By Marc LANGOUET ing ENSCR, Translated by
Nicolas Will
In a confined space, like the one in an aquarium, the regular
addition of food that necessarily contain a quantity, more or less
important, of nitrogenous compounds, will, without fault, lead to a
level of nitrate incompatible with the inhabitants life.
This phenomenon is now well known by most aquarists, in particular
those that maintain reef aquariums. The coral's tolerance regarding
nitrates is particularly small compared to other living
organisms.
Various solutions were proposed to avoid this problem: water changes,
algal turf scrubbers... The most common of all is probably the
protein skimmer, pillar of the Berlin Method, which consists in the
elimination of a maximum of nitrogenous compounds before they are
transformed into nitrates.
However, this method are not without difficulties and do not always
allow to easily get rid of the problem. I am mostly thinking about
aquariums well or very loaded by fish or about those that are hosting
corals or invertebrates needing frequent additions of food (a good
number of gorgonians or beautiful corals like Tubastraea aurea, the
Dendronephtya family or the Carotalcyon sagamianum).
These beautiful animals are rarely raised in aquariums because of the
fact that they need to be very regularly fed (which can be
automated), and this leads very quickly to high nitrate levels.
I will explain here the two original methods that I developed and
which use could quickly spread.
1. Autotrophic denitratation on sulfur
An article published by MARS (18/5/98) and written by Christophe SOLER gives a good picture of the method. I will just simply give historical precision and further information. It is my ex-professor Guy Martin from Ecole Nationale Supérieure de Rennes who is at the origin of this idea; he applied it to fresh water treatment for public water.
I tested this method with seawater, which was new, especially
since we didn't know if it would have toxic consequences for our
animals, as soon as 1991.
It is only by the end of 1994, after three years of experiments
without apparent toxicity in numerous aquariums and species present
at home, that I proposed this method to Michel Hignette, curator of
the MAAO aquarium. A pilot project was lunched under my care.
Since then the experiment was done on a much bigger scale, at the
MAAO, as well as in the Grand Aquarium in Saint-Malo, of which I was
technical and scientific director from June, 1st 1996 to mid-December
1997.
I wish to stress the fact that I am using since 1996 beads of sulfur
of a 3.5-mm diameter. This form is much easier to use than bars that
you have to break using a hammer.
The quantity of sulfur to use depends on the initial nitrate level
at startup and on the amount of food added. I consider that a sulfur
volume equal to 1% of the total water volume is enough when the
initial level is below 50 mg/l (NO3-).
The water flow that must go through the sulfur column depends on the
nitrate level of the water to be treated: the more nitrates, the
lower the flow must be, otherwise you will find part of the nitrates
will be found after the column.
At startup, you can count on 1 liter per hour and per sulfur liter in
the column. Then you can adjust in the following manner:
- If the flow rate is too low, you will get a rotten egg smell at the
column's exit due to a production of sulfurous hydrogen (H2S). This
will rarely happen for really low flow rates.
- If the flow rate is too high, you will detect nitrites or nitrates
in the output water.
- If the flow rate is correct, you should obtain 0 nitrates.
However, experiments show that the system is very tolerant regarding
the flow rate, which could go up to 5 liters per hour per sulfur
liter.
The water sent to the column could come from a filter derivation
or directly from the aquarium. The column must allow the produced
nitrogen to escape: for these reason a vertical circulation, from
bottom to top, seems a better choice, with a flow-rate setting at the
input, not at the output. The column's output can be open to the air.
The water exiting the sulfur column can be very acidic, but after my
experiments getting the gas out of the water (by using an air-stone
for example) allows to get a pH close to the original. The water's
acidity is then at least mainly linked to the presence of carbon
dioxide; thus the idea to use this water to make a calcium reactor by
making it flow in a second (and why not a third) columns, identical
in size to the one containing the sulfur, but this time filled with
maerl or some coral sand (the same that you are using for your
sandbed).
This output water also contains sulfates in quantities slightly
higher than at the input, but in 7 year of experiments it has never
been observed any consequence, even in aquariums that didn't get any
water changes for years. It must be noted about that subject that
there was an error in the publication made with the MAAO: the sulfur
level in natural seawater is near 900 mg/l; this sulfur is present
under the form of about 2.65 g/l sulfate (SO4--), quantity, which by
itself can explain that the system's addition in sulfate will be
without any notable consequence.
