Use of solvents to enhance PAH biodegradation of coal tar-contaminated soils

Bioremediation of coal tar-contaminated soils containing polycyclic aromati c hydrocarbons (PAHs) is highly challenging because of the low solubility a nd strong sorption properties of PAHs. Five coal tar-contaminated soils fro m former manufactured gas plant (MGP) sites were pretreated with two solven ts, acetone and ethanol to enhance the bioavailability of the PAH compounds . The biodegradation of various PAHs in the pretreated soils was assessed u sing soil slurry reactors. The total PAH degradation rated: for soils pretr eated with solvents were estimated to be about two times faster than soils that were not pretreated with solvents. For example, the total PAH first or der degradation rate constants were 0.165 +/- 0.032, 0.147 +/- 0.020, and 0 .076 +/- 0.009 day(-1) for Vandalia (EXC) soil that were pretreated with ac etone, ethanol. and with no solvent, respectively. A distinctive advantage for soils pretreated with solvents was the enhanced removal of 5-ring PAH c ompounds such as benzo(a)pyrene and to a limited extent 4-ring compounds su ch as chrysene. Even for soils with 3.5% or more organic carbon content (tw o soils out of five), the degradation rate constants of chrysene were found to be two times faster than soils that were not pretreated. The degradatio n rate constants of benzo(a)pyrene were enhanced by 2-6 times for all five contaminated soils that were pretreated with solvents. To further elucidate trends that control the solvent treatment, the percent improvement in degr adation rate constants (100 x rate constants for pretreated soils/rate cons tants for non-treated soils) for 16 PAHs were found to correlate well with the PAH partition coefficients (K-oc). Except for phenanthrene and the clay fraction of the soil, correlations between the percent improvement in degr adation rates constants and several physical properties of the soils were p oor and sporadic. This implies that the enhancement in PAH availability usi ng solvent treatment was driven by the distribution of the PAHs between the solvent and the adsorbed PAHs. (C) 2001 Elsevier Science Ltd. All rights r eserved.