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Development and implementation of the Bio-electro-Fenton process : application to the removal of pharmaceuticals from water

Abstract : Electrochemical advanced oxidation processes (EAOPs) constitute an efficient technology to treat the pharmaceuticals as they allow the formation of strong oxidants such as hydroxyl radicals able to remove nearly any type of organic contaminants thanks to their very high oxidation power. Among them the electro-Fenton and anodic oxidation processes are environmentally friendly methods as they use no chemical reagent (anodic oxidation) or only oxygen of air and iron ions as a catalyst (electro-Fenton).In this thesis, four pharmaceuticals from different families and structures were selected based on their toxicity and their occurrence in environmental waters and their removal from water was performed by EAOPs. The objectives of this work were to determine the best operating conditions at lab scale (current and catalyst concentration), investigate the kinetic of degradation and mineralization and finally propose a mineralization pathway based on aromatic intermediates, carboxylic acids and ions released to the solution.As these treatments were successfully applied, a lab scale pilot reactor composed alternately of BDD anodes and carbon felt cathodes with a bottom aeration system and working in the continuous mode was built to scale-up these processes in order to pre-industrialize them. Different configurations of electrodes were tested. The flow rate and the current were found to be more influent on the mineralization rate and on the energy consumption, respectively. To deeper understand the role of the flow rate and the configurations a hydrodynamic study was performed. The hydrodynamic results were gathered with a kinetic model for the mineralization to obtain a model predicting the percentage of mineralization at different position inside the reactor during the steady state. Thus, this model can help to optimize the operating conditions and to size future reactors depending on the mineralization objective of the treatment (high mineralization rate, combined treatment, high flow, …).To reduce operating cost, the combination of an electrochemical process and a biological treatment was then investigated. In this frame, it was found that electrochemical treatment can (i) degrade the hydrochlorothiazide (ii) reduce significantly the concentration of its aromatic intermediates as they were shown to significantly inhibit the bacterial activity, (iii) promote the formation of biodegradable molecules such as carboxylic acids. The biodegradation of four carboxylic acids formed during the electro-Fenton treatment of the hydrochlorothiazide at lab scale was also studied. It was demonstrated that they were sequentially degraded with different lag phases and kinetics of degradation. Thus to mineralize them, a “plug flow” type reactor is recommended. The combination of treatment was then applied with an electrochemical treatment performed at low current with a BDD anode and a Platine anode. A mineralization degree of 38% and 50% were obtained by the biological treatment enabling to globally reach a mineralization rate of 66% and 85% with the BDD and the Platine anodes respectively. Thus this combined treatment was successful and open the way for the scale-up of these processes.
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Hélène Monteil. Development and implementation of the Bio-electro-Fenton process : application to the removal of pharmaceuticals from water. Chemical engineering. Université Paris-Est, 2019. English. ⟨NNT : 2019PESC2045⟩. ⟨tel-02482881v2⟩

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