Effects of Biochar on Methane Oxidation and Properties of Landfill Cover Soil: Long-Term Column Incubation Tests

Landfill gas poses significant risk to global climate change. Landfill gas is composed of very high concentrations of methane (CH4), nearly 50% by volume. The present study investigates the use of biochar amendment to silty clay landfill cover soil as a means of reducing CH4 emissions via long-term soil column incubation experiments. Amendment ratios of 2% and 10% (by weight) biochar-amended soil were evaluated in column tests; amendments were either applied to the zone in which CH4 oxidation activity was expected to be highest based on previous literature reviews [0.20-0.40 m (20-40 cm) below the surface] or throughout the entire soil layer [0-0.60 m (0-60 cm) below the surface]. Columns were incubated under simulated landfill cover conditions by applying synthetic landfill gas (60% CH4 and 40% CO2) at the base and atmospheric air flushing the headspace for >400 days. Initial and terminal physicochemical properties of the cover substrates were assessed to relate CH4 removal efficiency and long-term performance to key cover properties. An increase in soil porosity, water holding capacity, hydraulic conductivity, and overall soil moisture throughout testing was observed with biochar addition. The soil column with the greatest amount of biochar amendment (10% by weight) also had the highest average CH4 removal efficiency across all test stages [CH4 loads of approximately 0.05-0.2 kg m(-2) day(-1) (50-200 g m(-2) day(-1))]. All tested designs displayed relatively high CH4 removal efficiencies (>90%) at the CH4 loads tested. The study results suggest that the long-term performance of soil covers for enhanced CH4 oxidation may be improved by the addition of biochar, which may help to reduce moisture loss and minimize desiccation cracking and fugitive emissions in actual landfill covers. (C) 2020 American Society of Civil Engineers.