P. Lubicki

Effect of short HV pulses on bacteria and fungi

The survival of three kinds of microorganisms under strong-pulse electric field conditions was investigated with a possible application of the electric pulse method for sterilization of consumable liquids. The results of the investigations of survival ratio of Gram-negative (Escherichia coli, Yersinia enterocolitica) and Gram-positive (Staphylococcus aureus, Listeria monocytogenes) bacteria and yeastlike fungi (Candida albicans) are presented. The HV pulses with peak voltage U=0 to 100 kV and rise time t/sub n/= 0.5 to 1.2 /spl mu/s were applied. The microorganisms were suspended in an NaCl solution with /spl gamma/=6 to 13 mS/cm conductivity and pH=7.2. The experimental setup and the dependency of the microorganism survival ratio on the rise time, peak voltage and on the number of pulses applied, are presented. It has been found that the lethal effect on microorganisms caused by HV pulses depends on the pulse parameters as well as on the kind of microorganism being treated. >

Removal of volatile organic compounds in water using low-energy electron beam

This paper presents the experimental results concerning removal of organic contaminants in water using low energy electron beam radiation. A laboratory scale apparatus for electron beam irradiation of water is described. The absorbed dose of radiation was controlled by water circulation time (1 to 10 min), accelerating voltage (100 to 170 kV), and electron beam current (0.5 to 1.2 mA) for a constant flow rate of 2 kg/min. The volume of the treated water was 1 dm/sup 3/. The electron beam was generated in vacuum (p<10/sup -5/ Pa), and electrons were injected into the water through the electron transparent window made of titanium foil with a thickness of 25 /spl mu/m TCE (trichloroethylene) and chloroform dissolved in deionized water were used in the experiment. The dependency of the relative concentration c=C/C/sub 0/; where C is the weight content of compound after electron irradiation and C/sub 0/ the initial contaminant concentration, on radiation energy density and the absorbed dose are presented. Although the initial contents of the compounds were higher than those occurring in real water sources, it has been found that it is possible to decompose both of the chemicals with high efficiency (total decomposition of TCE, and up to 90% reduction of chloroform) using a relatively low accelerating voltage (<200 kV). The results have indicated that the removal of TCE and chloroform mainly depended on the absorbed dose of electron radiation.

Removal of nitrobenzene and volatile organic compounds using electron radiation

Experimental results concerning removal of nitrobenzene and volatile organic compounds (VOCs), such as toluene, trichloroethylene and benzene with the use of low energy electron beam are presented. Lab scale apparatus for electron beam irradiation of water is briefly described. Total dose of /spl beta/ radiation was controlled by the time of water circulation (1-50 min.), accelerating voltage (V/sub a/=100-125 kV) and electron beam current (0.1-1 mA) for flow rate of 1 kg/min. The electron beam was generated in vacuum (p<10/sup -7/ Torr) produced by a system of diffusion-sorption-rotary pumps. Electrons were injected into the treated water through an electron beam permeable membrane made of boron nitride poly-crystalline ceramics with a thickness of 10 /spl mu/m. A low mass density (/spl sim/2 g/cm/sup 3/) of the ceramic material enables to obtain a high transmission of the electron beam even for a low accelerating voltage. Dependencies of the removed content of contaminants on the total dose of /spl beta/ radiation are presented. Despite using low energy electron beam, the results have indicated a significant removal of nitrobenzene and VOCs treated.

Pulsed corona discharge for advanced oxidation in water purification technology

The possibilities of developing oxidation processes that remove and ultimately destroy hazardous organic volatile chemicals prior to entry into the environment are being considered. Pulsed corona has received significant attention for decomposition of toxic chemicals and disinfecting of microorganisms. Short duration pulses produced by highly non-uniform fields can produce intense corona discharge in water, without actually leading to breakdown of water itself. The purpose of this work is to use such pulsed corona discharge for advanced oxidation in the presence of air bubbles for the removal of organic substances like trichloroethylene (TCE), benzene, and toluene which are common organics arising from industrial wastes.

Inactivation of Yersinia enterocolitica Gram-negative bacteria using high-voltage pulse technique

High voltage pulses of peak voltages U=5-75 kV and rise times t/sub p/=500-1300 ns were applied with repetition frequency f=1 Hz in order to cause the irreversible electroporation of Gram negative bacteria Yersinia enterocolitica (Y. enterocolitica). The bacteria were suspended in NaCl solution of pH=7.2 and conductivity /spl gamma/=0.8-1.3 S/m. The suspension was placed in glass tube immersed in the cylindrical electrode system gap filled with distilled water. Such an electrode system will protect the bacteria suspension from the chemical processes at the electrode-liquid interface due to conduction and prebreakdown phenomena. The current chopping electrode system was connected in parallel to the sample in order to avoid heat generation from direct discharge of the pulse through the suspension. The dependence of the survival ratio s=N/N/sub 0/ (the number of bacteria per cm/sup 3/ after pulse treatment, N, divided by the number of bacteria per cm/sup 3/ before treatment, N/sub 0/) of Y. enterocolitica on peak voltage of the pulse, number of pulses applied and on various rise times of pulses have been measured. The reduction by 6 orders of magnitude of Y. enterocolitica living cells per cm/sup 3/ was achieved. The results show that considerable inactivation of microbes can be achieved by the application of short (t/sub p/<1000 ns) high voltage pulses for bacteria suspension without directly exposing the bacteria suspension to the electrodes. It is therefore possible to use the electrode system proposed as a means for sterilization of liquid foods.

