Page 72 - Koi Net - On-Line Koi Magazine - Issue 94

Table 1 – Reaction routes in removal of Nitrogen Simplified scheme of the main reactions within the Biofilm
Reaction Main Process Organisms Status Examples of
Route Reaction Name Involved (General Knowledge) Studies at KHT N 2 N 2
C H O N+5O
1 5 7 2 - 2 Ammonification Bacteria Well known process
4CO +HCO +NH +H O
2
2
4
3
Water + +
+
2 NH +OH - NH +H O Ammonia Stripping (Physical Process) Well known process NH 4 O 2 NH 4
4 3 2 Phase
-
+
4CO +HCO +NH +H O Bacteria Algae
3 2 3 4 2 Assimilation Well known process Aerobic
C H O N+5O (Plants)
5 7 2 2 + Zone
-
+
NH +1.5O NO +2H + Tendaj, 1985; NH 4 AOB NO 2 - NOB NO 3 -
4 4 2 2 Nitritation Nitrosomonas Well known process
+H O Mossakowska, Interface
2
1997, 1994; Biofilm -
3
-
5 NO +0.5O NO - Nitratation Nitrobacter Well known process Plaza, 2001 N NO - NO , N 2
2 2 3 2 2 Anaerobic
DENITRIFIERS ANAMMOX NH 4 + Zone
C+2NO - Denitrification Plaza, 1995,
6 - 3 Denitratation Well known process
2NO +CO (Bacteria) 1991, 1990;
2 2 Carrier
Trela, 2000,
3C+2H O+4NO Denitrification 1998
7 2 - 2 Denitritation Well known process
2N +4OH +3CO (Bacteria)
2 2
Diffusion
Difficulties to ensure ammonium
8
oxidation to Nitrite, only
Main reactions in the one-stage
Trela, 2001; Partial Nitritation-Anammox reactor
+
NH +NO - Planctomycetales New process observed La Rocca, 2001;
9 4 2 Anammox
N +2H O during the last decade Horeglad, 2001; Some of the possibe parallel reactions
2
2
Plaza et al., 2002
Let’s talk a brief minute about the Biofilm as used in Above: A biofilm layer schematically looks like this
the water purification industry and due to this much is
Dissolved Ammonia is present in the water phase which
explained about it. A great deal of kaldnes is used in
goes together with oxygen into the top layer, the aerobic
that industry on which thick biofilm layers are formed.
layer, so called because there is still enough oxygen in
It has often been described, even in the Koi world that
it. This oxygen is used by heterotrophs and autotrophs
if this biofilm becomes thick enough, zones will be
to grow and convert Ammonia into nitrate. Once the
formed in the lower layer that are low in oxygen level.
oxygen has been used up considerably, the bacteria
The anammox reaction usually occurs by a group of
that convert nitrite (Denitrification) or ammonia or nitrate
bacteria called Brocadiales in this low-oxygen zone. In
into nitrogen gas via Anammox can do their job in the
these low-oxygen zones, certain types of bacteria, as
low-oxygen lower/deeper parts of the biofilm layer.
shown in Table 1, under 9, can convert Ammonia plus
nitrite into nitrogen gas plus water. This gas then On the next page a photo with colours has been made
evaporates from the water and you subsequently lose with a microscope and a fluorescence technique called
nitrogen from your system. FISH. It can clearly be seen here that the biofilm does
not have a neatly flat surface, but is rather formed with
bulges. In addition, you can see the green nitrosomonas
(Ammonia oxidising) at the top, the nitrospira stained
red underneath that (Ammonia and/or nitrite oxidising),
and below, in blue, Brocadia that perform the Anammox.
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