De-nitrification by the use of Sulphur in a fluidized bed reactor.

[Belgian Anthias]

Using sulphur de-nitrators have been tested in the past for a long time. All these test where made with tube reactors with a flow from bottom to top. Now we use fluidized bed reactors to prevent clogging and tunnelling.
In a tube reactor, when flow is increased one may find nitrite in the effluent of the reactor because the increased flow brought in more oxygen and more nitrate, less room for de-nitrification with as result an uncompleted Nitrate reduction and nitrite is formed. Decreasing the flow will correct this.
In a fluidized bed we experienced that the flow can be increased till the effluent has the same nitrate readings as the in-fluent without any nitrite is noted.
My way of thinking the following happens: as the flow increases more free oxygen becomes available and more nitrate is entered. When the flow becomes to high some nitrite will be formed in the reactor. As the water is mixed because the reactor is fluidized, the nitrite may be oxidised again in the oxygen rich water which aids in depleting the free oxygen which helps to stabilize the reduction of nitrate and no nitrite will be produced. There will be more nitrate and less free oxygen and so on. So the reactor becomes a little bit self-regulating?
Question: Is my way of thinking correct?
Is it theoretically possible to regulate the flow and the ability for nitrate reduction only by using nitrate readings of the system water? Will a fluidized reactor find its balance automatically?

 

[Randy Holmes-Farley]

In a fluidized bed we experienced that the flow can be increased till the effluent has the same nitrate readings as the in-fluent without any nitrite is noted.

Meaning you are not performing any denitrification?

Sure, how enough flow should do that, as the bacteria will consume the sulfur using O2 only, which is more efficient.

I don't know if any nitrite is produced or not in such a scenario, but I don't see any reason that large amounts would be produced.

 

[Belgian Anthias]

In this setting we have no markable de-nitrification though the bacteria are still active because when decreasing the flow the reactor responds and nitrate in the effluent will drop.
In a tube reactor, when flow is increased, at some point nitrite is detectable in the effluent. Doing the same in a fluidized bed reactor, same volume of sulphur, this point could not be found. This does not mean that nitrite was not formed in the reactor. When using tube reactors we where used to increase the flow a bit avoiding detectable nitrite because we suspected it to happen? When it occasionally happened flow was decreased a bit finding the balance this way. I suppose this procedure is not valid using a fluidized bed because what we suspect to happen possibly will not be detectable. I suspect that a fluidized bed reactor is self-regulating because the nitrite may come out as nitrate or is processed again to N when in balance as it normally should.
When the daily nitrate production is not reduced and nitrate builds up the flow is decreased a bit, when the nitrate level goes down flow is increased a bit till the wanted nitrate level in the system is reached. This can be fully automated only using the systems nitrate level because we do not have to find the balance of the reactor as we have to do when using a tube reactor. This of coarse when the reactor is big enough for the system, otherwise the flow can be decreased till the reactor becomes critical.
If this way of thinking is correct we will have a fully automated de-nitrification system soon and mismanagement of the reactor will not be possible any more. There will be the risk that mismanagement of the aqua system is not noted so a Max correction has to be build in? Or an alarm when the flow to the reactor becomes low?
Are there any problems that potentially may come up I did not think about?

 

[Randy Holmes-Farley]

In such a scenario (high flow and no net reduction in nitrate), you'd have a sulfate producing and alkalinity depleting reactor as aerobic bacteria consumed the sulfur.

Sounds like a poor idea, in my opinion.

 

[Belgian Anthias]

In such a scenario (high flow and no net reduction in nitrate), you'd have a sulfate producing and alkalinity depleting reactor as aerobic bacteria consumed the sulfur.

Sounds like a poor idea, in my opinion.

Yes, sure. We are aware that we are producing some sulphate and there will be effect on alkalinity as any bacterial activity in the nitrate chain will do.
When using 1% reactors and a system that is kept between 1 and 2 ppm of nitrate, always only a a part of the reactor will be anaerobic which we find good. We can have flow till 10% without any noticeable problems. Normal flow is +- 2-3% because we feed a lot of life food, also at night. It is possible that we are producing a little bit of nitrite which will be oxidized again and so have more effect on the alkalinity at higher flow levels. I do not know, we do not find it in the effluent. We have no means to measure it inside the reactor. We did not notice abnormal depletion of alkalinity. After aeration of the effluent the PH is about the same as the system water during the day.
When nitrate builds up suddenly in a system without a sulphur de-nitrator in use, the de-nitration process in live stone and sand bed will need some time to adapt and the process will not be completed. Probably nitrite will be formed due to uncompleted nitrate reduction which will be oxidized again. I do not think there will be a lot difference on the effect on alkalinity with or without the reactor when the effluent of the reactor is aerated before entering the system. In favour of the reactor is that the process can be controlled and managed. Without the reactor we have to wait and accept the laws of nature. And limit food.

