The fate of Microcystis aeruginosa cells during the ferric chloride coagulation and flocs storage processes

Abstract

Microcystis blooms could cause severe problems for drinking water supplies with their associated microcystins (MCs). As the majority of MCs are retained inside the cells, the effective removal of the intact Microcystis cells to avoid the release of additional MCs plays an important role in drinking water treatment. This study evaluated the effect of ferric chloride (FeCl₃) coagulation and the flocs storage process on the integrity of Microcystis aeruginosa cells and the intracellular MCs release (and possible degradation) in both processes. Multiple analysis techniques including scanning electron microscopy and chlorophyll fluorescence were used to assess the integrity of M. aeruginosa. In the coagulation process, the coagulant dosage and mechanical actions caused no cell damage, and all the cells remained intact. Furthermore, 100 mg/L FeCl₃ was effective in removing the extracellular MCs. In the flocs storage process, a number of intracellular MCs were released into the supernatant, but the cells remained viable up to 10 d.

Keywords:

• FeCl₃ coagulation
• MCs release
• cell integrity
• flocs storage
• MCs degradation

Acknowledgements

This work was supported by the International Cooperation Research of Shandong Province [2011176]; Science and Technology Development Project of Shandong Province [2012GHZ30020]; the International Science & Technology Cooperation Programme of China [2010DFA91150] and National Science Fund for Excellent Young Scholars [51322811]. The authors thank Findlay A Nicol of Shandong University of Finance and Economics for revising the English in the manuscript.