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IV. Wastewater Treatment
Topic IV. 3. Ammonification, Nitrification and
Denitrification. Cycle of Nitrogen in the Nature
Ammonification
Definition: Anaerobic processes of proteins and carbamide - CO(NH2)2
decomposition resulting in generation of ammonium salts and ammonia as
end-products.
 First faze - carbamide hydrolyses
CO( NH 2 ) 2  H 2 O  ( NH 4 ) 2 CO3
 Second faze - ammonification
( NH 4 ) 2 CO3  2 NH 3  CO2  H 2 O
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Nitrification
Definition: Aerobic processes leading to decomposition of ammonium salts
to nitrites and finally to nitrates (salts of the nitric acid) as end-products.
 First faze - performed by specific hemotrophic bacteria specie Nitrosomonas
2 NH 4  3O2  2 NO2  2H 2 O  4H   heat
 Second faze - performed by specific autotrophic bacteria specie Nitrobacter
2 NO2  O2  2 NO3  heat
 Autotrophes utilise the energy, released in ammonum oxidation for cells
mass building, delivering the necessary carbon out from CO2 in the air.
In this way cycles of C and N transformations interact in the Nature.
Dissolved organic substances strongly inhibit the autotrophes.
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Denitrification
Definition: Anaerobic processes leading to N2 as end-product in a
result of carbon assimilation by oxidation of organic substances

with NO3 as electrons acceptor.
5C 6 H 12O6  24 KNO3  24 KHCO3  6CO2  12 N 2  18H 2 O
 Processes of denitrification are due to activities of heterotrophic
facultative bacteria species, such as Pseudomonas and some other
facultatives
 Dissolved oxygen is a strong inhibitor for the processes of
denitrification
 In the processes of denitrification less oxygen is utilize than the
one, incorporated into the nitrates in the processes of nitrification
 Nitrogen-gas release in the atmosphere, further on is fixed in the
soil by specific bacteria (N-fixators) and is utilized by plants. In
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this way the cycle of N in the Nature is closed
Cycle of Nitrogen in the Nature
metabolism
Plants' proteins
fixing
dead
food
N2
Nitrogen
ammonification
NH3
compounds
Carbamide
NO3-
hydrolises
II faze
nitrification
I faze
nitrification
food
Animals' proteins
metabolism
dead
NO2-
denitrification
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