Pore-Size-Specific Evaluation of Commercial Biochars for Apparent Removal of the Boar-Taint Compounds Indole and Skatole Under Fecal Matrix Conditions

Indole and skatole are microbial tryptophan degradation products occurring in intestinal and fecal matrices and contribute to boar taint. Biochar is discussed as a carbonaceous adsorbent for reducing these compounds, but the link between pore-size-specific surface area and removal under complex fecal matrix conditions remains insufficiently understood. This study evaluated the apparent removal of skatole and indole by ten commercial biochar samples, including selected related material variants, under fecal matrix conditions to identify pore-size-specific descriptors associated with adsorption. With this approach, differences associated with drying, loading, biomass, and production were also explored. Pore-structural properties were characterized by nitrogen physisorption and compared across several data-reduction models. For interpretation, non-local-density-functional-theory-derived pore-size-specific surface area, ranging from 8.3 to 572.0 m2/g, was used to define functional pore-size classes relevant to small aromatic molecules. Geometry-based molecular dimensions and conservative molecular footprints of indole and skatole were used to estimate theoretical monolayer loading potential. Indole generally showed higher apparent loading than skatole, and apparent monolayer-reference ratios reached up to 20.57 for indole and 3.16 for skatole, confirming that experimentally observed apparent loading could exceed the conservative geometric monolayer reference. This indicates that surface area provides a structural reference rather than a direct prediction of removal under fecal conditions.