Electrochemical advanced oxidation processes (EAOPs) have been receiving recognition to eliminate efficiently organic and pharmaceutical pollutants from wastewater. It is made possible owing to in-situ electrogeneration of quasi non-selective oxidizing agent of hydroxyl radicals (●OH) and other mediated oxidants (e.g. hydrogen peroxide (H2O2), HClO/ClO-, Cl2, O3, …). Microfluidic thin-layer electrochemical cell has been shown to enhance mass transfer of pollutants towards the electrodes while hugely reducing specific power consumption and allowing operating with low-conductivity solutions. Nevertheless, EAOPs are prone to electrode fouling due to the occurrence of local alkalization on cathode surface. Therefore, the objective of this work was to newly investigate the role of ●OH on the formation of mineral electro-precipitation inside microreactor. The involvement of anodic activity is supposedly more significant under micrometric condition and it might play roles towards electro-precipitation on cathode as well as pollutant degradation. The experiments at various current densities were peformed using reclaimed municipal wastewater spiked with tylosin as model micropollutant. The results suggest using 0.8, 4 and 20 mA cm-2, Mg precipitated by 24, 96 and 82% and Ca deposited by 70, 73 and 61%, respectively after 5 h of electro-oxidation, with respect to their initial content in the matrice. More precipitation was observed using 4 mA cm-2 due to higher OH- production. Noticable decrease in electro-precipitation at the highest current density was attributed to concomitant hydrogen evolution reaction and the formation of CO3●- by ●OH. After 5 h of electro-oxidation, 8, 35 and 51% of organic mineralization was quantified using 0.8, 4 and 16 mA cm-2 respectively. Total degradation of tylosin was possible using 4 and 16 mA cm-2 only after 20 and 1 min of treatment, respectively, whereas 5 h of electrolysis was needed to oxidize 95% of initial tylosin content using 0.8 mA cm-2. In function of the kinetic regime of tylosin oxidation, its degradation fitted the mathematical models proposed. Considering that the highest quantity of undesirable chlorinated byproducts (ClO3- and ClO4-) was measured using 16 mA cm-2 (151 mg-Cl2 L-1), a compromise will be required to maximize the degradation efficiency, while minimizing the electro-precipitation and unwanted by-products formation.

Impact of electro-precipitation and current density on tylosin electro-oxidation in microfluidic reactor using reclaimed municipal wastewater

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