Role of interparticle and particle-surface interactions on virus removal by ultrafiltration membranes

GUILLERMINA J. GENTILE; MERCEDES C. CRUZ; MARÍA D. BLANCO FERNÁNDEZ; VERÓNICA B. RAJAL; MARIA M. FIDALGO DE CORTALEZZI

Salt Lake City

Congreso; AIChE Annual Meeting; 2015

The reduction and inactivation of viral pathogens in natural waters is a major goal to achieve, due to the close relationship between these organisms and disease outbreaks. Available treatments based on bacteriological criteria are not always effective since viruses are more resistant and difficult to remove.Membrane processes, like ultrafiltration, are increasingly used in potabilization to remove viruses and are a good barrier at nanometer level. The removal of virus particles is controlled by different mechanisms, such as electrostatic repulsion, attachment and size exclusion.Ultrafiltration membranes are not expected to achieve significant retention of viral particles by size exclusion, since their pore size is similar or larger than the virus diameter; electrostatic repulsion and aggregation are therefore the predominant mechanisms during virus filtration.Particles exhibiting the same charge as the membrane surface are generally less likely to be allowed through the membrane, as they are repelled on approach back to the bulk feed solution. Particle size increases due to aggregation, which occurs when electrostatic repulsive forces can be effectively overcome by van der Waals attraction forces, allowing attachment following inter-particle collision events. Electrostatic repulsion and attachment are strongly dependent on surface chemistry, pH, ionic strength, and chemical nature of the dissolved solids.Non-pathogen viruses have been extensively used as models in water research. Pseudomonas aeruginosa bacteriophage PP7 is a good surrogate for poliovirus in water treatment processes, since both are icosahedral and have similar diameter (25 - 30 nm).Previous work has shown that virus retention by polymeric ultrafiltration membranes was highly dependent on the water matrix. In particular, removal of PP7 was increased with high concentration of Ca2+, low concentration of Mg2+, simultaneous high or low concentrations of NO3- and HCO3-.The filtrations were performed at cross flow in a custom made membrane filtration unit, connected to a feed tank through a peristaltic pump, a permeate tank on a scales, and control instruments (two pressure gauges and a flowmeter).The objective of this work was to elucidate the mechanisms of virus filtration in relation to membrane surface - viral particle interaction and aggregation processes in order to be able to explain the experimental observations. Membrane surface and virus charges were measured, as well as particle size, for a variety of water matrixes. The inter-virus and virus-membrane interaction energy was modeled by Derjaguin, Landau, Verwey and Overbeek (DLVO) theory of colloidal stability.