Enzymatic and detergent cleaning of a polysulfone ultrafiltration membrane fouled with BSA and whey

Abstract

Optimisation of membrane cleaning protocols requires in depth understanding of the complex interactions between the foulant and the membrane. In addition it is important to consider the economic impact of cleaning procedures including the costs of the cleaning process itself together with the effect of the procedures on membrane lifetime and efficiency. For foulants containing proteinaceous components enzymatic cleaners play a vital role in scissioning specific points in the protein strands while detergent cleaners also interact with the protein strands at specific points but in addition rapidly solubilize any small loose protein fragments. Our results show that it is most effective to clean first with an enzyme and then with a detergent, or, if both are present in the same cleaner it must be formulated in such a way that the action of each component does not interfere with any others. Enzymatic cleaners are most effective when operated at a concentration that optimises the cutting of the proteins. Use of higher concentrations does not increase the enzymatic cleaning efficiency. The efficiency of detergent cleaners usually increases with concentration up to a point where the cleaner attacks the membrane itself. The use of a water rinse during the cleaning procedure can be an effective method of removing loose foulant pieces at little extra cost, but is only effective if the rinsing is carried out at the same temperature as the chemical cleaning, otherwise the rinsing causes compaction of the fouling layer. Pretreatment of a polysulfone membrane with enzymatic or detergent cleaners has no effect on subsequent fouling and cleaning. For multiple usage cycles the optimum operating conditions would be those in which the “active” sites on the membrane that are responsible for strong irreversible fouling remain occupied after the first cycle so that subsequent cycles achieve 100% flux recovery and therefore no further decline in membrane performance.