Infoscience

Thesis

A strategy for xenobiotic removal using photocatalytic treatment, microbial degradation or integrated photocatalytic-biological process

According to the limited natural resources and due to the risks of anthropogenic pollution, it appears necessary to react efficiently in order to remove existing contaminations and avoid the creation of new ones. Therefore, the purpose of this thesis is to propose a sustainable strategy for treating problematic pollutants with the most adequate process. First, an overview of the different treatment processes has been given. In particular, biological, photocatalytic and integrated biological-photocatalytic treatments have been described as efficient methods to remove xenobiotics. Biological treatment of contaminated environments and industrial effluents has been presented as the most attractive method on a cost-benefit extent. But for biorecalcitrant substances, the Advanced Oxidation Processes (AOP) have remained the most efficient methods although expensive. Therefore, the coupling of biological-photocatalytic has emerged as the best compromise for removal of recalcitrant xenobiotics. The first step of the treatment strategy has consisted of evaluating the biotraitability of 19 chemicals: pesticides, pharmaceuticals and volatile organic compounds (VOCs) have been assessed according to three biodegradability methods (Zahn-Wellens, Manometric Respirometry, Closed-Bottle tests), whose official protocols had to be adapted to the compound specificities (volatility, hydrophobicity). Structure-Activity Relationship (SAR) estimation models have also been used to compare and validate the experimental results. For the compounds which have been assessed as biotraitable (VOCs), further biodegradation studies have been led in order to improve the treatment (batch with pulses of substrate): automated monitoring of the biodegradation process, increased degradation yields and biomass productivity have been successfully completed for Toluene, Ethylbenzene, Xylenes, Chlorobenzenze and Dichlorobenzene removal. Conversely, the compounds assessed as biorecalcitrant have been oriented towards the TiO2 and photo-Fenton photocatalytic treatments. Thus, the degradation of four p-halophenols by TiO2 photocatalysis has been investigated and has demonstrated the halogen effect on removal rates, aromatic intermediates and toxicity variations. Finally, the treatment of five bioreacalcitrant pesticides (Alachlor, Atrazine, Chlorfenvinphos, Diuron, Pentachlorophenol) has been studied in order to develop a coupled photocatalytic-biological system: first, enhanced biotreatability has been evaluated using the Zahn-Wellens procedure and then fixed-bed bioreactors have been operated and permitted to find out the best moment for coupling.

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