HIGHUET has made the assumption that the reason why sulphate level in the system does not rise due to the use of a sulphur reactor is because most of the produced sulphate is hold back in the calcium reactors and removed when they are cleaned.

What difference it makes to alkalinity if aerobic activity occurs in a sand bed or in a sulphur bed, I do not know. Please help! When the difference is big enough this could be a reason to deplete the oxygen in a sand reactor before entering the sulphur reactor.

 

[Randy Holmes-Farley]

Yes, sure. We are aware that we are producing some sulphate and there will be effect on alkalinity as any bacterial activity in the nitrate chain will do.

I mean sulfur oxidizing bacteria using O2 if the flow is too high so lots of O2 is entering the system.

2S + 3 O2 + H2O --> SO4-- + 2H+

We did not notice abnormal depletion of alkalinity.

Did you measure alkalinity in the effluent, or just the tank? Were you passing it over aragonite, as many do?

HIGHUET has made the assumption that the reason why sulphate level in the system does not rise due to the use of a sulphur reactor is because most of the produced sulphate is hold back in the calcium reactors and removed when they are cleaned

I can't see how sulfate could be "held back" in a CaCO3/CO2 reactor. What form would it take?

How do you know it didn't rise, and over what period of time? It is huge to start with in seawater, and so even a tiny percentage change could mean a substantial alkalinity reduction.

 

[Belgian Anthias]

Yes, sure. We are aware that we are producing some sulphate and there will be effect on alkalinity as any bacterial activity in the nitrate chain will do.

I mean sulfur oxidizing bacteria using O2 if the flow is too high so lots of O2 is entering the system.

2S + 3 O2 + H2O --> SO4-- + 2H+



Did you measure alkalinity in the effluent, or just the tank? Were you passing it over aragonite, as many do?

HIGHUET has made the assumption that the reason why sulphate level in the system does not rise due to the use of a sulphur reactor is because most of the produced sulphate is hold back in the calcium reactors and removed when they are cleaned

I can't see how sulfate could be "held back" in a CaCO3/CO2 reactor. What form would it take?

How do you know it didn't rise, and over what period of time? It is huge to start with in seawater, and so even a tiny percentage change could mean a substantial alkalinity reduction.

We measure the alkalinity of the tank! PH is monitored at the effluent of the calcium reactors after aeration of the water.
When talking about a sulfur de-nitrator system we mean always a reactor filled with sulfur and an other reactor filled with minimal the same amount of calcium-carbonate. We use two calcium reactors with the same volume, one with oystergrid and one with pure calcium carbonate. We can select the calcium reactors and use them in series or in parallel or direct the flow as needed.
We do not use other means to correct alkalinity. We do regular water changes every two month 1/5 of the system water. The drained water is UV sterilized and used for food cultivation and quarantine aqua. It is still buffered. The fresh water is made of dechlorinated tab water which we let pass trough the de-nitrator and the diakat reactor to remove all nitrate and phosphate before entering the system. No osmose water needed!

HIGHUET has made the assumption that the reason why sulphate level in the system does not rise due to the use of a sulphur reactor is because most of the produced sulphate is hold back in the calcium reactors and removed when they are cleaned

It where the findings published by Michel Hignette and not Highuet as I mistakingly have mentioned.

How do you know it didn't rise, and over what period of time? It is huge to start with in seawater, and so even a tiny percentage change could mean a substantial alkalinity reduction

I do not know! I only have never noticed any problems. Others have published articles where they claim that sulfate build up in the system is very limited. Hignette is the only one I know who claimed it stays in the calcium reactors and he tested these systems for years.

I only have an idea of the sulfate production produced by nitrate reduction.

I based myself on an article of which I do not know the author:
In the presence of nitrate, the reaction produces sulphate ions
2 H2O + 5 S + 6 NO3- ---> 3 N2 + 5 SO4-- + 4 H+ (extract from Randy)
The balancing of the equation gives:
6 NO3- + 5 S + 2 H2O ----> 3 N2 + 4 H+ + 5 SO4--
So, for every 6 moles of NO3- you get 5 moles of sulphate produced. In mass units, 1 ppm of nitrate gives 1.94 ppm of sulphate.
For 1 ppm nitrate reduction per day, the sulphate will increase by about 2 ppm per day. Normal seawater contains 2,710 ppm of sulphate.
So to get a boost of 10% in the normal sulphate concentration will take 136 days with no water changes at all.
How much change in sulphate is too much? Let's use the variation between salt mixes as a guide to what is "OK".
In Craig's study, the sulphate ranged from 1440 ppm (Coralife; about 53% of seawater) to 3550 ppm (Seachem; about 31% more than seawater). Only 2 of the 8 salt mixes were within +/-10% of seawater. Most were substantially low. Instant Ocean was about 18% low, and could use a boost.

