Influence of organic matter on seawater battery desalination performance

Abstract

A rechargeable seawater battery desalination (SWB-D) system stores energy in a battery cell while removing salts from saline water via a sodium superionic conductor membrane and an anion exchange membrane. However, the electrochemical performance often degrades owing to the organic fouling generated on the ion exchange membranes. In this study, we investigated the fouling behavior of the SWB-D system by individually dissolving three different types of organic matter—humic acid, sodium alginate, and bovine-serum-albumin. In terms of the salt-removal performance of the SWB-D system, gradual degradation was observed over three charging cycles using hydrophobic humic acid (~13 %) and bovine-serum-albumin (~18 %), whereas no degradation was caused by hydrophilic sodium alginate. Continuous water flow mitigated the fouling behavior, and a large volume of saline water enabled longer charging. The increase in the electrical resistance of the SWB-D system was measured in the presence of organic matter using electrochemical impedance spectroscopy and the four-electrode method. Additionally, the presence of fouling layer was identified using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectrometry. In conclusion, the results demonstrated that the hydrophobic organic matter in the feed water could be unfavorable when operating the SWB-D system.