Understanding Membrane Fouling Mechanisms (II): Experimental Characterization of Foulant-Membrane Interactions

Understanding Membrane Fouling Mechanisms (II):

Experimental Characterization of Foulant-membrane Interactions

 Yaolin Liu¹*, Yuan Xiang², Yongsheng Leng², Baoxia Mi¹

1. Department of Civil and Environmental Engineering, University of Maryland, College Park, MD 20742

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

*yll@umd.edu

Keywords: membrane fouling, force measurement, direct observation

Membrane technology is an effective method for seawater/brackish water desalination and wastewater reclamation. However, the efficiency of membrane process is greatly hampered by membrane fouling.  Membrane fouling can cause severe membrane flux decline, worsen product quality, and shorten membrane life. There are numerous studies on membrane fouling. However, a molecular-level understanding of membrane fouling mechanisms is still absent, presenting a critical barrier to developing antifouling membrane materials and effective fouling control strategies.  Therefore, there is a pressing need to investigate the foulant-foulant and foulant-membrane interactions in molecular level in order to gain a better understanding of membrane fouling mechanisms. 

This study investigates the effects of surface functionality on foulant-membrane interaction forces and the deposition kinetics of foulants on membranes in filtration experiments.   We used atomic force microscopy (AFM) to measure foulant-foulant and foulant-membrane interaction forces.  A window-cell equipped membrane filtration system coupled with fluorescent microscope was used to directly observe the kinetics of foulant deposition, attachment and detachment onto/from membrane surfaces.  In order to study the effects of surface fuctionality on interaction forces and deposition kinetics, we selected several representing surface functionality (alginate, protein, –COOH, –NH₂, –CONH-, and polyethylene glycol(PEG)) for foulants and membranes.  To achieve various but controllable functionality for foulants, we used three surface functionalzed particles including carboxyl fluorescent nile red particle (–COOH), amino fluorescent nile red particle (–NH₂), and dimethylamino fluorescent purple particles (–CONH-).  These three particles were used to make particle probes for AFM force measurements, and they were also used in the deposition experiment to study depositon kinetics.  We used polyamide (PA) membrane as the based membrane and compared the performances of PA and PEG modified membranes.  The results from the force measurement and foulant deposition experiments will be combined with molecular simulation results to help achieve a molecular-level understanding of membrane fouling.