Evaluation of methods to determine biodegradable municipal waste diversion from landfill

The biological tests of biochemical methane potential (BMP) and dynamic respiration index (DRI) are recommended by the EA monitoring guidance (Environment Agency, 2005) to evaluate the performance of Waste Disposal Authorities (WDAs) in diverting biodegradable municipal waste (BMW) from landfills by means of mechanical and biological treatment (MBT). Because the biological tests are complex and time- consuming to conduct, chemical tests may provide rapid surrogate measurement of biodegradability. The relative contents of the cellulose, hemicellulose and lignin determined by fibre analysis have been used to assess the degree of decomposition in landfills. However, their relationship with biodegradability has not been well investigated and understood, particularly for mixed BMW. In this study, BMP and DRI, gravimetric test and chemical tests (fibre analysis and TC, TN) were conducted in parallel using a variety of MBT waste samples collected from anaerobic and aerobic degradation (composting) experiments in which real MSW or BMW was used. Two laboratory scale composting reactors were built where four batches of composting experiments were conducted. The results of these tests were compared to identify the correlations between them, especially the correlations between the biological tests and fibre analysis. Evaluations are made based on this study for tests of BMP, DRI4, gravimetric test and TCI TN ratio. The main findings are: (1) Based on the good correlation observed between fibre analysis and biological tests for the treated waste, three linear model equations are proposed to predict the biodegradability upon (C+H)/L ratio or C/L ratio for the BMW during or after the MBT process, thereafter to predict the amount of BMW diverted by MBT in terms of anaerobic biogas potential; (2) The cellulose and hemicellulose contents or the (C+H)/L ratio of the untreated BMW (fresh mechanically pretreated BMW) were not found to correlate directly with biodegradability. This is consistent with the former findings on the specific waste components (untreated waste) by Eleazer et al. (1997) and Godley et al. (2005). It is suggested that untreated BMW and treated BMW need to be investigated separately in examining the relationships between relative fibre content and biodegradability.