Inactivation Applications Of Atmospheric Pressure Nonquilibrium Plasmas

Atmospheric pressure non-equilibrium plasmas have been widely studied for bacterial inactivation, environment purification and food safety applications because of the unique strengths of generating abundant chemical agents and of operating at low cost without complicated vacuum chamber system. In the discharge region, the electrons gain energy from the high electric field. During the collisions with the heavy particles, the energetic electrons and the heavy particles lose their energy in a short period, transfer their energy to molecular rotational and vibrational states and result in an increase in the reactive species. In this paper, both AC power supply and nanosecond pulse power supply are employed to generate atmospheric pressure uniform non-equilibrium plasmas on inactivation applications of Candida albicans, Escherichia coli, tussah pebrine and tomato fulvum under several specially designed electrode configurations. The main investigation contents are described as follow:1. AC power supply is employed to generate atmospheric pressure uniform He/O2dielectric barrier discharge in the sealed plastic bag fixed on the surface of discharge quartz plate. The electrode arrangement is consisting of alternant high voltage electrodes and ground electrodes embedded in a specially designed quartz plate. Inactivation application of Candida albicans in the sealed plastic bag is carried out. The inactivation efficiency of Candida albicans is investigated under various He/O2ratios. The results show that at the applied voltage of9kV with a frequency of11kHz, He plasma containing about1%O2is able to entirely kill Candida albicans within a treatment time of5min. Measurements indicate that plasma-induced species such as O radicals and charged species play a major role in the inactivation process.AC power supply is employed to generate atmospheric pressure stable large-area air dielectric barrier discharge between the multiple-groove of the discharge device. The electrode arrangement is consisting of alternant high voltage electrodes and ground electrodes embedded in a multiple-groove quartz plate. Inactivation applications of Escherichia coli and Candida albicans on the surface of chopsticks are carried out. The effect of applied voltages on stable plasma propagation in the multiple-groove is studied by using intensified charge coupled device (ICCD) technology. The results indicate that the formation of the resverse self-built electric field caused by charges accumulation on the deliectric surface may be associated with the forming of the stable air dielectric barrier discharge. Moreover, the stable air multiple-groove discharge plasma is found to be very efficient in the inavtivation of Candida albicans and Escherichia coli on the chopsticks.Nanosecond pulse power supply is employed to generate atmospheric pressure uniform air dielectric barrier discharge on the surface of the micro structure discharge device. The discharge device is composed of well-aligned and microns-thick hollow quartz fibers with alternant high voltage electrodes and ground electrodes embedded in. Inactivation application of Candida albicans is carried out. The effect of discharge processing distance of the uniform air plasma on the inactivation efficiencies is systematically investigated. The results indicate that inactivation efficiencies of Candida albicans as a function of the discharge processing distance obtained at the pulse voltage of over30kV with a repetition frequency of150Hz are divided into three sections, which is corresponding to the density distribution of plasma induced reactive species:In the first section, plasma generated short-lived reactive species, charged species and long-lived reactive species lead to the synergistic effect on killing Candida albicans. In the second section, the density of short-lived reactive species is greatly decreased with the increasing of plasma processing depth. The inactivation process can be dominated by the charged species and long-lived species. In the third section, the density of surface charges is greatly decreased with the increasing of plasma processing depth. The inactivation process can be dominated by the long-lived species.2. AC power supply is employed to generate atmospheric pressure uniform brush-shaped dielectric barrier discharge by using array needle-plate micro structure electrode configuration. Inactivation application of Candida albicans is carried out. The effects of He/02ratios and discharge gaps on the uniformity of the brush-shaped discharge are discussed. Measurements show that at the applied voltage of7kV and frequency of9kHz with discharge gap varied from3-5mm in He condition or at the applied voltage of7kV and frequency of9kHz with He/O2ratio lower than4%under discharge gap of3mm, an uniform brush-shaped dielectric barrier discharge is successfully obtained. For Candida albicans inactivation application, the efficiency can reach as high as99%within a treatment time of180s by using99%He/1%O2brush-shaped discharge plasma.3. AC power supply is employed to generate atmospheric pressure plasma jet for the inactivation applications of tussah pebrine and tomato fulvum disease. The inactivation research of tussah pebrine disease resulting from Nosema bombycis (NB) spores is investigated by using99%He/1%O2plasma jet at the applied voltage of6kV with a frequency of9kHz. Both Giemsa dyeing measurement and tussah breeding experiment show that the atmospheric pressure He/O2plasma jet can effectively kill all the NB spores within an exposure time of5min. The results indicate that plasma-created reactive particles such as O and accompanied charged species play an important role in the inactivation processing. At the same applied voltage and frequency conditions, the99%Ar/1%O2plasma jet is employed for tomato folvum inactivation. Measurements indicate that the electrostatic force from the charge accumulation on the outer surface of the cell membrane cause the rupture of the outer membrane of cells and lead the tomato fulvum to death. Morever, plasma activated water is generated by using99.5%Ar/0.5%O2discharge under water. And it was found to be effective on Candida albicans inactivation.