Behaviors of Microcystis aeruginosa cells during floc storage in drinking water treatment process

This is the first study to systematically investigate the different behaviors of Microcystis aeruginosa in the sludges formed by AlCl(3), FeCl(3), and polymeric aluminium ferric chloride (PAFC) coagulants during storage. Results show that the viability of Microcystis aeruginosa in PAFC sludge was stronger than that of cells in either AlCl(3) or FeCl(3) sludge after the same storage time, while the cells’ viability in the latter two systems stayed at almost the same level. In AlCl(3) and FeCl(3) sludges high concentrations of Al and Fe were toxic to Microcystis aeruginosa, whereas in PAFC sludge low levels of Al showed little toxic effect on Microcystis aeruginosa growth and moderate amounts of Fe were beneficial to growth. The lysis of Microcystis aeruginosa in AlCl(3) sludge was more serious than that in PAFC sludge, for the same storage time. Although the cell viability in FeCl(3) sludge was low (similar to AlCl(3) sludge), the Microcystis aeruginosa cells remained basically intact after 10 d storage (similar to PAFC sludge). The maintenance of cellular integrity in FeCl(3) sludge might be due to the large floc size and high density, which had a protective effect for Microcystis aeruginosa.