Thomas E. Clevenger

A comparison of pulsed and continuous ultraviolet light sources for the decontamination of surfaces

The experimental results on the development of a decontamination process that uses ultraviolet light and chemical photosensitizer for disinfecting surfaces and solutions are reported. Reduction in the microbial viability as a function of applied UV fluence is presented for the inactivation of Bacillus subtilis spores. Results obtained with aqueous solutions and with surfaces indicate that pulsed UV light is more effective than continuous UV light. Nearly three orders of magnitude of enhanced inactivation have been achieved with the photosensitized UV process on surfaces.

Microbial Inactivation in Water Using Pulsed Electric Fields and Magnetic Pulse Compressor Technology

Pulsed electric field (PEF) disinfection is a promising technology for the nonthermal disinfection of water. Magnetic pulse compressors due to their high repetition rates and lifetimes, appear to be a promising alternative to the existing pulse forming circuits used for sterilization applications. The application of these systems for the purification of water has yet to be explored. The use of the short duration electrical pulses from the magnetic pulse compressor for inactivation of spores, bacteria (Escherichia coli) and viruses in drinking water is being investigated at the University of Missouri, Columbia. The test cell designed herein allows flowing tests for pulsewidths of 130-500 ns. The coupling of the magnetic modulator with the test cell and the inactivation protocols that aim at effective inactivation under optimal conditions are discussed. A 4 log reduction was seen for (Escherichia coli) E. coli at field strengths of 110 kV/cm and 70 pps, with a total energy consumption of 40 J/cm3. A comparative study of different parameters, e.g., pulsewidth, electrode gap, frequency, and electric field, which effect the microbial inactivation are also presented

The development of photosensitized pulsed and continuous ultraviolet decontamination techniques for surfaces and solutions

The experimental results of a decontamination process that uses an ultraviolet (UV) light and a chemical photosensitizer for disinfecting surfaces and solutions are reported. Reduction in the microbial viability as a function of applied UV fluence and initial photosensitizer concentration is presented for the inactivation of both the vegetative and spore forms of Bacillus subtilis niger. Encouraging results have been obtained with both aqueous solutions and surfaces; and with both continuous and pulsed UV light sources. Extrapolation of the results and an estimate of the process speed and efficiency permit a comparison with other decontamination methods.

The effect of high-dose-rate X-rays on E. coli 0157:H7 in ground beef

The emergence of pathogens in todays world has increased the need for new, portable, nonthermal sterilization technologies. The University of Missouri, Columbia in cooperation with the Institute of Electrophysics, Ekaterinburg, Russia, have built and tested a new accelerator based on solid-state opening switches for the disinfection of pathogens in food. The accelerator utilizes a new solid-state opening switch to generate 40 ns, 2OO-keV electron beam pulses. These pulses were then converted to Bremsstrahlung X-rays using an integral X-ray converter. The efficacy of treating E. coli 0157:H7. In ground beef was tested by irradiating frozen ground beef with the high-dose-rate 10/sup 7-6/ rads/s X-ray pulses. Comparison studies were also done with a Cobalt-60 source located at the Missouri University Research Reactor. The results of the study are presented in this paper.

The design and comparison of continuous and pulsed ultraviolet reactors for microbial inactivation in water

The following article discusses the design of a pulsed flashlamp reactor system for inactivation of microorganisms in drinking water. The results of a mathematical model for calculation of the flashlamp lifetime are reported, and the final design of the prototype UV reactor is shown. Experimental test results for static and flowing tests are also reported with a discussion of the DNA repair mechanisms that appear to be present when polychromatic light is used for inactivation of E. coli in water.

Decontamination of Soil Contaminated with Aroclor 1260 Using a Solvent Extraction Process and γ-Ray Radiolysis

Abstract Radiolytic dechlorination of halogenated organic compounds in soil has proved to require large γ-ray doses. In collaboration with INEEL, the University of Missouri investigated a new approach for the dechlorination of polychlorinated biphenyls in soil. The chemistry of an existing solvent extraction-floatation process was modified and then used to desorb Aroclor 1260 from a soil matrix. The chemistry of the floatation process was tailored to allow radiolytic dechlorination of the Aroclor 1260 once it was desorbed into the floatant. For the process, Soltrol 130 and an alcohol solution were used as the solvent-extractant. The efficiency of using gamma radiolysis to dechlorinate the Aroclor 1260-floatant solution was investigated using a Co-60 source located at the Universitys Research Reactor. When Aroclor 1260 was desorbed from the soil surface with the floatation process and irradiated, the dose constant (efficiency) was 40 times greater than when soil was irradiated alone.

