The effect of operating parameters on chloride ion release, current efficiencies, and energy consumptions of the electrochemical hydrodehalogenation (HDH) of dilute aqueous solutions of pentachlorophenol (PCP) and 2, 4-dichlorophenol (DCP) is reported. The parameters include the concentrations of PCP and DCP, applied current density, controlled cathode potential, temperature, and flow rate. Relatively high concentrations, high-temperature, and moderate current density (e.g., 10 mA cm(-2)) have the most beneficial effect on the HDH process. For example, the HDH of 20 mM DCP in an H-cell at 70degreesC gave current efficiencies up to 70% and an energy consumption of 2.6 kWh/kg DCP. Good results were also achieved in a solid polymer electrolyte zero gap flow cell, e. g., a current efficiency of 35% and an energy consumption of 4.5 kWh/kg. Encouragingly, the energy consumed for the HDH of 50 ppm PCP in water at ambient temperature is in a range of 28 and 80 kWh/kg PCP, which is much lower than previously reported.