Remediation of soils contaminated with PAHs and nitro-PAHs using microwave irradiation

The main goal of this study was the application of a bench-scale microwave (MW) heating treatment of soils contaminated with polycyclic aromatic hydrocarbon (PAHs) and nitro-PAHs (N-PAHs), investigating the effects of various operating conditions on contaminant removal kinetics. For simulated MW treatment, a fine sandy soil was artificially contaminated with PAHs or N-PAHs and irradiated for a period of 5-60 min, applying powers in the range of 250-1000 W. Kinetic models were fitted with contaminant residual concentrations in order to calculate the desorption parameters useful for studying the removal process. Results suggest that contaminant properties, especially polarity, significantly influence the maximum temperature reachable during the heating processes and the contaminant removal kinetics. The total PAH removal was achievable only for biphenyl (Bph) or fluorene (Flu), whereas residual concentrations were reduced to less than 2 mg kg-1 for anthracene (Ant) or phenanthrene (Phe). N-PAH concentrations lower than 0.05 ng kg-1 were observed for all the compounds investigated. Overall, different mechanisms, namely, thermal desorption, molecular bond breaking, selective heating and contaminant stripping took place during PAH or N-PAH removal. The kinetic parameters are useful for studying the removal process and for predicting the response of the remediation activities, as well as for guiding the design and the scale-up of microwave treatment systems. PAH/N-PAH removal mechanism results could also provide basic information and be helpful in order to improve the development of novel MW based-remediation technologies for soils contaminated with PAHs and their derivatives.