MOROCOMP (LIFE TCY05/MA000141) - Unit of Environmental ...

ammonium during composting did not coincide with a rapid increase in nitrates
concentration shown in Figure 9. The concentration of nitrates was very low initially
suggesting that nitrogen was lost during composting. Losses of nitrogen in this
composting process were governed mainly by volatilization of ammonia due to high
pH and temperatures values of the substrate. Agitation and aeration rate may have
also affected the rate of ammonia volatilization [30].
5.1.6.5. Nitrates (NO - 3-N)
As has been observed by recent studies, during composting the ammonium content is
reduced due to the stimulation of nitrification while the concentration of nitrates is
increased [31, 32, 33]. The conversion of ammonia to nitrates is due to the activity of
nitrifying bacteria as shown by the following reactions.
NH 2
− + −
3
+ O2
→ NO2
+ 3H
+ e
NO 2
− + −
2
+ H
2O
→ NO3
+ 2H
+ e
There are two different types of nitrification that occur during composting. The first
type is the heterotrophic nitrification which takes place at the initial phase of
composting. The conversion of ammonia to nitrates at the initial stage of composting
is exclusively due to the activity of heterotrophic nitrifiers [25, 34]. On the contrary
autotrophic nitrification is developed at a later stage of composting since bioxidation
of ammonium to nitrates during autotrophic nitrification is restricted by elevated
temperatures and by increased ammonium concentrations of the compostable matter
[35, 36]. Figure 9 presents the nitrates evolution during the 1 st composting trial.
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