An Explanation of Denitrification by Sulfur

[tony detroit]

Sulfur reactors are able to remove nitrate in both salt and freshwater tanks.
by J. Charles Delbeek, M.Sc.
Q. Do you know anything about nitrate reduction with the help of elemental sulfur? In Germany, there is a special filter promoted using small sulfur drops as a filter bed.
Rudolf Hester
A. The device you mention is known as a sulfur reactor and uses a process called autotrophic sulfur denitrification. Sulfur-based denitrification in freshwater is based upon autotrophic denitrification by sulfur-oxidizing bacteria, such as Thiobacillus denitrificans and Thiomicrospira denitrificans. Under aerobic conditions, these bacteria use oxygen as an electron acceptor, but under anoxic conditions, they oxidize various forms of reduced sulfur to sulfate, while reducing nitrate to liberate the oxygen for their own use. In addition to nitrate, T. denitrificans can also use nitrite. Autotrophic denitrifiers utilize inorganic carbon compounds (e.g., carbon dioxide, bicarbonate) as their carbon source. The process in seawater is not fully understood yet, but it does seem to work with the same result: the total removal of nitrate.
Professor Guy Martin, a specialist in water treatment at the Engineer National School of Chemistry in Rennes, France, is credited with originating the idea of using elemental sulfur and autotrophic bacteria to eliminate nitrate, but he only applied it to fresh water treatment for drinking water. Beginning in 1991, Marc Langouet, a past student of Dr. Martin, tested the method with seawater on his home reef aquariums - a risk given that no one knew if it would have toxic effects. By the end of 1994, after three years of experiments without apparent toxicity in numerous aquariums, Langouet proposed this method to Michel Hignette, curator of the Musée des Arts Africains et Océaniens (MAAO) Aquarium in

[hr]
. There, a pilot project was launched under his care. Since then, experiments have been done on a much bigger scale at the MAAO, as well as at the Grand Aquarium in Saint-Malo, where Langouet was technical and scientific director from June 1996 to December 1997.

 

[tony detroit]

The system uses small beads of elemental sulfur placed in a contact chamber. Tank water is introduced at the bottom of the chamber at a very slow rate and exits out the top. As the water moves slowly upward, oxygen is removed by bacteria, making the chamber more anaerobic the further up the water rises. At this point, the bacteria will use nitrate in the absence of oxygen so that by the time the water exits from the top of the chamber, most of the nitrate has been removed. The chemical reaction that takes place releases excess hydrogen ions, which makes the water acidic.
Nitrogen gas is also produced, and this leaves the water at the top of the chamber (one reason why a reverse-flow design is favored). It is believed that carbon dioxide is also produced in this process, further acidifying the water. To counter the acidity, the effluent from the reactor should pass through another column of crushed coral in which the acidic water will dissolve the coral gravel, raising the pH and generating calcium ions.

 

[tony detroit]

Another by-product of sulfur-based denitrification is sulfate. Passing the water through calcareous gravel precipitates this sulfate and prevents it from entering the aquarium. The sulfur beads can last a very long time, but the chamber of coral gravel will quickly turn to sediment and should be replenished on a regular basis. The use of a fluidized bed design for both the sulfur and the coral gravel reactors should help to reduce the build-up of sediments.
These reactors are very effective at removing nitrate. In a 16,000-gallon fish system at the MAAO, aquarists found that a sulfur-based denitrification system was able to reduce the nitrate ion level from a high of 320 mg/L to less than 10 mg/L in a month, so these reactors are very effective. The question is, however, whether we really need them in a reef aquarium in which nitrate levels are generally quite low to begin with.
This depends on how low such filters can bring the nitrate. Most reef aquariums still have nitrate levels that are a magnitude greater than those found in nature. If these filters can bring down aquarium levels to natural reef levels, they may well be worth the effort to use. On fish-only systems, these filters can easily help bring down nitrates to much lower levels. In addition, with the increase in the numbers of fish and the amount of food being added to reef tanks, a sulfur denitrator may be a necessary tool to remove excess nitrate. Finally, if aquarists want to keep many of the more delicate nonphotosynthetic corals, such as Dendronephthya, which require frequent feedings, these filters would again help keep nitrates under control.
Some of you may be wondering what all the fuss is about, since denitrification filters have been around for over 10 years. The difference is that those filters rely on heterotrophic bacteria to reduce nitrate to nitrogen gas. This means that you need to feed the bacteria a carbon source, usually methanol or ethanol, in a controlled manner, and adjust the amount in response to changes in nitrate levels. Too much alcohol, and you get hydrogen sulfide production. Too little, and you have nitrite and nitrate released back to the aquarium. These filters also produce a large amount of bacterial slime that needs to be removed on a regular basis.
The genius of the sulfur-based denitrators is that they do not need to be constantly adjusted, you don't need to feed them (other than to add some new sulfur maybe once a year or less), and they can also be used in conjunction with a calcium reactor to add calcium and alkalinity to the aquarium. Put simply, they are much easier to use with much less risk than alcohol-based reactors.
It is also possible to use this method in conjunction with a Jaubert plenum system, and most likely, with a deep sand bed system. By adding a thin layer of sulfur beads just above the plenum, or bare bottom of the tank in a deep sand bed, you can use the anaerobic environment there to allow sulfur-based denitrification to occur. This might allow Jaubert or deep sand bed systems to carry a heavier bioload by increasing their denitrifying capacity. You could also set up a system in a refugium or adjacent sump to allow you to add such a system to an existing tank without having to tear it down first.
The advantage of this system is that you don't need to add another piece of equipment, but I prefer the convenience of having a separate device I can remove without having to disrupt my tank. Several manufacturers are offering these systems in Europe, and some are now being imported to the United States (e.g., Knop, AquaMedic and Deltec).

