Mechanically–biologically treated municipal solid waste as a support medium for microbial methane oxidation to mitigate landfill greenhouse emissions

The residual fraction of mechanically–biologically treated municipal solid waste (MBT residual) was studied in the laboratory to evaluate its suitability and environmental compatibility as a support medium in methane (CH4) oxidative biocovers for the mitigation of greenhouse gas emissions from landfills. Two MBT residuals with 5 and 12 months total (aerobic) biological stabilisation times were used in the study. MBT residual appeared to be a favourable medium for CH4 oxidation as indicated by its area-based CH4 oxidation rates (12.2–82.3 g CH4 m−2 d−1 at 2–25 °C; determined in CH4-sparged columns). The CH4 oxidation potential (determined in batch assays) of the MBT residuals increased during the 124 d column experiment, from <1.6 to a maximum of 104 μg CH4 gdw-1 h−1 (dw = dry weight) at 5 °C and 578 μg CH4 gdw-1 h−1 at 23 °C. Nitrous oxide (N2O) production in MBT residual (<15 μg N2O kgdw-1 d−1 in the CH4 oxidative columns) was at the lower end of the range of N2O emissions reported for landfills and non-landfill soils, and insignificant as a greenhouse gas source. Also, anaerobic gas production (25.6 l kgdw-1 during 217 d) in batch assays was low, indicating biological stability of the MBT residual. The electrical conductivities (140–250 mS m−1), as well as the concentrations of zinc (3.0 mg l−1), copper (0.5 mg l−1), arsenic (0.3 mg l−1), nickel (0.1 mg l−1) and lead (0.1 mg l−1) in MBT residual eluates from a leaching test (EN-12457-4) with a liquid/solid (L/S) ratio of 10:1, suggest a potential for leachate pollutant emissions which should be considered in plans to utilise MBT residual. In conclusion, the laboratory experiments suggest that MBT residual can be utilised as a support medium for CH4 oxidation, even at low temperatures, to mitigate greenhouse gas emissions from landfills.