To address some of the fundamental questions regarding the functions of cathodes and anodes (e.g., iron and granular active carbon) and what happens when numerous particles (microscopic galvanic cells) are combined in the widely used and efficient wastewater treatment of an internal microelectrolysis (IME) reactor, we employed a specifically designed dual-cell IME reactor with single-couple electrodes and a narrow cell IME reactor with multi-couple electrodes. The simultaneous removal of 6.36mgL−1 and 2.93mgL−1 of 2,4-dichlorophenol within 30min from the graphite cathode and the iron anode cells, respectively, was observed in the dual-cell reactor. The innovative concept behind this phenomenon is that the anode, which is generally believed to be oxidative, could probably be reductive in an IME reactor. Thus, it is important to understand the unique performance of IME reactors. The group effect, which provides a 45% increase of open-circuit potential with just two additional electrode couples in aqueous solution, was tested and verified in a multi-couple electrode reactor. It suggests a complex potential distribution in the IME reactor and that compounds even with high redox potential could possibly be reduced, which was generally believed to be difficult to accomplish.