DIY sulphur denitrator

[robert]

FWIW, I believe that it is not clear that struvite will be insoluble in our reef systems. It is not a waste water system with high ammonia and phosphate. Only if ammonia is significantly above 0.05 ppm and phosphate above 0.1 ppm will it be insoluble.

Let's look at some real values.

The Ksp for struvite in seawater is 10-(13.08) = 8.3 x 10^(-14), which is from:

Solubility of Struvite in Seawater
http://www.the-conference.com/JConfAbs/5/449.pdf

where they also claim:
"As a result of this investigation and our experimental data about unseeded precipitation of calcium and magnesium phosphates from modified seawater solutions (Golubev et al.,1999), no magnesium (ammonium) phosphate can be inorganically precipitated in modern marine environments..."

But let's use their Ksp and see how our reef tanks match up.

The Ksp is:

[Mg++] x [NH4+] x [PO4---]

Magnesium in seawater is 1280 pppm or 0.053 M

Let's examine phosphate at 0.1 ppm = 0.1 mg/L = 1 x 10^(-6) M at pH 8.1 only 20% of it is present as PO4--- (and that number drops as the pH lowers), so the PO4--- is about 2 x 10^(-7)

Let's also examine ammonia at a fairly high 0.05 ppm, or 2.8 x 10^(-6) M and assume it is all ammonium

So the solubility product in this case is 0.053 x 2 x 10^(-7) x 2.8 x 10^(-6) = 2.9 x 10-14.

So the solubility product is lower than the Ksp in seawater, indicating that it will be soluble (and won't precipitate) under these conditions.

From your citation:
"no magnesium (ammonium) phosphate can be inorganically precipitated in modern marine environments"

and yet struvite is found produced by biofilms in the marine environment and in the beds of sulphur denitrators and as I cautioned, its presence is controversial. See my original post #29. The fact that much if not most data is the result of watse water treatment studies, does not preclude their use in the marine aquarium. Even carbon dosing has its roots in waste water treatment.

from
Sulfur To Reduce Nitrate in Fish Aquariums By J. Charles Delbeek
http://www.fishchannel.com/saltwater-aquariums/aquarium-care/sulfur-reactor.aspx

"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 Paris. 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."

The inorganic chemistry of free water is not directly applicable when it comes to the chemistry of biofilms and bacterial mats running in an anerobic environment with bacteria concentrating ions in micro-environments. The skeletons of the corals we keep are a product of bio-films which are unlikely to precipitate on their own.

 

[Randy Holmes-Farley]

You should reconize this from your paper on Phosphate in the Reef Aquarium.

Which is mirrored in Biogeochemistry by William H, Schlesinger.
In the second diagram, the first diagram is fresh water and the last artificial sea water.
From my post:
Phosphate Adsorption by GFO
pH—— % bound (%efficiency)
4 ——- ~93%
5 ——- ~82%
6 ——- ~62%
7 ——- ~41%
8 ——- ~19%
8.8 —— ~0 %

if this is freshwater data, may we deduce that it GFO binds preferentialy to the H2PO4 species - other wise the binding efficiency would be flat as a function of pH? It is difficult to assess how much of the HPO4 is bound. looking at the data and the curves, it would suggest that GFO doesn't bind HPO4 effectively at all; perhaps a few percent.

For the salt water, The fraction of phosphate as H2PO4 is 10% at a pH 7 of and virtually 0 as you approach 8. If it holds that this binding affinty held and if the lack of binding affinity for HPO4 holds for salt water, then this additional fraction which could be cleared by GFO running in a pH 7 environment could be a very significant multiple of what can be cleared at 8.

I think its worth testing.

I agree that I'd like to see data on seawater binding as a function of pH. It may bind better at some lower pH values, but it is not only the state of the phosphate that matters, but the state of the surface charge as well.

 

[Randy Holmes-Farley]

and yet struvite is found produced by biofilms in the marine environment and in the beds of sulphur denitrators and as I cautioned, its presence is controversial. See my original post #29. The fact that much if not most data is the result of watse water treatment studies, does not preclude their use in the marine aquarium. Even carbon dosing has its roots in waste water treatment.

I don't deny their utility at all. But I'm not sure what the presence or absence of struvite has to do with it.

