Air permeability of biochar-amended clay cover

Abstract

Biochar has a porous structure with high specific surface area and high adsorption. Moreover, it provides a suitable habitat for microorganisms that can reduce harmful gases. Adding biochar to a traditional landfill clay cover (i.e., biochar-amended clay cover) can increase soil porosity, improve soil air flow, and reduce landfill methane emissions which are an area of interest for many researchers. In the present research, the air permeability of biochar-clay is considered to be the main measure in evaluating the fluid-flow characteristic of the material. We discussed the influence of biochar content and particle size on air permeability of biochar-clay and its mechanism. The air permeability coefficient ka of biochar-clay mixture with different biochar content (0%, 5%, 10%, 15%, and 20%), dry densities (1.42 g/cm3, 1.56 g/cm3, and 1.65 g/cm3), and biochar particle size ranges ( 74 μm) were measured using a flexible wall air permeability testing device. Changes in soil pore structure were analyzed by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). The results show that when dry density was 1.42 g/cm3, the air permeability coefficient decreased as the biochar content increased. For biochar-clay mixture of 1.56 g/cm3 and 1.65 g/cm3, when the biochar content was 15%, the air permeability coefficient of biochar-clay mixture reached its lowest value. Comparing the air permeability coefficient of biochar-clay mixture with non-intersecting particle size groups of biochar, it was revealed that the permeability coefficient decreased as the biochar particle size decreased. Based on the pore structure of biochar-clay mixture with different biochar content and particle size, the influence biochar content and particle size on the air permeability was evident.