High Efficient Phosphate Removal and HAP Recovery by a Multi-Electrode System

Abstract

 Continuous experiments for phosphate removal and recovery from a synthetic wastewater containing calcium phosphate were carried out using an electrolytic reactor equipped with a multi-electrode system. Experimental results demonstrated that phosphate was removed by deposition of aggregates in reactor. In addition, it was found that removal rates and recovery rates of phosphate increased and, after reaching their maximum values, decreased with an increment of applied electric current. Deposit in reactor was recovered and was identified as hydroxyapatite (HAP) from XRD analysis. Furthermore, from comparisons of observed and calculated ions fluxes, it was shown that removal rates of phosphate had a maximum value at a certain electric current density and were controlled by either electrolytic production of hydroxyl ion or mass transfer of hydrogen phosphate ion depending on applied electric current density. Moreover, it was considered that the removal and recovery performance could be enhanced by using working electrodes having larger specific surface area.