Biochar-Amended Soil Cover for Microbial Methane Oxidation: Effect of Biochar Amendment Ratio and Cover Profile

Abstract

A long-term soil column study was carried out to investigate the methane (CH4) removal capacity of landfill cover soil and biochar-amended cover soil under simulated landfill cover conditions. Terminal batch assays were conducted following the long-term column tests to quantify potential oxidation rates in cover materials at three depths targeting the middepths of distinct soil layers in each column. Potential methane oxidation rates among the materials varied in response to moisture content and were also affected by the methane exposure history. During long-term incubation testing, 1%–biochar-amended soil columns had higher average methane removal efficiencies than an unamended soil control at inlet methane loads ranging from ∼5 to 2 g CH4·m−2·day−1. Methane oxidation rates in cover materials following exhumation varied widely following an initial lag phase, ranging from very low rates (<1 μg CH4·g−1·day−1) to relatively rapid rates similar to those observed in landfill cover soils (up to 27 μg CH4·g−1·day−1). Highest overall methane oxidation rates were observed in 1%–biochar-amended soils in both column and batch assays, and this is attributed to the favorable soil moisture regime promoted by the high water-holding capacity of biochar, as well as to its high internal porosity and surface area. In addition, the improved water retention of biochar-amended soil also enhanced the performance by reducing the formation of desiccation fissures and the emissions of landfill gas through these fissures via advective flow.