Nitrogen

[Gills 619]

What is the best way to reduce the level of desolved nitrogen in tank water

[Randy Holmes-Farley]

I assume you mean primarily nitrate, rather than N2?

There are many ways to reduce nitrate. I use organic carbon dosing and skimming, macroalgae growth, and GAC.

This article has more:

Nitrate in the Reef Aquarium
http://www.advancedaquarist.com/issues/august2003/chem.htm

and


The “How To” Guide to Reef Aquarium Chemistry for Beginners,
Part 4: What Chemicals May Detrimentally Accumulate
http://reefkeeping.com/issues/2007-09/rhf/index.php

[Gills 619]

Hi Randy, this is what I understand. Please feel free to help.
I use a sulphur denitrator that has cleaned my tank up like magic. I believe that the effluent is high in nitrogen which with phosphate is feeding my bright green cyno.

[badvegan]

I dont have the money to buy sulfer denitrators or any of the real expensive stuff... so i go with the organic carbon dosing mentioned above (i use cheap vodka and it does wonders) and put saw algae in my displays that do not have refugiums.

[Randy Holmes-Farley]

No, you are not significantly elevating tank N2 with a denitrifier. There is already a lot of N2 in tank water, and you cannot do anything about it. Air is 70% N2, so that is where it comes from. :)

Look for other ways to deal with cyano, which can be a tough nut to crack. :)

[UVvis]

No, you are not significantly elevating tank N2 with a denitrifier. There is already a lot of N2 in tank water, and you cannot do anything about it. Air is 70% N2, so that is where it comes from. :)

As mentioned, you can have increased N2 from a sulfur denitrification, but most small sized systems on the hobby side have enough gas exchange that you aren't going to build it up to a level worth worrying about. If it is, the issues aren't going to simply be increased algae.

Depending on the denitrification and condition of the sulfur, you can have some ammonia and nitrite in your effluent which some photosynthetic organisms prefer over nitrate forms. How are your flow rates through your reactor?

Nitrogen fixing organisms are going to have all the N2 they can use, so that isn't going to make matters worse.

[Gills 619]

As mentioned, you can have increased N2 from a sulfur denitrification, but most small sized systems on the hobby side have enough gas exchange that you aren't going to build it up to a level worth worrying about. If it is, the issues aren't going to simply be increased algae.

Depending on the denitrification and condition of the sulfur, you can have some ammonia and nitrite in your effluent which some photosynthetic organisms prefer over nitrate forms. How are your flow rates through your reactor?

Nitrogen fixing organisms are going to have all the N2 they can use, so that isn't going to make matters worse.

Thanks for your input. Reactor is running at a fast drip, just breaking into a run. Tank has never looked better besides for a renewed cyno outbreak.
I was concerned about the nitrogen as being the fuel for the new outbreak.

[tmz]

Ive used a sulfur denitrator . The flow rate of the effluent as a proportion of system volume is quite small and I don't think the N2 from NO3 reduction would have much if any effect as it would equilibiate with the air about as fast as it went into the system water. Besides it's not clear that extra N2 would advantage cyanobacteria in the aquarium even though cyano can fix it.
Reducing the phosphate might be a better target.

[UVvis]

From what I've seen, the problem is when people use only nitrate to look at the sulfur count. Lots of nitrate is converted to nitrite and ammonia from the reactor, so your overall denitrification might not be as much as assumed on nitrate values alone. (One of the reasons why 'nitrogen as ion' works better math wise).

Lower dissolved oxygen counts usually indicate more denitrification.

[Gills 619]

Thanks tmz, going to pic up phosban or equivalent tomorrow from the lfs

[tmz]

Uvis,

IME, the nitrite production stops after a day or two of cycling the reactor leaving no nitrite, ammonia or nitrate in the effluent. Even during the cycle , I don't think the N in the overall system would increase:it would just change it's form.
I usually drip the effluent into a bucket during this phase in any case.

Eventually(3 to 4 weeks in my case), the NO3 in the aquarium drops to near zero . Then hydrogen sulfide production in the reactor can be a problem unless flow is increased and/or sulfur volume is reduced sufficiently to avoid anoxia.

[UVvis]

Uvis,

IME, the nitrite production stops after a day or two of cycling the reactor leaving no nitrite, ammonia or nitrate in the effluent. Even during the cycle , I don't think the N in the overall system would increase:it would just change it's form.
I usually drip the effluent into a bucket during this phase in any case.

Eventually(3 to 4 weeks in my case), the NO3 in the aquarium drops to near zero . Then hydrogen sulfide production in the reactor can be a problem unless flow is increased and/or sulfur volume is reduced sufficiently to avoid anoxia.

