Removal of arsenic and selenium from brackish water using electrodialysis for drinking water production

Arsenic (As) and selenium (Se) are hazardous elements contaminating groundwater resources. In this work, arsenite (As$^{III}$), selenite (Se$^{IV}$) and selenate (Se$^{VI}$) removal from brackish water by a batch electrodialysis (ED) system was investigated with varied water quality (pH, feed concentration and feed salinity) and operative parameters (flowrate and electric potential). The results showed that As and Se removal was pH dependent. Rising salinity increased the amount of chloride ions and therefore delayed As and Se removal. Higher As and Se feed concentrations led to higher molar flux, although removal rates were independent of ion concentration. ED boundary layer thickness was reduced at higher flowrates (30 to 70 L/h), but this did not affect the removal of contaminants significantly (<5 %). Electromigration transport was the dominant mechanism for both Se and As species removal, as long as the compounds were charged. The ionic characteristics (diffusivity, ionic mobility, hydration number) were the determinant principle for removal. As and Se real contaminated groundwater samples were tested showing that ED can potentially be used as a resource recovery method for selective removal of more mobile ions.