Analysis of UF membrane fouling mechanisms caused by organic interactions in seawater

Abstract

Organic fouling remains a significant challenge in the application of ultrafiltration (UF) pretreatment systems in the desalination industry. In this study, the fouling potential of organic materials in seawater was investigated using model seawater solution containing humic acid and alginate. The buildup of organic fouling on UF membranes was studied after consecutive filtration cycles with periodical backwash. The effects of varying backwash conditions (duration, frequency, permeate/deionized water) on membrane performance were analysed. It was observed that the variation in filtration condition resulted in minor differences in membrane performance provided the total backwash volume applied remained constant. However, the substitution of permeate water backwash with deionized water improved fouling reversibility significantly. Furthermore, advanced characterisation of the membrane fouling layer after filtration revealed significant differences in foulant distribution due to the nature of the backwash solution. Deionized water backwash was found to be particularly effective in removing alginate from the membrane fouling layer, although the humic acid adsorbed onto the membrane surface were not significantly affected. However, permeability testing of the membranes after chemical cleaning revealed higher levels of irrecoverable fouling after deionized water backwash. From the data obtained in this study, a fouling mechanism is therefore proposed, in which the alginate fouling layer performs as a dynamic membrane, prefiltering smaller humic acid molecules and reducing adsorption on the membrane surface.