2S + 3 O2 + H2O --> SO4-- + 2H+
I suppose that when this happens oxygen is depleted fast? This raises the question again that sulfur should be reduced when the daily nitrate production is known.
I have always propagated the use of 1% reactors and we never had to blame the de-nitrator to have caused any problems. This eliminates the question of how much sulfur exactly should be used.
When using a fluidized reactor one can not assume that nitrite will be in the effluent when flow becomes high because it may not be detectable? So we have to find an other way to find out when flow will become to high. 0 nitrate in the effluent may also not be used as an indication that everything works fine! When ORP is used at what readings the alarms should be set?
We try to keep the flow at minimum the systems volume a day and this makes it easy manageable and does what we expect it to do.

Looking for answers!

We want to make a fully automated and save de-nitration system based on the nitrate readings in the system water. Some made an expensive automated carbon based system. We try to keep it simple.

 

[Randy Holmes-Farley]

We measure the alkalinity of the tank! PH is monitored at the effluent of the calcium reactors after aeration of the water.
When talking about a sulfur de-nitrator system we mean always a reactor filled with sulfur and an other reactor filled with minimal the same amount of calcium-carbonate. We use two calcium reactors with the same volume, one with oystergrid and one with pure calcium carbonate. We can select the calcium reactors and use them in series or in parallel or direct the flow as needed.

So as I've indicated in other posts in these discussions, that only "solves" the alkalinity depletion problem by replacing it with a rising calcium problem. That is because the alkalinity depletes, and you replace it with dissolving calcium carbonate, leaving the calcium from that dissolution to boost the calcium in the water.

So to get a boost of 10% in the normal sulphate concentration will take 136 days with no water changes at all.
How much change in sulphate is too much? Let's use the variation between salt mixes as a guide to what is "OK".

I don't know, but I agree that a 10% changes probably won't cause issues. That is why the sulfate addition from nitrate only is not that big of a problem. When you allow additional oxidation of the sulfur with O2, and especially with higher flow giving more than minimal O2 oxidation of sulfur, the numbers rise and might be a concern, although the alkalinity depletion is a bigger issue, IMO. Using the minimum flow rate to reduce the nitrate will minimize this concern.

 

[hedgedrew]

I know someone who had to pull a sulphur reactor in a large tank because sulfides through off balance of salt water and coral got irritated or bleached stn. I know you guys are focusing on alk here. But wondering if evidence of sulfur media itself could do damage to coral??

 

[Belgian Anthias]

So as I've indicated in other posts in these discussions, that only "solves" the alkalinity depletion problem by replacing it with a rising calcium problem. That is because the alkalinity depletes, and you replace it with dissolving calcium carbonate, leaving the calcium from that dissolution to boost the calcium in the water.

I don't know, but I agree that a 10% changes probably won't cause issues. That is why the sulfate addition from nitrate only is not that big of a problem. When you allow additional oxidation of the sulfur with O2, and especially with higher flow giving more than minimal O2 oxidation of sulfur, the numbers rise and might be a concern, although the alkalinity depletion is a bigger issue, IMO. Using the minimum flow rate to reduce the nitrate will minimize this concern.

As we want to know what happens we have mixed 5l sulfur with 1l sulfur from a working reactor and we have put this in a recipient with 60l water from our system with heavy aeration. PH of the water 8.1. If 2S + 3 O2 + H2O --> SO4-- + 2H+ we should have low PH readings very soon. Sulfate will be measured with SO₄²⁻ MQuantâ„¢ test strips.
We had sulfur in seawater that we have kept in an open recipient as a reserve without aeration for more than 6 months now. Sulfate readings are about the same as in the system. This sulfur we have used to do the test.

As the nitrate production depletes alkanity and autotropic activity by the use of sulfur thus the same to reduce it to N we are aware of the posible alkalinty problem. As far we where able to buffer the water at a PH above 8. We are aware that when the water is buffered below PH 8 at high alkalinity, making corrections is difficult to manage. Our system is air driven and CO2 build up is avoided as possible and we have two display aqua in the system, one is lit from evening till morning, the other from morning till evening. Maybe this is the reason we have no issues with keeping a stable PH.

