Abstract
Drinking water treatment plants throughout the world are increasingly facing the presence of toxic cyanobacteria in their source waters. During treatment, the oxidation of cyanobacteria changes cell morphology and can potentially lyse cells, releasing intracellular metabolites. In this study, a combination of techniques was applied to better understand the effect of oxidation with chlorine, ozone, potassium permanganate, and hydrogen peroxide on two cell cultures (Microcystis, Dolichospermum) in Lake Champlain water. The discrepancy observed between flow cytometry cell viability and cell count numbers was more pronounced for hydrogen peroxide and potassium permanganate than ozone and chlorine. Liquid chromatography with organic carbon and nitrogen detection was applied to monitor the changes in dissolved organic matter fractions following oxidation. Increases in the biopolymer fraction after oxidation with chlorine and ozone were attributed to the release of intracellular algal organic matter and/or fragmentation of the cell membrane. A novel technique, Enhanced Darkfield Microscopy with Hyperspectral Imaging, was applied to chlorinated and ozonated samples. Significant changes in the peak maxima and number of peaks were observed for the cell walls post-oxidation, but this effect was muted for the cell-bound material, which remained relatively unaltered.
Highlights
Rising temperatures and the eutrophication of freshwaters have contributed to an increase in the frequency of cyanobacterial blooms [1,2,3]
To the best of the author’s knowledge, this study presents the first assessment of the morphological deformation of cyanobacteria after oxidation with Enhanced Darkfield Microscopy with Hyperspectral Imaging (EDM/HSI)
Oxidant exposures (CTs) were calculated via decay rates according to Equation (1) with the rates and CTs shown in Table S1 of the Supplementary Materials
Summary
Rising temperatures and the eutrophication of freshwaters have contributed to an increase in the frequency of cyanobacterial blooms [1,2,3]. Cyanobacterial cells are of concern because they can produce and release cyanotoxins as well as taste and odor (T&O) compounds. T&O compounds affect the aesthetic water quality, result in customer complaints, and lower the trust customers have in their water [4]. Regulatory agencies have proposed and, in some cases, set health-based guidelines and threshold alert levels for both cells and their metabolites [7,8,9]. The removal of cyanobacteria and their metabolites is often a challenge for conventional water treatment (i.e., coagulation, flocculation, sedimentation and filtration) with both cyanotoxins and/or
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