Ozone treatment of PAH contaminated soils: operating variables effect.

A three-level full factorial design has been conducted to assess the influence of gas flow-rate, ozone concentration and reaction time on the remediation of soil contaminated with four PAHs (namely acenaphthene, phenanthrene, anthracene and fluoranthene). Under the operating conditions investigated, reaction time and ozone concentration seem to exert a slight positive effect, whereas gas flow-rate does not affect the process efficiency. Average conversions (related to non-ozonated samples) are in the proximity of 50, 70, 60 and 100% for acenaphthene, phenanthrene, anthracene and fluoranthene, respectively. A high conversion percentage is obtained in the first minutes of the process. Ozone decomposition on soil surface can be modelled by its reactions with easily oxidizable organic matter, recalcitrant ozonation intermediates and inorganic active sites.

Remediation of PAH spiked soils: concentrated H2O2 treatment/continuous hot water extraction-oxidation.

Artificially contaminated soil with four different polynuclear aromatic hydrocarbons (acenaphthene, phenathrene, anthracene and fluoranthene) has been separately treated by two different processes: (A) concentrated hydrogen peroxide at mild conditions of temperature (343-393 K) and pressure (0.5 MPa) and (B) hot water extraction at relatively high temperature (523-657 K) and pressure (10 MPa). Both methods achieve acceptable PAH removal percentages from soil. Acenaphthene (the most soluble PAH) is completely removed with treatment A regardless of the operating conditions used. Under optimum conditions, the rest of PAHs are also eliminated to a high extent with both technologies. Temperature and hydrogen peroxide amount seem to play a major role in process A. Similarly, temperature and water flowrate are the most influencing parameters in process B. In the latter case, a post-stage for the extracting water cleaning is required.

Supercritical CO(2) extraction of PAHs on spiked soil Co-solvent effect and solvent regeneration by ozonization.

The supercritical CO(2) extraction of four PAHs (acenaphthene, phenanthrene, anthracene and fluoranthene) from an artificially contaminated soil has been investigated. The effect of temperature (40-60 degrees C), pressure (300-500 bar) and extraction time (90-150 min) has been assessed by conducting a Box-Behnken experimental design. The results suggest the existence of perturbation variables other than the aforementioned controlled variables leading to a significant dispersion of extraction recoveries. With the exception of anthracene, an optimum in temperature (50 degrees C) is envisaged when extracting the PAHs. Analogously, with the exception of anthracene (positive effect), pressure does not have a significant influence. The recovery yield increases as extraction time is increased to a value of 120 min. No further improvement is experienced thereafter. If a co-solvent is used (H(2)O(2) aqueous solution) a beneficial effect can be noticed. Hydrogen peroxide concentration did exert no significant influence in the process. Methanol used to collect the extracted PAHs could be regenerated by gaseous ozone and reused in several consecutive runs.