Impacts of Potassium Permanganate and Powdered Activated Carbon on Cyanotoxin Release

Bench-scale trials were performed to (1) expose Microcystis aeruginosa cells to potassium permanganate (KMnO4) doses of 1, 3, and 5 mg/L at contact times (CTs) of 15, 30, and 90 min, pH levels of 7 and 9, and turbidities of 0.1, 5, and 20 ntu, respectively; (2) compare the impacts of oxidation alone and oxidation plus powdered activated carbon (PAC) for the final 60 min of CT; and (3) evaluate the impact of these treatment conditions on extracellular microcystins (MCs), extra-plus intracellular (combined) MCs, cell membrane integrity, and chlorophyll a concentrations. Toxin releases from the cells were observed at both pH levels. The greatest toxin releases were observed at the lowest KMnO4 doses. The toxin releases were accompanied by relatively stable total cell counts, increases in membrane-compromised cells, and decreases in chlorophyll a. The application of 10 mg/L PAC resulted in extracellular toxin concentrations that were markedly lower than those observed in oxidant-only situations.