In recent years, microalgae have attracted considerable attention in the environmental, industrial, and health fields as promising sources for biofuels and value-added products. However, membrane-based separation processes used for microalgae harvesting often suffer from severe fouling, which limits filtration efficiency and increases operational costs. Even when microalgal cells are removed from culture broth prior to filtration, significant membrane fouling still occurs, indicating that soluble organic matter plays a critical role in pore blockage and flux decline. These soluble organic substances, although smaller than the membrane pore size, can strongly influence filtration performance through adsorption, aggregation, and complex formation.

In this study, the membrane fouling behavior caused by organic substances derived from microalgae was investigated using model protein–polysaccharide systems. Bovine serum albumin (BSA) and lysozyme (Ly) were selected as representative proteins, and their mixtures with sodium alginate were subjected to constant-pressure filtration through a PVDF microfiltration membrane (pore size: 0.1 µm). The influence of protein type and solution pH on permeate flux decline and fouling mechanisms was evaluated. ATR-FTIR analysis of the fouled membranes revealed characteristic absorption bands corresponding to both polysaccharides and amide groups, indicating the coexistence of carbohydrate and protein residues on the membrane surface.

The results demonstrated that [...] produced greater fouling resistance than single-component systems, suggesting the formation of protein–polysaccharide complexes that enhanced irreversible adsorption. Notably, FTIR spectra obtained after filtering actual microalgae culture broth—after removal of the cells—showed similar [...] to those observed in the model systems. This similarity supports the hypothesis that [...] are key contributors to membrane fouling. These findings provide new insight into the fouling behavior of microalgae-derived organic matter and contribute to a deeper understanding of how organic complexes affect membrane filtration processes.