An emerging threat to membrane application is the seasonal proliferation of algae in water sources such as rivers, reservoirs and lakes. This study investigated the link between feed parameters and the membrane performance of a pilot-scale microfiltration (MF) plant for 7 months. The seasonal succession of algae in relation to temperature dynamics was monitored. Temperature-dependent seasonal patterns for algae species were observed. The water temperatures during the dominance of cyanobacteria, especially Microcystis, were relatively higher (over 25 °C) than those during the dominance of diatoms. Diatoms did not much affect membrane performance (less than 0.2 kgf/cm2), however, under the cyanobacterial dominance condition, especially Microcystis sp., transmembrane pressure (TMP) reached up to the limited level (0.4 kgf/cm2) within one month. Concurrently UV absorbance at 254 nm wavelength and dissolved organic carbon values increased significantly during the Microcystis bloom and the build-up rate of TMP increased up to 0.005 kgf/cm2/day. Membrane autopsy also showed that during the dominance of diatom, application of cleaning agents can fully remove foulants on the membrane surface. However, during the dominance of cyanobacteria, there is a lot of Al, Si and organic complex on the fouled membrane, indicating the formation of Al-organic complexes that contributed to the residual membrane fouling. It is suggested that the irrecoverable fouling layer still contained some Al, mostly in complex with organics. Thus, organic matter originated from cyanobacteria may cause a serious impact on membrane fouling by forming the complex with metal ions originated from coagulant.
Keywords: Membrane fouling; Microcystis sp.; algae; membrane autopsy.