Granted we are dealing with reactors on different scales, the biological and chemical reactions are the same. My experience with small units is limited.

Hydrogen sulfide mostly comes from sulfate being reduced. While this does indicate anoxic conditions, we have other factors at play too. Nitrate, nitrite, carbonates, and dissolved oxygen are being consumed by the autotrophic bacteria we have colonizing the sulfur. Denitrification, in general, requires anoxic conditions.

A healthy sulfur bed decrease the concentrations of all of the above. The overall in system inorganic nitrogen loading is certainly decreased. The problem is that many just check nitrates only. Over time I've noticed that flow changes can shift denitrification around, and some ammonia or nitrite can be produced. The other aspect is that we are mostly concentrating on our autotrophic production on the reactor. There is no reason that other anoxic loving bacteria will not pop up and consume either the autotrophic bacteria we want, or other in stream waste products.

It's when the sulfates that the thiobacillius produces are being converted to hydrogen sulfides, your sulfur has been overcolonized or clogged by biological materia.

From what I've seen, any change in flow rate will produce some nitrite, and the sulfur is changing constantly. Ammonia is seen more often when you have some die off or overpopulation of certain biological components. Sulfur beds seem to be most productive when the dissolved oxygen is under 1mg/L closing in on zero. At this level I tend to see maximum denitrification, as well as some stripping of carbonates, pH reduction, depleted DO, and usually hydrogen sulfide levels in the 0-2ppb range.

[tmz]

Hi,

Denitrification, in general, requires anoxic conditions.


I differentiate anoxia and hypoxia when thinking about denitrification. Anoxia being devoid of oxygen even that in nitrate setting the stage for sulfate reducing bacteria. Hypoxia being low in use oxygen with to a point where the facultative heterotrophs go after the NO3 for the O. Eventually, they will exhaust the NO3 if it's not replenished it as it is used .

The autotrophic sulfur denitrator activity involves:

nitrate,suflur,carbon dioxide and water converting to nitrogen gas,sulfate .water and an oraganic.
NO3, S ,CO2 and H2O------>N2,SO4--,H2O , C5H7O2

All in all ,the N2 production combined with equilibration of this gas with the air would it seems to me lead to a net reduction in N in the aquarium .

[UVvis]

We both agree that the point is overall Nitrogen reduction by N2 offgas.

What I'm a bit confused about is mentioning facultive heterotrophs scavaging for oxygen. While I do not doubt that they can use nitrate for the oxygen, all the literature on the topic seem to prefer using sulfur as the electron donor for autotrophic bacteria. The facultive heterotrophs should be pulling some nitrate out, as well as sulfates which can lead to the sulfide production. But the heterotrophs would be reliant primarily on carbon source for energy versus the sulfur versus autotrophs using the sulfur. So why would you need the sulfur at that point?

Unless the larger reactors are geared more to autotrophic anoxic conditions and smaller sized ones more for facultive heterotrophy.

[philbo32]

We both agree that the point is overall Nitrogen reduction by N2 offgas.

What I'm a bit confused about is mentioning facultive heterotrophs scavaging for oxygen. While I do not doubt that they can use nitrate for the oxygen, all the literature on the topic seem to prefer using sulfur as the electron donor for autotrophic bacteria. The facultive heterotrophs should be pulling some nitrate out, as well as sulfates which can lead to the sulfide production. But the heterotrophs would be reliant primarily on carbon source for energy versus the sulfur versus autotrophs using the sulfur. So why would you need the sulfur at that point?

Unless the larger reactors are geared more to autotrophic anoxic conditions and smaller sized ones more for facultive heterotrophy.

You seem to be oversimplifying the whole concept of heterotrophic bacteria, there are many different species of heterotrophic bacteria and they all interact differently and require different conditions from there environment to survive. Sulphur reducing bacteria usually require an anoxic environment, although they can cause anaerobic corrosion of metal. These bacteria tend be different to other types of heterotrophic bacteria. Other heterotrophic bacteria thrive in an aerobic environment and use oxygen as an electron receptor, others require an hypoxic environment to become active. Then there are others which can use nitrate as an electron receptor in an oxic environment (aerobic denitrifiers).

[tmz]

I appreciate your information.

I only mentioned heterotrophic activity to give context to my meaning for anoxia.

Though I do suppose heterotrophic denitrication activity occurs at some level in a sulfur denitrator as organics are produced by the autotrophic activity with the sulfur . Many folks use porous media( such as Seachem matrix media) with the sulfur to provide surface area for such activity. I don't since I think it ultimately encourages sulfate recuction in the pores of the media where flow is even slower than the rest of the reactor.