Typical Denitrification Filter Capacity (in ppm/day)?

[Heathcliff37]

As the title suggests, what is a typical reef tank’s capacity to denitrify nitrates measured in ppm per day?

I am particularly interested in the rate of nitrate reduction due purely to anerobic bacterial denitrification, although I am also curious how much algae and other uptake methods could increase it as well.

For example, if the typical system produces 1 ppm nitrate per day and can filter out 1 ppm nitrate per day, even with a large 50% reduction in feeding (nutrient import) the biological filter could only reduce nitrates at a rate of 0.5ppm per day. If someone suddenly has 20 ppm nitrates, it would take (roughly) 40 days for nitrates to approach zero, assuming all biological and kinetic factors maintain the same rate.

Alternatively, if the filter denitrifies 5 ppm per day, then a 50% reduction in nitrates can reduce the nitrates from 20 ppm to nearly zero in about only 8 days.

I am curious about this for academic purposes and also because I had an accident in one of my tanks and now my nitrate is at 20 ppm and I’m considering whether I should do water changes or just cut back feeding for a while.

I know the rate is highly variable based on system factors; I’m just curious what the ballpark/order of magnitude range is. 0.1 ppm? 1 ppm? 5 ppm? 10ppm? etc.

Thank you so much!

 

[Dan_P]

As the title suggests, what is a typical reef tank’s capacity to denitrify nitrates measured in ppm per day?

I am particularly interested in the rate of nitrate reduction due purely to anerobic bacterial denitrification, although I am also curious how much algae and other uptake methods could increase it as well.

For example, if the typical system produces 1 ppm nitrate per day and can filter out 1 ppm nitrate per day, even with a large 50% reduction in feeding (nutrient import) the biological filter could only reduce nitrates at a rate of 0.5ppm per day. If someone suddenly has 20 ppm nitrates, it would take (roughly) 40 days for nitrates to approach zero, assuming all biological and kinetic factors maintain the same rate.

Alternatively, if the filter denitrifies 5 ppm per day, then a 50% reduction in nitrates can reduce the nitrates from 20 ppm to nearly zero in about only 8 days.

I am curious about this for academic purposes and also because I had an accident in one of my tanks and now my nitrate is at 20 ppm and I’m considering whether I should do water changes or just cut back feeding for a while.

I know the rate is highly variable based on system factors; I’m just curious what the ballpark/order of magnitude range is. 0.1 ppm? 1 ppm? 5 ppm? 10ppm? etc.

Thank you so much!

@taricha has thought about this recently and performed some measurements. @Lasse has such a wide range of knowledge that he might know the exact number. @Randy Holmes-Farley probably wrote an article on this topic.

 

[Randy Holmes-Farley Verified Community Expert]

I do not think most people know if there is any actual denitrification in their tank as opposed to aerobic consumption of nitrate, or if both, how much of each when nitrate is declining.

 

[Lasse]

I can´t give a typical figure but I had one occasion there I succeeded with my reversed flow DSB to bring down 50 ppm nitrate to around 5 in 17 days. My measurements was done with diluted samples and Hanna low nitrate checker but I checked my readings the 6/5 - 21 with OCEAMO lab in Austria for nitrate and my checker said 32 ant the lab result says 35 mg/L

Sincerely Lasse

 

[Heathcliff37]

I can´t give a typical figure but I had one occasion there I succeeded with my reversed flow DSB to bring down 50 ppm nitrate to around 5 in 17 days. My measurements was done with diluted samples and Hanna low nitrate checker but I checked my readings the 6/5 - 21 with OCEAMO lab in Austria for nitrate and my checker said 32 ant the lab result says 35 mg/L

Sincerely Lasse

That’s some great science! Do you have a more detailed post somewhere else you could link, or could you tell me, did you reach the 50 ppm and then start the reverse flow DSB, or did you reach it and stop feeding less and let it fall back down?

 

[Heathcliff37]

I do not think most people know if there is any actual denitrification in their tank as opposed to aerobic consumption of nitrate, or if both, how much of each when nitrate is declining.

Don’t you think that in any established tank with live rock there would be significant denitrification?
I know I’ve had several freshwater tanks with crushed coral and concrete that have had consistently undetectable nitrate with zero nutrient export, near zero biomass growth, and significant nutrient import.

