Phenolic Acid Sorption to Biochars from Mixtures of Feedstock Materials

In an effort to customize biochars for soil amendments, multiple feedstocks have been combined in various ratios prior to pyrolysis at 350 °C. The resulting variation in the chemistry and structure can affect the adsorption capacity of biochar and thus influence the bioavailability of many chemical compounds in the soil system including phenolic acids. This study examines the sorption of C-labeled ferulic acid, syringic acid, and chlorocatechol to four biochars prepared from individual feedstocks and four biochars produced from mixed feedstocks using batch equilibration. Pure feedstock biochar sorption followed switchgrass<swine solids<poultry litter<pine chip for both ferulic (Kd=1.4–75 L kg ) and syringic acid (Kd=0.07–6.03 L kg ). Sorption appeared to be influenced by the properties of the biochars as well as the structure of the chemicals. All biochar Kd values, except pine chip, were consistently lower than that of the reference silt loam soil. The sorptive properties of biochars produced from combined feedstocks could not be predicted from their pure feedstock components, and sorption coefficients were both higher and lower than the individual parent materials’ biochars. Further research is necessary to understand the characteristics of these combination biochars, particularly their sorption, which this study has shown is not merely an average of its components.