2. Pr. Jaubert's method boosted by sulfur
Pr. Jaubert's method is now more and more known; I've been using
it since 1994. It consists in placing nitrates reduction into
nitrogen and the calcium reactor directly inside the aquarium. The
reduction is done in the lower part of a thick layer (8 to 10-cm) of
sand (J. Jaubert pers. comm.). This method works very well; however,
it seems limited to aquariums with low fish load, or not fed very
often, most probably by lack of organic elements in the sand's lowest
part, a limiting factor for anaerobic bacteria development, which
transforms nitrates into nitrogen by using carbonated matter (organic
matter).
It also seems that only well-lit aquariums can work following this
method, even if we don't have any complete explanation yet.
Finally, the substrate's surface that is covered by the rocks must
not be over 25% of the total surface (J. Jaubert pers. comm.).
If, for a reason or another, nitrates are persistently present in
the water, we can boost the system to make them disappear, faster, by
accelerating the bacterial process by introducing organic compounds
in the lower layer of sand (glucose, by example, by introducing a
tube that penetrates under the layer, the other extremity sticking
out of the water in the air).
To push Pr. Jaubert's method beyond its limits, i.e. in a heavily fed
or under-lit aquarium, without adding glucose under the sandbed, and
still conserve its advantages, i.e. its extreme simplicity, no
external reactor, no flow rate to set, incorporated calcium reactor,
etc. an idea came to me, a few years ago, to get rid of the limiting
factor that is made of the quantity of organic compounds present in
the lower layer of sand by boosting the system with a thin layer of
sulfur in the form of beads at the same level. This allows the system
to work in an autotrophic way instead of a carbon-heterotrophic-only
way.
The device that I successfully experimented is made of a traditional floor net, from an under-gravel filter without up-lift (the water flows only naturally through the sand, just like in Pr. Jaubert's method).
I established at the end of August 1998 an experimental protocol.
I completely rebuilt a 100-liters aquarium that was established a few years back with 6 to 8-cm of coral sand and a few live rocks. It must be noted that this aquarium, even if it was setup following the Jaubert principle, had nitrate level rises during feeding periods.
Even empty of any animal and not fed for months, its nitrate level
did not diminish. It is the perfect example of a scarcely lit Jaubert
aquarium that does not work fast enough, most probably because of a
lack of nutrients for the anaerobic bacteria present in the lower
layer.
I setup the system by layering sulfur beads between the UGF plate and
the sand, 1/2 cm thick, sandwiched between two plastic mosquito nets.
The 65 to 70 liters of water contained 35 mg/l of nitrate (NO3-).
I reused this water to fill the new setup. Five days later the
aquarium had a nitrite level above 10 mg/l. I was using live sand
that was already full of aerobic bacteria. It was the first step of
the transformation of nitrate into nitrite using sulfur that was
starting, and not the transformation of ammoniac into nitrite like
happens traditionally in a newly established tank.
On the tenth day, the nitrite level was of about 1 mg/l; the
transformation of nitrite into gaseous nitrogen was on going. In a
system of this type, where the water flow is produced by natural
diffusion through the sandbed and not forced through a filter, it is
logical that the evolution is slower than in systems using
reactors.
On the eleventh day no nitrite was left and the nitrite level was
below 5 mg/l.
On the Twelfth Day the nitrate level was not measurable at all (below
1 mg/l).
On the 24th day the aquarium was still without any nitrate, even if it received every day a cube of frozen artemias (around 1-cm3), which is pretty high for a 65-liters tank. The Tubastraea aurea in this aquarium for two months was nearly opened all day long, liking the strong water flow in the tank and the daily addition of food. It was the same for some Actinias equina and two Carotalcyon sagamianum specimens. The pH was around 7.7, because of Carbon dioxide present (degassing raises the pH) but this didn't look like it bothered the invertebrates. The KH was between 6 and 7. It was the same as the one from the Channel water that I used to fill the tank.
This very interesting method could perfectly be established in the
sump of an existing aquarium so that the whole setup doesn't have to
be rebuilt. The low pH will most probably shock some of you, but it
should be noted that with Pr. Jaubert's method, the pH and KH are
generally lower than those found using the Berlin method (at least in
the morning concerning the pH). It is without noticeable consequence
for the animals. My aquarium is not lit (only by ambient light in the
room). It is not aerated by any other mean than a normal air/water
interface, this interface being slowly moved because I preferred to
direct current in the direction of the corals to bring then food.
