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Mechanistic, interfacial and modeling studies of electro-precipitation during electrochemical advanced oxidation process in a thin-film reactor : case study with reclaimed municipal wastewater

Abstract : The thesis work evolves around the characterization and quantification of cathodic mineral electro-precipitation taking place during an electro-oxidation treatment of wastewater. The electro-oxidation process was conducted in scalable submillimetric electrochemical reactor with 50 cm² surface area. Submillimetric, or also denoted as microfluidic, reactor design was chosen owing to the potential that it could offer towards its environmental application. For instance, mass transfer and redox reactions were intensified with huge cut in total operational expense owing to significant drop in internal cell resistance. Despite its interest, the quantity of research work devoted to this topic has been underwhelming. Furthermore, no report has yet been made in the literature on the formation of electro-precipitation inside a thin film cell, as opposed to the mineral scaling study performed in conventional rotating disk setup. Once the cathode is totally passivated by the electro-precipitation, the electro-oxidation efficacy is undoubtedly compromised. Hence, it justifies the need for the sequence of research works conducted throughout this thesis. Decisive parameters on the kinetics of electro-precipitation were scrutinized, i.e. the applied current density (japp), the interelectrode distance (delec), the matrix of effluent to be treated and the cathode material. Theoretical predictive models were proposed alongside several experimental results acquired. The objective was to establish the operating conditions by which less mineral scaling was formed without giving an impacting on the electro-oxidation efficiency to maximize its durability.Under the operating conditions applied, only Mg(OH)₂, CaCO₃ and Ca₃(PO₄)₂ precipitates were present. Other precipitates were not thermodynamically favoured. Mg(OH)₂ precipitation was highly dependent on japp whilst CaCO₃ and Ca₃(PO₄)₂ easily occurred even at low japp. A theoretical model correlating mass transfer coefficient (km) and delec in wide range of delec (100 to 3000 µm) was developed. Mass transfer correlation for microfluidic reactor under the form of dimensionless Sherwood number was also proposed for convenient scale up/scale down application. With regard to electrochemical cell configuration, more deposition was observed in submillimetric range due to the involvement of more vigorous concomitant H₂ evolution in macrometric setup. When the comparison was made with real wastewater, more electro-deposition occurred due to co-precipitation of dissolved organics and inhibiting effect of sulfate in simulated effluent. When higher japp was adopted, more organic mineralization, higher pharmaceutics degradation and less mineral scaling were noticed but it was accompanied with higher power consumption and significantly higher release of undesirable byproducts. Finally, the use of porous carbonaceous cathode only yielded in more electro-precipitation and higher undesirable byproducts.
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Submitted on : Wednesday, June 1, 2022 - 9:15:27 AM
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Faidzul Hakim Adnan. Mechanistic, interfacial and modeling studies of electro-precipitation during electrochemical advanced oxidation process in a thin-film reactor : case study with reclaimed municipal wastewater. Chemical and Process Engineering. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0249⟩. ⟨tel-03683905⟩

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