Oxygen and the Nitrogen cycle

[crass]

Hi

I was have a look at the LFS today and got asked a question I couldnt answer. The guy has had his tank for 3 months now and he asked me this.

Does Oxygen effect the nitrogen cycle? by this he ment does NO2 break down O2 to make NO3? his point was... if this would help keep nitrates down because apparently ozone reactors help with this and thats O3? so in theory adding more air or using an oversized skimmer would do the same.

We all understand the importance of aeration and how it helps in the aquarium and how low oxygen de-nitrification bacteria help.

guess I'll learn something new today

thanks in advance
Dean

 

[mojoreef]

Not really Dean, NO2 is reduced by bacteria via oxidization to nitrate. SO you could say that this process only happens in oxygenated areas/surfaces. O3 is ozone and it is unto itself a radical that is capable of direct oxidation. But its not something where you could say that more airation will help the nitrification process. Using ozone will help you with a number of things though, direct oxidation, the break down of proteins that will then be able to be skimmed (where as prior they would not) the elimination of several free swimming protozoans and so forth.

Mojo

 

[BigAl07]

I think someone is looking at the Nitrogen Cycle and trying to find a "Cheat". What's happening is the person suggesting (If I understand the question correctly) that adding more O2 to the system might help reduce NO3 in a system. If you look at which bacteria does what you'll more accurately understand why this is incorrect.

In very simplistic terms the nitrogen cycle starts with a dead organism. Bacteria quickly break it down into more fundamental forms. Organism > NH3/NH4 (ammonia) > NO2 (Nitrite) > NO3 (Nitrate) > Nitrogen Gas and released into the atmosphere at the waters surface. Of course this process is much more complex that I have it stated but to keep this on track and simplistic there's no need to delve any deeper into the inner workings of it.

The bacteria that handle the first few steps of the "Nitrogen Cycle" (organics broken down into NH3/NH4 then broken down into NO2 and then into NO3) are Aerobic in that they live in a highly oxygenated area of the aquarium. Usually in the upper level of sand and on the bio-film layer of rock and everything else in the tank. This is why Bioballs (or any BioMedia) are so GOOD at what they do (colonizing with a heavy population of aerobic bacteria because of LOTS of surface area). The problem is they are TOO good at that part of the equation but due to their design unable to carry on the next steps. This is why tanks with Biomedia have elevated levels of NO3 (and are often called Nitrate Factories) because that's as far as they can go.

Now the bacteria to convert NO3 (this is assuming no plants or macroalgae are in the system consuming NO3) is Anaerobic in that they grow and thrive in an area free of oxygen in their immediate environment. The Anaerobic bacteria are responsible for breaking down Nitrates into Nitrogen gas which leaves the aquarium and enters the atmosphere at the waters surface. This is why I say increasing the levels of O2 in the system wont help these anaerobic bacteria in the least.

Now there are other methods and "devices" for denitration of the tank but they really aren't in the scope of this thread so no need to "muddy" the waters.

 

[mojoreef]

The Anaerobic bacteria are responsible for breaking down Nitrates into Nitrogen gas which leaves the aquarium and enters the atmosphere at the waters surface.

That process only works for about he first couple of months Al, beyond that their is always going to be the presence of ammonia in/on the sand/lr and because ammonia represses assimilative nitrate reductase, the first enzyme in this nitrate reduction pathway it just coverts the nitrate into ammonium and then sends in back into the cycle again.

Mojo

 

[BigAl07]

That's why I added "in very simplistic terms" to my post. This thread could very easily get VERY technical and lose it's scope and audience.

 

[mojoreef]

Agreed, but its an important one. A lot of folks thing that a sand bed actually exports and it doesnt so it kind of changes the whole dynamic. People tend to think is set and walk away but its not and it needs to be maintained if its going to last for long periods of time.

Mojo

 

[BigAl07]

Very true and very well put. I've enjoyed reading your input on "Skimmer Basics".

 

[Boomer]

Short note:

NO2 is reduced by bacteria via oxidization to nitrate.

Cant' happen must be a typo Mojo.

Reduced NO2- gives NO not NO3-. Reduced more or less means to loose O and Oxidation means to gain O. Technically speaking reduction and or oxidation has nothing to do with O but often does. Think of the R in Reduced to mean receive, as it receives an electron ad the O Outs an electron. Iron is a good example: Fe++ and Fe+++. A neural element has the same number of electrons as protons. So, if Fe Outs an -electron, it has one more +proton and become Fe+ another Fe++ and another Fe+++, this is all oxidation. Then if Fe+++ gets reduced, receivers an electron, we are back to Fe++. If we look a chloride Cl- it has one more electron, it has Received more -electron, becomes reduced and has one more -elector than +protons in Cl, thus has a - charge.

"NO2 is oxidized by bacteria via oxidization to nitrate."

NO2- + CO2 + 0.5 O2 + Nitrobacter → NO3-
and
NO2− + H2O → NO3− + 2H+ + 2e−

BUT...there is a reduction series also

NO3- + 2e- + 2H+ → NO2- + H2O



and this can give


NO2- + 2 H+ + e- → NO + H2O

and when the NO gets converted N2 you can get this

N2 + 8 H+ + 8 e− → 2 NH3 + H2

and this ^ is what can happen to a SB if it is not cared for. There will be a shift in Faculative Anaerobic to Obligated Anaerobic (see BELOW) and we DO not want that.


Now the bacteria to convert NO3 (this is assuming no plants or macroalgae are in the system consuming NO3) is Anaerobic in that they grow and thrive in an area free of oxygen in their immediate environment.


This is a no-no an yields hydrogen sulfide. You always want we-tad of O2 in the SB, that is what Faculative Anaerobic means and if not you will end up with what Mojo is driving at

N2 + 8 H+ + 8 e− → 2 NH3 + H2

we DO NOT want Obligated Anaerobic = in an area free of oxygen

And raising O2 levels in a tank with increase Nitrification rate constants, this has been proven with Bio-Balls but this it not somewhere we need to go with. Most tanks have enough O2 for Nitrification. If they did not you would see elevated NH3/NH4+ and NO2- all th time.

Ozone, O3, is another beast, as Ozone will DIRECTLY convert NO2- to NO3- via oxidation and/or some ammonia to a degree.

NO2- + O3 → NO3- + O2 and this yielded O2 will be sucked up so fast you will see no rise in the tank O2.

 

[mojoreef]

Cant' happen must be a typo Mojo.

Yea Fat finger and slow brain to hand function >>>>