 

[Lasse]

That’s some great science! Do you have a more detailed post somewhere else you could link, or could you tell me, did you reach the 50 ppm and then start the reverse flow DSB, or did you reach it and stop feeding less and let it fall back down?

Here is my OCEAMO reports of my Nitrate measurements during time

Because an experiment using a bokashi solution - my nitrate skyrockets. I injected this solution below my plenum (a common under gravel filter plate) using the same pump that I before used for organic carbon (needed for denitrification). When I saw this peak - I stop the injection of bokashi solution and start injecting DOC (ethanol - 8 % ) again and you can see the fast denitrification. During this time - I also feed with around 0.5 g N each day (40 g combined frozen artemia and fresh water cyclops)

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

Don’t you think that in any established tank with live rock there would be significant denitrification?
I know I’ve had several freshwater tanks with crushed coral and concrete that have had consistently undetectable nitrate with zero nutrient export, near zero biomass growth, and significant nutrient import.

There likely is, but it is nearly impossible to distinguish denitrification from simple consumption by growth of organisms. Bacteria easily grow unseen on porous substrates for fairly extended periods.

Lasse's experiments, for example, do not prove denitrification is the process that lowered nitrate in his system.

 

[Lasse]

Lasse's experiments, for example, do not prove denitrification is the process that lowered nitrate in his system.

IMO - Denitrification is the only possibility I can see in this case because there was no change in growth of macroalgae in my refugium or microalgae in my DT if I compare the time 45 ppm disappear to the time when concentrations stabilize at 5-10 ppm. But that´s true - I can´t prove it

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

IMO - Denitrification is the only possibility I can see in this case because there was no change in growth of macroalgae in my refugium or microalgae in my DT if I compare the time 45 ppm disappear to the time when concentrations stabilize at 5-10 ppm. But that´s true - I can´t prove it

Sincerely Lasse

Couldn’t it have been tissue growth?

 

[Lasse]

Couldn’t it have been tissue growth?

Could yes - but I do not think so of a couple of reasons. I did not see any more growth during this "nitrate going down period" compared with before and after when nitrate was around 3 - 10 mg/L. However - I got back to my figures from the actual time and discover that the start of the NO3 rise was earlier than I thought before. Before I start dosing bokashi solution - soon after I had move my large clam (weight - around 3 kg!) However - the decline of my nitrate start directly after I have stopped to dose EM and start to dose DOC again - making the bed more anaerobic. I can´t reach my notes and graphs for the moment - but I will come back with graphs later on

Sincerely Lasse

 

[taricha]

I am particularly interested in the rate of nitrate reduction due purely to anerobic bacterial denitrification, although I am also curious how much algae and other uptake methods could increase it as well.

I am curious about this for academic purposes and also because I had an accident in one of my tanks and now my nitrate is at 20 ppm and I’m considering whether I should do water changes or just cut back feeding for a while.

I know the rate is highly variable based on system factors; I’m just curious what the ballpark/order of magnitude range is. 0.1 ppm? 1 ppm? 5 ppm? 10ppm? etc.

In my system years ago I tracked my NO3 consumption to be ~2.3 ppm NO3 per day on average over a couple of months. That's 2.3ppm per day dosed NO3 above what I was feeding in fish food. If I didn't add NO3 - my tank runs consistent zeros.

But probably none of it was denitrification - I removed and massed a continuously growing ball of chaeto from the sump and could do a very rough Nitrogen and phosphorus balance between all inputs and the algae removed and get similar numbers. If I had massed and characterized the skimmate + sludge produced, I could probably have made the accounting tighter.


Lasse dropping NO3 from 50 to 5 in 17 days also works out to a number of similar size: 2.6 ppm NO3 / day. His is the best possible shot at doing true denitrification because he brings NO3 down by carbon dosing ethanol up through a sandbed where he's measured ORP to ensure adequately reducing conditions.

If Lasse isn't doing denitrification, then nobody (outside of a sulfur denitrator) actually is.


BTW, Random thing I tried once. I pushed a couple of NaNO3 pellets into my sandbed and measured NO2 production in the sandbed porewater around the pellet areas over the next couple of days that was 10x higher than the near zero detected elsewhere.
So the organisms needed to do it are there, it's just a question of the conditions and how much NO3 actually gets to low O2 spaces where some organic carbon is available.

