Solid phase treatment of an aged soil contaminated by polycyclic aromatic hydrocarbons

Application of advanced oxidation processes and electrooxidation for the remediation of river sediments contaminated by PAHs

This study was performed to assess and compare the effectiveness of electrochemical oxidation and chemical oxidation with hydrogen peroxide and modified Fenton's reagent for the remediation of sorbed polycyclic aromatic hydrocarbons (PAHs) in river sediments. The initial total PAH concentration in the sediment samples ranged from about 1032.8 mg/kg(DW) to 2816.4 mg/kg(DW) and a 90% degradation was required to meet the remediation goals. Several tests were performed at laboratory scale, the removal efficiency being evaluated in terms of contaminant removal and of ecotoxicity. The chemical oxidation tests resulted in about 95% total PAH degradation, when a sufficient oxidant dose was used (i.e. about 50-100 mmol of H2O2 per 30 g sediment samples), but proved to increase the ecotoxitity of the treated sediments significantly. Electrooxidation showed degradation efficiencies above 90%, with a negligible residual toxic effect, after 4-week treatments at constant voltage gradients of 1-2 V/cm. This technique seems to be effectively applicable either for the in situ or for the ex situ recovery of the target sediments.

Effects of enrichment with phthalate on polycyclic aromatic hydrocarbon biodegradation in contaminated soil

The effect of enrichment with phthalate on the biodegradation of polycyclic aromatic hydrocarbons (PAH) was tested with bioreactor-treated and untreated contaminated soil from a former manufactured gas plant (MGP) site. Soil samples that had been treated in a bioreactor and enriched with phthalate mineralized (14)C-labeled phenanthrene and pyrene to a greater extent than unenriched samples over a 22.5-h incubation, but did not stimulate benzo[a]pyrene mineralization. In contrast to the positive effects on (14)C-labeled phenanthrene and pyrene, no significant differences were found in the extent of biodegradation of native PAH when untreated contaminated soil was incubated with and without phthalate amendment. Denaturing-gradient gel electrophoresis (DGGE) profiles of bacterial 16S rRNA genes from unenriched and phthalate-enriched soil samples were substantially different, and clonal sequences matched to prominent DGGE bands revealed that beta-Proteobacteria related to Ralstonia were most highly enriched by phthalate addition. Quantitative real-time PCR analyses confirmed that, of previously determined PAH-degraders in the bioreactor, only Ralstonia-type organisms increased in response to enrichment, accounting for 89% of the additional bacterial 16S rRNA genes resulting from phthalate enrichment. These findings indicate that phthalate amendment of this particular PAH-contaminated soil did not significantly enrich for organisms associated with high molecular weight PAH degradation or have any significant effect on overall degradation of native PAH in the soil.