 

[tony detroit]

The above was cut and pasted just so I don't steal anybody's credit.

 

[dburr]

I did not read all of it, but I wanted to say, I thought sulfur was a by-product of denitrifacation????
Now you add it?
I will come back later and read the thread tonight when I have more time.

 

[dburr]

Interesting, if it disolves CC why use it with a calcium reactor? Sounds like it is a nitrate reducer AND a CR. Adding more fish is a bonus.:joy:
Thanks for the read.

 

[nm reef]

Very interesting indeed...but I wonder how practical the method is...and how effective it would be on smaller systems. It seems that most of the reefs we keep already maintain a very low nitrate level...so why the concern and need for additional methods to reduce what we already eliminate....good info though.:thinking:

 

[reefnut]

Sounds pretty cool to me... how big are these units?? Sounds like they could get pretty tall??

 

[007]

I wonder if a standard phosban would work . . . . :thinking:
Got any extra phosbans around Tony?

 

[shoreliner11]

Maybe you can clear this up for me. It says as oxygen is removed by bacteria...which I know is very possible but at what flow rate. I was always under the impression that bacteria feeding off oxygen would not be a quick thing to take place. Anyone know what the flow rate actually is in one of these?

 

[tony detroit]

Originally posted by 007
I wonder if a standard phosban would work . . . . :thinking:
Got any extra phosbans around Tony?
I just may if that other guy doesn't show up to get this one. Only difference is most use a recirc pump. The korallin model is actually the exact same thing as their calcium reactor to a T. I spoke with a dealer I know, I'm probably going to try the H and S.
As stated earlier, I certainly do not think anybody needs one of these, they're just one more layer to add to my safety net.

 

[daveb]

It sounds to me like this system will not only reduce our already low nitrate levels, but will allow us to increase bio-loads and still lower nitrate levels even more, while increasing bio-loads. This allows us to keep more hard to keep corals that require a lot of feeding. Feeding which is hard to do right now because of the inability to manage the nitrate produced by the required feeding.. If this system is capable of compensating for that type of overfeeding, and increased bioload, your 100 gallon tank just became a lot bigger in a way....
I will be following this closely, since the only real problem I have right now is balancing feeding with nitrate control, while keeping EVERYTHING in the tank fed and healthy...
I have used ALGONE since I started my Reef Tank... and those packets have a very very strong SULPHUR smell when they have done all the denitrification they can do. And, I also became so confident in my system I stopped using the ALGONE for while.. WITHIN a week of stopping ALGONE, I had much higher NITRATES, and a nice lush growth of hair algae starting in my tank..
Upon restarting the use of ALGONE, which I actually just toss the packet into an area of my sump designed for just that type of thing, the NITRATES immediately started dropping.. at the end of the week, all the patches of hair algae are dying and receding.. It would not surprise me to find out that the process ALGONE uses is very similar to this SULPHER based system. And if these REACTORS or Fluid bed type systems are even more efficient than the ALGONE I will definitely give one a try...
Dave

 

[stuckinfla]

Thank you Tony, very interesting. I like the idea of the larger bio-load!!:yes:

 

[tony detroit]

Keep in mind this isn't a free ticket to 50 fish in a 25gallon. Ya still gotta be careful. If you do some searching on google, you'll find a large number of the european aquarists have been running these units for years.
DaveB, perhaps there are other things you can do with your system to help it. Describe it in detail and we'll see what we can do in the equipment forum. There are a number of ways to combat algae.