Page 79 - Koi Net - On-Line Koi Magazine - Issue 92

The following graph shows that in Ebeling’s tests, just The dotted line is the total amount of nitrogen added
over two-thirds of the Ammonia present is eventually (about 50.4 grams in the form of Ammonia is excreted
converted into nitrate via autotrophic bacteria at 40-45%. by the shrimp per kg of food), due to the removal of
biomass (sediment) it would end up on the solid line,
and the squares indicate the actually measured amount
100% of total nitrogen, which is therefore considerably lower.
Removal of Ammonia-Nitrogen 60% bacteria, or by nitrogen gassing. In the following
So you lose a percentage in another way, which can
80%
partly be explained by the growth of heterotrophic
experiment, Ebeling added extra carbon via sucrose to
the food (somewhat similar to Koi food, but then a bit
40%
more), and again determined what happened:
20%
Mass balance on nitrogen for
0%
the heterotrophic system with 250
12.4% 15% 20% 25% 30% 35% 40% 45% 50% 55%
carbon supplementation at
Protein 50% of feed rate as sucrose
Heterotrophic Bacteria
and periodic harvesting of 200
Autotrophic Bacteria
Nitrogen (mg/L-N) 150
excess bacterial biomass.
Ebeling has done an interesting experiment with shrimp 100
breeding. This was a RAS, so a tank of water with filter
and shrimp in it that were fed. The waste was processed 50
in the filter. Here he fed 35% protein food and
determined where the Ammonia ended up and plotted it 0
against the theoretically present total nitrogen levels: 0 10 20 30 40 50 60 70
Days
Mass balance on nitrogen for Total Nitrogen – Model Cumulative Total Nitrogen from food
the autotrophic/heterotrophic 300 Total Nitrogen – Experimental Data Measured Total Nitrogen
system without carbon
supplementation and with 250
periodic harvesting of excess
Nitrogen (mg/L-N) 150 By regularly removing the sediment, the extra formed
bacterial biomass. 200

biomass at the bottom of the tank, the nitrogen level
really remained completely under control. The measured
100
nitrogen levels exactly followed the cleaning schedule. It
50
was also examined what percentage of the nitrogen still
present was in the form of nitrate. This turned out to be
0
0 10 20 30 40 50 60 70 almost everything without the addition of sucrose,
Days
and after sucrose addition only a few percent of the
Total Nitrogen – Model Cumulative Total Nitrogen from food nitrogen. Interestingly, Ebeling says that about 1.6% of
Total Nitrogen – Experimental Data Measured Total Nitrogen
the nitrogen binds in autotrophic biomass and no less
than 36% in heterotrophic biomass.

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