Standardization of BOD5/COD ratio as a biological stability index for MSW

► BOD5/COD on eluate of leaching test to assess the biological stability of waste. ► COD fractioning method: differentiation between soluble and colloidal fraction. ► Leaching test conditions: dynamic and static, 6 or 24-h duration, L/S=10l/kgTS. ► BOD5/COD and BOD5/CODsol are both consistent and significant as stability indices. The control of biodegradable substances is the key issue in evaluating the short and long-term emission potential and environmental impact of a landfill. Aerobic and anaerobic indices, such as respirometric index (RI) and biomethane potential production (GB21), can be used in the estimation of the stability of solid waste samples. Previous studies showed different degrees of relationship between BOD5/COD ratio compared with RI4. Aim of this study is to standardize the parameter BOD5/COD ratio and to test the methodology under different operating conditions (dynamic or static leaching and leaching duration, 6 and 24-h) keeping constant temperature and liquid/solid ratio (L/S=10l/kgTS), with the introduction of a COD fractioning method. The COD fractioning is based on the differentiation between the soluble fraction (CODsol) and the colloidal fraction (CODcoll) using a flocculation method. The BOD5/COD and the BOD5/CODsol indices are both consistent and significant and can be used as stability indices. The BOD5/COD ratio does not seem to be influenced, for the same test duration, by the type of test, static or dynamic. In the same way the longer test duration (24-h) does not influence significantly the values of BOD5/COD ratio. As a consequence a leaching test duration of 6-h is preferable to avoid the beginning of the hydrolysis and oxidation processes.