The rate and efficiency of iron generation in an electrocoagulation system

The rate and efficiency of iron generation in a bench-scale electrocoagulation (EC) system was investigated when variations were made to operating voltage, cathode material and electrolyte composition. Two electrolytes were tested, one with organic compounds (naphthalene, acenaphthene and 4-nonylphenol) and one without. While aromatic structures often make good corrosion inhibitors, in this case they had no discernible effect. This is a positive indicator that EC systems will not have adverse effects when treating wastewaters associated with oil and gas production. Using a stainless steel cathode rather than an aluminium one resulted in 35% more production of iron at the anode per volt per minute; it also resulted in greater iron production given equivalent quantities of power. This occurred because the rate-limiting hydrogen evolution reaction at the cathode occurs more quickly on iron than on aluminium. It was also observed that the EC system (using either cathode) produced more iron per unit power when operated at lower voltages. At lower voltages, the corrosion that occurred spontaneously in the absence of an applied current contributed more significantly to the total amount of iron released. This research suggests that it is more efficient to design EC systems using iron-based cathodes rather than aluminium ones. It also indicates that it is more energy efficient to use more electrodes at low power, rather than fewer electrodes at high power.