Investigating seawater battery desalination system through experimental and modeling analysis

Abstract

In addressing the water shortage problem, a seawater battery desalination (SWB-D) system has emerged as a promising electrochemical desalination technology, offering the dual benefits of generating drinking water and storing energy within the battery. Despite its potential, the practical application of the system is hindered by limited exploration of the organic matter impact and by higher energy consumption compared with conventional reverse osmosis (RO) systems. In response, this study first investigated the influence of organic matter on the membranes in terms of energy charging capacity and desalination performance through charging experiments and instrumental analysis. In order to address the excessive energy consumption, we also utilized a redesigned SWB-D system, termed a Na metal electrode-based hybrid redox flow battery desalination (NRFDB-D) system. The second phase of the investigation focuses on optimizing the NRFDB-D system by exploring catholyte concentration and osmosis through experiments and modeling, aiming to minimize specific energy consumption (SEC). First, the organic fouling behavior in the SWB-D system was examined by individually dissolving three different types of organic matter—humic acid, sodium alginate, and bovine-serum-albumin (Chapter 3). The salt removal performance degraded with hydrophobic organics, while hydrophilic sodium alginate caused no decline. Continuous water flow mitigated the fouling behavior, and a large volume of saline water enabled longer charging. Electrical resistance increase was measured in the presence of organic matter using electrochemical impedance spectroscopy and the four-electrode method. Additionally, the presence of a fouling layer was identified using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectrometry. Second, the NRFDB-D system was investigated in terms of the catholyte concentration and the osmosis through experiment and modeling, achieving the minimum SEC (Chapter 4). The NRFDB-D experiment revealed the correlation between the catholyte concentration and the osmosis. Response surface methodology (RSM) analysis demonstrated optimal operating conditions in the NRFDB-D system, yielding the lowest SEC across various feedwater concentrations and salt removal rates. The optimized NRFDB-D system efficiently desalinated low-salt water (12,500 mg/L) and seawater (35,064 mg/L), exhibiting a lower SEC compared with the RO system. Additionally, utilizing the optimized NRFDB-D as a part of desalination (45% salt removal) could offset each system limitation, including concentrated brine generation and divalent ions removal in the feedwater. These studies could be expected to contribute to the practical application of the desalination technologies using the SWB, thereby improving its performance as well as promoting environmental sustainability.