Modelling and cost evaluation of electro-coagulation processes for the removal of anions from water

Abstract

A mathematical model previously proposed by our group has been modified for its application in the modelling of arsenates, nitrates and phosphates electro-coagulation with iron and aluminium. It classifies the coagulant and pollutant species attending to their reactivity in the electro-coagulation process on the basis of the experimental behaviour of the system. The enmeshment of anionic pollutants in a growing coagulant precipitate and their direct precipitation are the mechanisms considered. A good reproducibility of the experimental data is obtained (with r2 above 0.9) with a small number of parameters. The model has been used to predict the amount of coagulant dose required under given conditions for the removal of the anionic pollutants, which allowed obtaining the costs of the electro-coagulation corresponding to the raw material, iron or aluminium sheets, and the energy costs for their electro-dissolution. Results showed that iron electro-coagulation is cheaper than aluminium electro-coagulation, and that the current density does not have an important influence on the costs within the range studied (0.2–4.0mAcm−2). Attending to the results, arsenate and phosphate removal by electro-coagulation seem to be attractive from the economic point of view.