Studies On the Interactions of Biological and Natural Organic Matter On Polyelectrolyte and Silver Nanoparticle Modified Microfiltration Membranes

Organic matter and biological organisms are major contributors to irreversible fouling, flux decline and reduced membrane life in membrane separation processes. The aim of this study was to reduce the interaction of both organic matter and biological organisms on the membranes by modifying the surface of commercially available polyethersulfone (PES) membranes using the polyelectrolyte multilayer modification method with polystyrenesulfonate (PSS), poly(diallyldimethylammonium chloride) (PDADMAC) and silver nanoparticles (nanoAg) integrated onto the surface as stable, thin (15 nm) films. PSS increases the hydrophilicity of the membrane and increases the negative surface charge, while integration of nanoAg into the top PSS layer imparts biocidal characteristics to the modified surface. Studies were performed by filtering aqueous solutions of humic acid (5 mg L^-1 and 20 mg L^-1), a suspension of Escherichia coli (E. coli, 10⁶ CFU mL^-1) and a mixture of both foulants through unmodified and modified PES membranes under batch conditions. The permeability, flux decline and fouling resistances were calculated for each modification and compared to the unmodified membrane. Microscopic evaluations and culture studies were also performed. The results confirmed that the modification of membranes by polyelectrolyte layers and silver nanoparticles significantly reduced organic and biological interactions with the membrane.