Mechanism of Cryptosporidium, Giardia, and MS2 virus removal by MF and UF

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Abstract
Protozoan removal was a function of size, whereas virus removal was influenced by physical straining or adsorption, cake layer formation, or the fouling state of the membrane.Water quality regulations dealing with microbial removal have increased interest in using microfiltration (MF) and ultrafiltration (UF) as barriers against protozoan cysts and viruses. Consequently, a study was conducted to evaluate the removal of these organisms by a variety of MF and UF membranes and to elucidate removal mechanisms. All of the hollow‐fiber membranes evaluated removed Giardia muris cysts and Cryptosporidium parvum oocysts to below detection limits. No cysts or oocysts were detected in the permeate as long as the membrane remained intact. Physical straining of these organisms from the feedwater appeared to be a primary mechanism of action. The extent of virus removal was membrane‐specific, with removals ranging from 6 logs. Three phenomena appeared to contribute to virus removal: physical sieving or adsorption, cake layer formation, and fouling state of the membrane. The relative contribution of each of these was a function of water quality, time of operation or filtration, and membrane characteristics.