Impact of chlorination on cell inactivation, toxin release and degradation of cyanobacteria of development and maintenance stage

Abstract

Toxic cyanobacterial blooms in source waters could impair drinking water quality and chlorine was a common oxidant to treat cyanobacteria in drinking water treatment plants. In natural freshwaters, cyanobacterial bloom is a successive process, mainly including development and maintenance stage. However, previous studies only focused on one stage of cyanobacteria. Here, we collected Microcystis of both stages in lab-scale. Then, cellular characteristics and associated effects of chlorination on cell inactivation, toxin fate of both stages was compared. Results showed Microcystis of both stages remained high photosynthetic capacity, but maintenance stage exhibited higher cell-density and extracellular organic matters, leading to lower chlorination exposure with the same initial dosage of chlorine. However, Microcystis of both stages could be completely inactivated via disrupting membrane integrity, and Microcystis at maintenance stage was less resistant to chlorine attack attributed to poor cellular surfaces. Membrane destruction resulted in the complete release of intracellular toxin for both stages, but with sufficient chlorination exposure, there was no increase of extracellular toxin attributed to faster extracellular toxin degradation than intracellular toxin release. Besides, due to elevated toxin degradation efficiency via chlorination at maintenance stage, its initial higher total toxin could be degraded to below detection limits with lower ct value of 21 mg min L−1 than development stage (30 mg min L−1). These results suggested chlorination could be a feasible option to treat cyanobacteria-laden waters at development and maintenance stage of a successive bloom.