Chemical–biological treatment of pyrene

Pyrene of natural and anthropogenic sources is one of the toxic, mutagenic polycyclic-aromatic hydrocarbons (PAHs) listed as priority pollutants. This study focuses on an integrated approach for the degradation of pyrene involving chemical oxidation followed by biological treatment. The objectives were to: (1) provide mechanistic details in the degradation of pyrene subject to ozone treatment; (2) test the combined technique of ozone pretreatment followed by biological degradation; and (3) test a pretreatment column to promote efficient use of chemical oxidants and biodegradability. Batch and packed column reactors were used to examine the degradation pathways of pyrene subject to ozonation in the aqueous phase. After different ozonation times, samples containing reaction intermediates and byproducts from both reactors were collected, identified for organic contents, and further biologically inoculated to determine biodegradability. The O3-pretreated samples were incubated for 5, 10, 15, and 20 days, after which BOD, COD, and toxicity tests along with qualitative and quantitative GC/FID and GC/MS analyses of pyrene, intermediates, and products were performed. Intermediates identified at different stages included 4,5-phenanthrenedialdehyde, 2,2′,6,6′-biphenyltetraaldehyde, and long-chain aliphatic hydrocarbons, which suggested that the degradation of pyrene was initiated by O3 via ring cleavage at the 4,5- and 9,10-bonds and that further oxidation ensued via reactions with both O3 and OH√ until complete mineralization. Intermediates formed during chemical oxidation were biodegradable with a measured first-order rate constant (k0) of 0.24 day−1. The integrated chemical–biological system appears to be feasible for treating recalcitrant compounds, and a chemical pretreatment column is particularly useful in promoting soluble intermediates from otherwise highly insoluble, inaccessible pyrene.