But, you say that someone has detected struvite in a marine sulfur denitrator used on a reef aquarium?

 

[Randy Holmes-Farley]

Have you measured to see how low the pH gets in your denitrator?

 

[Randy Holmes-Farley]

My point with the struvite solubility issue is that you stated it was "insoluble in our systems" and I showed that isn't true. I don't deny that there may be places with locally high ammonia and/or high phosphate (which might be under a biofilm that for some reason was producing ammonia) where it might precipitate, but if exposed to tank water, it will redissolve.

 

[robert]

My point with the struvite solubility issue is that you stated it was "insoluble in our systems" and I showed that isn't true. I don't deny that there may be places with locally high ammonia and/or high phosphate (which might be under a biofilm that for some reason was producing ammonia) where it might precipitate, but if exposed to tank water, it will redissolve.

and if it were to be exposed and redissolve, (as I understand it), in seawater struvite goes to bobbierite, newberite and ultimately it transforms to octa-calciumphosphate. (At the pH and ionic concentrations of Ca and Mg found in normal sea water) and from there it precipitates on a clacite seed and ends up in the sandbed, filter or skimmer. - No?

 

[robert]

I will say that there is evidence to believe that high dissolved organic carbon may be worse for coral health than either high nitrates and/or phoshates. With your understanding of the chemistry in our systems...I you were do design a nutrient export/sequestration system that didn't rely on DOC, what would it be?

 

[Randy Holmes-Farley]

I will say that there is evidence to believe that high dissolved organic carbon may be worse for coral health than either high nitrates and/or phoshates. With your understanding of the chemistry in our systems...I you were do design a nutrient export/sequestration system that didn't rely on DOC, what would it be?

Growing macroalgae.

 

[Randy Holmes-Farley]

and if it were to be exposed and redissolve, (as I understand it), in seawater struvite goes to bobbierite, newberite and ultimately it transforms to octa-calciumphosphate. (At the pH and ionic concentrations of Ca and Mg found in normal sea water) and from there it precipitates on a clacite seed and ends up in the sandbed, filter or skimmer. - No?

I've not seen transformation data for struvite in seawater. Why wouldn't it just dissolve into ions?

 

[PaulKreider]

"grabs notebook"

 

[robert]

I've not seen transformation data for struvite in seawater. Why wouldn't it just dissolve into ions?

Now thats above my pay-grade, I figured you would know...

struvite MgNH4PO4*6H2O
newberryite MgHPO4.3H2O
bobierite Mg3(PO4)2.8H20
Octacalcium phosphate Ca8H2(PO4)6.5H2O

Golubev S.V., Savenko A.V. Solubility and
stability of magnesium phosphates in sea water
Lomonosov’s Moscow State University

...Struvite is found to be unstable both in the calciumfree
and in the normal sea water. In all experiments the
phosphorus concentration is lower than the ammonia concentration.
Decrease of the phosphorus concentration in
the normal sea water occurs in all experiments at the constant
calcium content in the solution.

...These facts allow a conclusion that
solubility of unstable struvite is accompanied by the precipitation
of Mg3(PO4)2*xH2O.

...Newberite is stable in sea water at pH<7; in more
alkalic environment it transforms to octa-calciumphosphate
in normal sea water, or to bobierite in calciumfree
sea water.

A bit muddled because they co-mingle data between calcium free sea water and calcium-steady sea water.
I'm left with the impression, that net is a reduction in the phosphate contribution that might be expected from struvite, by the reduced soluability of resultant forms (and hence perciptation) and the transformation of some of these further to OCP.

At any rate it might suggest that struvite forms in sea water but is unstable and is converted to other precipitates....so the observation of MAP (which was postulated to be significant to explain the higher phosphate removal of the mixed media reactor)- might be an intermmediate or transitional step in a more involved process.

The next flush of the denitrator, I'll save and dry the sludge - and run some tests on it...could be interesting.

 

[robert]

Would you care to discuss bacteral load in the reef system as I have some very contrary data...
We can open a different thread.

 

[robert]

Getting this thread back on track...The sulphur denitrator has been running at a slow drip for a week and today I took a water sample...

Its cycled and is just begging to remove nitrate...pretty much right on schedule.

