Impact of low coagulant dosages on protein fouling of ultrafiltration membranes

Abstract

Biopolymers have been identified as the primary source of fouling for ultrafiltration (UF) membranes, however the relative contribution of its components (e.g., proteins and polysaccharides) to fouling are still unclear. Previous natural water studies have shown that applying low doses of coagulant (< 1 mg metal/L) significantly reduces membrane fouling. The impact of inline coagulation on UF fouling for three different model protein solutions was examined at bench-scale. Results show that when compared to no coagulant addition, a low coagulant dose (2 μM Al or 0.3 mg/L alum) is capable of significantly reducing membrane fouling when considering feed solutions containing bovine serum albumin (BSA) and ovalbumin (OVA). Conversely, the same alum dose resulted in the most fouling when considering β-lactoglobulin (BLG). Protein rejection was also correlated with irreversible fouling resistance, suggesting fouling mitigation was due to weakened protein-membrane interactions instead of a more reversible fouling layer. Fouling trends for BSA and OVA were similar to those in previous studies with natural surface waters, which suggest that proteins are major contributors to UF fouling which may be mitigated with low dosages of coagulant. It is hypothesized that at low alum doses, the surface hydrophobicity of the protein and the fouling layer is altered, leading to weaker interactions and thereby reducing fouling.