Removal of nitrates from groundwater by electrocoagulation

Abstract

In this study, coagulation and electrocoagulation processes were compared with regard to their respective efficiencies as to the removal of nitrates from water. The results indicate that electrocoagulation is an effective technology for nitrate removal because nitrate anions preferentially adsorb onto the surfaces of growing metal-hydroxide precipitates. Other similar results were observed when using iron or aluminium electrodes whenever coagulation reagents, aluminium or iron, were plotted in molar units and the same adsorption isotherm was obtained. Since electrocoagulation merely acts as a dosing coagulant technology, current density does not influence the removal of nitrates from water. However, it strongly affects the feasibility of nitrate removal because current density increases the operational cell potential. In other words, current density influences the power consumption that is required to provide a specific dose of reagent. On the other hand, the coagulation results indicate that this technology is not suitable for removing nitrate from water. The huge increase in conductivity observed during coagulant dosing (in comparison to the conductivity that was obtained when using electrocoagulation) appears to promote competition among nitrates and coagulant counter ions. It also decreases the widths of the double layers that form around the precipitate particles. Both of these processes most likely explain why nitrates cannot be removed from water using a coagulation process.