Don't freak when you see my levels...

Right -> Tank water: darn disgusting but all fish and corals are doing well. No algae - zoos multiplying - No cyano. Inverts and snails OK.
Center -> Denitrator output: obviuos drop
Left - > control - test kit looks in order - nice 0.

The tank is 36" deep so the water clarity is very good.

 

[robert]

This week I'll slowly open it up a little - a trickle - It should be outputting a flat "0" by next weeked.

I did make one change - I added a gate valve to the output for better control. The ball valve I used before was just too fickle.

 

[robert]

When I say the tank is 36" deep - I mean from front to back...

 

[CJR]

Robert, resurrecting an old thread as I'm build a sulphur denitrator, some questions for you regarding your design. 1) Most of the commercially available ones are recirculating with a small 1/4" outflow as you noted in a post. Yours is noted as a slow flow system which you note helps reduce the sloughing of the films. After running for these months, do you see any reason to make it a recirculating type? 2) I didn't notice a way to expel the N gas that can build up, how do you handle this in this design? 3) Size, you mention early on that this reactor could handle 500 gallons, what volume of media are you using to achieve this? On the inlet pipe that feeds to the bottom of the unit, is there a void area at the bottom to allow free flow or because you use coral pieces there is enough room between them that the pipe just opens at the bottom? Didn't appear to be anything visible in the photo. My tank will be roughly half that size. 4) Don't think I am up to melting sulphur over the coral skeletons, so what sulphur product would you suggest? Any guidance on the ratio of sulphur media, to coral bits to GFO? 5) Thanks for your postings, I'm very anxious to try a sulphur denitrator when I start my tank up. I'm using dead rock, pukani, and hope to use the bacteria in a bottle ( a la Dr. Tim's ) to quick cycle the tank. Do you suggest starting the denitrator offline ahead of cycling, in parallel, or after the cycle is complete? Lots of questions, thanks for your reply.

 

[robert]

"Robert, resurrecting an old thread as I'm build a sulphur denitrator, some questions for you regarding your design.

1) Most of the commercially available ones are recirculating with a small 1/4" outflow as you noted in a post. Yours is noted as a slow flow system which you note helps reduce the sloughing of the films. After running for these months, do you see any reason to make it a recirculating type? "

Short answer - No. I'm not trying to acheive a zero reading on a single pass through the reactor, rather it is sufficient for my purposes to simply see a visable reduction on the nitrate test kit as the effluent exits the reactor. This allows me to run the flow through the reactor a little higher. In some of my prior DIYs I did use a recirculation pump inside the chamber - it was always questionable as to whether it was running, was it clogged etc...I left it out on this one - its simpler this way - and I don't seem to miss it.

"2) I didn't notice a way to expel the N gas that can build up, how do you handle this in this design?"

Since the effluent pipe is flush with the bottom of the lid and I'm using a pump to push water into the chamber - any gas collected must go out the effluent pipe and no gas collects within the chamber itself. If the intake pump is shut off - then yes - the top of the chamber fills with N gas - but in operation it cannot.


"3) Size, you mention early on that this reactor could handle 500 gallons, what volume of media are you using to achieve this? On the inlet pipe that feeds to the bottom of the unit, is there a void area at the bottom to allow free flow or because you use coral pieces there is enough room between them that the pipe just opens at the bottom? Didn't appear to be anything visible in the photo. My tank will be roughly half that size. "

I'm guessing about 2 gallons total of the 50:50 sulphur/coral mix - with a cup and a half - two cups of rinsed GFO mixed in. I'll actually go out and measure the volume when I get a chance - the intake is 1/2" pvc run down to within a 1/4" of the bottom. Its simply open on the bottom as you state. My chamber is rather wide - a taller narrower chamber would be more efficient but it wouldn't fit under my cabinet as well.


"4) Don't think I am up to melting sulphur over the coral skeletons, so what sulphur product would you suggest? Any guidance on the ratio of sulphur media, to coral bits to GFO? "

50:50 - if your not going to melt the sulphur to the coral no worries, I didn't melt them together in my first setups and they also worked well. I only did this to maximize the boundary contact for maximal phosphate retention. Its not that necessary. I used Carribsea L.S.M.

http://www.marinedepot.com/CaribSea...Filter_Media-CaribSea-CS0528-FIFMCHSM-vi.html

Its a rather non-uniform mix of sulphur - everything from dust to chunks. I rinsed it lightly before adding to the chamber - and then ran the creactor overnight in a bucket of tank water wide open to flush it out a bit before I set it in my sump.


