ABSTRACT
81Controlling fouling in seawater reverse osmosis and ultrafiltration systems applied for pretreatment is a major challenge, in particular during algal blooms. This study aims to investigate the fouling potential and fouling behavior of algae and released organic matter in ultrafiltration membranes. For this purpose, four marine algae were cultivated namely: Chaetoceros affinis (Ch), Rhodomonas balthica (Rb), Tetraselmis suecica (Te), and Phaeocystis globulosa (Ph). During the growth and stationary/decline phase, the algal cell density, chlorophyll-a, biopolymer, transparent exopolymer particles (TEP) concentration and MFI-UF10kDa (membrane fouling potential) were measured. Fouling experiments were executed with capillary ultrafiltration, filtration inside to outside, and backwashable and nonbackwashable fouling was monitored.
During the growth, stationary/decline phase of the algal species remarkable differences were observed in the production of biopolymers, TEP and MFI-UFwkDa . Membrane fouling potential (MFI-UF 10 kDa) was linearly related to algal cell density and chlorophyll-a concentration, biopolymer concentration, TEP, during the growth phase of the algal species. After the growth phase, the relationship between MFI-UF10kDa and algal cell density and chlorophyll-a concentration did not continue. In experiments with capillary ultrafiltration, membranes (150 kDa) fed with water having 0.5 mg-biopolymer-C/L back washable fouling coincided with the MFI-UF150kDa TEP for Rh, Te, and Ph. Back washable fouling of Ch deviated and was substantially higher. The non-back washable fouling of the ultrafiltration membranes varied strongly with the type of algal species and coincided with MFI-UF150kDa and TEP concentration. Rh demonstrated the highest and Ph the lowest non-back washable fouling (at a level of 0.5 mg-biopolymer-C/L in the feed water. This non-backwashable fouling is attributed to polysaccharides (stretching OH) and sugar ester group (stretching S=O) present in the AOM.
Overall, this study highlights the importance of having better monitoring methods, types of bloom-forming algae and characteristics of AOM they released to predict the nonbackwashable fouling in dead-end UF membranes.
