Nitrate and the BIO filter!

[Belgian Anthias]

What to do with the nitrate produced by biofilters? Or live rock, sandy bottom, and in or on any other place where a biofilm can or may grow? The question has banned the biofilter and replaced it by a lot of discussable methods and palliative measures.

An aquarium grows, creatures grow and multiply, produce waste. Also in ultra LNS nitrate will accumulate.
What about increasing the live support capacity of a mixed reef aquarium and supplying the demands of the growing community? How this can be done? It is not nitrate which is the limiting factor but the capacity to remove ammonia-nitrogen. The introduction of denitrators or other nitrate removal substitutes do not change a thing for that matter. When the limit of the ammonia reduction capacity is reached one will know it when it is to late.

A reason why nitrate will accumulate in an aquarium may be the fact there is not enough suitable usable sulphur available, also in a seawater aquarium despite of the presence of a high quantity of sulphur compounds in the water.

The solution is very simple and is based on a biofilm. In a normal biofilm, mineralization, nitrification and denitrification are to a greater or lesser extent taking place. In a biofilm that removes 100% of the ammonia produced and fed to it, approximately 3/5 of the nitrogen is released in the water column in the form of nitrate. On average, only 2/5 of the nitrogen is effectively removed by the biofilm. . Part of that 2/5 is removed prophetically by heterotropic denitrification depending on the availability of suitable organic carbon compounds in the anaerobic zone of the biofilm, a part by sulphur bacteria using the hydrogen sulphide formed by and within the biofilm by transforming it to sulphur or sulphate, converting nitrate to nitrogen gas.
By providing elemental sulphur as a base for the growth of the biofilm, the base can be used as substrate suitable for the growth of autotrophic sulphur bacteria, which growth is not limited any more by the limited availability of HS which will cause the residual nitrate to be converted into nitrogen gas, whereby 100% of the ammonia nitrogen can be effectively removed.
As it is ammonia nitrogen which is removed from the system the live support capacity of the system may be increased considerably.

it is an application of BADES.

 

[Randy Holmes-Farley]

I'm not a big fan of sulfur denitrators or adding sulfur since it depletes alkalinity. I think other methods may be better (e.g., organic carbon dosing).

 

[Belgian Anthias]

Most of the links don't work.

I'm not a big fan of sulfur denitrators or adding sulfur since it depletes alkalinity. I think other methods may be better (e.g., organic carbon dosing).

As thus ammonia reduction ( nitrification). Normally measures against depletion of alkalinity are present in the system. When using a sulphur based bio-filter ( BADES bio-filter) there is no need for measures to compensate for alkalinity depletion caused by nitrification as the complete ammonia- nitrogen removal cycle, nitrification and denitrification, is already compensated for when leaving the biofilm.


The purpose is simultaneous nitrification and denitrification on a base of elemental sulphur. All reactions take place within the biofilm. In practice a mix of sulphur and aragonite or oystershell may be used as a base.
As the denitrification is mixotropic and a part of the produced nitrate is reduced using HS the effect on alkalinty is minimal. Mixing the sulphur with lime will solve the problem completely.

55S + 44CaCO 3 + 50NO 3- + 18H2O + 4NH4+ → 4 C5H7O2N + 25N 2 + 55SO4 2- + 44Ca 2+ + 24HCO3- ( T.C. Zhang 2004)

I am not a fan of denitrators! When they are kept anoxic they are very vulnerable for mismanagement and for this reason not suitable for to be used in a live support system.
Anyway, a sulpur denitrator must not be kept anoxic and works very well at a flow of once or twice the total volume of the system each day. Denitrators do not add anything to the carrying capacity of the system which is the aim.

Just adding some sulphur is enough. A bioreactor is used when the user wants full control over the nitrate removal rate and the nitrate level. No need for a denitrator. A normal aerobic biofilter with sand as a base for the biofilm removes +- 25%, with sulphur as a base everything can be removed.


