Advanced Electro‐Oxidation with Boron‐Doped Diamond for Acetaminophen Removal from Real Wastewater in a Microfluidic Reactor: Kinetics and Mass‐Transfer Studies

Abstract

The removal of hazardous organic micropollutants in municipal wastewater treatment plants (WWTP) has become a common concern for public decision-makers and stakeholders. An advanced electro-oxidation with boron-doped diamond (BDD) anode material is proposed to remove acetaminophen as a representative micropollutant in synthetic solution. A customized microfluidic reactor was run in batch mode, and the main operating parameters (i. e. current density, interelectrode distance and solution conductivity) were optimized by minimizing the energy requirement. An optimal current density of 4 mA cm À 2 and an optimal interelectrode distance of 500 μm were newly obtained and explained. Mass transport limitation was observed at lower gaps, with a 3.4-fold decrease in the mass transfer coefficient from 500 μm to 50 μm intervals. In addition, the kinetics of degradation decreased dramatically after a certain electrolysis time. This was attributed to the increase in gas bubble production with treatment time. An increase in the solution conductivity from 0.23 to 2.0 mS cm À 1 increased the degradation rate efficiency twofold and decreased the specific energy from 0.88 to 0.17 kWh g À 1 at 85 % acetaminophen decay yield. The influence of a real matrix from low-conductivity reclaimed WWTP (0.86 mS cm À 1 ) highlighted slightly lower kinetics of degradation, but similar energy efficiency until 60 % of pollutant degradation and higher energy efficiency than in conventional macro-reactors.[a] Dr. E. Mousset, M. Puce, Dr. M.-N. Pons

Mineral cathodic electro-precipitation and its kinetic modelling in thin-film microfluidic reactor during advanced electro-oxidation process

“…pH (Mettler Toledo InPro 4260i) and conductivity (Mettler Toledo InPro 7100i) were measured at regular time. The electrochemical cell was similar to the one described in previous work [16]. It consisted of a planar-electrodes filter-press type cell.…”

“…0.4 and 4 mA cm -2 . The latter was selected because it has been defined as optimal current density from previous work where similar reactor setting was used to degrade pharmaceutical pollutants [16]. All experiments were carried out at least in duplicate to ensure reproducibility.…”

“…It allows mineralization of organic pollutants without the addition of supporting electrolyte. The micrometric inter-electrode distance vastly accommodates the phenomenon of limitation by mass transfer and ohmic resistance [15] in the case of effluent having relatively low ionic conductivity [16].…”

Photoelectrochemical reactors for treatment of water and wastewater: a review

“…Moreover, the electrode distance can be better controlled and easily optimized in flow cells by varying it from a few tens of microns until several centimetres (Scialdone et al 2010). It leads to better mass transport of targeted compounds towards the electrodes, with mass transport coefficient improved by two to more than ten times (Anglada et al 2010;Mousset et al 2019b).…”

Influence of number of azo bonds and mass transport limitations towards the elimination capacity of continuous electrochemical process for the removal of textile industrial dyes

“…A km value of 1.7 10 -6 m s -1 was therefore obtained in this study. This value is in the same range of values given in literature for a stirred tank reactor ( 5.9 10 -6 m s -1 ) (dos Santos et al, 2014;Mousset et al, 2019b;Rocha et al, 2012). The CODin values used for calculation are reported in Table SM-7.…”