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Non-thermal Processing withPlasma Technologies
Brendan A. Niemira
Food Safety and Intervention Technologies Research UnitU.S. Department of Agriculture, Agricultural Research Service
Eastern Regional Research Ctr.600 E. Mermaid Ln, Wyndmoor, PA, USA
Cold plasma: this isn’t it
B.A. Niemira.
Non-thermal plasma• What is a plasma?
– Fourth state of matter– Equivalent to a highly energetic form of ionized gas
B.A. Niemira
SOLID
ENERGY
LIQUID
ENERGY
GAS
ENERGY
PLASMA
• Why is it sometimes called “cold” plasma?– For food processing, intended to operate at
conventional room temperatures
Non-thermal plasma• Inputs to the system
– energy (electricity, microwaves, etc.)– carrier gas: air, a pure gas (He, O2, N2, etc.) or a
defined gas mixture• Output
– self-quenching plasma– resolves to UV light and ozone– chemical residues are expected to be minimal to
non-existent• New technology for food processing
– adaptation from existing applications– regulatory status
B.A. Niemira
Non-thermal plasma
B.A. Niemira
OxygenNitrogen Carbon dioxide
Injected volatiles
Ozone
UV light
NOx
ElementalOxygen
Freeradicals
e-
Nanoparticles
Making cold plasma: gas and pressure
pd = pressure*distance between parallel plates
One atm., 760 torr
Making cold plasma: gas and pressure
Cost of feed gas
Ease
of i
oniz
atio
n
Higher voltagerequired;
equipment = $$$
$ $$$$$$$$
Lower volatagerequired;
equipment = $
He, Ne, ArH2N2, Air
Non-thermal plasma: technologies• Remote treatment and enclosed
chambers• Contact with electrodes, corona
discharges• Direct applications• In-package treatments
B.A. Niemira
OAUGDP (Kayes, M.M. et al., 2007. Foodborne Path Dis 4(1). DOI:
10.1089/fpd.2006.62)
Enclosed plasma treatment chambers
Microwave pumped plasma, enclosed chamber (Amidi, M., et al.
2007. Food Science Australia)
Enclosed plasma treatment chambers
Dielectric barrier discharge, applied to E. coli on almonds (Deng, S. R. et al. 2007. J. Food Sci.
72(3):M62-M66.)
Electrode contact plasma treatment
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
0 5 10 15 20 25 30 35
Treatment time (second)
Surv
ival
cou
nts
air nitrigen co2 argon
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
00 10 20 30 40
Lo
g(N
/No
)
Time (s)
16 kV
20 kV
25 kV
Direct application of plasma, open air
(Niemira and Sites. 2008. J Food Prot.)
USDA-ARScold plasma research subjects
Feed gas: 99.5% He, 0.05% O2
Direct application of plasma, carrier gas
Perni, S. et al. 2008.JFP, 71(2):302–308
Honeydew
Mango
In-package treatments: ozone generation
E. coli O157:H7 inactivation on spinach (Klockow, P.A., K. Keener. 2009. LWT)
“Electrodes were placed above and below the bag, oriented on top of each other to allow for maximum ozone production. Electrodes rested on top of each other with the bag in between having an approximate gap distance of 3-3.5 mm [1/8 inch]. The system was then activated
for a 5-min treatment.”
“Treated samples showed varying levels of discoloration”
In-package treatments: ozone generation• PlasmaLabel. (Schwabedissen, A. et al. 2007.
Contrib. Plasma Phys. 47, 551-558 )• Electrically conductive labels on
inside surface– Rigid container, clamshell, bag, etc.
• Cold plasma generated by induction• 4 log cfu reduction of B. subtillis on
agar, 10’ treatment.– Ozone concentration inside the
package to 2000 ppm• Sensory impact?• Optimization
– shape of the applied electrodes– method of application (screen-
printed, applied, bonded, etc)
(+)
(-)
Plasma treatment of liquids• Air plasma microjet in a quasi-steady gas cavity
– reduces pH to 3.0-4.5 after 10’.– NO3- & NO2- increases to 37 mg · L−1 and 21 mg · L−1
after 20’– Suspended Staphylococcus aureus inactivated by pH 4.5.– Mode of action: perhydroxyl radical (HOO•) reaction
with cell membranes (Liu et al, 2010, Plasma Processes and Polymers 7(3-4):231-236)
• Thin film application• Continuously renewed liquid surface• Co-injected spray into plasma discharge
– Can yield H2, H2O2 or NOx, depending on plasma feed gas (Burlica et al., 2010. Ind. Eng. Chem. Res., 49(14):6342–49)
B.A. Niemira
Commercial Equipment
Ingersoll-Rand
PlasmaTreat
Enercon Industries
Non-thermal plasma: conclusions• Many different ways to make plasma• How well it works is determined by:
– Type of plasma– Nature of power delivered– Feed gas composition
• What are you trying to achieve?• What product are you trying to treat?• What kind of packaging are you using?
B.A. Niemira
[email protected]/Niemira
B.A. Niemira
Non-thermal plasma: technologiesA. remote exposure
reactor (Gadri et al., 2000)
B. plasma pencil (Laroussi and Lu, 2005)
C. plasma needle (Sladek and Stoeffels, 2005)
D. gliding arc (Niemira et al., 2005)
E. microwave plasma tube (Lee et al., 2005)
F. dielectric barrier discharge (Deng et al., 2005)
G. resistive barrier discharge (Laroussi et al., 2003)
NTP Technology Class
I. Remote treatment II. Direct treatment III. Electrode contact
Nature of NTP applied Decaying plasma (afterglow) - longer lived chemical species
Active plasma - short and long-lived species
Active plasma - all chemical species, including shortest lived and ion bombardment
NTP density and energy Moderate density - target remote from electrodes. However, a larger volume of NTP can be generated using multiple electrodes
Higher density - target in the direct path of a flow of active NTP
Highest density - target within NTP generation field
Spacing of target from NTP-generating electrode
Approx. 5 - 20 cm; arcing (filamentous discharge) unlikely to contact target at any power setting
approx. 1 - 5 cm; arcing can occur at higher power settings, can contact target
approx. ≤ 1 cm; arcing can occur between electrodes and target at higher power settings
Electrical conduction through target
No Not under normal operation, but possible during arcing
Yes, if target is used as an electrode OR if target between mounted electrodes is electrically conductive
Suitability for irregular surfaces
High - remote nature of NTP generation means maximum flexibility of application of NTP afterglow stream
Moderately high - NTP is conveyed to target in a directional manner, requiring either rotation of target or multiple NTP emitters
Moderately low - close spacing is required to maintain NTP uniformity. However, electrodes can be shaped to fit a defined, consistent surface
Examples of technologies Remote exposure reactor, plasma pencil
Gliding arc; plasma needle; microwave-induced plasma tube
Parallel plate reactor; needle-plate reactor; resistive barrier discharge; dielectric barrier discharge
Non-thermal Processing with�Plasma Technologies Cold plasma: this isn’t itNon-thermal plasmaNon-thermal plasmaNon-thermal plasmaMaking cold plasma: gas and pressureSlide Number 7Non-thermal plasma: technologiesSlide Number 9Slide Number 10Slide Number 11Direct application of plasma, open airUSDA-ARS�cold plasma research subjectsDirect application of plasma, carrier gasIn-package treatments: ozone generationIn-package treatments: ozone generationPlasma treatment of liquidsCommercial EquipmentNon-thermal plasma: [email protected] �www.tinyurl.com/NiemiraNon-thermal plasma: technologiesSlide Number 22