Carbon dosing removes nothing. Only adds. A skimmer removes max +- 35% of TOC and is very selective in removing live bacteria causing an unbalance.
To assimilate 1 gram of NO3-N 8 grams of biomass ( protein) is produced . This is the equivalent of 20 grams of food with 35% protein. When this is added and consumed +- 80% is released back in the system producing +- 4ppm nitrate. Most of the cultivated biomass will not be available for skimming. What happens with the rest of the produced protein? Most of it will be consumed. After some time of dosing carbon hydrates one thus not know for sure if the nitrate assimilated by the new dose is natural or the result from previous dosing. Carbon dosing does not increase the carrying capacity of a closed system at all . Carbon dosing let grow the system which may be a good thing as long as the carrying capacity is not reached.
Vinegar, sugar and vodka are added to seawater in a closed system!?
LNS have low phosphate! What if the carbon hydrates accumulate? Heterotropic ammonia reduction producing bacterial slime clogging everything, interruption of the nitrogen cycle, oxygen depletion, this when suddenly enough phosphate comes available due to feeding?
When carbon dosing must be used to assimilate nitrate, nitrification and denitrification is not in balance and alkalinity is depleted when no special measures are taken. The more often must be dosed the bigger the unbalance.
Carbon dosing using vinegar, vodka or sugar? No thank you!

Using sulphur as a base for a growing biofilm removes ammonia- nitrogen effectively from the system, for ever. Carbon dosing promotes nitrate-nitrogen assimilation but removes nothing with the exception for the unknown and unpredictable quantity which may be removed by a skimmer.

In which way carbon dosing would be better?

No other method available which I know of and have studied will give better results in removing ammonia-nitrogen out of the system. Used in a reactor one has full control over the nitrate removal rate and the nitrate level.

 

[Randy Holmes-Farley]

As thus ammonia reduction ( nitrification). Normally measures against depletion of alkalinity are present in the system. When using a sulphur based bio-filter ( BADES bio-filter) there is no need for measures to compensate for alkalinity depletion caused by nitrification as the complete ammonia- nitrogen removal cycle, nitrification and denitrification, is already compensated for when leaving the biofilm.


The purpose is simultaneous nitrification and denitrification on a base of elemental sulphur. All reactions take place within the biofilm. In practice a mix of sulphur and aragonite or oystershell may be used as a base.
As the denitrification is mixotropic and a part of the produced nitrate is reduced using HS the effect on alkalinty is minimal. Mixing the sulphur with lime will solve the problem completely.

55S + 44CaCO 3 + 50NO 3- + 18H2O + 4NH4+ → 4 C5H7O2N + 25N 2 + 55SO4 2- + 44Ca 2+ + 24HCO3- ( T.C. Zhang 2004)

That is not correct and your own equation proves it.

The process involving sulfur and ammonia to N2 involves loss of alkalinity. A big loss!

Yes, you can compensate for the alk part of it by adding alkalinity back. You do that in your equation by dissolving some calcium carbonate:

CaCO3 + H2O ---> Ca++ + 2HCO3-

or

44 CaCO3 + 44 H2O -- > 44 Ca++ + 88HCO3-

If we remove that part of the process from your equation (subtract from both sides), we get:

55S + 50NO 3- + 18H2O + 4NH4+ + 64HCO3- → 4 C5H7O2N + 25N 2 + 55SO4 2- + + 26H2O

Hence it is causing a big loss of alkalinity (16 equivalents of alkalinity for each ammonium consumed).

The problem with your approach, using dissolution of calcium carbonate as your equation shows to offset the alkalinty loss, is that the calcium will be constantly rising.

 

[Randy Holmes-Farley]

When carbon dosing must be used to assimilate nitrate, nitrification and denitrification is not in balance and alkalinity is depleted when no special measures are taken. The more often must be dosed the bigger the unbalance.
Carbon dosing using vinegar, vodka or sugar? No thank you!

.....

In which way carbon dosing would be better?

No other method available which I know of and have studied will give better results in removing ammonia-nitrogen out of the system. Used in a reactor one has full control over the nitrate removal rate and the nitrate level.

You are mistaken.

Consuming nitrate by dosing organic carbon EXACTLY offsets the alkalinity that is depleted when ammonia is converted into nitrate. Hence the process taking place in the tank is exactly neutral toward alkalinity.

