Ultra-filtration (UF) systems remove virtually all particulate, colloids, bacteria, virus, pyrogens, and high molecular weight organics. UF elements with MWCO (molecular weight cut-off) ranges from 6,000 to 10,000 are typically used as the final filter in ultrapure water systems. Elements with 50,000 to 100,000 MWCO can be used as pretreatment of RO systems.