Effects of extracellular organic matter on chitosan coagulation-microfiltration harvesting of Microcystis flos-aquae

[Display omitted] •EOM deteriorated the coagulation-filtration performance of M. flos-aquae.•EOM-containing M. flos-aquae cells formed relatively large and loose flocs.•Loose EOM-containing flocs resulted in a high filtration resistance.•The proton-active functional groups in EOM affected floc characteristics. Extracellular organic matter (EOM) is considered an important cause of membrane fouling when harvesting Microcystis cells using filtration technology. Coagulation pre-treatment has increasingly been applied as an effective method to alleviate membrane fouling. However, the effects and mechanisms of EOM on coagulation-microfiltration of Microcystis cells remain unclear. This study investigated the coagulation-microfiltration performance of EOM-free and EOM-containing Microcystis flos-aquae and explored the effect mechanisms of EOM from the perspective of floc characteristics and deposited algal cake structure. The results showed that the presence of EOM decreased the average flux from 4256.4 L/(m2·h) to 3378.4 L/(m2·h) at the optimal chitosan dosage of 15.11 mg/g. Electrostatic adsorption and/or bridging between carboxyl and amino/hydroxyl groups in EOM and chitosan resulted in a loose floc structure and high compressibility of the cake layer, thus reducing the filtration performance. In addition, interception of EOM in the cake layer contributed to membrane fouling during coagulation-microfiltration. These results revealed the mechanism by which EOM hinders coagulation-filtration performance, which would be helpful for the development of efficient coagulation-filtration-based microalgal harvesting techniques.