In a lighted aquarium and with a good surface movement, or with an
air stone, the dissolved Carbon dioxide should be eliminated in a
better way, and the pH should be higher. The sulfur surface may not
cover the tankís entire surface like I did.
I am personally convinced that this CO2 presence in the water in not necessarily a problem, but time will tell. As soon as I can lay my hands of some Dendronephtyas, gorgonians, Sphaerella krempfis, sponges, etc. I will add them to this aquarium. Feeding should be automated and more regular, simple flakes are enough to open the Tubastraea aurea.
Please send me your experiments in this field.
To be continued...
Marc LANGOUET.
6/11/98
Note 1
Note 2
or to Récif France Britanny, which will forard
Question: Marc evokes Degassing (escape of produced nitrogen) in his publication. Having no sump for my aquarium, I want to place the column below in the stand; it will then be full of water. I will fill the column with sulfur and maerl (50/50). I want to fix the output in the air, above water surface. Will it be enough for degassing? Can it work like this while being as efficient?
Marc's answer: There is no problem with a column filled with water; the water flow must be from bottom to top of the sulfur maerl column. It must be noted that this mix is not a good idea as the maerl will be transformed into puree with time, and you will have to throw away the whole because it will clog... You should better separate the sulfur and the sand because sulfur can be kept: it doesn't deteriorate.
Question: Must sulfur be regularly
added?
Marc's answer: Sulfur is used, but it is very low.
It corresponds to
In practice I never added any sulfur in years, even less changed it.
Question: What is the exact use of the air escape? Is it fundamental?
Marc's answer: The air escape is the to help nitrogen getting away, if you work with high nitrate levels. If this level is low, this degassing will be small and I don't think this would be a problem to send this water into a calcium hydroxide reactor. The experiment is left to you.
Question: What is the cost of sulfur?
Marc's answer: Sulfur's cost is about US$2 per kg
Question: I built a reactor following MARS' plan with 2x
5-liters columns; one contains sulfur beads, the other some
calcareous substrate. In 8 days, nitrate, which used to be at about
25 mg/l in my 400-liters aquarium, are now at zero at reactor's
output. A month after the setup nitrates is between 0 and 5mg/l in
the aquarium. It's really working!
But as nothing is easy in reefkeeping, there are other parameters
changed by the sulfur reactor.
Calcium was at 410 mg/l before y using limewater as make-up water
(5-liters per day, whichís low because my tank is closed and
using fluos). After a month the level is at 490 mg/l at reactor's
output! Great! Is it the substrate column doing anything?
However the pH is from 0.6 to 0.8 lower at reactor's output. In the aquarium it went down from 8.2 to 7.8 in a month (7.05 at reactor's output). How can I cleanly raise the pH without disturbing the animals? Will this pH drop ever stop? Is it because of sulfur denitratation system?
MARS' Answer: The flow rate through the reactor is not given. Maybe you can tweak that (higher or lower) to lower the acid dosing in the aquarium like in a Calcium carbonate/CO2 reactor. Also like in a calcium reactor if the substrate is too big, water flows too fast and doesn't dissolve it and doesn't lose acidity. To correct this, either lengthen the circuit or get finer substrate.
MARS' comments:
This method has now been used for a while by a good number of
hobbyists who all saw their nitrates level drop. One thing to look at
(beginners beware!) would be, as nitrates consumption is huge, to
lower skimming quality (to be kept to remove the compounds not
removed by the sulfur reactor?). Plankton would be protected. As the
sulfur reactor is making acid, calcium production is allowed by
adding a calcium reactor in-line. No more CO2 bottle. A number of
question marks are left, but the system is charming! We can imagine
small autonomous aquariums, but why not also large (>1,000-liters)
ones equipped with modest and cheap skimmer (like the super skimmer)
and this revolutionary system that is sending the rest to the
museum?
Since we are thinking of revolutionary concepts, here is one
elaborated by Christophe Soler: instead of setting up a conventional
calcium reactor after the sulfur denitrator, take a kalk-reactor
filled, not with coral sand, but with calcium carbonate powder. Acid
water flowing slowly (5 l/h for a 500-liters tank) will dissolve
easily this powder that is offering a much greater contact surface
than sand. The produced calcium level should be equally greater. The
internal mixing of the reactor will prevent the formation of mud. To
be tested! Anyone?