When constant transmembrane pressure (TMP) is applied to pressure-driven membrane processes, fouling formation on the surface results in flux decline. When operating conditions exceed a critical value, and/or when filtration is no longer sustainable, physical or chemical cleaning protocols are implemented to recover some of the original hydraulic performances. Specifications from membrane suppliers (or original equipment manufacturer (OEM) data) provide an approximation for the level of flux to be obtained for a given driving force.
The level of flux reversibility is proportional to the strength of the cleaning process and is generally slightly lower than 100 %. In other words, cleaning strategy can generally not guarantee full recovery of flux performances. The fraction of the flux recovered during cleaning is defined as the reversible flux decline (Fig.
1).
