DNRA and dosing carbohydrates.

[Belgian Anthias]

Dissimilatory Nitrate Reduction to Ammonium

Normally +- 15% of the total nitrate reduction by denitrification will be DNRA, performed by anaerobe heterothrops, needing organic carbon. Denitrification does remove nitrogen from the system by transforming it to N2, nitrogen gas. DNRA will keep the nitrogen in the system, transforming it to NH3. It is shown that DRNA is effected by the availability of organic carbon and will increase in relation to the amount of organic carbon present. Bacteria performing DNRA grow twice as fast as heterotropic denitrifiers and DNRA may outperform denitrification at a high C:N ratio.

Keeping on a high C:N ratio will not only limit nitrification, reduce, even remove the nitrification capacity and this way shift the carrying capacity of the system towards heterotropic ammonia reduction but also will limiting the production of nitrogen gas, keeping the nitrogen in the system, available to support growth. This means the carrying capacity of the system may become completely dependable of daily dosing.
Not only 40x more biomass is produced to reduce the same amount of NH4-N but also twice as much to reduce the same amount of NO3-N while removing nothing from the system.

It is often said and written that carbohydrates dosing is very innocent, well, it isn't! And only when the produced bio-mass is harvested the containing nitrogen will be removed.

If used for a reason, carbohydrates should be dosed on a known and measurable parameter, for example based on the daily NO3-N overproduction, this to prevent a to high C:N ratio at all times.

 

[Randy Holmes-Farley]

FWIW, I'm not a fan of dosing carbohydrates. I have seen a higher proportion of people report issues with sugar dosing, for example, than vodka or vinegar.

I personally prefer vinegar for organic carbon dosing, with the amounts used based on some sort of trial and error approach, either by nutrient measurement, or visual tank observation (or both).

FWIW, I personally do not think that production of ammonia is an issue.

 

[Belgian Anthias]

Dosing carbon based on trail and error reports of which the errors where never well understood or recognized is what most users do. When doses are based on the daily nitrate overproduction overdosing is not possible and a high C:N ratio is avoided. Visual observation will warn the reefkeeper when it went wrong, when it is to late. Prevention is always better as correcting , if still possible, if not to late, and the best prevention is not using it at all.
A lot of supplements are added to aquaria which may contain an unknown amount of carbohydrates, safe to use in reef aquaria!? They are not!
As most users of carbohydrate dosing think they are removing nitrogen, the production of ammonia by DNRA is certainly an issue when this ammonia is produced with nitrogen which in normal circumstances would not be available any more as it would be removed by natural denitrification. It has a negative effect on the carrying capacity of the system!
The fact that adding carbohydrates prevents the removal of nitrogen by keeping it in the system was at my knowledge never reported in the aquarium literature.

 

[Randy Holmes-Farley]

The fact that adding carbohydrates prevents the removal of nitrogen by keeping it in the system was at my knowledge never reported in the aquarium literature.

Perhaps there is some language misunderstanding between us, but I certainly would not assume that all nitrogen taken up by organisms when organic carbon dosing is removed from the system. I'd personally be surprised if even half of it (when dosing vinegar) is removed from the system. It ultimately ends up in lots of different organisms, from bacteria to corals to fish, and stays in the system. That's a large part of why I dosed to vinegar: to feed organisms, not just to export N.

I do not assume that one "needs" to have ANY of the nitrogen actually removed from the system. If it all ended up in organisms, is that undesirable?

 

[Belgian Anthias]

Perhaps there is some language misunderstanding between us, but I certainly would not assume that all nitrogen taken up by organisms when organic carbon dosing is removed from the system. I'd personally be surprised if even half of it (when dosing vinegar) is removed from the system. It ultimately ends up in lots of different organisms, from bacteria to corals to fish, and stays in the system. That's a large part of why I dosed to vinegar: to feed organisms, not just to export N.

I do not assume that one "needs" to have ANY of the nitrogen actually removed from the system. If it all ended up in organisms, is that undesirable?

It is assumed to much nitrogen is present in the system when carbon is dosed as adding carbohydrates is promoted to "remove" nitrate, which it does not when dosed correctly as it will mainly induce the reduction of ammonia.
When dosing induces the reduction of nitrate a high C:N ratio is maintained , nitrification is inhibited, limiting the autotropic carying capacity, and DNRA replaces denitrification limiting the nitrogen export. Is this good or bad? To avoid the system becomes unstable and dependable of dosing, a high C:N ratio should be avoided at all times.

I think one may assume max 20% of the by dosing produced protein may actually be removed as part of the induced growth is bentic and recycled in a microbial community, a lot is consumed producing some ammonia and ureum and only +- 30% may be removed from DOC present in water column. As the removal by a skimmer and or GAC is selective maybe it is better to try to keep all nutrients in the system, incorporate them into growth? Cultivate shrimp for consumption?
How much nitrogen may be exported this way is something I have to look into but I assume it is a lot less. How far the decay of the protein may be evolved, if the Nitrogen group is still attached or not. Is an amino acid of which the nitrogen group is detached ( glycolyse and or ketogene) still part of skimmable TOC?



Maybe I am old school, but for me the base for a stable system is the installed autothropic ammonia reduction capacity. Minimizing the risk for human and technical errors is part of good management. For closing the nitrogen cycle one does not need any supplemental organic carbon.
Adding carbohydrates based on the nitrate level , as a lot of people do, does effect the base for a stable system.
Trail and error? Not in a live support system!