- Surfactant cleaning of ultrafiltration membranes is essentially a sequence of three stages. The micelles, formed when the dose of nonionic surfactant exceeds the critical micelle concentration, transport to the membrane surface, partially disassemble, and bind to proteins. The binding first results in protein dislocation but then continues to surfactant occupation of the membrane surface including the sites released by the proteins. The membrane surface gradually becomes more hydrophilic and ripe for the adsorption of micelles that now build a cake layer. The developed cake is responsible for an increased protein retention and severe fouling. The surfactant cleaning time needs to be optimized to maximize the protein solubilization and to prevent the growth of a micelle cake. Circulation of a cleaning solution accelerates the surfactant transport to the membrane surface but facilitates micelle pore blocking. The induced internal fouling can counteract the benefits of reduced cleaning times due to circulation. Water flow can disassemble the external cake and wash away surfactant monomers, but will barely release clogged pores.