Engineering (Feb 2022)
Electrochemical Removal of Chlorophenol Pollutants by Reactive Electrode Membranes: Scale-Up Strategy for Engineered Applications
Abstract
Chlorophenols (CPs) are significant refractory pollutants that are highly toxic to humans and other organisms. Reactive electrode membranes (REMs) show considerable potential in the electrochemical removal of refractory pollutants by allowing flow-through operations with convection-enhanced mass transfer. However, relevant studies are commonly performed on the laboratory scale, and there is no straightforward method that guarantees success in scaling up engineered REM reactors. In this study, we demonstrated that a tubular concentric electrode (TCE) configuration with a titanium suboxide ceramic anode and a stainless-steel cathode is suitable for large-scale CPs removal. Both theoretical and experimental results showed that the TCE configuration not only allows the electrode surface to be orthogonal to electric field lines everywhere, but also has an ohmic resistance that is inversely proportional to the length of the electrode. In addition, the TCE configuration can be operated in either the anode-to-cathode (AC) or the cathode-to-anode (CA) mode based on the flow direction, creating adjustable conditions for selective degradation of CPs. This was confirmed by 98% removal of 2,4-dichlorophenol (2,4-DCP) and 72.5% removal of chemical oxygen demand (COD) in the CA mode, in which the kinetic constant was one order of magnitude higher than that for the AC mode under flow-through single-pass operations. This can be explained by the lower activation energy and free energy in the CA mode, as revealed by theoretical calculations and experimental measurements. The TCE configuration is also suitable for a numbering-up strategy to scale up the electrochemical reactor without increasing the ohmic resistance or decreasing the specific electrode area, achieving 99.4% removal of 2,4-DCP with an energy consumption of 1.5 kW·h·m−3 when three TCE modules were employed. This study presents a suitable electrode design configuration for the REM reactor, offering effective strategies to bridge the “Valley of Death” encountered when scaling up the electrochemical removal of CP pollutants.