"5) Thanks for your postings, I'm very anxious to try a sulphur denitrator when I start my tank up. I'm using dead rock, pukani, and hope to use the bacteria in a bottle ( a la Dr. Tim's ) to quick cycle the tank. Do you suggest starting the denitrator offline ahead of cycling, in parallel, or after the cycle is complete? Lots of questions, thanks for your reply."

You can add the denitrator at any time...but I've always added them after the cycle is complete and the tank has built up a little nitrate.

 

[ryanuy]

Hi Robert! Sorry for reviving an old thread but I also had a few questions.

1. Are you still running your denitrator up to today?

2. Have you ever had H2S get dumped into your system after the denitrator gets clogged? If not, how do you avoid this when the reactor gets slowly clogged over time?

3. How do you get the phosphate retention on the coral skeletons? I just mix the sulphur media with the coral skeletons and GFO that will do the trick?

I was going to use a calcium reactor and modify it to be a denitrator and theres an option for the effluent to go to another cannister before going back to the main tank. Could i use this chamber for the GFO instead of mixing it with the sulphur to make it easier to change without having to mess with the sulfur media?

Thanks!

 

[robert]

Hi Robert! Sorry for reviving an old thread but I also had a few questions.

1. Are you still running your denitrator up to today?

Yes - absolutely - been running sulphur for a very long time now.

2. Have you ever had H2S get dumped into your system after the denitrator gets clogged? If not, how do you avoid this when the reactor gets slowly clogged over time?

Sure - this was especially common when I used 1/4 inch air tubing for the feed and outflow from the denitrator. A while back I switched to 1/2" PVC to feed the denitrator and put a gate valve on the outflow. Now, if I notice the flow restricting the gate valve makes it much easier to correct without dumping H2S into the tank.

3. How do you get the phosphate retention on the coral skeletons? I just mix the sulphur media with the coral skeletons and GFO that will do the trick?

Limited phosphate retention takes place where the coral stone / sulphur mixture come into contact with each other - phosphate is removed even without the gfo.

I was going to use a calcium reactor and modify it to be a denitrator and theres an option for the effluent to go to another cannister before going back to the main tank. Could i use this chamber for the GFO instead of mixing it with the sulphur to make it easier to change without having to mess with the sulfur media?

Good idea - I do - a second chamber with coral stone mixed with either a small amount of raw iron or GFO (but no sulphur) will also precipitate excess iron from the system. This chamber will turn black as iron is precipitated and helps control algae. For me this is especially nice since I feed nori daily for my tangs. You shouldn't have to change this very often at all.

Thanks!

NP - good luck.

 

[ryanuy]

Thanks for the reply! I didnt think you would still be checking on threads this old.

1. Have you ever found the H2S toxic to any of the tank inhabitants during the times it was dumped into your system by the reactor? Some of the posts I read blame the H2S for nuking their tanks and killing off livestock and making the water cloudy.

2. When the H2S is dumped in as well, how do you manage the tank? Do you like a massive water change or do you just leave everything there and let the tank fix itself? How often does your reactor get clogged as well? Like how many times a year?

3. How do you correct the flow issues that occur in the reactor when it gets clogged? Do you take it out and clean it or do you just run it full bore for an hour or so? Do you also correct this the moment you notice the flow even slightly is slower than normal?

4. Have you read the other thread on here by Belgian Anthias about the BADESS system where he runs the reactor with a higher flow rate where the reactor does not become anoxic and is still effective at controlling nitrates? What do you think about running this?

https://www.reef2reef.com/threads/sulphur-in-the-reefaquarium.492492/page-2#post-5311945



I was planning to run my reactor a little faster than normal. I dont need zero nitrate in the effluent(but of course it would be nice). Just a nitrate level that is lower than my main tank is good enough. Would this lower the chances of the reactor getting clogged since its running a bit faster?

Sorry for asking so many questions! Just wanna be sure before I run another thing on my reef.