Alice Antony, Judy Blackbeard, Mark Angles, Greg Leslie. Non microbial indicators for monitoring virus removal by ultrafiltration membranes. Journal of Membrane Science. Dec 2013.
The integrity of 0.04 µm polyvinylidene fluoride hollow fibre ultrafiltration (UF) membranes was assessed by challenge tests with citrate stabilised silver nanoparticles. Spherical, zerovalent, nanosilver particles maintained a net negative surface charge (−25±4 mV) and narrow size distribution (60±10 nm) in aqueous suspension for 72 hours. Nanoparticle challenge testing of intact UF hollow fibre membranes demonstrated rejection efficiency as high as 2.9 log removal value (LRV), without affecting the hydraulic performance of the membranes. Challenge testing of deliberately compromised membranes through a sequence of breaches indicated that the nanoparticles can detect a loss of integrity in the filtration area of 3×10−5%, equivalent to 3 damaged fibres in 100,000 fibres. The LRV decreased from 2.8 to 1.3 with one pin hole of 100 μm thickness. Membranes were exposed to hypochlorite in order to mimic membrane ageing; exposure to 2,500 and 5,000 mg L−1.h of hypochlorite decreased the rejection efficiency of the particles by 0.2 and 0.9% with a corresponding loss in the intrinsic membrane resistance of 19 and 38%, respectively. Deliberate membrane compromise through chemical exposure was useful for generating membrane degradation that represented the initial stages of membrane failure due to routine chemical exposure. Considering the practical limitations of incorporating challenge testing with MS2 bacteriophage in full scale plants, silver nanoparticles have the potential to be an alternative indicator for challenging UF membranes for validation purposes.
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