Page 77 - Koi Net - On-Line Koi Magazine - Issue 92

It is quite logical that the autotrophe system is the main So far, the Koi hobby has often looked at the wastewater
mechanism, at least regarding the values we measure. industry in terms of the bacteria that convert Ammonia
Once the ponds are matured we normally only measure to nitrate via nitrite. One of the nice things that has
some increased nitrate values from time to time, but been determined is there is the percentage of nitrogen
that was it. And so Ammonia or nitrite can disappear used for cell growth in those systems. It is determined
directly what we don’t know about? And an excess of that 0.124 grams per gram of Ammonia is used for cell
nitrate will disappear somewhere, right? It doesn’t keep growth. So say 12.4%, and that in the optimal
accumulating, so it’s going somewhere, it has to. circumstance whilst there is always a huge amount of
Bacterial growth in which nitrogen is used also Ammonia available to the bacteria. In our ponds, that
increases in a pond, but at some point it reaches a percentage will not be higher. Of this amount, also by far
balance if there is simply no longer food for them, but I the highest percentage is for heterotrophic bacteria, and
will explain this in more detail later on. only a small (negligible) percentage for the growth of
autotrophic bacteria. What was that again? Heterotrophic
In the fish culture industry, many details are now known bacteria extract their energy from converting organic
about RAS systems and their biofilters. As an average compounds (substances containing C, carbon) such as
directive, it can be assumed that for each gram of TAN sugar/sucrose (C 12 H 22 O 11 ) and autotrophic bacteria (the
(nitrogen from/in Ammonia) 4.57 grams of oxygen is nitrifying bacteria) extract their energy from substances
needed to eventually convert it into Nitrate. It has also that are inorganic (such as Ammonia and nitrite that do
been determined that as long as the oxygen level not contain carbon).
remains above 4mg/l, this whole process works fine. It
is also known that the higher the Ammonia level, the The heterotrophs do use Ammonia, but in the presence
more effective the biofilter can process Ammonia. of a carbon source like glucose. The stoichiometric
equation, so the comparative molecular formula
indicates this can be made as follows:
-
Ammonia Concentration NH 4 + 1.18 C 6 H 12 O 6 + HCO 3 + 2.06 O 2 forms
+
C 5 H 7 O 2 N + 6.06 H 2 O + 3.07 CO 2
Lpm
13.2 15.7 22.0 30.5
If bacteria grow, they use nitrogen to eventually form
44.6 54.2 80.6
Biofiltration C 5 H 7 O 2 N. This is the average molecular presentation of
Nitrification biomass. Carbonate, Ammonia and glucose are used to
Nitrification
make biomass, water and CO 2 . This process also
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Removal Rate (g/m 3 per day) 600 become harmful to our Koi if their concentration in the
goes the other way when a bacterium dies. These
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heterotrophic bacteria grow faster which can also
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pond becomes too high. Often this happens when there
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is too much dirt present in the pond and the biological
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material goes ‘rotten’. How large is the amount of
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100
heterotrophic bacteria? This effect seems to depend on
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 nitrogen that is captured in ponds as growth of
the protein percentage of the food fed. We still know
Ammonia-Nitrogen Concentration (mg/L)
from the first part of this series of articles that in the Koi
Ammonia concentration itself will affect the nitrification rate directly.
world about 40-45% protein content in the food is used.
Recirculating Aquaculture Systems Short Course.
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