Industrial application of a new respirometric test to different sludge and organic waste mixtures to be composted

In order to optimize the sizing and the operation of its composting plants and face a growing market, a new respirometric test called BIODEC has been developped and patented by Suez Environnement in association with Cemagref. The first industrial application of this test was operated in 2005 in the Research and Technical Centre (CIRSEE) of Suez Environnement through the building and the technical validation of a 4 cells respirometric device which has been used on several sludge and organic waste feedstocks already treated in Suez Environnement composting plants. The respirometric analysis of each industrial mixture supplies one experimental and one modelled respirometric curves, the compostability index, the duration of the test and the AT4 equivalent. The results obtained on 5 sludges of different origins and qualities and mixed with wood pallets showed different levels of O2 consumption but with a systematic important and short peak and significant variations (10 to 32%) of the compostability index. Concerning the 2 first samples of the same mechanically pre-treated refuse, the results showed levels of O2 consumption similar to those of sludges but without peak and with and with a great variation of composition from a sample to another. It seems already obvious that the BIODEC test is reliable and able to characterize the potential of biodegradation of organic waste mixtures. It allows the operators firstly to differentiate and compare the potential and dynamics of degradation of the different analysed mixtures and secondly to improve the quality of the initial mixture and the performances of the composting process. Further studies are led to study and identify more particularly the specific contribution of the bulking agent to the potential of degradation of the sludge mixtures.