It is better because the overall process has no net effect on alkalinity, and because the bacteria feed filter feeders.

 

[Belgian Anthias]

You are mistaken.

Consuming nitrate by dosing organic carbon EXACTLY offsets the alkalinity that is depleted when ammonia is converted into nitrate. Hence the process taking place in the tank is exactly neutral toward alkalinity.

It is better because the overall process has no net effect on alkalinity, and because the bacteria feed filter feeders.

As far as I know to assimilate 5 gr NO3-N, heterotropic bacteria metabolism consumes 76.5gr carbohydrates 23.8 gr oxygen and 18gr alkalinity (3.57 g Alk/g N) (Ebling et Al 2006)
This does not take into account the alkalinity loss due to nitrification, the production of the nitrate assimilated. At high C:N ratio nitrification may be bypassed as ammonia will be used, producing 40 x more biomass. When nitrification takes place in a biofilm growing on aragonite than nitrification has no negative effect on alkalinity. Also in such a biofilm BADES takes place. It is a natural process which takes place everywhere. It takes place in every thank and is responsible for +- 5 % of the denitrification, this without adding any sulphur.

So we disagree towards alkalinty

Correct , most bacteria are not removed and feed the filter feeders, rotifiers, copepods, corals, scrimp, and a lot of planktonic predators. But 80% of it is released back into the system as ammonia. They feed the pray for other predators and so on. When the predators die everything is released back into the system. This may go on until the carrying capacity is reached.

When looking to only one process, autotropic denitrification by T. denitrificans with elemental sulphur, carbonate is used but only on that place where the reaction takes place on the sulphur, an other reaction taking place on the chalk a fraction later may create carbonate. Ph and alkalinity are measured in the water column and are a result of the sum of all these reactions.

The BADES process consumes carbonate? YES A BADES biofilter depletes alkalinity of the system? NO

I must say that in a BADESS the biofilm grows on a base of a mix of oyster shell grit and sulphur granulate. There is no special effect on the alkalinity in the water column caused by BADES
Practically the sulphur must be mixed with at least the same quantity of calcium carbonate. Calcium is produced. Is this bad in a reef aquarium?

 

[Randy Holmes-Farley]

Sorry, No. That is incorrect.

I agree with the equations in your reference, and they are the same ones that I often use my articles. But you have misunderstood the processes involved. There is no net consumption of alkalinity.

Ebling et Al 2006:

https://cals.arizona.edu/azaqua/ist...ichiometry of photo-auto-hetero - Ebeling.pdf

Equation 16 shows:


NH4+ + 1:18 C6H12O6 + HCO3- = 2:06 O2 --> C5H7O2N + 6:06 H2O + 3:07 CO2

" This equation predicts that for every g of ammonia– nitrogen converted to microbial biomass, 4.71 g of dissolved oxygen and 3.57 g of alkalinity (0.86 g inorganic carbon) and 15.17 g carbohydrates (6.07 g organic carbon) are consumed. Also 8.07 g of microbial biomass (4.29 g organic carbon) and 9.65 g of CO2 (2.63 g inorganic carbon) are produced"

This seems, at a first glance, to be consuming one unit of alkalinity (HCO3-) for each ammonia consumed), but that does not hold up to a deeper understanding of the processes involved.

The thing that you (and perhaps the author) are neglecting is that the nitrogen compound that is the product of metabolism by fish and other organisms is NOT NH4+. It is NH3.

The metabolism reaction is exactly the reverse of equation 3 in your reference. The product of the metabolism of organic matter with nitrogen in it is NH3. Of course, the reaction can be written as if it is NH4+, but when you do that, you necessarily produce alkalinity. That is what the reverse of equation 3 actually shows. Production of NH3 and then combination of that with some of the CO2:

NH3 + H2CO3 ---> NH4+ + HCO3-

And the reverse of equation 3 shows this "production" of HCO3- explicitly. Same for phosphate.

Consequently, the overall round trip from fish food to ammonia to production of biomass by consumption of ammonia to biomass formation with organic carbon has NO NET EFFECT ON ALKALINITY.

