Single-solute and bi-solute sorption of phenanthrene and dibutyl phthalate by plant- and manure-derived biochars.

The spatial arrangement of biochar and the exact underlying interaction mechanisms of biochar and hydrophobic organic compounds both remain largely unknown. The sorption of dibutyl phthalate (DBP) and phenanthrene (PHE) to plant- and manure-derived biochars in both single- and bi-solute systems was investigated. The significant positive relation between surface polarity and ash content suggests that minerals benefit the external distribution of polar groups on particle surfaces. PHE and DBP sorption by the biochars was regulated by their surface polarity. The PHE generally displayed a pronounced enhancement of DBP sorption, likely resulting from the formation of biochar-PHE-DBP complexes, suggesting that DBP and PHE had different sorption sites on the biochars. The enhancement of Cd(2+) (a soft Lewis acid) on DBP sorption implied that π-π interactions should not dominate DBP sorption by biochars. The influence of Cd(2+) on PHE sorption by biochars would depend on the balance between suppressive sorption by Cd(2+)PHE bonding and enhanced sorption by Cd(2+)-complexed functionalities, and the amounts of Cd(2+) adsorbed by biochars determined the relative role of increased sorption by Cd(2+) in the overall PHE sorption.