Denitrifying population dynamic and evolution of nitrogen gas during a composting process

Little information exists about nitrogen losses through microbial activity during treatment of solid urban waste (SUW) by processes such as composting. In the present study, in addition to evaluating the pattern of nitrogen losses by denitrification at different stages of the process, a comparison between the method of Pochon and Tardieux, and an improved gas chromatographic method for estimating denitrifying populations was undertaken. Though the MPN (Most Probable Number) enumerations were higher using the colorimetric method than the gas chromatographic one, the pattern of the two graphs showing numbers of denitrifiers during composting were the same. The highest numbers were revealed immediately after loading the reactor (107-108/g d.w.), lower numbers of denitrifiers were found in the second sampling corresponding to the thermophilic phase (103-104/g d.w.). These numbers increased gradually as the waste material stabilized (10th to 123rd day of composting) to again reach values of 107-108/g d.w.