Effects of the ionic strength of sodium hypochlorite solution on membrane cleaning

Chemical cleaning is conducted to recover the permeability of membranes when other physical cleaning methods are not effective. This research examined cleaning by sodium hypochlorite solution with a focus on how the ionic strength of the solution affects its efficiency during flux recovery. Ultrafiltration membranes with various molecular weight cut-offs were clogged with bovine serum albumin, then flushed with sodium hypochlorite solutions of different ionic strengths. On increasing the ionic strength of the solution, the speed of flux recovery was retarded at first, before the recovery suddenly accelerated. The effects of ionic strength on both the reaction and diffusion of the cleaning process were investigated to understand the mechanism. It was inferred that the diffusivity of the foulant inside the membrane pores was altered under conditions of high ionic strength, which led to this unique tendency. This finding provides insight into the fouling mechanism and the movement of foulants inside the membrane pores.