Electrodialysis process for carbon dioxide capture coupled with salinity reduction: A statistical and quantitative investigation

Rejected brine and CO₂ are the two most common pollutants associated with the desalination process. The current study focuses on the sustainable and efficient handling of these emissions. Herein, a method is presented that can effectively manages waste fractions and results in value-added products. A multi-chamber electrodialysis was studied to remove salt from the water and capture CO₂ to produce hydrochloric acid, carbonates/bicarbonate salt mixture, and irrigation standard water. The effects of process variables (sodium chloride concentration, voltage/area, and CO₂ flow rate on CO₂ uptake, current efficiency, % salt removal, waste-to-product ratio, and energy consumption were optimized using a central composite design. It was found that high voltage and high CO₂ flow rate were beneficial for high CO₂ uptake. Current efficiency for salt removal improved with low voltage and high salt concentration. In contrast, increasing voltage and reducing salt concentration reduced the waste-to-product ratio and improved % salt removal. A salt concentration of 0.76 M, a voltage/area of 2344 V/m², and a CO₂ flow rate of 1.3 l/min were optimum parameters, resulting in a CO₂ uptake of 11 g/M NaCl, a current efficiency of 87 %, a salt removal percentage of 28 %, a waste-to-product ratio of 2.2, and energy consumption of 123 Wh/M NaCl. Under optimum conditions, the process was analyzed over time to determine the variations within the system caused by ion transfer. The sodium carbonate and bicarbonate liquid mixture was freeze-dried and quantified using Fourier transform infrared spectroscopy (FTIR).