The concern about calcium we probably underestimate. For the moment we have no issues but in a heavily fed fish only thank this may be a problem which has to be solved.

This article does minimizes the problem a little bit:
2. CALCIUM SUPPLEMENTATION

Randy ( I think the author means you) takes a crack at how much calcium might be produced in the below

To estimate the magnitude of the effect, we start with a liberal estimate of how much nitrate might be removed. Say 10 ppm of nitrate per week.

10 ppm nitrate = 0.16 mmole/L of nitrate

Since 4 moles of H+ are produced for every 6 moles of nitrate consumed, this will produce 0.107 mmoles/L of H+ per week

How much calcium this could produce?
Assume that it takes one proton to dissolve one calcium carbonate:

CaCO3 + H+ ---> Ca++ + HCO3-

Clearly, this is a substantial overestimate because much of the acid will be used up driving the pH down to the point where CaCO3 can even begin to dissolve. Consequently, we have an upside limit of

0.107 mmoles of Ca++ per week

since calcium weighs 40 mg/mmol, that's 4.3 ppm Ca++ per week.

For comparison, an aquarist adding 2% of the tank volume in saturated limewater daily is adding on the order of 16 ppm of calcium per day.
Consequently, this method may not be especially useful for maintaining calcium and alkalinity levels.

Anyway, thank you for your reactions and show of interest. I will post the results of the tests within a month.

 

[Belgian Anthias]

I know someone who had to pull a sulphur reactor in a large tank because sulfides through off balance of salt water and coral got irritated or bleached stn. I know you guys are focusing on alk here. But wondering if evidence of sulfur media itself could do damage to coral??

First of all: this should, can and will not happen using a correct managed sulfur de-nitrator!

Sulfide can be formed if flow is to low, reactor is clogged or tunneling.
Anyway, the production is very low and should not have any influence in a large system.Sulfide is part of the sulfur chain and is processed in a normal aqua. It may occur in live sand, stone etc without noticing it.
I hope this guy found the reason of the unbalance. Sulfides? I do not think so, or there had to be a lot. PH? Did this guy a PH correction?

See water contains +- 3000ppm sulfate which means there is about 950 ppm of sulfur in natural seawater. http://www.lenntech.com/composition-seawater.htm. Pure sulfur is inert and will not dissolve in water.

 

[Belgian Anthias]

fluidized bed and ORP

fluidized bed and ORP

This post is about the use of fluidized bed reactors instead of tube reactors for sulfur de-nitration. In a tube reactor flow must go from bottom to top, in a fluidized bed the water is mixed. it is obvious that a fluidized bed can not be managed the same way as a tube reactor and that bacterial and chemical processes to reduce nitrate will be conducted differently. As flow regulation is the key for good management of a reactor we try to find out how it is best managed using a fluidized bed reactor and why!
Information and experiences about fluidized bed sulfur reactors are welcome.
We assume that the process in a fluidized bed is a bit self-regulating and the point of balance is difficult to find for minimizing the effect on alkalinity.
We are also interested in experiences with ORP readings as aid for good management.
In a tube reactor ORP readings are not reliable because when tunneling appears readings are not correct. A fluidized reactor eliminates the possibility of tunneling and clogging.

 

[Randy Holmes-Farley]

As we want to know what happens we have mixed 5l sulfur with 1l sulfur from a working reactor and we have put this in a recipient with 60l water from our system with heavy aeration. PH of the water 8.1. If 2S + 3 O2 + H2O --> SO4-- + 2H+ we should have low PH readings very soon.

All bacteria, including sulfur bacteria, need sources of nutrients such as N and P to grow. The bacterial growth may only proceed until the nutrients are gone in a closed test, and so might not reflect what would happen if you exposed the sulfur to an ongoing reef tnak.

 

[hedgedrew]

Yes I noticed the orp in the tube was off and bs. Ok thx. I'm not thrilled wiyh these sulfur tubes. I tried it first in hospital tank. Didn't want to chance to cycle it in main tank.

