Multiwalled Carbon Nanotube Filter: Improving Viral Removal at Low Pressure

The effective removal of viruses by a multiwalled carbon nanotube (MWNT) filter is demonstrated over a range of solution chemistries MS2 bacteriophage viral removal by the MWNT filter was between 1 5 and 3 log higher than that observed with a recently reported single-walled carbon nanotube (SWNT) filter when examined under similar, loadings (0 3 mg/cm(2)) of carbon nanotubes (CNTs). The greater removal of viruses by the M W NT filter is attributed to a more uniform CNT-filter matrix that allows effective removal of viruses by physicochemical (depth) filtration Viral removal by the MWNT filter was examined under a broad range of water compositions (ionic strength, monovalent and divalent salts, solution pH. natural organic matter, alginate, phosphate. and bicarbonate) and filter approach velocities (0 0016, 0.0044, and 0 0072 cm/s) Log viral removal increased as the fluid approach velocity decreased, exhibiting a dependence on approach velocity in agreement with colloid filtration theory for Brownian particles Viral removal improved with increasing ionic strength (NaCl), from 5 06 log removal at 1 mM NaCl to greater than 6.56 log removal at 100 mM NaCl Addition of calcium ions also enhanced viral removal, but the presence of magnesium ions resulted in a decrease in viral removal Solution pH also played an important role in viral removal, with log removals of 8 13, 538, and 4 00 being documented at solution pH values of 3 0, 55, and 9 0, respectively Dissolved natural organic matter (NOM) had a negligible effect on viral removal at low concentration (1 mg/L), but higher concentrations of NOM significantly reduced the viral removal by the MWNT filter, likely due to steric repulsion Addition of alginate (model polysaccharide) also caused a marked decrease in viral removal by the MWNT filter This highly scalable MWNT-filter technology at gravity-driven pressures presents new, cost-effective options for point-of-use filters for viral removal