The same is true if you convert the ammonia along the way to nitrate. The overall round trip from fish food to ammonia to nitrate to production of biomass by consumption of nitrate to biomass formation with organic carbon has NO NET EFFECT ON ALKALINITY.

 

[Randy Holmes-Farley]

Calcium is produced. Is this bad in a reef aquarium?

I think so.
It precludes your ability to use a balanced method of calcium and alkalinity addition, such as a CaCO3/CO2 reactor to maintain alkalinity, without calcium continually climbing. It is just another way of saying your sulfur process depletes alkalinity while most other nitrate reduction methods do not (macroalgae growth, and organic carbon dosing, and ordinary denitrification).

 

[Belgian Anthias]

What we want is to get away from the LNS ( low nutrient system) and have the possibility to increase the live support capacity of a mixed reef to our needs. An aquarium system that may grow with its habitants. That this can not be done with any nitrate removal method is obvious, certainly not with carbon dosing. Alkalinity is not the first obstacle where I was thinking about for finding the solution. Alkalinity is not really a problem in a reef aquarium as there are a lot of solutions available to correct it. What to do with the nitrate produced by a bio-filter?
I found the solution in the application of BADES in a normal bio-filter or -reactor.
What about alkalinity, Ph, sulphate, phosphate, hydrogen sulphide, calcium, carbonate, ammonia, nitrite and nitrate? Who is doing what? Who or what is responsible? So I looked it up to find out. I also studied other methods and compared. Non of them was found suitable. Not controllable , not predictable, not reliable etc. Most add nothing to the live support capacity of the ZMAS
Most important in finding the solution was the study of the biofilm, a very special environment, not at all comparable with what is going one in the water column where it grows although it is influenced by it.
All nitrogen cycle processes in one and the same biofilm, in one and the same reactor, just by adding elemental sulphur ?

 

[Belgian Anthias]

Sorry, No. That is incorrect.

I agree with the equations in your reference, and they are the same ones that I often use my articles. But you have misunderstood the processes involved. There is no net consumption of alkalinity.

Ebling et Al 2006:

https://cals.arizona.edu/azaqua/ista/ISTA7/RecircWorkshop/Workshop PP & Misc Papers Adobe 2006/7 Biofiltration/Microbial Floc Systems/2006 Aquaculture Stoichiometry of photo-auto-hetero - Ebeling.pdf

Equation 16 shows:


NH4+ + 1:18 C6H12O6 + HCO3- = 2:06 O2 --> C5H7O2N + 6:06 H2O + 3:07 CO2

" This equation predicts that for every g of ammonia– nitrogen converted to microbial biomass, 4.71 g of dissolved oxygen and 3.57 g of alkalinity (0.86 g inorganic carbon) and 15.17 g carbohydrates (6.07 g organic carbon) are consumed. Also 8.07 g of microbial biomass (4.29 g organic carbon) and 9.65 g of CO2 (2.63 g inorganic carbon) are produced"

This seems, at a first glance, to be consuming one unit of alkalinity (HCO3-) for each ammonia consumed), but that does not hold up to a deeper understanding of the processes involved.

The thing that you (and perhaps the author) are neglecting is that the nitrogen compound that is the product of metabolism by fish and other organisms is NOT NH4+. It is NH3.

The metabolism reaction is exactly the reverse of equation 3 in your reference. The product of the metabolism of organic matter with nitrogen in it is NH3. Of course, the reaction can be written as if it is NH4+, but when you do that, you necessarily produce alkalinity. That is what the reverse of equation 3 actually shows. Production of NH3 and then combination of that with some of the CO2:

NH3 + H2CO3 ---> NH4+ + HCO3-

And the reverse of equation 3 shows this "production" of HCO3- explicitly. Same for phosphate.

Consequently, the overall round trip from fish food to ammonia to production of biomass by consumption of ammonia to biomass formation with organic carbon has NO NET EFFECT ON ALKALINITY.

The same is true if you convert the ammonia along the way to nitrate. The overall round trip from fish food to ammonia to nitrate to production of biomass by consumption of nitrate to biomass formation with organic carbon has NO NET EFFECT ON ALKALINITY.

