Biological stability assessment of MSW organic fractions by means of respirometric and germination tests

Composting is the mostly applied method for recovering the organic waste by producing an organic soil conditioner. Furthermore, the organic fraction of unsorted municipal solid waste (OFMSW) should be treated in mechanical biological treatment (MBT) plants in view of reducing its environmental impacts. In both cases, it is essential the assessment of biological stability as well as the phytotoxicity of the final product. The aim of this work was to evaluate the maturity evolution during the composting process of OFMSW at full scale. Samples were collected from two Sicilian (Italy) plants and were subjected to the following analytical measures: volatile solids (VS), dynamic respirometric index (DRI), carbon-to-nitrogen (C/N) ratio and germination index (GI). Results showed that some parameters such as pH and water content values can affect the respirometric test response and the proper activity of microorganisms responsible for biodegradation at full scale. For the unsorted waste, the DRI values suggested that depending on the initial values the stabilization duration might be increased prior to landfilling. DRI revealed to be effective for the assessment of the matrix stability, even if the simultaneous measurements of different indices can provide a reliable information of biological stability and maturity of the organic matrices.