Application of Pulsed Electric Fields and Magnetic Pulse Compressor Technology for Water Sterilization

The increasing demand for clean drinking water has significantly intensified the need for long lifetime, inexpensive water sterilization systems. The notably high lifetime, compact size, reliability and repetition-rates of magnetic pulse compressors present them as a promising alternative to the existing circuits used for PEF applications. The application of these systems for the purification of water has yet to be explored. The use of the short duration electrical pulses from the magnetic pulse compressor for inactivation of spores, bacteria (Escherichia coli) and viruses in drinking water is being investigated at the University of Missouri-Columbia. Coupled with the demand for clean drinking water, inexpensive water treatment systems based on high rep- rate magnetic pulse compression technology could play a significant role in point of use systems. The test cell designed herein allows static and flowing tests for pulse widths of 100-500 ns. The viability of the selected pathogens after treatment is assayed after a specific number of pulses are applied. The protocols and test data are also presented. The integration and design of a test cell for rapid testing of the microorganisms is also presented along with the circuit topology of the magnetic pulse compressor.

A comparison of pulsed vs. continuous ultraviolet light sources for the de-contamination of surfaces

The experimental results in the development of a decontamination process that uses ultraviolet (UV) light and chemical photosensitizer for disinfecting surfaces and solutions are reported. Reduction in the microbial viability as a function of applied UV fluence is presented for the inactivation of Bacillus subtilis niger spores. Preliminary results obtained with both aqueous solutions and surfaces indicate that pulsed UV light is more effective than continuous UV light. Nearly two logs of enhanced inactivation have been achieved with the photosensitized UV process.

A pulse power flashlamp system for water decontamination

The emerging threat of water borne pathogens has significantly heightened the requirements for point of use and point of distribution water treatment systems. One such system, based on flow through ultraviolet reactors, is viewed by many today as the technology of choice for small-scale water treatment systems. However, existing reactor technology is based on continuous wave ultraviolet lamps that require a warm-up phase and must be kept on continuously in point of use systems: resulting in inefficient power utilization and reduced lamp lifetime. As an adjunct to reactor technology, pulse power based flashlamp systems are being developed as an alternative to the continuous lamp systems. The target pathogens include, but are not limited to, cryptosporium parvum, escherichia coli O157:H7, and viruses. The design parameters required to achieve the 10/sup 8/-10/sup 9/ pulse lifetimes required for commercial point of use systems and small, instant start systems are presented. Parameters including, peak current, explosion limit, conversion efficiency and lifetime considerations for xenon flashlamps are discussed along with the effect of pulsed ultraviolet light on escherichia coli.

A comparison of the destruction of E. Coli O157:H7 in ground beef using pulsed X-rays and gamma rays

In December 1997, the US Food and Drug Administration approved the irradiation of red meat. Depending on the dose applied, exposure of food to ionizing radiation has been found to be effective in destroying pathogenic bacteria, parasites, and some viruses. This paper discusses experiments conducted at the University of Missouri-Columbia, which compare the effectiveness of pulsed X-rays for destruction of E. Coli O157:H7 in frozen ground beef, and the use of gamma rays from a Cobalt-60 radioisotope. Two different sources were used to irradiate the cultures. The source of X-rays, was a novel, compact, desk top, 220 keV, accelerator provided by the Russian Academy of Sciences. A Cobalt-60 source was made available by the University of Missouris Nuclear Research Reactor Facilities. The results of the tests indicate that pulsed X-ray sources have the same effect on E. coli O157:H7 as Cobalt-60 in frozen ground beef. The results of the experiment and the dose required for elimination of E. Coli O157:H7 in frozen ground beef are reported.