See table 4
And I agree when the reaction is reversed it removes nothing. But this proves my point that finally, exept for the small part removed by the skimmer, that at the end carbon dosing removes nothing but adds. This means that continuing carbon dosing leads to a decrease of the usable live support as the capacity is filled up by the dosing.

 

[Randy Holmes-Farley]

See table 4
And I agree when the reaction is reversed it removes nothing. But this proves my point that finally, exept for the small part removed by the skimmer, that at the end carbon dosing removes nothing but adds. This means that continuing carbon dosing leads to a decrease of the usable live support as the capacity is filled up by the dosing.

Certainly, trace elements are removed, if that is what you mean. N and P are also exported if skimmed out.

 

[Randy Holmes-Farley]

What we want is to get away from the LNS ( low nutrient system) and have the possibility to increase the live support capacity of a mixed reef to our needs. An aquarium system that may grow with its habitants. That this can not be done with any nitrate removal method is obvious, certainly not with carbon dosing. r

Huh? Can't be done?

I ran a non ULNS system for 20 years using several fine methods to control nutrients, including growing macroalgae and organic carbon dosing. It does not become ULNS unless you overdo any of these methods.

 

[Lasse]

@Randy Holmes-Farley

Are you sure that the fishes not transport NH4 through the gills? My old textbooks say so. Fishes are also able to get out of excess nitrogen against a concentration in form of NH4. However if NH3 concentration is high in the water - NH3 will be transported through diffusion into the fish and kill it.

I have seen articles that try to state that there is different processes in fresh contra salt water. In Fresh water it should be an active NH4 transport through ion pumps but in saltwater it should be a passive transport of NH3. I was not convinced of the salt water theory.

When you say that the process of handling nitrogen through the system has no effect on alkalinity - do you mean that the nitrification and denitrification take out each other?

I have been working for many years with fish farming in closed systems - first in system with only nitrification. To have the system going we need to put in alkalinity the whole time because the nitrification process consume alkalinity.

Now I´m running a system that both nitrificate and denitrificate - i.e. has both aerobic and anaerobic systems in the plant. When we start a line - we will have a lot of alkalinity consumed of the nitrification process and the nitrate level arise. After 2 months - the denitrification process in the anaerobic part starts and we see a huge rise in alkalinity during the time we still have stored nitrate in the system (the denitrification process (in our system) consume nitrate in a faster paste than the nitrification produce nitrate and can use the “stored nitrate” that was produced before the denitrification kicked in). After a while – the nitrate concentration going down and the alkalinity is also going down. In the moment that there is no more “stored nitrate” in the system and the denitrification process only have the daily nitrate production from the nitrification to process – the system begin to have so low alkalinity - again that we have to ad alkalinity every day in form of HCO3. I have start 7 system with this technique – all of them with the same starting procedure

In my world (fresh water) – nitrification consume alkalinity – denitrification produce alkalinity but not so much as the nitrification consume when you have come in a steady process after app. 3 – 4 months

With denitrification I mean the classic method that normal need a addition of organic carbon source. However in our system - we let the anaerobic process produce this by itself - therefore it will take up to two months before it starts

Sincerely Lasse

 

[Randy Holmes-Farley]

@Randy Holmes-Farley

Are you sure that the fishes not transport NH4 through the gills? My old textbooks say so. Fishes are also able to get out of excess nitrogen against a concentration in form of NH4. However if NH3 concentration is high in the water - NH3 will be transported through diffusion into the fish and kill it.

I don't know, but from the standpoint of alkalinity effects, it doesn't matter which form they actually excrete. The product of the metabolism of a neutral organic is neutral NH3. It might be combined with H+ before or after excretion, but that reaction with H+ boosts alkalinity.

 

[Randy Holmes-Farley]

When you say that the process of handling nitrogen through the system has no effect on alkalinity - do you mean that the nitrification and denitrification take out each other?

I have been working for many years with fish farming in closed systems - first in system with only nitrification. To have the system going we need to put in alkalinity the whole time because the nitrification process consume alkalinity.

