Exploring the effects of Ozone on Freshwater Cyanobacteria and Green Algae in Surface Waters
Date Issued
May 29, 2024
Abstract
Cyanobacteria, also known as blue-green algae, present a persistent environmental concern due to
the ability of some species to produce and release toxic metabolites (also known as cyanotoxins) in
surface waters [1]. Fueled by nutrient enrichment from various sources like agricultural and sewage
runoffs, these blooms have become increasingly persistent and prevalent globally. The proliferation
of cyanobacteria and cyanotoxins in freshwater sources have far-reaching consequences.
Cyanotoxins, such as microcystins and anatoxins, which have been detected in drinking water
treatment plants and networks globally, result in a range of adverse health effects, including liver
cirrhosis, gastrointestinal issues, and neurological symptoms [2]. Moreover, the aesthetic effects of
cyanobacterial blooming directly impact recreational activities, fisheries, and the ecological balance
of aquatic ecosystems [3]. Given these challenges, effective treatment strategies are imperative to
mitigate the impact of cyanobacteria in water sources. Ozonation has emerged as a promising
oxidizing method for addressing cyanobacterial issues in water treatment. Specifically, ozone has
the potential not only to disrupt the cellular structures of cyanobacteria but also to degrade
cyanotoxins simultaneously [4]. Therefore, we investigated how different species react with ozone,
determined the effective dose so that the cells are adversely damaged, and recorded the effect of
the age of a bloom on ozone dosing. In this study, we tested three different cyanobacteria species,
Microcystis spp., Aphanizomenon spp., and Cylindrospermopsis spp., as well as a green alga,
Scenedesmus obliquus. All species were individually exposed to four ozone concentrations ranging
from 0.5 – 4 mg/L at a controlled temperature (20 °C). Pure cultures were maintained in a BG-11
growth medium, and cells were inoculated in surface water collected from the Kouris reservoir in
Cyprus. Results have shown that cyanobacteria are more sensitive to ozone treatment than green
algae. A 4 mg/L ozone dose effectively disrupts the cyanobacterial biomass, and cells cannot
recover. On the other hand, smaller doses showed a severe implication on cells’ vitality for the first
2 hours. However, the cells recovered over the next three days. Interestingly, the age of the culture
plays a significant factor in the response of the cells to the different doses.
the ability of some species to produce and release toxic metabolites (also known as cyanotoxins) in
surface waters [1]. Fueled by nutrient enrichment from various sources like agricultural and sewage
runoffs, these blooms have become increasingly persistent and prevalent globally. The proliferation
of cyanobacteria and cyanotoxins in freshwater sources have far-reaching consequences.
Cyanotoxins, such as microcystins and anatoxins, which have been detected in drinking water
treatment plants and networks globally, result in a range of adverse health effects, including liver
cirrhosis, gastrointestinal issues, and neurological symptoms [2]. Moreover, the aesthetic effects of
cyanobacterial blooming directly impact recreational activities, fisheries, and the ecological balance
of aquatic ecosystems [3]. Given these challenges, effective treatment strategies are imperative to
mitigate the impact of cyanobacteria in water sources. Ozonation has emerged as a promising
oxidizing method for addressing cyanobacterial issues in water treatment. Specifically, ozone has
the potential not only to disrupt the cellular structures of cyanobacteria but also to degrade
cyanotoxins simultaneously [4]. Therefore, we investigated how different species react with ozone,
determined the effective dose so that the cells are adversely damaged, and recorded the effect of
the age of a bloom on ozone dosing. In this study, we tested three different cyanobacteria species,
Microcystis spp., Aphanizomenon spp., and Cylindrospermopsis spp., as well as a green alga,
Scenedesmus obliquus. All species were individually exposed to four ozone concentrations ranging
from 0.5 – 4 mg/L at a controlled temperature (20 °C). Pure cultures were maintained in a BG-11
growth medium, and cells were inoculated in surface water collected from the Kouris reservoir in
Cyprus. Results have shown that cyanobacteria are more sensitive to ozone treatment than green
algae. A 4 mg/L ozone dose effectively disrupts the cyanobacterial biomass, and cells cannot
recover. On the other hand, smaller doses showed a severe implication on cells’ vitality for the first
2 hours. However, the cells recovered over the next three days. Interestingly, the age of the culture
plays a significant factor in the response of the cells to the different doses.
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