Characterisation of transparent exopolymer particles (TEP) produced during algal bloom: a membrane treatment perspective

Abstract

Algal blooms are currently a major concern of the membrane industry as it generates massive concentrations of organic matter (e.g. transparent exopolymer particles [TEP]), which can adversely affect the operation of membrane filtration systems. The goal of this study is to understand the production, composition and membrane rejection of these organic materials using different characterisation techniques. Two common species of bloom-forming freshwater and marine algae were cultivated in batch cultures for 30 days and the productions of TEP and other organic matter were monitored at different growth phases. TEP production of the marine diatom, Chaetoceros affinis, produced 6–9 times more TEP than the freshwater blue-green algae, Microcystis. The organic substances produced by both algal species were dominated by biopolymeric substances such as polysaccharides (45–64%) and proteins (2–17%) while the remaining fraction comprises of low molecular weight refractory (humic-like) and/or biogenic organic substances. MF/UF membranes mainly rejected the biopolymers but not the low molecular weight organic materials. MF membranes (0.1–0.4 μm) rejected 42–56% of biopolymers, while UF membranes (10–100 kDa) rejected 65–95% of these materials. Further analysis of rejected organic materials on the surface of the membranes revealed that polysaccharides and proteins are likely responsible for the fouling of MF/UF systems during an algal bloom situation.