Feasibility of biochar depth insertion using permeation method in sandy soil for carbon sequestration: a multiphase coupled fluid modelling approach

Biochar, a by-product of biomass pyrolysis, is increasingly recognized for carbon sequestration; however, its field-scale use remains limited by uncertainties in practical application methods, placement depth, and delivery efficiency. This study addresses this gap by evaluating pressure-driven biochar slurry permeation in sandy soil using a coupled multiphase porous-media CFD framework. The numerical model underwent a two-stage validation process: first, to verify the porous-media setup and analyze the pressure and velocity responses of saturated sand, and next to validate the hydraulic behaviour of biochar-amended sand against the existing literature. Field-scale simulations were then performed to assess factors (injection time, pressure, inlet diameter, biochar concentration, and application depth) affecting slurry spread and biochar retention. Results highlight that increasing injection pressure and inlet diameter enhance plume spread and retention, while higher BC% reduces slurry mobility under the same conditions. Application depth significantly influenced target-zone placement, underscoring the importance of deep biochar insertion in sandy soils. While this study focused on slurry permeation in homogeneous soil, further research on biochar-soil interactions and clogging mechanisms is needed for effective field carbon sequestration. The findings advocate for deep biochar insertion to enhance resource use and carbon sequestration, aligning with UN Sustainable Development Goals 12 and 13.