DIY Sulfur Denitrator

[Belgian Anthias]

The orp in my reactor is -245
Is there a magical orp number the reactor should run at ?

Hello,

I would like to know more about the effect of the nitrate level in the system on the ORP of the sulphur reactor effluent.
When nitrate levels in the aquarium system change up or down does this reflect on ORP reading of the reactor? ( same flow). i would like to know if the quantity of nitrate entering the reactor has any noticable influence on the ORP reading. (same flow)
Maybe you can help me out here.
Thank you.

 

[Greg 45]

Hoping this helps . Amount of nitrates in tank started at 40 to 60ppm
tank is dropping at around 10ish now
Flow through the reactor is 25 ml a minute
The only way the orp changes for me is if I increase the flow / at the point the effluent will not be reading zero .

 

[tmz]

I would like to know more about the effect of the nitrate level in the system on the ORP of the sulphur reactor effluent.

Nitrate,NO3, increases ORP.

The effluent NO3 level depends mostly on the amount of nitrate flowing into the reactor and the amount of sulfur in the reactor vs. the amount of NO3 used by anaerobic activity in the reactor.

 

[Greg 45]

tmz trying to answer the question the best that I can.
When the reactor was new it takes some time to start working
As the nitrates in tank started to degrease the orp has not changed staying at -245
the effluent remains at 0

 

[tmz]

Gregg,

It wasn't my question but thanks for the information. It was Belgian's question.

I'm only providing information on the effect of NO3 on ORP and then likely fate of NO3 in a sulfur reactor.

I personally haven't used ORP to monitor or regulate a sulfur denitrator and don't know whether or not that can be useful given the complexities of ORP .
So, I'm interested in analysis and information from those experimenting with it.

FWIW, my tanks run ORP from 320 to 38O mv most of the time with NO3 at 0.2ppm .NSW varies but somewhere between 250mv and 450 mv seems about right for most reef tanks. Don't know if there is an optimal number or what it might be for anaerobic nitrate reduction in a sulfur reactor

 

[tmz]

The only way the orp changes for me is if I increase the flow

Does ORP go up or downwhen the flow is increased?

 

[Greg 45]

To add to that you are correct about orp / and I feel the hobby grade probes are useless / they state we need to monitor through out the day . In a few weeks I am having built GF signet system which has all quality approved probes. I will up date tank reading with this new probe. I have given up on hobby grade equipment to monitor tank parameters.

 

[Belgian Anthias]

tmz trying to answer the question the best that I can.
When the reactor was new it takes some time to start working
As the nitrates in tank started to degrease the orp has not changed staying at -245
the effluent remains at 0

ORP did not change decreasing the nitrate level from +- 40ppm to +- 10ppm. correct?
Flow is now +-25ml/min = +- 1.5l/h. Did you change ( increased or decreased) the flow to keep ORP at-245?

 

[Greg 45]

Correct flow has not changed
25ml/min orp still at -245

 

[Belgian Anthias]

ORP changes?

ORP changes?

Correct flow has not changed
25ml/min orp still at -245

Thank You very much.
I suspect that some day the level will not descend any more when the flow is not increased. When that point is reached I would like to know if there will be any change in ORP reading. Thanks.

 

[Belgian Anthias]

ORP and autautrophe denitrification.

ORP and autautrophe denitrification.

Autotrobe denitrification may start at a ORP reading of +50 mv. Biological Phosphorus release between -100 and -225mv; Sulfide formation may occur between -50mv and -250mv.( from wastewater treatment)
We do not use ORP in BADESS. For autotrophe denitrification I would try to keep it above - 100mv ( +- -50mv) and see how this works.

 

[Belgian Anthias]

How big the reactor must be?

How big the reactor must be?

In a 600 gal aquarium system I intent to keep the nitrate level at 0.2ppm. I want to keep a lot of fish and the daily nitrate production to remove is estimated to be 0.5ppm daily. This means that the total volume of the system must pass the reactor 2.5 times daily to be able to remove 0.5ppm daily ( 0.5ppm/ 0.2ppm), this is 1500 gal daily= 62 gal/h or 240l/h
I want to build a sulphur denitrator which is able to keep the nitrate level at the desired level of 0.2ppm.
How big the reactor has to be to be able to deplete the oxygen entered and maintain ORP at +- -50mv supposing the reactor is filled with sulfur.
I estimate that the reactor must have a volume of at least 50l or 13gal.

