New insight into the residual inactivation of Microcystis aeruginosa by dielectric barrier discharge

Abstract

We report the new insight into the dielectric barrier discharge (DBD) induced inactivation of Microcystis aeruginosa, the dominant algae which caused harmful cyanobacterial blooms in many developing countries. In contrast with the previous work, we employed flow cytometry to examine the algal cells, so that we could assess the dead and living cells with more accuracy, and distinguish an intermediate state of algal cells which were verified as apoptotic. Our results showed that the numbers of both dead and apoptotic cells increased with DBD treatment delay time, and hydrogen peroxide produced by DBD was the main reason for the time-delayed inactivation effect. However, apart from the influence of hydrogen peroxide, the DBD-induced initial injures on the algal cells during the discharge period also played a considerable role in the inactivation of the DBD treated cells, as indicated by the measurement of intracellular reactive oxygen species (ROS) inside the algal cells. We therefore propose an effective approach to utilization of non-thermal plasma technique that makes good use of the residual inactivation effect to optimize the experimental conditions in terms of discharge time and delay time, so that more efficient treatment of cyanobacterial blooms can be achieved.Water eutrophication has become a serious global problem, which can cause harmful cyanobacterial blooms 1,2 . Among the blooming cyanobacteria, Microcystis aeruginosa produces and releases toxins which pose constant threat to our environment and human health. Therefore, there is an urgent need to develop efficient techniques to control and reduce the adverse impact of blooms. To suppress or remove cyanobacteria blooms, various methods have been adopted such as chemical treatment [3][4][5] , UV radiation 6,7 , ultrasound irradiation 8-10 , electron beam irradiation 11 and non-thermal plasma oxidation technology 2,12-16 . However, the chemical methods such as excessive use of algaecides can lead to secondary pollution, while the physical methods such as UV radiation, sonication and electron-beam irradiation have the limitation for bloom control with high efficiency or on a large scale.As an emerging technology, plasma oxidation technology has received special attention and been applied extensively in wastewater treatment 17 . Being one of advanced oxidation processes (AOPs), it possesses both the physical and chemical processing traits, and exhibits the advantages in simpler equipment, easier operation, higher energy efficiency and environmental compatibility 2,18,19 . Among various plasma techniques, the non-thermal atmospheric dielectric barrier discharge (DBD) may be a most promising one. In fact, non-thermal DBD has been widely applied in inactivation of pathogen 20,21 , chemical synthesis 22 , film deposition 23 , material surface modification 24 and etc. When plasma takes place either over the solution surface or in the solution, a variety of physical and/or chemical processes are initiated. Besides

Plasma‐activated water: Physicochemical properties, microbial inactivation mechanisms, factors influencing antimicrobial effectiveness, and applications in the food industry

“…Zhang et al (2017) compared the effectiveness of four different processes against S. aureus using a DBD plasma source, and 3 log reduction was obtained in an indirect treatment, while the inactivation rate for a direct treatment was 7 log under the same conditions. Pemen et al (2017) observed 0.8 log reduction of Staphylococcus epidermidis with indirect plasma treatment at 90 W after 20 min, whereas 2.4 log reduction was achieved after 3 min direct plasma treatment at lower power of 60 W. The higher inactivation rates obtained with direct treatment were reported to result from the fact that short-living reactive species, such as atomic oxygen or hydroxyl radicals can cause initial damage during the direct discharge period, and the inactivation efficiency can be further enhanced by the long-living reactive species generated in water (Li et al, 2015;Zhang et al, 2017). Another factor correlated with PAW antimicrobial efficiency is the generation mode, that is, whether the plasma plume is above or beneath the water surface.…”

“…Moreover, the SEM images of S. aureus after PAW treatment showed that the level of morphology damage depended on the working gas as well, which was in accordance with the inactivation efficacy. Though it is difficult to conclude which working gas works the best for inactivation effect of PAW, there seems to be an agreement that the addition of a small amount of oxygen to noble gas can improve the antimicrobial efficacy of PAW (Ikawa, Kitano, & Hamaguchi, 2010; Smet et al., 2019), and the usage of air as working gas usually leads to greater inactivation efficacy than noble gases (Li, Zhang, & Huang, 2015), which were the same cases for direct plasma treatment (Galvin et al., 2013; Lee et al., 2012; Surowsky, Fröhling, Gottschalk, Schlüter, & Knorr, 2014). The phenomenon may be mainly due to the higher concentration of ROS formed in plasma in the presence of oxygen, including hydroxyl radicals, singlet oxygen, atomic oxygen, ozone, which have been regarded to make dominating contribution to the antimicrobial property of PAW (Rowan et al., 2007; Vlad & Anghel, 2017; Zhang et al., 2012).…”

“…Pemen et al. (2017) observed 0.8 log reduction of Staphylococcus epidermidis with indirect plasma treatment at 90 W after 20 min, whereas 2.4 log reduction was achieved after 3 min direct plasma treatment at lower power of 60 W. The higher inactivation rates obtained with direct treatment were reported to result from the fact that short‐living reactive species, such as atomic oxygen or hydroxyl radicals can cause initial damage during the direct discharge period, and the inactivation efficiency can be further enhanced by the long‐living reactive species generated in water (Li et al., 2015; Zhang et al., 2017).…”

Potential Applications of Non-thermal Plasma in Animal Husbandry to Improve Infrastructure

“…Microcystins are toxins produced by cyanobacteria, and can cause detrimental effects on farm animal health (53). Moreover, DBD-generate -NTP has been shown to inactivate residues of cyanobacteria which cause algal bloom in water (54). Another study has reported that pulsed plasma gas discharge destroys waterborn enteroparasites which infect both farm animals and humans.…”

A Critical Review on Selected External Physical Cues and Modulation of Cell Behavior: Magnetic Nanoparticles, Non-thermal Plasma and Lasers

“…We observed the specific apoptotic physiological hallmarks, such as phosphatidylserine exposure on the cell membrane and increased expression of proteins with caspase-like substrate specificity [116]. Moreover, another study has shown the NTP- induced PCD in microorganisms [149]. Li et al explained the Microcystis aeruginosa inactivation by intracellular accumulation of plasma- produced ROS leading to apoptosis [149].…”