Microwave heating coupled with UV-A irradiation for PAH removal from highly contaminated marine sediments and subsequent photo-degradation of the generated vaporized organic compounds

The aim of this work was to demonstrate the concept of a combined MW-UV-A treatment for the successful remediation of PAH-contaminated marine sediments and the successive photo-degradation of the generated vaporized organic compounds, entrapped in the exhaust gas line. The role of Tween 80 and citric acid as degradation enhancers was also investigated, considering variable MW/UV operating conditions and irradiation times. Main results revealed a very rapid sediment temperature increase during MW heating (up to ∼380 °C), due to the dielectric properties of both sediment minerals and adsorbed PAHs, which highlighted their great ability to passively convert MWs into heat and in turn allow a very effective PAH-decontamination. PAH removal was higher than 85% after 1-min MW irradiation mainly due to “selective heating” and contaminant stripping removal mechanisms. Longer times led to the total removal of the contaminants. The addition of enhancing agents showed an improvement of the MW performance in the order: MW < MW + Tween 80 < MW + Tween 80 + citric acid. UV light irradiation of condensate from the unenhanced MW treatment resulted in an effective PAH-photo-removal in 34 min, with maximum values in the range 80.0–98.9%. However, the presence of enhancers in the sediments before MW irradiation lowered the contaminant removals (56.0–91.7%) by UV-A. The fate of PAH and their by-(photo)-products during UV irradiation, suggested molecular bond breaking as further contaminant removal mechanism. Overall, obtained data demonstrated the concept of the combined MW-UV-A treatment and the critical role of the enhancers in the photo-degradation, which elected unenhanced MW as the best choice.