Variations of floc morphology and extracellular organic matters (EOM) in relation to floc filterability under algae flocculation harvesting using polymeric titanium coagulants (PTCs)

[Display omitted] •Hydrolyzed speciation of titanium salts had important effects on microalgae removal.•Different mechanisms were dominant in coagulation process of PTCs.•PTC1.0 exhibited better performance in microalgae flocculation and sedimentation.•The microalgae flocs formed by PTC1.0 coagulation showed better filterability.•PTCs coagulation resulting in decrease in EOMs content and densification of algae floc. The work evaluated the algae cells removal efficiency using titanium salt coagulants with different degree of polymerization (PTCs), and the algae cells aggregates and extracellular organic matter (EOM) under chemical flocculation were investigated. The results indicated that PTCs performed well in algae cells flocculation and separation. The main mechanism using PTCs of low alkalisation degree for algae flocculation was associated with charge neutralization, while adsorption bridging and sweep flocculation was mainly responsible for algae removal by PTCs of high alkalisation degree treatment. In addition, the flocs formed by PTC1.0 showed the best filtration property, and EOM reached the minimum at this time, indicating the flocs formed by PTC1.0 were more compact than other PTCs, which can be confirmed by SEM analysis. Three-dimensional excitation emission matrix fluorescence (3D-EEM) and high performance size exclusion chromatography (HPSEC) revealed that the EOMs were removed under PTCs flocculation, which improved floc filterability.