 

[CHSUB]

This post is about the use of fluidized bed reactors instead of tube reactors for sulfur de-nitration. In a tube reactor flow must go from bottom to top, in a fluidized bed the water is mixed. it is obvious that a fluidized bed can not be managed the same way as a tube reactor and that bacterial and chemical processes to reduce nitrate will be conducted differently. As flow regulation is the key for good management of a reactor we try to find out how it is best managed using a fluidized bed reactor and why!
Information and experiences about fluidized bed sulfur reactors are welcome.
We assume that the process in a fluidized bed is a bit self-regulating and the point of balance is difficult to find for minimizing the effect on alkalinity.
We are also interested in experiences with ORP readings as aid for good management.
In a tube reactor ORP readings are not reliable because when tunneling appears readings are not correct. A fluidized reactor eliminates the possibility of tunneling and clogging.

i use an ORP controller with a fluidized sulfur reactor. the controller turns a dosing pump on when the ORP is -230 and off when ORP goes above -220. i process about 14 gallon of water per day. i found this to be the easiest way to run the reactor.

 

[hedgedrew]

Chsub. You run with lot of sps?? Sulfur bother corals at all??

 

[tmz]

FWIW,
I run a sulfur denitrators on my friend's tanks and some of my tanks off the main system which now relies for nitrate control , primarily on organic carbon dosing with some refugia for controlling nitrate.
I built and used my reactor on the main system to take down high nitrates(60 ppm to 80ppm range) about 6 years ago with success over the course of several weeks taking nitrates to near zero.

There were no negative effects on sps or other animals observed.

Mine has has a circulating pump and a feed pump not unlike a calcium reactor.I'm not a sure what the OP means by "fluidized " .

I used much less sulfur than the OP rigidly prescribes. I used 3 liters for the the 575 gallon system. The Op's method absolutely requires 2% of the water volume be the amount of sulfur for tanks with nitrate at 50 ppm or more( 15 times as much as I needed) and that it never be adjusted. He has stated there is no such thing as excess sulfur.



Sulfur denitrators are effective for reducing nitrate. They do reduce alkalinity and produce sulfate .
I have to pay attention and reduce the amount of sulfur in use and increase the effluent flow as nitrate in the tank drops to low levels. Otherwise, anoxia and H2S production will occur in the reactor. As a safety running the effluent through some gfo can accelerate oxidation of any H2S that inadvertently occurs while tuning the reactor in to an optimal level of sulfur and flow for your tanks daily needs.

Using excessive amounts of sulfur is ill advised;imo ,sulfur should be balanced to the nitrate level in the tank ,the overall water volume and the dilly input of foods;not just the water volume.

Higher flow adds more oxygen and more nitrate from the tank water to the reactor. However, nitrate may be not be reduced at all with high flow and excessive amounts of sulfur and oxygen. The facultative bacteria just use the oxygen preferentially in their aerobic mode with no useful benefit of any kind and no anerobic nitrate reduction .The volume of active
bacteria is related to the amount of sulfur used for energy available to them.
As Randy noted , the same negative effects on alkalinity, and sulfate production occur with no nitrate reduction via the aerobic activity ; more so actually with excessive sulfur and flow.
The higher flow provides more oxygen which can insure against anoxia in the reactor but at the expense of excessive sulfate production and alkallinity depletion.

Balancing the amount of sulfur and the effluent flow rate to provide optimal conditions for anaerobic activity without anoxia minimizes the sulfate production and alkinity depletion. Tuning that in for a specific tank can take a little give and take initially.

 

[hedgedrew]

Sounds like some balancing act. Watch out for too much oxygen. Watch out for channeling? Watch out for too little oxygen and hydogen sulfide. Watch out for alkalinity issues. Whatch out for rising sulfates. I'm sure I'm missing some. Maybe I should switch to bio pellets. Lol

 

[Belgian Anthias]

Sounds like some balancing act. Watch out for too much oxygen. Watch out for channeling? Watch out for too little oxygen and hydogen sulfide. Watch out for alkalinity issues. Whatch out for rising sulfates. I'm sure I'm missing some. Maybe I should switch to bio pellets. Lol

Using fluidised bed reactors eliminates clogging and tunnelling. Same for BIO filters.
Alkalinity is always an issue in a closed system. H2S is easily controlled and avoided.
BIO pellets? Ask the same questions and what are the answers?

 

[Belgian Anthias]

i use an ORP controller with a fluidized sulfur reactor. the controller turns a dosing pump on when the ORP is -230 and off when ORP goes above -220. i process about 14 gallon of water per day. I found this to be the easiest way to run the reactor.

Can you tell me where and how you measure the effluent of the reactor or is ORP measured inside the reactor?
14 Gal/day. What is the system volume?
Some have published target readings between -100mv and -250mv and - 50mv is to high and -300mv is to low.
You use a narrow range between - 230mv and - 220mv close to the -250mv which is assumed to be save. I may assume that the flow is made as low as possible this way?