Ultrafiltration (UF) is a cross-flow process similar to reverse osmosis. The membrane rejects particulates, organics, microbes, pyrogens and other contaminants that are too large to pass through the membrane. UF has a stream to waste (concentrate) that can be recirculated. In polishing applications, this is generally 5% of the feed flow. Membranes are available in both polymeric and ceramic materials. The former is available in spiral wound and hollow fibre configurations and the ceramic membranes are available in single and multiple channel configurations. Ultrafiltration is frequently used downstream of ion exchange deioniser or reverse osmosis/continuous electrodeionisation processes for microbial and endotoxin reduction. The rating of UF membranes varies in molecular weight cut-offs from 1 000 to 100 000 and UF has reduction of endotoxin (pyrogens) from 2 log₁₀ to 4 log₁₀. UF is capable of consistent production of water meeting the USP WFI endotoxin limit of 0.25 Eu/ml. UF membranes can be sanitised with a variety of chemical agents such as sodium hypochlorite, hydrogen peroxide, peracetic acid and with hot water and / or steam.