Impact of potassium permanganate on cyanobacterial cell integrity and toxin release and degradation

Abstract

Potassium permanganate (KMnO4) is commonly used as a pre-treatment oxidant to remove soluble manganese (Mn) and iron (Fe) which can contribute to dirty water in drinking water supplies. Because Mn and Fe problems are commonly associated with thermal stratification in summer and autumn, they frequently coincide with the presence of cyanobacteria. The use of KMnO4 as an oxidant for Mn and Fe control therefore needs to consider the potential impacts on cyanobacterial cell integrity and toxin release. This study aims to assess the effect of KMnO4 on cyanobacteria cell integrity, toxin release and toxin oxidation. A toxic strain of Microcystis aeruginosa was exposed to various concentrations of KMnO4 and the cell integrity of cyanobacteria was measured with flow cytometry. Further the intra- and extra-cellular toxin concentrations were quantified and it was apparent that KMnO4 reduced both the intra- and extra-cellular toxins at low initial concentrations of 1 and 3 mg L(-1) without complete cell lysis. However, the cell integrity of cyanobacteria was compromised at KMnO4 concentrations of 5 mg L(-1) and 10 mg L(-1) and led to intracellular toxin release. In the 10 mg L(-1) KMnO4 treatment, the total toxin was oxidised after 7h contact time. A model describing the two step process of release and degradation was developed and may provide a tool to assess the risk water quality posed by toxin release. Consequently, it may be possible to use KMnO4 as a pre-treatment for Mn and Fe at concentrations<3 mg L(-1) and short contact time when cyanobacteria are also present.