Comparative studies of several oxidants for Polycyclic Aromatic Compounds (PAH and Polar PACs) degradation from DNAPL contaminated sub-soils : Batch and column experiments

International audienceRemediation of industrial wastelands is for many reasons (health and environmental impact, land use...) of great concern. Coking plants, for instance, may have impacted the soil with PAHs inherited from coal-tar storage and dissemination. This work focuses on improving the effectiveness of in situ chemical oxidation (ISCO) to reduce DNAPL (Dense Non-Aqueous Phase Liquids) remaining after pumping in the saturated zone. The study is part of the BIOXYVAL project, dedicated to the remediation of a former coking plant in the north east of France.The efficiency of different oxidants, based on oxido-reduction or radicalar mechanisms, was compared through batch experiments on spiked sand or soil after 7 days. PAH degradation and formation/elimination of polar Polycyclic Aromatic Compounds (PACs), which have a higher mobility in groundwater and can be more toxic than PAHs, were monitored. Column experiments were also studied with some oxidants. Firstly, by spiking glass beads or soil with DNAPL by drainage/imbibition, followed by water flushing to mimic the removal of the DNAPL by pumping. Oxidants were then flushed through the column, and water quality was monitored throughout the experiment.Best degradations (batch) were obtained with permanganate and heat-activated persulfate, which decreased up to 98% and 96.1% PAH, respectively. Good degradation were also obtained with classical Fenton at pH 3 (93.9% PAH removal). However, Magnetite Fenton-like oxidation was not very effective (28.5% degradation of 16-US EPA PAH). All these oxidants were compared to potassium ferrate (FeVI ), an innovative oxidant, mainly applied in water treatment. The results highlighted that ferrate managed to reach 77.9% depletion of PAH in our conditions, and some optimizations were tested (sequential addition, co-oxidation.. O-PACs were formed as intermediate by-products when reaction went through an oxido-reductive pathway. Ferrate and permanganate were continued in laboratory column tests