Enhancement of PAH biodegradation in soil by physicochemical pretreatment

The effects were studied of short-term heating of contaminated soil and its soaking in an organic solvent on the subsequent biodegradation of PAHs. In a clayey dredged sludge with a high organic-matter content (12%), heating at 120 degrees C for one hour increased the degree of degradation after 21 days of an aged PAH contamination from 9.5 +/- 0.7% to 27 +/- 5%. Lower tem peratures resulted in smaller increases. The observed increase in biodegrad ation is caused by either transfer of PAHs from sorption sites with low des orption rates to those with high ones or transformation of slow-sorption si tes into fast-sorption ones. Soaking of the above sludge in a 4:1 (v/v) ace tone-water mixture increased the degree of degradation from 9.5 +/- 0.7% to 20.4 +/- 1.4%, probably as a result of dissolution of the PAHs in the pore liquid during soaking. Thermal pretreatment of a contaminated sandy soil w ith a low organic-matter content showed no significant effect on the degrad ation of aged PAHs. Soaking of the sandy soil increased the degradation of only PAHs of high molecular weight, namely from 24 +/- 5% to 48 +/- 7%. (C) 1999 Elsevier Science Ltd. All rights reserved.