In-situ modification of soil organic matter towards adsorption and desorption of phenol and its chlorinated derivatives

The demineralized (DM), nonhydrolyzable carbon (NHC) and black carbon (BC) components in a soil sample were sequentially isolated via in-situ modification method involving acid hydrolysis and a combustion method at 375 °C for 24 h. The bulk soil and components were used to investigate adsorption-desorption isotherm of phenol and its chlorinated derivatives {2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP) and pentachlorophenol (PCP)}. Except for phenol, other sorption isotherms are nonlinear and well fitted by the Freundlich model (0.940 ≥ R2 ≤ 0.998) while linear sorption model gave the best fit for phenol (0.994 ≥ R2 ≤ 0.996). The normalized organic carbon distribution coefficient (log Koc) measured for the natural organic matter (NOM) isolates ranged from 3.5-5.4 and much higher than that for the bulk sample (2.4-3.3). The NHC and the bulk possessed the highest and least sorption capacities respectively. Sorption affinity at the experimental pH was found to be consistent with solute hydrophobicity and extent of chlorination in the order PCP < 2,4-DCP < 2,6-DCP < Phenol. Maximum sorption capacities were reached at pH close to chemical's respective pKa values. The hysteretic index (H) values for all the samples were greater than zero. The results suggest that in-situ removal of soil organic matter (SOM) at varying degree can positively influence adsorption-desorption potential of phenol and its chlorinated derivatives.