Using Advanced Spectroscopy and Organic Matter Characterization to Evaluate the Impact of Oxidation on Cyanobacteria

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.

Diversity Assessment of Toxic Cyanobacterial Blooms during Oxidation

“…Additionally, oxidation may further hinder the ability to identify cells because of its impact on the cell structure. Oxidation at higher dosages can cause significant morphological deformation of the cyanobacteria species, especially for H 2 O 2 and KMnO 4 in our study [ 63 ]. Flow cytometry conducted using the method described by Moradinejad et al (2019) showed partial membrane damage (up to 80%) under the soft-oxidation conditions performed in this study (data not shown) [ 63 ].…”

“…Unlike 1 August, the Shannon diversity is no longer correlated with Dolichospermum . These differences could reflect the morphological differences between the dominant genera ( Microcystis vs. Dolichospermum) as a unicellular aggregate that are less resistant to oxidation as compared to filaments [ 63 ]. Chlorine and KMnO 4 exposures had a low impact on Microcystis and Dolichospermum .…”

“…Unlike 1 August, the Shannon diversity is no longer correlated with Dolichospermum. These differences could reflect the morphological differences between the dominant genera (Microcystis vs. Dolichospermum) as a unicellular aggregate that are less resistant to oxidation as compared to filaments [63] Figure S2 shows the cyanobacterial composition following oxidation at genus level. Results show no significant variation in the relative abundance of Dolichospermum and Microcystis following Cl 2 , KMnO 4 oxidation.…”

Delayed Release of Intracellular Microcystin Following Partial Oxidation of Cultured and Naturally Occurring Cyanobacteria

“…Therefore, guidance for the application of pre-oxidants during a cyanobacteria bloom is warranted. While previous studies have generally assessed the complete oxidation of cyanobacteria cells and release of cyanotoxins, particularly with respect to microcystin [12][13][14][15][16][17][18][19], low oxidant exposures (concentration × time (CT)) resulting in incomplete cell oxidation continue to require further examination. Furthermore, delayed release has been observed up to 120 min after the chlorination of cells [17].…”

Ferrate(VI) pre-treatment and subsequent chlorination of blue-green algae: Quantification of disinfection byproducts

“…In recent studies of drinking water treatment, flow cytometry was increasingly used for detecting cell activity and membrane integrity after oxidation processes ( Moradinejad et al, 2019 , Wert et al, 2013 , Xie et al, 2013 ). Wert et al used a flow cytometer along with chlorophyll-a measurements to investigate cyanobacterial cell damage and lysis ( Wert et al, 2013 ).…”