Insight into coagulation/flocculation mechanisms on microalgae harvesting by ferric chloride and polyacrylamide in different growth phases

FeCl3 and polyacrylamide (PAM) had been used to investigate the effect of coagulation, flocculation, and their combination on algae cells and extracellular organic matter (EOM) at different phases. PAM tended to aggregate particle-like substances, while FeCl3 could interact with EOM. The content of EOM kept rising during the algae growth cycle, while OD680 peaked at about 3.0. At stationary phase I, the removal efficiencies of UV254, turbidity and OD680 of the suspension conditioned with FeCl3 + PAM reached (88.08 +/- 0.89)%, (89.72 +/- 0.36)% and (93.99 +/- 0.05)%, respectively. Nevertheless, PAM + FeCl3 exhibited the worst efficiency because of the release of EOM caused by the turbulence. The results suggested that algal cells served as a coagulation aid to facilitate floc formation, while excessive EOM deteriorated harvesting performance. The process of FeCl3 + PAM at stationary phase I appears to be a promising technology for microalgae harvesting.

Automated summary

The effect of coagulation, flocculation, and their combination using FeCl3 and PAM on algae cells and extracellular organic matter (EOM) was investigated. FeCl3 + PAM exhibited the highest removal efficiency during stationary phase I.