Gaseous Emissions from Composting Bark/Manure Mixtures

Compost Science & Utilization, (2005), Vol. 13, No. 1, 14-26

P. Morand (1), G. Peres (1), P. Robin (2), H. Yulipriyanto (1) and S. Baron (1)
1. UMR 6553, CNRS/Université de Rennes I, Paimpont, France
2. UMR SAS, INRA/ENSAR, Rennes, Cedex, France

About 25 m3 of a poplar bark-poultry dung mixture were composted in a covered place with natural ventilation, air entering the lower part and going out through four shafts in the upper part. The gaseous emissions were measured and analyzed. The first heap (initial C/N of 28) was monitored for one month, then turned and more dung added. The second heap (initial C/N of 8) was monitored for seven months with two intermediate turnings. For the whole experiment, N losses were estimated at 61-74% of initial N, of which 62% was lost as NH3 (38-46% of initial N) and 1% as N2O (0.6-0.7% of initial N). N-NOx losses were 1000 times lower than N-NH3 losses. N2O and NOx were found only at the end of the periods before the piles were turned. As for carbon, C-CO2 emissions were estimated at 45-55% of initial C content, the ratio of CH4 to CO2 in the effluent air was 1 to 100 on average, with significant variations. The global warming potential of CH4 and N2O was estimated at respectively 25% and 50% of total CO2 emissions. N-NH3 losses need to be considerably reduced by maintaining a higher C/N ratio with available carbon. The method described here was less restricting and less costly than continuous monitoring, and its degree of precision was about 25%. It required that the naturally-ventilated composting box itself be covered to reduce the effects of climatic variations, and that the ventilation be sufficient to ensure that the composting process was not disturbed.

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