Fluid Dynamics and Mass Transfer Study of Electrochemical Oxidation by CFD Prediction and Experimental Validation

Multivariate optimization of characteristic parameters of continuous-flow system with a front buffer tank for industrial reverse osmosis concentrate treatment

Industrial reverse osmosis concentrate (ROC) was electrochemically oxidized using a continuous-flow system (CFS) with a front buffer tank. Multivariate optimization including Plackett-Burman (PBD) and central composite design based on response surface method (CCD-RSM) was implemented to investigate the effects of characteristic (e.g., recirculation ratio (R value), ratio of buffer tank and electrolytic zone (R_V value)) and routine (e.g., current density (i), inflow linear velocity (v) and electrode spacing (d)) parameters. R, v values and current density significantly influenced chemical oxygen demand (COD) and NH₄⁺-N removal and effluent active chlorine species (ACS) level, while electrode spacing and R_V value had negligible effects. High chloride content of industrial ROC facilitated the generation of ACS and subsequent mass transfer, low hydraulic retention time (HRT) of electrolytic cell improved the mass transfer efficiency, and high HRT of buffer tank prolonged the reaction between the pollutants and oxidants. The significance levels of COD removal, energy efficiency, effluent ACS level and toxic byproduct level CCD-RSM models were validated by statistical test results, including higher F value than critical effect value, lower P value than 0.05, low deviation between predicted and observed values, and normal distribution of calculated residuals. The highest pollutant removal was achieved at a high R value, a high current density and a low v value; the highest energy efficiency was achieved at a high R, a low current density and a high v value; the lowest effluent ACS and toxic byproduct levels were achieved at a low R value, a low current density and a high v value. Following the multivariate optimization, the optimum parameters were decided to be v = 1.2 cm h^-1, i ≥ 8 mA cm^-2, d ≥ 4, R_V = 10-20 and R = 1 to achieve better effluent quality (i.e., lower effluent pollutant, ACS and toxic byproduct levels).

Numerical Study on Hydrodynamic Characteristics and Electrochemical Performance of Alkaline Water Electrolyzer by Micro-Nano Surface Electrode

This study constructed a two-dimensional alkaline water electrolyzer model based on the two-phase flow Euler–Euler model. In the model, the micro-nano surface electrodes with different structure types and graphic parameters (distance, height, and width) were used and compared with the vertical flat electrode to evaluate their influence on electrolysis performance. The simulation results show that the performance of the micro-nano surface electrode is much better than that of the vertical flat electrode. The total length of micro-nano structural units relates to the contact area between the electrode and the electrolyte and affects the cell voltage, overpotential, and void fraction. When rectangular structural units with a distance, height, and width of 0.5 µm, 0.5 µm, and 1 µm are used, the total length of the corresponding micro-nano surface electrode is three times that of the vertical flat electrode, and the cathode overpotential decreases by 65.31% and the void fraction increases by 54.53% when it replaces the vertical flat electrode.

Electrochemical incineration of glyphosate wastewater using three-dimensional electrode

Anodic oxidation of recalcitrant organic compounds is still challenging concerning to the anode material and mass transport limitations imposed by the low concentration. In this work, we studied the degradation of a real wastewater containing glyphosate using an electrode of PbO2 electrodeposited on a three-dimensional matrix of reticulated vitreous carbon (RVC). The high mass transfer rate provided by the RVC/PbO2 anode is demonstrated. A Box-Behnken factorial design was used for a systematic analysis of the effects of current density, flow rate and temperature on the degradation and mineralisation kinetics, current efficiency and specific energy consumption. The optimised degradation performance was achieved applying 30 mA cm-2, 3000 mL min-1 and 50°C. As the flow rate increases from 150 to 1500 mL min-1, the current efficiency increases from 18% to 65% and the energy consumption dropped from 72 to 33 kWh kg-1 due to the mass transfer enhancement promoted by the porous matrix. The efficacy of the electrochemical process for the treatment of real effluents using the three-dimensional PbO2 has been demonstrated.

Using modulated current for energy minimization in the electrochemical treatment of effluents containing organic pollutants

Anodic oxidation of recalcitrant organic compounds suffers from loss of efficiency as the concentration decreases, leading to high energy consumption. Here, we propose a modulated current (MC) technique to control and maintain the applied current as close as possible to its limiting value throughout the electrolysis, thus ensuring high mineralization current efficiency. The efficacy of this technique was first validated for caffeic acid (CA) electrooxidation using a boron-doped diamond (BDD) anode and was then confirmed for the degradation of a wastewater containing phenolic compounds from wet coffee processing. Combining MC and constant current (CC) operation for CA electrolysis resulted in a substantial reduction of the specific energy consumption from 256 to 52.4 kWh kg^-1 TOC, due to improvement of the mineralization current efficiency from 17.9 to 77.1%. The MC+CC technique was also successful in reducing the energy consumption for a real coffee processing wastewater mineralization, demonstrating its suitability as a simple and effective tool that can be used to reduce the energy costs in electrochemical treatment of effluents containing organic pollutants.