Non-thermal Processing with Plasma Technologies Brendan A. Niemira - - PowerPoint PPT Presentation

Non-thermal Processing with Plasma Technologies

Brendan A. Niemira

Food Safety and Intervention Technologies Research Unit U.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

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Non-thermal plasma

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Oxygen Nitrogen Carbon dioxide Injected volatiles Ozone UV light NOx Elemental Oxygen Free radicals 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 ionization

Higher voltage required; equipment = $$$

$ $$$$$ $$$

Lower volatage required; equipment = $ He, Ne, Ar H2 N2, Air

Non-thermal plasma: technologies

• Remote treatment and enclosed

chambers

• Contact with electrodes, corona

discharges

• Direct applications
• In-package treatments

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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 5 10 15 20 25 30 35 Treatment time (second) Survival counts air nitrigen co2 argon

• 4.5
• 4
• 3.5
• 3
• 2.5
• 2
• 1.5
• 1
• 0.5

10 20 30 40 Log(N/No) Time (s)

16 kV 20 kV 25 kV

Direct application of plasma, open air

(Niemira and Sites. 2008. J Food Prot.)

USDA-ARS cold 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

• n 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)

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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

Brendan.Niemira@ars.usda.gov www.tinyurl.com/Niemira

B.A. Niemira

Non-thermal plasma: technologies

• A. 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
• ccur at higher power

settings, can contact target

• approx. ≤ 1 cm; arcing can
• ccur 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