Effect of hydrogen peroxide on natural phytoplankton and bacterioplankton in a drinking water reservoir: Mesocosm-scale study

Allan A Santos,Dayvson O Guedes,Mário U.G Barros,Samylla Oliveira,Ana B.F Pacheco,Sandra M.F.O Azevedo,Valéria F Magalhães,Carlos J Pestana,Christine Edwards,Linda A Lawton,José Capelo-Neto

doi:10.1016/j.watres.2021.117069

Abstract

Cyanobacterial blooms are increasingly reported worldwide, presenting a challenge to water treatment plants and concerning risks to human health and aquatic ecosystems. Advanced oxidative processes comprise efficient and safe methods for water treatment. Hydrogen peroxide (H2O2) has been proposed as a sustainable solution to mitigate bloom-forming cyanobacteria since this group presents a higher sensitivity compared to other phytoplankton, with no major risks to the environment at low concentrations. Here, we evaluated the effects of a single H2O2 addition (10 mg L−1) over 120 h in mesocosms introduced in a reservoir located in a semi-arid region presenting a Planktothrix-dominated cyanobacterial bloom. We followed changes in physical and chemical parameters and in the bacterioplankton composition. H2O2 efficiently suppressed cyanobacteria, green algae, and diatoms over 72 h, leading to an increase in transparency and dissolved organic carbon, and a decrease in dissolved oxygen and pH, while nutrient concentrations were not affected. After 120 h, cyanobacterial abundance remained low and green algae became dominant. 16S rRNA sequencing revealed that the original cyanobacterial bloom was composed by Planktothrix, Cyanobium and Microcystis. Only Cyanobium increased in relative abundance at 120 h, suggesting regrowth. A prominent change in the composition of heterotrophic bacteria was observed with Exiguobacterium, Paracoccus and Deinococcus becoming the most abundant genera after the H2O2 treatment. Our results indicate that this approach is efficient in suppressing cyanobacterial blooms and improving water quality in tropical environments. Monitoring changes in abiotic parameters and the relative abundance of specific bacterial taxa could be used to anticipate the regrowth of cyanobacteria after H2O2 degradation and to indicate where in the reservoir H2O2 should be applied so the effects are still felt in the water treatment plant intake.

Highlights

Cyanobacterial blooms in freshwater are directly related to anthropogenic eutrophication and represent a major concern for drinking water supply (Pearl and Otten, 2013; Codd et al, 2016; Huisman et al, 2018)
We evaluated the effects of H2O2 on phytoplankton, bacterioplankton and abiotic parameters using a mesocosm system into a hypereutrophic reservoir located in a semi-arid region, subjected to high irradiance, high temperature and presenting a high carbon content
The heterotrophic bacterial community composition changed over time and was dominated by taxa that presented resistance to H2O2, Exiguobacterium

Summary

Introduction

Cyanobacterial blooms in freshwater are directly related to anthropogenic eutrophication and represent a major concern for drinking water supply (Pearl and Otten, 2013; Codd et al, 2016; Huisman et al, 2018). The higher sensitivity of cyanobacteria to H2O2 compared to eukaryotic phototrophs can be explained by the absence of compartmentalized organelles protected by membranes, as well as the lack of Mehler reaction as found in higher plants and algae (Latifi et al, 2009; Allahverdiyeva et al, 2013; Passardi et al, 2007). This reaction consists of O2 reduction to superoxide anion (O2−) by electrons from photosystem I (PSI). Cyanobacteria do not possess an anti-ROS system as efficient as that of green algae and higher plants (Passardi et al, 2007)

Methods

Results

Discussion

Conclusion