Free chlorine formation during electrochemical regeneration of a graphite intercalation compound adsorbent used for wastewater treatment

Abstract

An innovative process aiming at the removal and oxidation of refractory and toxic organic contaminants from wastewater has been developed at the University of Manchester. The process is based on the adsorption of organics onto a graphite intercalation compound (GIC) adsorbent followed by its electrochemical regeneration. This paper investigates the formation of free chlorine species during the electrochemical regeneration of GIC adsorbent in a sequential batch reactor under a range of experimental conditions including the initial concentration of chloride ions, current density and pH. The effect of chloride ions concentration showed that the generation of free chlorine was occurring under the influence of mass transfer. It has been shown that the effect of increasing the current density on the rate of formation of free chlorine was larger than that achieved by increasing the chloride contents of catholyte. However, the current efficiency was not found to be improved with an increase of current density. The concentration of free chlorine formed during electrochemical oxidation of water with sodium sulphate as catholyte was significantly lower than that obtained during electrochemical regeneration in the presence of the GIC adsorbent that highlighted the significance of GIC particles in enhancing the rate of formation of free chlorine. These findings regarding the formation of free chlorine during electrochemical regeneration of GIC adsorbent has important implications for optimising the conditions to minimise the formation of chlorinated breakdown products and for electrochemical disinfection.