Yes, if denitrification is complete (meaning no nitrate accumulates). Since nitrate normally accumulates, alkalinity is depleted in many fish systems, as you noted.

The same is true of phosphate. If it accumulates, alk will depleted, but there is a lot less of it, typically.

 

[Randy Holmes-Farley]

I work through the math of these processes here:

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-12/rhf/index.htm


Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:


(1) NH3 + 2O2 --> NO3- + H+ + H2O
For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

However, the news is not all bad. When this nitrate proceeds further along the nitrogen cycle, depleted alkalinity is returned in exactly the amount lost. For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

(2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2
In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

(3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-
Again, one bicarbonate ion is produced for each nitrate ion consumed.

It turns out that as long as the nitrate concentration is stable, regardless of its actual value, there is no ongoing net depletion of alkalinity. Of course, alkalinity was depleted to reach that value, but once it stabilizes, there is no continuing alkalinity depletion because the export processes described above are exactly balancing the depletion from nitrification (the conversion of ammonia to nitrate).

There are, however, circumstances where the alkalinity is lost in the conversion of ammonia to nitrate, and is never returned. The most likely scenario to be important in reef aquaria is when nitrate is removed through water changes. In that case, each water change takes out some nitrate, and if the system produces nitrate to get back to some stable level, the alkalinity again becomes depleted.


If, for example, nitrate averages 50 ppm at each water change, then over the course of a year with 10 water changes of 20% each, the alkalinity will be depleted by 1.6 meq/L (4.5 dKH) over the course of that entire time period. This process is one of the primary reasons that fish-only aquaria that often export nitrate in water changes need occasional buffer additions to replace that depleted alkalinity.

While the magnitude of the depletion described in the paragraph above is fairly easy to understand, it also can be converted into units that clarify the imbalance. The impact of alkalinity depletion on the calcium and alkalinity demand balance depends, of course, on the amount of calcium and alkalinity added (and consumed) over the course of that same year.

For a typical reef aquarium (assuming a daily addition of saturated limewater equal to 2% of the tank's volume), the amount of alkalinity added during the course of a year is 297.8 meq/L. Likewise, the amount of calcium added is 5,957 ppm Ca++, given the ratio of 1 meq/L of alkalinity for every 20 ppm of calcium that has been discussed above. If that 1.6 meq/L of alkalinity is added to create a larger demand of 299.4 meq/L over the course of a year, the new ratio for the total demand becomes 19.90 ppm Ca++ per 1 meq/L of alkalinity. Consequently, while this effect of nitrate production on alkalinity is enough to be noticed over the course of a year, it is substantially smaller than the other effects discussed in this article, and is unimportant for aquaria that maintain low nitrate levels.

 

[ChrisOFL]

I have a bio-brick in my aquarium that is doped with sulfur and made with aragonite. If I dose carbon heavily I will see my alkalinity drop noticeably from the increased sulfur denitrification. It is extremely effective but is something to be cautious about with sulfur dentrification.

 

[Lasse]

Yes, if denitrification is complete (meaning no nitrate accumulates). Since nitrate normally accumulates, alkalinity is depleted in many fish systems, as you noted.

The same is true of phosphate. If it accumulates, alk will depleted, but there is a lot less of it, typically.

For the alkalinity lost in the nitrification step – do you have calculatet with the nitrification bacteria’s own consumption of CO3 or HCO3 as their inorganic carbon source ?

My experiences in a total closed system with complete nitrification and denitrification is that it eats alkalinity when the denitrification consume all nitrate produced by nitrification. Buts not so much as if it only has been nitrification. PH around 7 - heavy aerated but no losses of NH3 because of pH around 7

Sincerely Lasse

 

[Belgian Anthias]

You are mistaken.

Consuming nitrate by dosing organic carbon EXACTLY offsets the alkalinity that is depleted when ammonia is converted into nitrate. Hence the process taking place in the tank is exactly neutral toward alkalinity.

It is better because the overall process has no net effect on alkalinity, and because the bacteria feed filter feeders.

Huh? Can't be done?

