Electrocoagulation for Water Treatment: the Removal of Pollutants using Aluminium Alloys, Stainless Steels and Iron Anodes

The development of effective and sustainable wastewater treatments is becoming increasingly important. Electrocoagulation is one of the more promising approaches as it is simple and efficient and, compared with traditional processes, has the advantages of short treatment times and low sludge production. The objective of this research was to determine the feasibility of the electrocoagulation technique as a method to remove pollutants from wastewater. Electrocoagulation tests were first carried out in phosphate-containing solutions with an aluminium-magnesium and a stainless steel electrode. Several operating conditions, such as the initial concentration of phosphates, current density, initial pH and sodium chloride concentration, were varied and the corresponding effects were investigated. Removal efficiencies of 95.9% and 79.7% were observed after 60 min with the aluminiummagnesium and the stainless steel electrodes, respectively, using an initial phosphate concentration of 150 mg L-1, an initial pH of 5.0, a current density of 11.0 mA cm-2 and a ratio of the surface area of the electrode to the volume of the solution of 11.7 m-1 and 10.5 m-1 for the aluminium-magnesium and the stainless steel electrodes, respectively. The electrochemical behaviour of several electrode materials was then correlated with the removal and energy performance of these electrodes in the treatment of phosphates, an azo dye and zinc ions dissolved in synthetic wastewaters. The synthetic wastewaters were designed to contain a mixture of ions with different conductivity values. Pure iron and an aluminium-indium-zinc electrode were identified as the most promising materials, giving low corrosion potentials and active dissolution. Excellent removal efficiencies for the three pollutants were observed using the pure iron electrode (96%, 99% and 100% for phosphates, azo dye and zinc ions, respectively) with an energy consumption of 0.52 Wh. The aluminium-indium-zinc alloy required the lowest energy supply of 0.26 Wh, gave excellent removal for both the phosphates and zinc ions (95% and 100%, respectively). However, only a moderate efficiency, 78%, was observed for the removal of the azo dye. A screening design of experiment, DoE, was carried out to determine the most significant factors affecting the electrocoagulation removal process. These factors were identified as the current density and the ratio of the surface area of the electrode to the volume of the solution, SA/V