PAH release during water desorption, supercritical carbon dioxide extraction, and field bioremediation

Removal rates of polycyclic aromatic hydrocarbons (PAHs) from manufactured gas plant (MGP) soils were determined using water desorption for 120 days a nd mild supercritical carbon dioxide extraction (SFE) for 200 min. Both tec hniques were used to compare the changes in desorption rates for individual PAHs from untreated and treated soils that were obtained from a field biot reatment unit after 58, 147, and 343 days. Water desorption profiles (plott ed in days) and SFE profiles (plotted in minutes) were very similar regardl ess of whether a PAH was rapidly or slowly removed. Water and SFE profiles were fit with a simple two-site (fast and slow) model to obtain the fractio n of each PAH that was rapidly released (F). There was agreement between th e F values obtained from water desorption and SFE for PAHs ranging from nap hthalene to benzo[a]pyrene from all soils, with an overall correlation coef ficient (r(2)) of 0.81. F values from water desorption and SFE also agreed with the actual removal of PAHs obtained after 147 and 343 days of field re mediation (r(2) ca. 0.80). The use of shorter desorption times (2-4 days fo r water and 20-40 min for SFE) allowed F values to be estimated for all PAH s and showed excellent agreement with the removal of individual PAHs obtain ed with 147-343 days of field remediation (r(2) > 0.9). The comparisons ind icate that shortterm SFE can provide a reasonable estimate of the fraction of a PAH that is readily released and available for microbial treatment.