INTEGRATED PROCESSES FOR REMOVAL OF PERSISTENT ORGANIC POLLUTANTS: SOIL WASHING AND ELECTROCHEMICAL ADVANCED OXIDATION PROCESSES COMBINED TO A POSSIBLE BIOLOGICAL POST-TREATMENT
Soils contaminated by hydrophobic organic pollutants like Polycyclic Aromatic Hydrocarbons (PAHs) are a common concern since they are extremely difficult to remove and their potential toxicological impacts are significant.
As an alternative to traditional thermal or physical treatments, soil washing and soil flushing processes appear to be conceivable and efficient approaches, especially for higher level of pollution. However, the treatment of highly loaded soil washing/flushing solutions is another challenge to overcome. In that way, a new integrated approach is suggested: soil washing/flushing processes combined to an Electrochemical Advanced Oxidation Process (EAOP) in a combination with a recirculation loop (to save extracting agents) and/or a biological post-treatment step (to minimize energy cost).
Extraction efficiency of the extracting agent like hydroxypropyl-beta-cyclodextrin (HPCD) is compared to the traditional non-ionic surfactant Tween 80 in synthetic and real soil washing solutions. A new simple fluorescent sensitive and selective quantification method is developed to monitor Tween 80 oxidation. Two EAOPs were compared: Electro-Fenton (EF) and Anodic Oxidation (AO). Platinum (Pt) (in EF process) and Boron-Doped Diamond (BDD) (in both treatment) anodes are the respective electrodes employed to recycle effluents and to consider a biological post- treatment, respectively. Regarding the extracting agent recovery, the biodegradability evolution of effluent and the energy consumption (in kWh (kg TOC)-1) during EAOP, HPCD is more advantageous than Tween 80. However, in terms of extraction efficiency, costs of extracting agents and impact on soil respirometry, Tween 80 is much more efficient. By considering all these advantages and drawbacks, Tween 80 could still appear to be the best option.