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1.4 Objective and structure of this thesis The aim of this thesis was to understand, by following a rigorous experimental approach, some of the physical phenomena involved in the disinfection or/and sterilization processes of the bacterial spores with inactivation agents produced within a low pressure RF discharge. Much of the work has been carried out to establish the relative effects of each killing agent generated by plasma [70-75]. From this point of view, the discrimination of the role of different inactivation agentsischallenging,becauseitisdifficult to isolate the effect of one particular agent by suppressing the production of others. Regarding the heat effects on the contaminated samples the conditions to op- erate the discharge were changed. The plasma was pulsed to bring the advantage of a much low heat absorbed by the treated objects. Moreover, how the kinetics of microorganisms inactivation is affected by pulsed plasma operation mode (i.e., pulse characteristics) has not yet been systematically studied. Therefore, the present thesis covers in its second part the aspects of the sterilization with pulsed plasma. It is necessary to mention that, for microbiological testing procedures, Bacillus subtilis spores (Bss) were used. Thethesisisorganizedasitfollows: Chapter 2 contains the description of the experimental RF plasma reactor, including the treatment chamber geometry and the electrical circuitry used to accomplish the experimental investigations. Microbiological procedures are pre- 19
sented by both theoretical and experimental approaches. Electrical and optical plasma diagnostics are described at the end of the chapter. In Chapter 3, the investigation of the competitive effects of plasma killing agents is conducted. The inactivation of a population of Bss is analyzed in a low pressure high density RF inductively coupled oxygen plasma (ICP). The experi- ments were especially designed to allow the discrimination of the influence of each inactivation agents on bacteria samples. The decimal reduction values (D-values), characteristic for the action on the spores of heat, optical radiation and plasma particles, respectively, were estimated for different RF injected powers. Based on the obtained experimental results the injected RF power sensitivity of the spore inactivation kinetics was also established, by determining and using the Z-value corresponding to the employed inactivation method. In Chapter 4, theeffects of pulsed plasma on the Bss inactivation kinetics are evaluated. The inactivation rates were calculated from the bacteria survival curves and their dependencies on the pulse characteristics (i.e., pulse frequency and duty cycle) were compared with those of the plasma parameters. The low temperature treatment of the contaminated samples surfaces is emphasized as a major advantage of pulsed discharges. Chapter 5 summarizes the results obtained in the present thesis and outlines the future research of the author on this topic. The relations existent among different parts of the present research are pre- 20
Page 1 and 2: PLASMA STERILIZATION USING LOW PRES
Page 3 and 4: my appreciation especially for the
Page 5 and 6: Iis ion saturation current [µA] t
Page 7 and 8: CONTENTS 1 PRINCIPLES OF SURFACE DI
Page 9 and 10: 4 EFFECTS OF LOW TEMPERATURE PULSED
Page 11 and 12: and intuited to bring new important
Page 13 and 14: Figure 1.1: Schematic representatio
Page 15 and 16: Table 1.1: Common disinfection and
Page 17 and 18: the radiation energy is resonantly
Page 19 and 20: ers of heat, optical radiation and
Page 21 and 22: Table 1.2: Main plasma sources used
Page 23 and 24: microorganism population as a respo
Page 25 and 26: UV Photon Before After DNA Figure 1
Page 27: to sterilize medical tools, but the
Page 31 and 32: Plasma Sterilization Using Low Pres
Page 33 and 34: Figure 2.1: Experimental set-up. MB
Page 35 and 36: Figure 2.3: Electronic circuit of t
Page 37 and 38: such circumstances, the inactivatio
Page 39 and 40: ment time t is N = N0e −αt ≡ N
Page 41 and 42: shows the number of the viable micr
Page 43 and 44: has n −1 0 > 281.25 µm 2 availab
Page 45 and 46: 1 st 2 nd ( I) TNTC (II) TNTC (III)
Page 47 and 48: U LC blocking filter 19.74 pF 20.24
Page 49 and 50: Figure 2.8: Experimental set-up use
Page 51 and 52: the reactive species from plasma ar
Page 53 and 54: Temperature measurement Relative in
Page 55 and 56: MR MP SH Figure 3.2: Experimental a
Page 57 and 58: a fast temperature increasing rate.
Page 59 and 60: D h (min) 10 3 10 2 10 1 10 0 100 2
Page 61 and 62: MR QP SH Figure 3.6: Experimental a
Page 63 and 64: The contribution of photons and hea
Page 65 and 66: D (min) 10 3 10 2 10 1 10 0 Dν D h
Page 67 and 68: N/N 0 (%) 10 2 10 2 10 2 10 2 10 2
Page 69 and 70: D (min) 10 2 10 1 10 0 D h+ν+p D h
Page 71 and 72: holder is mainly given by particle
Page 73 and 74: 3.5 Power sensitivity of spore inac
Page 75 and 76: If for a reference treatment temper
Page 77 and 78: of the sample was achieved. Moreove
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microorganisms were disposed in mon
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The pulse period covered a wide int
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in chapter 2. The treatment time of
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4.2.2 Injected RF power In order to
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ton =500µs, and the duty cycle was
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T ( 0 C) 120 100 80 60 40 20 I 0 5
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N/N 0 (%) 10 2 10 2 10 2 10 1 10 1
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elow 70 ◦ C. 3. Increasing the in
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the second phase of the inactivatio
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k 1, 2 (min -1 ) 1.2 1.0 0.8 0.6 0.
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I (arb. unit) 140 120 100 80 60 40
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I (arb. unit) 5 4 3 2 1 0 0.000 0.0
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I > (arb.unit) 1.0 0.9 0.8 0.7 0.6
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shown in Fig. 4.14. It can be seen
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I is (mA) 0.25 0.20 0.15 0.10 0.05
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value. When ton has been kept const
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survival curve characteristics were
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of the effects produced by differen
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solutely necessary for a profound u
Page 117 and 118:
Conferences 1. Bacillus spores ster
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[9] W. A. Rutala, D. J. Weber, J. H
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[34] J. H. Young: Sterilization wit
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[57] M. K. Boudam, M. Moisan, B. Sa
Page 125 and 126:
[79] J. Schneider, K. M. Baumgartne
Page 127 and 128:
[100] S. Villeger, S. Cousty, A. Ri
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