Amido black staining of ultrafiltration membranes fouled with BSA

Characterisation of membranes in order to determine how clean the membranes are is usually determined by (1) comparing the initial and final clean water flux (2) the product flux in the following run, (3) FTIR analysis, (4) streaming potential and (5) contact angles. However, these techniques do not provide information about where the remaining foulant resides. In this paper clean water flux results were combined with dye tests (Amido black) to reveal how clean the membranes really were after cleaning with both formulated and industrial cleaners. The dye tests not only identified the remains of protein foulant on the membrane after cleaning but also the presence of surfactant adsorbed to membranes and protein. Also, the dye tests showed for similar relative water fluxes (after fouling, cleaning and rinsing), for three different cleaners, the membranes were cleaned to vastly different degrees. In addition to this by combining the dye test results with the surface tension and pH of the cleaning solution, it was possible to determine the optimum pH and surface tension required for complete removal of protein deposits, without modifying the membrane too drastically. The role of sodium hydroxide (NaOH) and surfactant in the cleaner was investigated and it was found that for successful removal of proteins from membranes the cleaner needed to contain both NaOH and surfactant.