Reconstruction and Removal Mechanisms of Gel-like Membrane Fouling for Seawater Desalination: Experiments and Molecular Dynamics Simulations

Abstract

Anti-gel fouling is a key problem faced by membrane desalination, especially for applications in organic acid-rich seawater. In this paper, a chemical crosslinking-based method was used to reconstruct and characterize the gel pollutants produced under the actual operating conditions of seawater desalination. In addition to the calcium alginate/calcium humate three-dimensional network skeleton, salt ions (K+, Na+, Mg2+, Cl−) in solution were also considered to ensure that the reconstructed gel was similar to pollutant gels on membranes under practical operating conditions. Characterizations showed that the reconstructed gel has high thermal insulation and stability, thus adjusting the temperature has no removal effect. Two detergents (sodium citrate and sodium hydroxide) were investigated, and their gel-removal mechanism was elucidated by molecular dynamics simulation. Numerical analysis showed that the electrostatic attraction interaction had a significant role in the gel cleaning process. Owing to the attraction of the lower electrostatic potential region in the cleaning agent, the ion exchange between Na+ in the cleaning agent and Ca2+ in the gel led to the breaking of the Ca2+-induced intermolecular bridge in the complex. As the adhesion of fouling gels decreased, the gel water solubility was increased, resulting in a decrease in weight and strength of the gel. Therefore, the integrity of the gel fouling layer was weakened and can be effectively removed. This study provides a theoretical basis for the removal of gel-like membrane fouling during actual seawater desalination.