I took nothing! Nature does it for us. It is the end result that counts, not a single process. But to have an idea of what will be the end result one must have an idea of the different processes taking place.
BADES is an acronym for
Biological
Anaerobic
Denitrification using
Elemental
Sulfur, a natural process taking place everywhere in the tank. What BAD should stand for?
A sulfur denitrator or a BADES system does
NOT ALWAYS deplete system alkalinity.
Sulfate reduction in combination with the oxidation of reduced sulfur compounds will cause an overall increase in alkalinity as illustrated by the reduction of sulfate to sulfide and subsequent re-oxidation to sulfate
VanRijn2005)
SO4 2- + 10H+ + 8e- ⇒ H2 S + 4H2 O
( (Alkalinity gain= 2 meq alkalinity per mole SO4 2- of 100 mg CaCO3 /mole SO4 2- )
5H2 S + 8NO3 - = + 5SO4 2- + 4N2 + 4H2 O + 2H+
(Alkalinity consumption = 2 meq per 5 moles H2 S of 20 mg CaCO3 /mole H2 S)
VanRijn2005)
As with heterotrophic denitrification, the combined autotrophic denitrification by means of sulfur derivatives, the reduction of sulfate to sulfide, the oxidation of sulfide and the reduction of nitrate has the same positive effect on the alkalinity by increasing it with 3.57mg CaCO3. (VanRijn2005)
ref:
MB CMF de Haes 2017-2019
If nitrate is limited available ( often the case in an anoxic kept sulfur denitrator once the nitrate level is descending due to the limited flow) a lot of HS may be produced and HS reduction may become partial depending on the HS/nitrate ratio there where the action is, producing S which only anaerobically can be used when HS or other sulfur compounds availability is insufficient, the BADES process. All these processes also take place in a normal nitrifying biofilm and everywhere in the tank.
It all depends on how a denitrifying filter is managed. Without adding elemental sulfur BADES will take place, although very limited. The bacteria responsible for BADES are always present everywhere as they make use of constantly produced HS, aerobically using oxygen and anaerobically exporting nitrate. A normal aerobic remineralization filter has a certain denitrification capacity, which can be influenced by managing elemental sulfur availability.
If nitrate becomes limited available most denitrification taking place will be autotrophic and by using HS, not S
So, the reaction you consider a problem does NOT represent the whole picture, it is only a small part of what really happens. and which may take place everywhere a calcium carbonate substrate is available, in the entire tank.
Yes , I consider calcium production desirable because most reefers have to add calcium.
Using BADES, calcium production can be managed and depends on the amount of nitrate exported by BADES which is manageable as desired. If too much calcium is produced the production rate can be controlled. Normal use, the calcium production will be insufficient for replacing the consumption.
One can use two reactors, one containing sulfur, the other containing shell grit. See
MAAO.
I prefer to use a mixed substrate because the processes producing acids can take place where the substrate needed is made available.
To lower the nitrate level only a little more as the daily nitrate overproduction must be removed daily, which means a good BADES System should be able to remove +- 2ppm Nitrate daily, more should be planned for a high nutrition system.
Using an anoxic sulfur denitrator, a minimal daily flow of the total tank volume is needed to keep the nitrate level at +-2ppm ( having 2ppm overproduction daily) This when 0 nitrates in the effluent are targetted, which I do not recommend using BADES.
According to the Zhang formula, approximately 1.76mg Ca is produced per 3.1mg NO3. If 10 ppm nitrate is removed per week and is removed by BADES, MAX 5.68 ppm calcium can be added on a weekly basis. According to your own calculation, only MAX 4.3 ppm of calcium may be added. (HolmesFarley 2003) The formula of Zhang takes into account the bacterial growth needed and is closer to reality. In practice, the calcium production will be a lot less.
In a reef tank, calcium and carbonate are NOT consumed in balance . There ALWAYS will be an imbalance.
Remineralization including nitrification and denitrification takes place everywhere in the tank. Depending on the substrate there where the processes take place, alkalinity will be consumed or calcium produced. A reef tank is filled up with calcium carbonate and acids are produced everywhere, dissolving substrate. Also, the consumers of calcium do not all consume carbonate or bicarbonate from the surrounding water, some calcareous algae produce calcium carbonate internally using Ca and CO2. For a lot of marine algae, internal calcification is a survival strategy, for fast retrieving available CO2 as it is limited available in seawater. The calcification rates of corals, which take place on the outside, are mainly driven by CO3 availability, if there where the action is calcium availability is not limited.
Also, Gypsum may be produced, etc... etc.....
For these reasons, a CO2-driven calcium reactor does increase the unbalance because the
total consumption and production of calcium and or carbonate are NOT in the balance of CaCO3. We do have to manage the calcium content anyway. Such a CO2-driven calcium reactor does include a much greater risk than a BADES system ever can produce.
Instead of exporting nitrate using BADES one is able to stop the production of nitrate by eliminating the installed nitrification capacity by adding carbohydrates, messing up the entire natural balance in the tank. Also, these processes may consume alkalinity which must be managed and it has been shown to harm, even kill corals. (ref:
MB vodka dosing. CMF De HAES 2017 ) The export rate depends on a skimmer and is unknown but has been shown to be max +- 35%. The risks, the many side effects, and possible problems caused by human error are much higher compared to using a BADES System for exporting nitrate. Using BADES the nitrate export rate is known and can easily be managed as desired, without removing from the naturally installed carrying capacity present in the system.
Using a denitrator, it is the intention to only export nitrate, leaving other building materials and nutrients behind.
it may have a lot more side effects than only calcium production. For exporting nitrogen and other nutrients and building materials I prefer to make use of Active Algae Management, AAM,
cultivating algae in a refuge, and maintaining the desired minimal carrying capacity by active feeding. To export nitrogen one has to harvest.
BADES may be the best solution available if it is the intention ONLY to export safely stored nitrogen considered not needed. To fix the N/P ratio also AAM can be used.
In practice the calcium production will be a lot less as part of the denitrification will be heterotrophic and or autotrophic using HS instead of S, processes removing nitrate and boosting alkalinity if HS is produced by the reduction of sulfate.
BADES can also be used to increase the natural denitrification capacity of a normal nitrifying remineralization biofilm.
I do not see how calcium production of a correct managed BADES System may become a problem in a reef aquarium, a problem that is not taken care of by normal system management.
Why BADES is BAD? Compared to? For exporting safely stored nitrogen, Nitrate!!!
Does the cure include higher risks compared to the risks represented by the nitrate reserve? Which are?
One must be aware only exporting nitrate does not solve a nutrient problem. For this one has to correct the source, why usable nitrate can build up slowly in a well-lit aquarium? In most cases, increasing nutrient reserves are the messengers, the results of an existing problem, not the cause.
