Contaminant removal mechanisms in microwave heating remediation of PAH-contaminated soils

Polycyclic aromatic hydrocarbon (PAH) contamination represents a very relevant environmental problem worldwide. Due to PAH persistence, bioaccumulation and mutagenic effects on human health, restoration techniques for PAH - contaminated soils have recently attracted particular attention. Several chemical-physical treatments have been proposed for this purpose; however, they may often be expensive or require combined-multi-step processes. On the other hand, thermal treatments were shown to be more effective, but generally requiring high fuel costs. Recently, microwave heating (MWH) has been proposed as a cost - effective thermal treatment. The main goal of this study was to assess the potential application a microwave heating (MWH) treatment of soils contaminated with PAHs, investigating the effects of various operating conditions on contaminant removal kinetics and mechanisms. A sandy soil was artificially contaminated with PAHs and irradiated for a period of 5-60 min, applying powers in the range of 250-1000 W. Main results suggest that PAH polarity features, significantly influence the maximum temperature achievable during the MWH and the contaminant removals. Specifically, total removal was achievable only for biphenyl and fluorene, while concentrations lower than 2 mg kg-1were found for anthracene and phenanthrene. Several mechanisms, namely, thermal desorption, molecular bond breaking, selective heating and contaminant stripping took place during PAH removal. Observed mechanisms could provide basic information and be helpful in order to improve the development of novel MW based - remediation technologies.