Decomposition of chloroform and trichloroethylene in deionized water with the use of low voltage electron beam

Paper presents the experimental setup and the results of the laboratory scale experiment concerning a water purification by electron beam irradiation. The setup was designed to use the circulation water flow in order to control (by the time of circulation) the absorbed dose of radiation. The electron beam was generated in vacuum p=10/sup -5/ Torr, and accelerated using the voltage within the range of V=100-185 kV. Electrons were injected into the water through titanium foil with thickness d=25 /spl mu/m. The electron beam current was within the range of I=0.5-1.2 mA. Trichloroethylene (TCE) and chloroform water solutions were used in the experiment. Although the initial contents of the compounds were higher than those occurring in real water sources and during drinking water treatment, it has been found that it is possible to decompose both of the chemicals with high efficiency L total decomposition in the case of TCE, and up to 90% of reduction for chloroform- using a relatively low accelerating voltage. The dependencies of the relative contaminant concentration (c=C/C/sub 0/, where C is a weight content of compound after electron irradiation, C/sub 0/ is an initial concentration of a contaminant) on the time of water circulation, and on the absorbed dose are presented. The results have indicated that the relative removal of TCE and chloroform mainly depends on the absorbed dose of electron radiation.

Effect of water conductivity on its pulse electric strength

The dependence of the impulse electrical strength of water on conductivity was investigated in nonuniform electric field-point-plate electrode system. The voltage pulses, with the rise time t/sub r/=1 /spl mu/s, and time to half-decay t/sub 1/2/=30 /spl mu/s, were generated by a Marx bank. Conductivity was varied by the use of different CuSO/sub 4/ concentrations in distilled water. The voltage and current during the electrical breakdown were recorded by using a pulse voltage divider and current shunt. The dynamic resistance calculated from current and voltage waveforms during electrical breakdown, is also presented. On the basis of these waveforms, the dependencies of the time to breakdown and breakdown voltage on the conductivity for two polarizations of the point electrode are plotted. Investigations made by means of static photography were carried out. It was found that the electrical strength of water depends strongly on the polarity of point electrode and the conductivity of the water. The electrical strength of water decreases, and time to breakdown increases, as water conductivity is increased.

Boron nitride electron permeable windows used in electron beam water treatment

The paper presents results of experiment concerning the removal of toluene with the use of low energy electron beam. The use of low accelerating voltages was possible due to an implementation of 10 /spl mu/m thick boron nitride (BN) layer as an electron permeable window. The results concerning the removal of toluene from aqueous solutions by low energy electron beam are presented. A relatively high efficiency of the contamination decomposition (65%) was obtained for low energy electron beam. The ceramic window allows to apply an incident beam power density of about 500 W/cm/sup 2/ and the power losses in the beam are only about 10% for an accelerating voltage being as low as 100 kV. Very low absorption of electrons and outstanding thermal and mechanical properties of BN make it possible to use such windows in electron beam radiation processes in which low accelerating voltages are utilized.

Effect of spontaneous polarization on electron emission from PZT ferroelectric ceramics under high pulsed electric field

The paper describes measurements of electron emission current from PZT ferroelectric materials under external pulsed electric field. The investigations were carried out in a vacuum of 10/sup -1/ Pa. Thyratron based high voltage pulse generator was used to obtain the high voltage pulses. The pulse applied to the ferroelectric cathode had the following parameters: peak voltage of up to 10 kV, rise time of 80 ns, time to half-decay of about 1 /spl mu/s, and pulse repetition rate of up to 200 pps. PZT ceramic pellets were prepared so that the ratio of Zr/Ti was equal to 13/7. The pellets were poled under a dc electric field of up to 7 kV/cm at various temperatures and times, so that the different values of spontaneous polarization, P/sub s/, were obtained. P/sub s/ was estimated on the basis of the E-P hysteresis measurements, which were carried out by means of the Sawyer-Tower bridge. The emitted peak current density was found to be up to 0.8 A/cm/sup 2/, and the total emitted charge per pulse was up to 0.3 /spl mu/C. It has been found that the charge emitted from PZT cathode under high voltage pulsed polarization reversal strongly depends on the P/sub s/. Generally, the higher the polarization P/sub s/ (the higher the saturation of E-P hysteresis), the higher the charge emitted from PZT ferroelectric cathode.

Removal of organic compounds from aqueous solutions by electron radiation technique

The paper describes the experiment concerning low and medium energy electron beam water treatment. The design and construction of the lab scale electron beam water treatment apparatus are described. The irradiator can utilize two types of electron permeable windows, namely 15 /spl mu/m or 25 /spl mu/m titanium foils, and 10 /spl mu/m boron nitride ceramic window. The electron beam is generated in high vacuum (<10/sup -5/ Pa). The closed water circulation system enables adjustment of the dose of electron radiation not only by the beam power and flow rate of water but also by varying treatment time. The dependence of relative concentration on absorbed dose of electron radiation is presented for several contaminants, such as trichloroethylene (TCE), benzene, toluene, chloroform and nitrobenzene. The absorbed dose was calculated on the basis of the measurements of the current transmission and electron energy attenuation while the electron beam passes the permeable window. Effect of electron beam power utilization, accelerating voltage and beam current on the removal rate of the contaminants is presented. The obtained results suggest that the relative content of organic contamination decreases exponentially with an increase in the absorbed dose. It has been found that a substantial removal of the investigated contaminants (80-99%) can be obtained for a relatively low voltage range (100-180 kV).