 

[Randy Holmes-Farley Verified Community Expert]

BTW, Random thing I tried once. I pushed a couple of NaNO3 pellets into my sandbed and measured NO2 production in the sandbed porewater around the pellet areas over the next couple of days that was 10x higher than the near zero detected elsewhere.
So the organisms needed to do it are there, it's just a question of the conditions and how much NO3 actually gets to low O2 spaces where some organic carbon is available.

That's always been a bit confusing to me as well. O2 diffuses faster than ethanol in water, so if O2 is depleted and is not getting in fast enough to replace it, then ethanol diffusion in will also be slow.

Hence my thought that a lot of ordinary carbon dosing pushes aerobic consumption.

 

[Lasse]

But probably none of it was denitrification - I removed and massed a continuously growing ball of chaeto from the sump and could do a very rough Nitrogen and phosphorus balance between all inputs and the algae removed and get similar numbers. If I had massed and characterized the skimmate + sludge produced, I could probably have made the accounting tighter.


Lasse dropping NO3 from 50 to 5 in 17 days also works out to a number of similar size: 2.6 ppm NO3 / day. His is the best possible shot at doing true denitrification because he brings NO3 down by carbon dosing ethanol up through a sandbed where he's measured ORP to ensure adequately reducing conditions.

If Lasse isn't doing denitrification, then nobody (outside of a sulfur denitrator) actually is.

My chaeto did not go very well during this period and the way I skim is very, very dry. I empty my skimmate once a month or more seldom than that. I feed with around 30 g frozen food a day and if I use the average 16 % protein and 8 % N in that protein - I feed with around 0.4 N a day. For frozen fresh food the uptake in fish normally is calculated as around 0.2 to 0.25 % it means that (if I use the highest figure) around 0.3 g N will in worst scenario be converted to NO3. Let us say that half of this N will be converted to NO3 - it gives us around 0.66 g NO3 a day -> 660 mg a day. I have 300 L water -> a rise of 2.2 mg/l (ppm) NO3 a day. My whole consumption of NO3 these days where around 4.8 ppm NO3 a day.

Hence my thought that a lot of ordinary carbon dosing pushes aerobic consumption.

IMO - thats right but dosing DOC have two tasks in denitrification - drive the heterotrophic consumption and works as electron donor in the metabolism. The last task is crucial and that's the reason why I do not believe in denitrification as a major game changer in normal tanks - not even in passiv DSB (if they ar not very old and mature and contain a lot of organic matter) In the earlier days of carbon dosing - it was often reported fast change of PO4 but not any down going trends of NO3 for the first months.

However - in a special designed equipment - it works very well.

My system is build of two major parts - dosing DOC below the sand bed and dosing aquarium water in the same spot. I use ethanol as DOC and the aquarium water I dose contain both NO3 and of cause O2. I measure the redox potential and in anaerobic conditions you can see it as an indicator of available oxygen - addition of O2 will rise the redox potential and consumption will lower the same potential. I use my redox probe as an controller - if redox rise over a set point - it ad DOC and if decrease below - I add aquarium water (read O2) The GHL allow me to program the addition of DOC to vary in amount depending of distance between nominal and actual values. the pause between addition is constant and can be decided by me. With the water addition - i have chose to vary the lengths of the paus and have the amount constant. Yo can see this in this day 5:th of may. First - of some reason - the system is not balanced and the dosing try to balance the value between -194 and - 196 mV. After a while it stabilize itself and now is the oxygen consumption the same as the oxygen addition through the water coming in - no needs of more DOC. This is a situation that I not so satisfied with because there will probably no be any DOC in order to work as electron donnors - all is used in the "oxygen regulation" and is internally produced. I have had a rising trend of NO3 for the last months but some changes in the regulation of dosing have make it go down the last weeks. This day - 5/5 I add 2.6 ml 8% ethanol and around 260 L of aquarium water below my sand bed

For the moment - I have problem to access my waterflow data from the occasion with high NO3 in May last year but I hope the GHL people will sort this up and that I can show it later. But the DOC addition during this period was huge - around 900 ml 8 % ethanol

Sincerely Lasse