to the bacteria, so they are always active, reducing first the available oxygen, then the nitrate, then the sulphate. Thus, the tendency of the redox potential is to drift downwards, from high to low. When it gets to the bottom of the ideal range for denitrification (determined either through trial and error or, preferably, a controller) the dosing pump flushes in fresh tank water. Since this new water has a high ORP, the redox potential rises quickly. At the upper end of the optimal range, the pump shuts down, and the cycle repeats. This would be termed a batch approach, since the tank water is being treated in batches, while the food is administered continuously.

The approach I suggested is simply a reversal of this. The water flows in a constant slow stream, bringing a fresh supply of nitrates. This keeps pushing the redox level upwards. When it gets to the upper end of optimal range, the dosing pump (again, triggered by trial and error or preferably a controller) squirts in a dose of alcohol. This triggers a flurry of bacterial activity that pushes the redox potential downwards, which causes the pump to stop. This would be a continuous design, since the water flows through the unit continuously while the food is introduced in batches.

The two methods are similar; both achieve the same end. To me, however, the second approach instinctively feels more efficient. Both would likely function identically in the presence of low nitrates. As the nitrate level rises, however, I believe the second approach will show a greater ability to respond. The reason for this is that carbon is a limiting factor. Since the carbon available in the batch approach is a fixed level, the unit can only introduce nitrate containing water at a rate that matches the carbon supply. It is possible to have substantially more nitrate in the incoming water than the carbon can reasonably counter in a short time; this means the batches are slow and the unit takes a long time to process much water.

The continuous unit processes a fixed amount of water, so you always know it is filtering enough water to keep the system nitrate-free. If the nitrate level goes up, the unit escalates the amount of alcohol introduced, leading to an increased bacterial population capable of better handling the elevated nitrates.

I don't know how significant the distinction really is, but that's what my gut tells me. I hope this helps, and I hope you can see the benefit of the controller. You don't have to use one, but I really believe it's worth it to keep the unit operating at peak efficiency all the time.

[BigShot]

Huge thanks for your help ButterfyBoy. Great explaination!
Some followup questions if you don't mind:
1) With the method I described (manually) it seems that the Aqua Medic nitrate reductor 400 for instance has an input for a syring (with alcohol). What I'm wondering is do I have to squirt this alcohol in everytime the water rotates through the reductor??? or will it somehow suck it from the syringe? :-)
Or perhaps I can just aquirt some in the morning or evening?
2) So with your method I woudl need 2 pumps right? One for the dosing of alcohol and the other for the continuous flow through the reductor?
It wouldn't be a totall guess work on my side. I do have an ORP probe, but it's a part of AquaZone Plus 200 ozonizer. I guess I could stick in in the nitrate reductor for some time to help me estimate the flow rate...
One problem I'm having though is to setup and control this flowrate properly, which pumps to use etc... kind of confusing with all the choices out there.

Thanks again,
Luke

[BigShot]

One more thing... would the sulphur based reactor be better alternative to carbon/alcohol ones? I'm not sure who makes them, but I've heard they are very efficient.

Luke

[ButterfyBoy]

Lets see...

1) I'm not familiar with the Aquamedic Nitratreduktor 400 per se. I used to have one of the Nitratreduktor 1000 when they first came out (when they were just a big square thing, before they got all that fancy-shmancy styling they have now :eek1: ). That unit was actually designed to accept solid food pellets that would dissolve slowly to eliminate problem of having to feed regularly. I assumed that the smaller units would be the same, but maybe not? Ideally you want a constant or near constant food supply available. The ideal way to do it if you were using a liquid food would be to drip a dilute food in with something like a drip doser for kalk rather than trying to feed it by hand frequently.

2) Technically, yes, in some form you require two pumps. But you really only need one dosing pump, to feed the alcohol. For the slow continuous feed of fresh water, since it is basically constant, I just tee off the pump from the main sump. Sort of like a saddle valve on a water main to feed and R.O. unit. Then just drain back into the sump.

For an application like this, I think that dosing pumps are probably going to be all pretty suitable. You might want to look into a refurbished medical unit, or one of the cheap hobbyist units like the vario. I wouldn't spend a whole lot of money. Some units are variable in their flow, but they tend to be expensive. Far cheaper to buy a fixed flow unit and control how much water it moves by switching it off and on with a timer.

I used to have an excellent link on Sulphur denitrators, but I dont seem to be able to find it right now. I will see if I can dig it up for you and post it, probably tomorrow.

I've yet to try a sulphur unit, but I'd like to build one some day and try it out (i'm pretty interested in denitrators, if you havent guessed already :lol: ). They will lower your pH a little, so that's something you need to watch (most people use a second chamber with aragonite to help counter this problem). They will also gradually raise the sulphate concentration of an aquarium, but the jury is still out as to whether this is an issue or not. Seawater has about 2700ppm sulphate naturally, so it has to go up a fair way to have any substantial impact. I know of some public aquaria using the method that have had it get pretty high, but probably nothing to be concerned with in a typical home tank.

As for companies that make them, I know Schuran makes one, and maybe Azoo. And you can always DIY.

[BigShot]

Thanks again for your help.
one thing I've heard abot the sulphur denitrators is that they are only about 30% effective in saltwater. Not sure how much truth there was to it.

Luke

[BigShot]

One more thing... you mention that the alcohol is the carbon source. So why would the denniballs get used up in the denitrators?
I'm a bit confused here.
Also, what do you think about the DYI coil denitrators (no alcohol) ?

[ButterfyBoy]

Okay, here's the link I promised you:
http://mars.reefkeepers.net/USHomePage/USArticles/SulphurDenitrator.htm
Also, a brief but interesting article on sulphur systems appeared in the Fall 2000 / Volume 17 issue of SeaScope.

I've also heard that sulphur systems are less efficient in saltwater. Is it true? Possibly, even probably, though I don't understand the chemistry clearly enough to make that judgement myself. I guess what I'd ask is, does it matter? Also, 30% less efficient than what? Freshwater? Generally, since we already do a much better job at limiting nitrate accumulation in saltwater tanks anyway, it shouldn't *need* to be as efficient. I'd be surprised if there are many saltwater tanks out there where the nitrate content is less than 30% lower than a comparably-sized freshwater system. Also, 30% less efficient than the freshwater versions is still 70% more efficient than not having one at all, right? ;)

Regarding the deniballs, alcohol is *one* possible carbon source -- one that is commonly used because it is cheap, easy to get, free of nitrogen and phosphorous in its compostion, and being a liquid can be easily handled by dosing pumps or drip dosers. But it isn't the only possible carbon source. Any number of sugars, etc, can be used. Deniballs are an alternate carbon source of some sort in a plastic form (I don't know what the actual composition is).

Coil denitrators certainly work. However, they are less controllable, and essentially limited by the low levels of carbon found in the form of dissolved organics in the tank. So they work, but they can't process huge volumes of water, nor can they work quickly. They rely more on the "slow and steady" principle. I guess where I would stand on coils is something along the lines of, not ideal, but much better than nothing.

[BigShot]

Thanks for all the help ButterfyBoy

[ButterfyBoy]

You're welcome

[H20ENG]

We had a company out to look at their unit. Cant recall the name, I'll try to find it.
A friend of mine at another aquarium built his own using 2 fluidized beds, carbon as the media, fed with methanol via injector pump. I think it was a batch system, but it worked.
I know you can use an ORP meter to gauge system operation.
I'll have to dig out the info.