Regulation of electrochemically generated ferrous ions from an iron cathode for Pd-catalytic transformation of MTBE in groundwater

A novel Pd-based electro-Fenton (E-Fenton) process has recently been developed to transform organic contaminants in groundwater. However, it only produces H₂O₂ and requires addition of Fe²⁺. In this study, an innovative approach is developed to effectively regulate the generation of Fe²⁺ from an iron cathode in a three-electrode system in addition to H₂O₂ production. The Fe²⁺ is then used for the Pd-catalytic transformation of methyl tert-butyl ether (MTBE) in groundwater. Results from batch experiments suggest Fe²⁺ accumulation follows pseudo-first-order kinetics with rate quantitatively regulated by current and pH, and MTBE can be completely transformed. In a specially configured three-electrode column using iron as the first cathode, the localized acidic conditions develop automatically in the iron cathode and Pd zone by partitioning the current between the two cathodes, leading to controllable generation of Fe²⁺ and H₂O₂. Effects of electrolyte concentrations and types as well as humic acid on MTBE transformation are slight. The stable transformation (∼70%) in a long-term study (20 days) suggests this improved Pd-based E-Fenton process is sustainable to produce Fe²⁺, H₂O₂, and appropriate pH conditions simultaneously for transforming organic contaminants. This study presents a new concept of generating Fe²⁺ from an iron cathode for the processes requiring Fe²⁺.