UVC photolysis of phenanthrene in cyclodextrin solutions generated from contaminated soil washing

Ultraviolet-C (UVC; 254 nm) photolysis was applied to achieve simultaneous removal of phenanthrene and recovery of the extraction ability of cyclodextrin (CD) in soil washing solutions. β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HPCD) were found to have comparable abilities to solubilize phenanthrene in aqueous solutions and extract phenanthrene from spiked agricultural soil or kaolinite. Only loosely bound phenanthrene is extractable to CDs, and approximately 30% of initially spiked phenanthrene is non-extractable. β-CD and HPCD showed comparable retardation effects on the UVC photolysis of phenanthrene, and HPCD was more persistent than β-CD during UVC photolysis of soil extraction solutions. After three extraction–UVC photolysis cycles, the extraction efficiency of the regenerated β-CD and HPCD solutions were 77% and 93% of the corresponding fresh CD solutions. In contrast, the apparent photolysis kinetic constant of phenanthrene in regenerated HPCD extraction solutions decreased significantly more than that in regenerated β-CD extraction solutions. 9,10-Phenanthrenequinone and its hydroxylation derivate, and three other oxygenated products were the detected intermediates that were generated during the UVC photolysis of phenanthrene, and CD or leached soil organic matter did not alter the degradation pathway. A combination of enhanced extraction and UVC photolysis is a promising method for treatment of extraction solutions from soil contaminated by phenanthrene or other polycyclic aromatic hydrocarbons.