The cell damage of Microcystis aeruginosa in PACl coagulation and floc storage processes

Abstract

The damage of cyanobacterial cells and the release of their intracellular microcystins (MCs) present an enormous threat to drinking water. Effective control of cyanobacteria both in coagulation and floc storage processes plays an important significance in avoiding the additional release of MCs during water treatment. In this paper, the cell integrity acted as a key factor to assess the damage of polyaluminum chloride (PACl) coagulation/flocculation process on Microcystis aeruginosa cells. Effects of coagulant dose, coagulation stirring and floc storage time were comprehensively evaluated to regulate M. aeruginosa cell lysis and MCs release. Results showed that all cells were removed intactly by the surface charge neutralization with PACl in the coagulation process. While in floc storage process, PACl caused obvious damage to cells and led to a large amount of MCs release afterthe protective effects of EPSs produced by M. aeruginosa cells were destroyed or decomposed. Coagulation stirring could cause cells lyse earlier than the natural lysis, but this damage was slighter than that of coagulant PACl, which obviously aggravate the cell lysis of M. aeruginosa in flocs after 2days. This study is not only significant for the effective removal of cyanobacterial cells from drinking water sources but instructive for the prevention of secondary pollution of MCs during water recirculation from the sludge treatment to the head of the process.