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

carbon for each part of nitrogen by weight, although ratios from 20:1 up to 40:1 can
give good composting results [24, 25, 37, 38]. Low ratios supply the mixture with
excess of nitrogen which is lost as ammonia gas 6 creating undesirable odors whereas
high C:N ratios cause shortage of nitrogen and the degradation rate of the composting
material remains relatively low since micro-organisms must go through many lifecycles,
oxidizing off the excess carbon until a more convenient C:N ratio for their
metabolism is reached. In addition nitrogen limitation may lead to extensive organic
acid formation from carbonaceous waste, which tends to lower the pH and thereby
retard the microbial activity. The ratio is weighted in favor of carbon, because uses for
carbon outnumber those for nitrogen in microbial metabolism and synthesis of
cellular materials. Not only is carbon utilized in cell wall or membrane formation,
protoplasm, and storage products synthesis but also an appreciable amount is also
oxidized to CO 2 in metabolic activities. On the other hand, nitrogen has only one
major use as a nutrient namely as an essential constituent of protoplasm.
Consequently, much more carbon than nitrogen is required. Figure 10 presents the
carbon nitrogen ratio evolution during the 1 st composting trial.
[C/N]
18
16
14
12
10
8
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Days
Figure 10: Changes in C:N ratio during the 1 st composting trial
According to Figure 10 during the 1 st composting trial, the C:N ratio presents a
steadily downwards inclination. This inclination can be explained by the carbon loss
6 leads to excess ammonia formation, which increases the pH and thereby enhances ammonia
volatilization
46