I ran a non ULNS system for 20 years using several fine methods to control nutrients, including growing macroalgae and organic carbon dosing. It does not become ULNS unless you overdo any of these methods.

Sorry, No. That is incorrect.

I agree with the equations in your reference, and they are the same ones that I often use my articles. But you have misunderstood the processes involved. There is no net consumption of alkalinity.

Ebling et Al 2006:

https://cals.arizona.edu/azaqua/ista/ISTA7/RecircWorkshop/Workshop PP & Misc Papers Adobe 2006/7 Biofiltration/Microbial Floc Systems/2006 Aquaculture Stoichiometry of photo-auto-hetero - Ebeling.pdf

Equation 16 shows:


NH4+ + 1:18 C6H12O6 + HCO3- = 2:06 O2 --> C5H7O2N + 6:06 H2O + 3:07 CO2

" This equation predicts that for every g of ammonia– nitrogen converted to microbial biomass, 4.71 g of dissolved oxygen and 3.57 g of alkalinity (0.86 g inorganic carbon) and 15.17 g carbohydrates (6.07 g organic carbon) are consumed. Also 8.07 g of microbial biomass (4.29 g organic carbon) and 9.65 g of CO2 (2.63 g inorganic carbon) are produced"

This seems, at a first glance, to be consuming one unit of alkalinity (HCO3-) for each ammonia consumed), but that does not hold up to a deeper understanding of the processes involved.

The thing that you (and perhaps the author) are neglecting is that the nitrogen compound that is the product of metabolism by fish and other organisms is NOT NH4+. It is NH3.

The metabolism reaction is exactly the reverse of equation 3 in your reference. The product of the metabolism of organic matter with nitrogen in it is NH3. Of course, the reaction can be written as if it is NH4+, but when you do that, you necessarily produce alkalinity. That is what the reverse of equation 3 actually shows. Production of NH3 and then combination of that with some of the CO2:

NH3 + H2CO3 ---> NH4+ + HCO3-

And the reverse of equation 3 shows this "production" of HCO3- explicitly. Same for phosphate.

Consequently, the overall round trip from fish food to ammonia to production of biomass by consumption of ammonia to biomass formation with organic carbon has NO NET EFFECT ON ALKALINITY.

The same is true if you convert the ammonia along the way to nitrate. The overall round trip from fish food to ammonia to nitrate to production of biomass by consumption of nitrate to biomass formation with organic carbon has NO NET EFFECT ON ALKALINITY.

The author explains ammonia reduction, the tree possible ways to do it and what happens. Most of the ammonia is present as NH4. Vodka dosing is about nitrateassimilation. Heterotropic ammonia reduction needs a high C:N ratio, to high for a reef aquarium, as a very high biomass production, a high oxygen consumption and a very high CO2 production is the result. The biomass produced, which is +- 40x higher compared to autotropic ammonia reduction, can not be consumed and will clog everything. Nitrification will stop because of the competition for oxygen. Of cours in function of available quantity ammonia. Heterotropic ammonia reduction is not something I think about. Although is used with great success in Belize systems.

 

[Randy Holmes-Farley]

For the alkalinity lost in the nitrification step – do you have calculatet with the nitrification bacteria’s own consumption of CO3 or HCO3 as their inorganic carbon source ?

My experiences in a total closed system with complete nitrification and denitrification is that it eats alkalinity when the denitrification consume all nitrate produced by nitrification. Buts not so much as if it only has been nitrification. PH around 7 - heavy aerated but no losses of NH3 because of pH around 7

Sincerely Lasse

In any organism that uses bicarbonate or carbonate as a CO2 source (many photosynthetic organisms do so, for example), there is no loss of alkalinity because they only use the CO2, and they must spit out the alkalinity as OH- or something like it:

HCO3- taken up ---> CO2 inside, used for some purpose + OH- excreted

There are a variety of processes even in a fish only system that do deplete alkalinity, and these, oddly enough, include the deposition of calcium carbonate by fish as a means of osmotic regulation.

I show some references to that in the answer to this reef chemistry question of the day:

https://www.reef2reef.com/threads/r...day-230-osmoregulation-by-marine-fish.328231/