The effect of particle composition on filter removal of sub-30nm particles from UPW
Don Grant - CT Associates, Inc.
This paper describes use of a new particle counting technique that allows measurement of removal of particles as small as 5 nm in diameter from UPW. In this technique filters are challenged with particles ranging from 5 to 100 nm in diameter. Total concentrations ranging from 107/mL to 1010/mL ? 5 nm are used. Filter inlet and outlet concentrations are measured using a Liquid Nanoparticle Sizer, an instrument that allows very accurate resolution of particle size down to < 5 nm. The instrument has 64 size channels per decade of size (e.g. between 10 and 100 nm). Examples of retention of 30 nm polystyrene latex (PSL), gold, and silica particles by commercially available filter cartridges with a 30 nm removal rating are included in the paper. The filters were found to have high retention efficiency for the PSL and gold particles, and significantly lower retention of the silica particles. These results indicate that adsorption plays a significant role in the retention of PSL and gold particles, while sieving is the dominant capture mechanism for silica particles. In addition, silica particles represent “real world” particles since silica is commonly found in UPW. Hence, silica particles are the preferred particle type for determining particle retention efficiency of filters used in UPW systems.
CTA publication #104: Presented at the Executive Forum at ULTRAPURE WATER Micro 2011, Portland, OR