Methane oxidation and attenuation of sulphur compounds in landfill top cover systems: Lab-scale tests

In this study, a top cover system is investigated as a control for emissions during the aftercare of new landfills and for old landfills where biogas energy production might not be profitable. Different materials were studied as landfill cover system in lab-scale columns: mechanical-biological pretreated municipal solid waste (MBP); mechanical-biological pretreated biowaste (PB); fine (PBS_f) and coarse (PBS_c) mechanical-biological pretreated mixtures of biowaste and sewage sludge, and natural soil (NS). The effectiveness of these materials in removing methane and sulphur compounds from a gas stream was tested, even coupled with activated carbon membranes. Concentrations of CO₂, CH₄, O₂, N₂, H₂S and mercaptans were analysed at different depths along the columns. Methane degradation was assessed using mass balance and the results were expressed in terms of methane oxidation rate (MOR). The highest maximum and mean MOR were observed for MBP (17.2gCH₄/m²/hr and 10.3gCH₄/m²/hr, respectively). Similar values were obtained with PB and PBS_c. The lowest values of MOR were obtained for NS (6.7gCH₄/m²/hr) and PBS_f (3.6gCH₄/m²/hr), which may be due to their low organic content and void index, respectively. Activated membranes with high load capacity did not seem to have an influence on the methane oxidation process: MBP coupled with 220g/m² and 360g/m² membranes gave maximum MOR of 16.5gCH₄/m²/hr and 17.4gCH₄/m²/hr, respectively. Activated carbon membranes proved to be very effective on H₂S adsorption. Furthermore, carbonyl sulphide, ethyl mercaptan and isopropyl mercaptan seemed to be easily absorbed by the filling materials.