Oxidative degradation of pyrene in contaminated soils by δ-MnO2 with or without sunlight irradiation

The enhanced oxidative degradation of pyrene in quartz sand and alluvial and red soils by micro–nano size birnessite (δ-MnO2) in the presence and absence of sunlight was investigated. The degradation of pyrene by δ-MnO2 in quartz sand showed very little synergistic effect of sunlight irradiation on δ-MnO2 oxidizing power. However, pyrene degradation by δ-MnO2 in alluvial and red soils was greater under solar irradiation than the combination of photooxidation of pyrene and oxidation of pyrene by δ-MnO2. The oxidative degradation percentages of pyrene by δ-MnO2 under sunlight irradiation are 94.8, 97.7, and 100% for alluvial soil, red soil, and quartz sand, respectively. Oxidative degradation percentages of pyrene by δ-MnO2 in alluvial and red soils with irradiation of sunlight almost attained a maximum at 1 h with a 5% (w/w) dose of the amended oxidant. Due to their different total organic carbon (TOC) contents, the sequence of enhanced oxidative degradation of pyrene by δ-MnO2 in quartz sand and alluvial and red soils was quartz sand > red soil > alluvial soil. Further, this study revealed that δ-MnO2-enhanced oxidative degradation of pyrene is very pronounced in contaminated soils in situ even at deep soil layers where irradiation by sunlight is very limited.

Research highlights
► Synergistic effect of sunlight irradiation and δ-MnO2 promoted pyrene degradation.
► Oxidative pyrene degradation in soils by δ-MnO2 without sunlight irradiation can attain a high extent.
► Soil organic matter retarded pyrene degradation by δ-MnO2.
► Oxidative power of δ-MnO2 in deep soil layers cannot be overlooked.