 

[rclendan]

Wow... I had no idea that when I posted the original carbon question I would be sparking such a controversy. I only wanted to discuss experimentation with optimizing the denitrator that I was already running. I observed that if I added a small amount of carbon in the form of sucrose, just to cycle the unit after cleaning, It would become extremely efficient for a short period of time, until the carbon source was depleted, then it would settle to a less efficient, but acceptable (0 Nitrate) flow rate. I postulated that the added carbon must be a) feeding T. denitrificans, b) helping to maintain a low ORP through the respiration of aerobic species, or c) it could be creating conditions favorable to anoxic denitrator species (like a Carbon denitrator. Although, the unit never goes anoxic). Whatever the mechanism, it does work. Dripping a 0.15% sucrose solution works as a delivery method, but the dosing lines get hopelessly clogged with biomass from opportunistic bacteria. With regards to the use of C02 as an alternative, everything I read about these denitrifying bacteria confirms that they are carbon fixing and can get at least part the carbon they need from dissolved CO2 like green plants do. Thus the idea of adding a small amount of CO2 to the unit to stimulate growth seemed reasonable.

excerpts from micobe Wiki:

https://microbewiki.kenyon.edu/index.php/Thiobacillus_denitrificans

Studies on fixation of carbon dioxide of T. denitrificans found that it is capable of synthesizing hexose phosphates from carbon dioxide by a cyclic mechanism which is similar to that found in green plants.

T. denitrificans grows aerobically on thiosulfate, tetrathionate and thiocyanate; it also grows anaerobically on thiosulfate, tetrathionate, thiocyanate, sulfide or elemental sulfur.

H2S + HS- + NO3- + CO2 + HCO3- + NH4+ --> SO42- + N2 + C5H7O2N (biomass) + H+ + H2O

The ideal temperature and pH for growth is 28-32 degrees Celsius and 6.8-7.4, respectively.

T. denitrificans clearly needs some form of carbon as all life does, The question is: in what form, and what is the limiting amount of carbon for a particular colony, and is my aquarium water below that optimal limit?

My test is almost set up. I have acquired a 5 lb. CO2 cylinder and regulator. I will run an experiment in the next few weeks, collect as much data as I can, and maybe we can settle this once and for all.

 

[Belgian Anthias]

Wow... I had no idea that when I posted the original carbon question I would be sparking such a controversy. I only wanted to discuss experimentation with optimizing the denitrator that I was already running. I observed that if I added a small amount of carbon in the form of sucrose, just to cycle the unit after cleaning, It would become extremely efficient for a short period of time, until the carbon source was depleted, then it would settle to a less efficient, but acceptable (0 Nitrate) flow rate. I postulated that the added carbon must be a) feeding T. denitrificans, b) helping to maintain a low ORP through the respiration of aerobic species, or c) it could be creating conditions favorable to anoxic denitrator species (like a Carbon denitrator. Although, the unit never goes anoxic). Whatever the mechanism, it does work. Dripping a 0.15% sucrose solution works as a delivery method, but the dosing lines get hopelessly clogged with biomass from opportunistic bacteria. With regards to the use of C02 as an alternative, everything I read about these denitrifying bacteria confirms that they are carbon fixing and can get at least part the carbon they need from dissolved CO2 like green plants do. Thus the idea of adding a small amount of CO2 to the unit to stimulate growth seemed reasonable.

excerpts from micobe Wiki:

https://microbewiki.kenyon.edu/index.php/Thiobacillus_denitrificans



T. denitrificans clearly needs some form of carbon as all life does, The question is: in what form, and what is the limiting amount of carbon for a particular colony, and is my aquarium water below that optimal limit?

My test is almost set up. I have acquired a 5 lb. CO2 cylinder and regulator. I will run an experiment in the next few weeks, collect as much data as I can, and maybe we can settle this once and for all.

