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

[ % ]
6
5,5
5
4,5
4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
[ Days ]
Figure 40: Changes in total nitrogen content [%] during the 4 th composting trial
The 4 th composting trial acquired the highest nitrogen content in comparison to the
previous trials due to the origin of the composted raw material which comprised only
of secondary sludge and perlite as an additive. The collected secondary sludge had
increased nitrogen content as has been shown in Table 32 whereas the carbon content
is low proportionally to the nitrogen content. According to Figure 40 the nitrogen
content in the beginning of the process was 5.74% of which a significant amount was
lost as ammonia and/or ammonium as the composting kept developing due to the
excess of nitrogen in the substrate. Studies have shown that during the first phase of
the process the combination of high ammonium concentration, high temperatures, and
raised pH lead to high ammonia losses. Also, high aeration of the composting piles
increases the rate of volatilization of the ammonia formed [65]. As has been sated the
level nitrogen losses by ammonia volatilization varies and can amount up to 50% of
the initial total nitrogen depending on the raw material that is used for composting
[22, 23]. On the 13 th day nitrogen content acquired its minimum value of 4.55%, from
that day onwards and as the substrate passed from the thermophilic stage to a second
mesophilic phase the nitrogen content started to increase. This increase is probably
attributed to the processes of nitrogen fixation by the activity of azotobacters which
recover a proportion of nitrogen that has been lost as ammonia [2, 28]. The nitrogen
content at the end of the 4 th composting trial on the 20 th day was 5.12%.
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