Further steps in the standardization of BOD₅/COD ratio as a biological stability index for MSW

In recent decades the definition of standard test methodologies suitable for use in assessing the biological stability of solid waste has become increasingly imperative. To meet this requirement, the BOD₅/COD ratio, measured on waste eluate, has been proposed by Cossu et al. (2012) as a more appropriate parameter than the traditional respirometric indices and biogas production measured directly on solid samples. However, to ensure reproducibility, the parameter should undergo standardization of operational conditions. Previous studies have demonstrated that: the testing mode (static or dynamic) does not influence test representativeness; the long testing time (>6h) does not influence BOD₅/COD ratio; COD measured on unfiltered or filtered samples is consistent and significant in both cases. The main aim of this study was to further promote the standardization of this parameter. A series of static leaching tests on representative samples of five types of waste was carried out under different operative conditions: contact time, liquid to solid ratio and pretreatment. The results obtained demonstrate: the apparent adequacy of a short contact time (2h), which is highly preferable and would speed up the procedure; a low liquid to solid ratio (5 l/kgTS) which is recommended as a water saving strategy; the applicability of centrifugation of the eluate prior to analysis which is faster that filtration method.