Sequential Dosing of Potassium Permanganate for Removal of Microcystin-LR During Pre-Oxidation
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Date
2021-12
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The Ohio State University
Abstract
Harmful algal blooms are made up of cyanobacteria that can release microcystins (MC's) into drinking
water sources, which are toxic to humans. MC's can be removed during drinking water treatment using
permanganate pre-oxidation. While permanganate is effective for removing microcystins, it is also non-specific and has the ability to react with dissolved organic matter (DOM) and cyanobacterial cells that exist in the water. Permanganate's reactions with DOM and cells cause competition for MC-LR removal.
Additionally, reactions with cells can cause them to lyse and release intracellular MC's into the water.
Preliminary work within our group suggests that a sequential dosing technique of permanganate pre-oxidation can reduce competition by DOM. Sequential refers to the additional of fractional doses of permanganate over time as opposed to a single large dose. Kinetic models fitted to observational data of sequential dosing and singular dosing found that competition by DOM decreased with each sequential dose. In the presence of microbial DOM, sequential dosing increased MCLR removal and in
the presence of terrestrial DOM sequential dosing decreased removal.
A propidium Iodide (PI) staining assay was developed in order to quantify cell lysis cyanobacterial cells.
This assay was validated with the Bioluminescence Assay using Vibrio fischeri. When the PI assay was
used to quantify cell lysis of Microcystis cells, no significant cell lysis was observed using 10 ppm of
potassium permanganate. Because of this, sequential dosing was tested using V. fischeri cells instead.
Sequential dosing of permanganate in the presence of V. fischeri cells saw similar amounts of cell lysis
when compared to a single dose of permanganate. This suggests that the rate of competition caused by
cells does not change between doses of permanganate, unlike in the presence of DOM.
The removal of MCLR by permanganate in the presence of both DOM and V. fischeri cells was estimated
using a kinetic model. In only the presence of 5 mg/L of microbial DOM and 100 nM of MC, we predict
one dose of 12 µM permanganate to remove 92% of MCLR after 40 minutes and two doses of 6 µM to
remove 99% of MCLR after 80 minutes. After adding competition by V. fischeri cells (optical density =
0.44), removal by one and two doses of permanganate was predicted to decrease to 50% and 60% total
MCLR removal, respectively.
Our simulation suggests that the presence of both cells and DOM have the ability to significantly impact
MCLR removal in the worst-case scenario. However, sequential dosing was expected to increase MCLR
removal by 10%. This simulation assumed that the cells present would be V. fischeri, which is not
representative of an actual cyanobacterial bloom. Additional work should be done to more carefully
examine the cyanobacterial cells interactions with permanganate.
Description
Keywords
Harmful Algal Blooms, Drinking Water, Water Treatment, Algal Toxins, Cell Lysis, Propidium Iodide