Towards a more realistic heterogeneous electro-Fenton

Abstract

With the aim of bringing the heterogeneous electro-Fenton (EF) treatment one step closer to a more realistic operation, the scaling-up of that technology was evaluated. Assays were performed firstly at lab scale in a stirred-tank reactor and then at bench scale in a flow setup including a jet aerator and a microfluidic flow-through electrochemical cell. A fluidized-bed reactor was added to the bench-scale installation in order to retain the solid catalyst, iron-containing alginate beads. To the best of the authors' knowledge, there are no precedent studies reporting a heterogeneous EF treatment in a similar bench scale-configuration. Hydrogen peroxide generation and clofibric acid removal were assessed at both scales at current intensities of 0.12 and 0.25 A. Results showed that the scaled-up treatment was more efficient and cost-effective: at bench scale 18 times more volume was treated, the mass production of hydrogen peroxide was 28 higher and the specific cost for the removal of clofibric acid was cut by more than half. The most efficient treatment turned out to be the EF performed at 0.12 A at bench scale. Those results highlighted the importance of the reactor design in the scaling-up process. Additionally, aromatic intermediates were detected by liquid chromatography-mass spectrometry (LC-MS) and a degradation route was suggested. Carboxylic acids were also measured by HPLC confirming that the pollutant is mineralizing.

Heterogeneous Advanced Oxidation Processes: Current Approaches for Wastewater Treatment

“…The activation of the above-mentioned precursor compounds is carried out via multiple alternatives such as the use of transition-metal-based catalysts (Fe, Mn, Co, Cu, V, Ru, Mo, Cr, Ce), heat, UV radiation or visible light, ultrasound and/or alkalinity of the liquid medium [25][26][27]. However, AOPs based on the Fenton process possess some drawbacks hindering their large-scale application: the narrow working pH range, the complexity of the real water matrices favoring the precipitation of the transition metals present in the catalyst, leading to the formation of sludge, and undesirable by-products [19,20,28]. Some of these disadvantages related to Fenton-based and photocatalytic-based processes are alleviated using heterogeneous catalysts [10,29].…”

Exploring the pressurized heterogeneous electro-Fenton process and modelling the system

“…The setup consisted on several elements: 1) a biphasic tank, which was partially filled with the solution, containing air in its upper part; 2) a pump, that provided a constant flow rate of 140 L h -1 ; 3) a jet aerator, where the pressure drop caused the aspiration of gas from the top of the tank; 4) a microfluidic flow-through electrochemical cell, with an anode-cathode layout; 5) a fluidized-bed reactor that contained the catalyst for the heterogeneous electro-Fenton assays; 6) a heat exchanger to maintain the solution temperature at 22 ºC, and 7) a compressed oxygen cylinder to pressurize the system. A schematic representation of the installation is shown in the graphical abstract, and more detailed information can be found elsewhere [21].…”

“…The cathode was elaborated by depositing onto each side of a titanium mesh (Xian Howah Technology Co., Ltd.) a 100 mL mixture of 1 g L -1 of carbon black and 5 g L -1 of polytetrafluoroethylene dispersed into isopropanol. The procedure was described in detail elsewhere [21]. Both electrodes were 8 x 9.5 cm, with a wet geometrical area of 33 cm 2 and a surface area of 49.5 cm 2 determined in a previous study [24].…”

“…In a previous work, we have reported the degradation of clofibric acid by a heterogeneous electro-Fenton treatment at bench scale, using the jet aerator coupled with a microfluidic flowthrough cell and a fluidized-bed reactor [21]. The aim of the present work is to go one step further, by exploring the effect of combining the mentioned reaction system with pressure, only scarcely reported at lab-scale reactors [22,23].…”

“…Therefore, the effect of pressure was tested for the first time for a heterogeneous electro-Fenton process in a bench-scale setup, as far as the authors are aware. The installation used in our previous study ( [21]) was pressurized this time, analyzing the improvements achieved in clofibric acid degradation with the combined pressurized jet aerator system.…”