Removal of total dissolved solids, nitrates and ammonium ions from drinking water using charge-barrier capacitive deionisation

A charge-barrier capacitive deionisation system was tested for electrochemical removal of Total Dissolved Solids (TDS), nitrates and ammonium ions. Several experiments were conducted with inorganic species spiked in tap water. The system efficiency was first evaluated using experimental statistical designs with different concentrations of NaCl (150 to 3000 mg/L). The raw water conductivity and the targeted residual TDS in treated water were the key process variables. Power consumption increased linearly as the difference between these two values increased. Water recovery rate and electrical consumption, which varied respectively from 63.9% to 95.8% and from 0.45 to 5.35 kWh/m(3), were adequately described by a simple linear regression model (R-2: 0.98 and 0.99, respectively). Additional experiments performed on nitrates (100 mg N-NO3/L) and ammonium ions (1000 mg N-NH4/L) showed high levels of removal. A rise in TDS concentration led to a decrease in their removal due to the competition for electrodes carbon adsorption sites. It was concluded from this study that this technology offers an innovative alternative for demineralising water. However, assays should be conducted in natural waters and in a steady-state manner to confirm data obtained and get long-term performance. (C) 2009 Elsevier B.V. All rights reserved.