Interesting but I have some remarks:
How do you know you are feeding and cultivating T.denitrificans? There will be a lot of diff species of bacteria active depleting the oxygen. Nitrifying and de-nitrifying species.
A sulfur de-nitrator works fine without adding carbon. When the reactor is big enough it is very effective and reliable.
There is CO2 present in the effluent due to dissolving of the calcium carbonate. This shows when the effluent is aerated and PH increases to reach normal values.
The big advantage of a sulfur-denitrator is that one can know how much nitrate is removed daily and the reactor does not need daily accurate dosing of food (carbon). When bacteria are cultivated by feeding carbon the nitrate in there tissue will be released back in the system when they die. Probably most of them succumb before leaving the reactor producing a lot dead bio-load and waste which results in a not wanted bioifilm on the media which means a lot of cleaning and an increased risk for clogging and dis-function.

Anyway, I am interested in the results of this interesting initiative.

 

[rclendan]

I get what you are saying, but based on my observations, I am arriving at a different conclusion..

As I wrote, I am not sure that most of the carbon is not just reducing ORP, or feeding T.denitrificans (I assume both). I do know that my denitrator works a lot better (much higher 0 ppm nitrate flow rate from a small denitrator) if I add carbon in the form of a small amount of sucrose. I am trying CO2 in place of sucrose to avoid the problems with liquid dosing, and to verify a hypothesis.

If you look at the chemistry, there is no CO2 produced from T.denitrificans respiration. You can see that the stoichiometry shows the production of free hydrogen ions (H+) that mix with water to form hydronium H3O+ as the source of acidity to dissolve the Calcium Carbonate in the reactor, so no direct CO2 is produced in the output products of respiration or feeding. The bacteria consume the free CO2 right out of the water, that is what carbon fixing is.

H2S + HS- + NO3- + CO2 + HCO3- + NH4+ --> SO42- + N2 + C5H7O2N (biomass) + H+ + H2O

Aeration of the effluent, in any case, probably just facilitates the equilibrium reaction in the presence of carbonate:

2 H2O <--> OH− + H3O+

CaCO3 + H+ -> Ca+2 + HCO3-

Thus alkalinity is used up. If T.denitrificans was a carbon dioxide emitter, it would have probably green house gassed our planet to death long ago. There have even been studies looking at these microbes as potential carbon sinks for use in large scale, deep aquifer, carbon sequestration from fossil fuel combustion.

 

[tmz]

This is what happens
11 S + 10 NO3- + 4.1 HCO3- + 0.5 CO2 + 1.71 NH4+ + 2.5 H2O

--->

0.92 C5H7NO2 +11 SO4-- + 5.4 N2 + 9.62 H+

note: 0.5 CO2 is used in forming the organic (C5H7NO2)


CO2 and HCO3 are used by the sulfur bacteria for the C in the organic C5H7NO2 .


Since there has been back and forth on organic carbon dosing and the C for the sulfur bacteria, it might help to briefly clarify terms at this point.

We often use the term carbon to describe several molecules :

Organic carbon is a carbon atom,C, bound to hydrogen and other elements in organic compounds; the bond is a life energy source for heterotrophic organisms including heterotrophic bacteria.

CO2 is inorganic it is used not produced by chemolithoautoptrophic baceteria like sulfur bacteria T. nitrificans, which get their energy from sulfur and do produce organic carbon using CO2. They don't benefit from orgnaic carbon dosing,they make their own orgnic carbon and use CO2.

Dosing some CO2 might be helpful if you suspect it's low but I'm not clear on how it would be given the carbonate in play and tank water flowing in carries it in too .

Take a look at the +9.62H.That is a significant increase in acicdity and reduces pH and alkalinity. Dosing extra CO2 will also add more H+ as the CO2 hydrolizes( CO2 + H20 ----> CHO3 + H) fruther reducing the pH. In your trial , I'd monitor pH in the reactor if adding extra CO2 to the reactor; it might go below the tolerance or optimal range for T nitrifcans. Per the link you cited:

The ideal temperature and pH for growth is 28-32 degrees Celsius and 6.8-7.4, respectively. Although Thiobacillus denitrificans is an anaerobic organism, it can live under aerobic conditions.

