Understanding Membrane Fouling Mechanisms (I): Molecular Simulations of Foulant-Membrane Interactions

Understanding Membrane Fouling Mechanisms (I): Molecular Simulations of Foulant-membrane Interactions

Yuan Xiang¹, Yongsheng Leng¹, Yaolin Liu², Baoxia Mi²

1. Department of Mechanical & Aerospace Engineering, The George Washington University, Washington DC 20052

2. Department of Civil & Environmental Engineering, University of Maryland, College Park, MD 20742

leng@gwu.edu

Keywords:membrane fouling, molecular dynamics simulation

Water scarcity is one of the most challenging problems throughout the world. Membrane technology services as an effective approach to addressing water shortages. However, the productivity of the membrane processes is severely hampered by the long-standing problem of fouling. Fouling seriously deteriorates membrane performance, including causing flux decline and worsening effluent quality. In order to deal with this problem, an in-depth understanding of fouling mechanisms is essential. In recent years, molecular dynamics (MD) simulation have contributed significantly to the nanoscale understanding of water and solute transport mechanisms in membrane. Integration of molecular simulation approaches with experimental characterization will improve our molecular-level understanding of fouling and drastically aid designing of antifouling membrane.

This study investigates the algorithm to build the amorphous polyamide (PA) membrane model, which could accurately represent membrane properties, including density, chemical composition, functional group and degree of cross-linking, based on the XPS measurement of the O/N ratio. The initial configuration of PA membrane was built via the configurational-bias Monte-Carlo simulation (CBMC). A solvated membrane layer and bulk solution layer are included in the simulation system to study the surface interaction and transport phenomena. Alginate is used as foulant. For the membrane-foulants system immersed in aqueous electrolyte solutions, the foulants, membrane, water molecules and dissolved ions are modeled using the consistent-valance force field (CVFF). We investigated the local hydrophobic/hydrophilic interactions between foulant-foulant and foulant-membranes. The competition mechanism of hydrophobic/ hydrophilic interactions in molecular binding process has been analyzed, which will be compared with the experimental results.