The group "Allgemeine Elektrotechnik und Plasmatechnik" at the faculty for engineering and information science.

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The role of humidity and UV-C emission in the inactivation of B. subtilis spores during atmospheric-pressure dielectric barrier discharge treatment

Experiments are performed to assess the inactivation of Bacillus subtilis spores using a non-thermal atmospheric-pressure dielectric barrier discharge. The plasma source used in this study is mounted inside a vacuum vessel and operated in controlled gas mixtures. In this context, spore inactivation is measured under varying nitrogen/oxygen and humidity content and compared to spore inactivation using ambient air. Operating the dielectric barrier discharge in a sealed vessel offers the ability to distinguish between possible spore inactivation mechanisms since different process gas mixtures lead to the formation of distinct reactive species. The UV irradiance and the ozone density within the plasma volume are determined applying spectroscopic diagnostics with neither found to fully correlate with spore inactivation. It is found that spore inactivation is most strongly correlated with the humidity content in the feed gas, implying that reactive species formed, either directly or indirectly, from water molecules are strong mediators of spore inactivation.

FieldValue
Publisher
Authors
Release Date
2021-02-03
Resources
Identifier
cd9d302c-3d59-4e1c-b8b9-f56dea614534
Permanent Identifier (URI)
Is supplementing
Plasma Source Application
Plasma Source Specification
Plasma Source Properties
The DBD is driven by damped sine wave pulses with a frequency of around 500 kHz. The pulse repetition frequency can be varied between 100 Hz and 4 kHz and the high voltage amplitude can be set within the range of 0 kVpp to 28 kVpp.
Plasma Source Procedure
The DBD is placed inside a vacuum vessel made of aluminium which is mounted to a miniature flow passage and a vacuum pump (Trivac D16BCS-PFPE, Leybold, Germany) in order to operate the DBD in a defined atmosphere. The total gas flow is adjusted via two mass flow controllers (El-Flow Prestige, Bronkhorst, Germany) and amounts to 2 slm. In this study, different nitrogen/oxygen (purity 5.0, Air Liquide, Germany) gas mixtures, namely N2:O2 99.9%:0.1%, 80%:20%, 50%:50%, 20%:80% and 0.1%:99.9%, are chosen as the process gas. For experiments carried out in synthetic air (N2:O2 79%:21%) in combination with different humidity content, the feed gas is partly passed through a gas washing bottle filled with distilled water.
Plasma Medium Name
Plasma Medium Properties
The DBD is placed inside a vacuum vessel made of aluminium which is mounted to a miniature flow passage and a vacuum pump (Trivac D16BCS-PFPE, Leybold, Germany) in order to operate the DBD in a defined atmosphere. The total gas flow is adjusted via two mass flow controllers (El-Flow Prestige, Bronkhorst, Germany) and amounts to 2 slm. In this study, different nitrogen/oxygen (purity 5.0, Air Liquide, Germany) gas mixtures, namely N2:O2 99.9%:0.1%, 80%:20%, 50%:50%, 20%:80% and 0.1%:99.9%, are chosen as the process gas. For experiments carried out in synthetic air (N2:O2 79%:21%) in combination with different humidity content, the feed gas is partly passed through a gas washing bottle filled with distilled water.
Plasma Medium Procedure
Before gas mixtures were changed, the vessel was completely evacuated, to minimise impurities.
Plasma Target Name
Plasma Target Properties
All inactivation measurements are carried out by placing the spore covered sample on a grounded aluminium plate underneath the driven electrode inside the vacuum vessel.
Plasma Diagnostic Properties
Capacitive voltage divider (P6015A; Tektronix) Current monitor (Model 2877; Pearson Electronics) Digital oscilloscope (LeCroy9459 DUAL 350 MHz; LeCroy) Echelle spectrometer (ESA 4000; LLA Instruments, Germany) Humidity probe (Testo 435, Testo SE & Co KGaA, Germany) Deuterium lamp (L9518, Hamamatsu Photonics K.K, Japan) Broad-band spectrometer (QE65000, Ocean Optics, Germany)
Plasma Diagnostic Name
Language
English (United Kingdom)
License
Public Access Level
Public
Funding Agency
Project
Contact Name
F. Kogelheide
Contact Email

Data and Resources

Project Contact Name: 
P. Awakowicz