 

[tmz]

I do know that my denitrator works a lot better (much higher 0 ppm nitrate flow rate from a small denitrator) if I add carbon in the form of sucrose. I am trying CO2 in place of sucrose to avoid the problems with liquid dosing, and to verify a hypothesis.

Could you state the hypothesis?

I think the sucrose was likely feeding heterotrophic denitrifying bacteria not the T. nitrificans which is is a faucultative obligate chemolithotroph . Do you have reason to think otherwsie?

It could be the heterotrophs were encouraged by the organic carbon addition adding some some CO2 useful to the obigate chemolithoautotrops in the process but they might have just outcompeted the auotrophs for other nutrients like N and oxygen for example. It would be cool if the heterotropjhs and autotrophs balanced but heterotrophs are quite competitive often noted to outcompete autotrophic populations particularly ammonia oxidizers. I've though about combining organic carbon dosing with sulfur denitrication but backed away because of concern over heterotrophic dominance.

Good luck with your experiment. LEt us know how it turns out.

 

[rclendan]

I think the sucrose was likely feeding heterotrophic denitrifying bacteria not the T. nitrificans which is is a faucultative obligate chemolithotroph . Do you have reason to think otherwsie?

You may be correct. Although, there is a study that shows autotrophic bacteria are not uniquely inhibited by organic matter, and that all obligate autotrophic bacteria so far tested can assimilate and metabolize externally supplied organic compounds. Not my area of expertise though.

See: The obligate autotroph — the demise of a concept

That being said, the increase seems too high to be just ORP related. And wouldn't the normal heterotrophs require anoxic conditions before they could reduce Nitrates? The denitrator is not completely anoxic. I also agree that pH monitoring is critical to avoid excessively low pH. I am adding fittings to accommodate two probes in the lid to continuously monitor pH, and ORP. when this is done, I think my sulfur denitrator will end up being re-tasked as a calcium reactor, since I am effectively turning it into one. I will then most likely build a much larger S denitrator.

I guess another good test would be to run the denitrator with no sulphur, just aragonite, and add sucrose as a control for heterotrophic denitrification.

 

[Belgian Anthias]

What happens when H+ reacts with calcium carbonate in water with no free oxygen and no nitrate when passing the the calcium-reactors ?

Why does the PH raises to a normal value when the low oxygen effluent is aerated?

BADESS is a maintenance free system. Dosing CO2 from a bottle eliminates this advantage.
This may result in a dangerous overdosed CO2 calciumreactor!

Why making it difficult when just installing bigger or more reactors solves the problem?

 

[rclendan]

Why does the PH raises to a normal value when the low oxygen effluent is aerated?

Aeration of the effluent mechanically facilitates the equilibrium reaction in the presence of carbonate. If there was no carbonate, aeration would lower pH by adding CO2:

When there is more H3O+ than OH- , the addition of bicarbonate absorbs the protons and eventually with enough addition will start to deprotonate water and produce more OH- than H3O+ and thus you have a basic solution. These equilibrium reactions would be happening all the time:

2 H2O <--> OH− + H3O+

and

CaCO3 + H+ -> Ca+2 + HCO3-

HCO3- + H2O <-> CO3-- + H3O+

BADESS is a maintenance free system. Dosing CO2 from a bottle eliminates this advantage.
This may result in a dangerous overdosed CO2 calciumreactor!

Largely agree, I am more interested in why carbon improves performance so much. If T. Denitrificans is truly an obligate autotroph, then indeed CO2 is the only way to get carbon they need to them and my sucrose additions are doing something else. A small amount of CO2 (6-10 bubbles a minute) should not appreciably alter aquarium parameters. and if I am correct, the bacteria will consume it. At any rate, I don't see CO2 dosing as a permanent solution; a larger unit would process more water at a lower efficiency, but would be low maintenance.

Why making it difficult when just installing bigger or more reactors solves the problem?

It's the geochemist in me I guess, I want to verify and understand the mechanism. Plus some may have limited space and this addition could provide a way to run a small denitrator (like mine) much more efficiently.