Sorption and desorption kinetics of PAHs in coastal sediment

Sorption and desorption kinetics of PAHs (naphthalene, phenanthrene and pyrene) in coastal sediment were investigated. Several kinetic models were used to analyze the kinetics: one-site mass transfer model (OSMTM), pseudo-first-order kinetic model (PFOKM), pseudo-second-order kinetic model (PSOKM), two compartment firstorder kinetic model (TCFOKM) and modified two compartment first-order kinetic model (MTCFOKM). Among the models, the MTCFOKM was the best in fitting both sorption and desorption kinetic data, and therefore could predict the most accurately. In MTCFOKM, the fast sorption fraction (f′ 1, s ) increased with the hydrophobicity (K ow ) of the PAHs, whereas the fast desorption fraction (f′ 1, d ) decreased. The fast sorption rate constant (k′ 1, s ) was much greater than the slow sorption rate constant (k′ 2, s ). Effect of aging on the desorption kinetics was also analyzed. The f′ 1, d in MTCFOKM decreased but the slow desorption fraction (f′ 2, d ) increased with aging, indicating that slow desorption is directly related to aging.