Liquid purification or separation – Processes – Utilizing electrical or wave energy directly applied to...
Reexamination Certificate
2002-07-12
2004-06-15
Lawrence, Frank M. (Department: 1724)
Liquid purification or separation
Processes
Utilizing electrical or wave energy directly applied to...
C210S764000, C422S029000, C205S742000
Reexamination Certificate
active
06749759
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for disinfecting water and other dense fluid media in a dense medium plasma environment.
BACKGROUND OF THE INVENTION
Decontamination and disinfection of potable water, water used in food-processing industries, and water frequently in contact with human beings (e.g. water in swimming pools and spa pools), are major health issues currently under intense scrutiny due to heightened awareness. Disinfection is defined as the killing or inactivation of disease-causing organisms. The levels to which microbial colony forming units are permitted in various waters fit for human contact is carefully regulated. Conventional approaches employed for the inactivation of toxins, such as hydrolysis, electrochemical oxidation, solvated electron technology, plasma arcs, and chemical treatments are complex processes with significant limitations related to the generation of toxic side-products or low efficiencies for large scale applications.
Technologies based on atmospheric pressure plasma environments present an alternative approach to the disinfection of water. However, most of the processes available today were developed for low pressure environments, which are plagued by the need for complex and expensive vacuum systems, batch-type processing, and difficult robotics handling. These characteristics make conventional plasma technologies economically viable only for applications where the economies of scale processing are targeted toward the creation of high value-added items.
Gas phase discharges have been studied extensively for their ability to sterilize microorganism-contaminated solid surfaces. However, technologies for decontaminating fluids, and water in particular, are considerably less developed. The destruction of living cells, such as
Saccharomyces cerevisiae
(yeast cells) and
Bacillus natto
, has been studied in pulsed high voltage cylindrical discharge reactors in various electrode configurations. These studies show that yeast cell populations in deionized water can be destroyed using a wire-cylinder electrode configuration under 20 kV/cm, 140 &mgr;s pulse width, and 250 Hz pulse frequency conditions.
The pulsed high-voltage discharge-mediated formation of chemical species and their effects on microorganisms has also been studied. Using a needle-plate electrode configuration, the formation of .OH and .H free radicals has been monitored by Optical Emission Spectroscopy. The studies indicated that .OH and .H free radicals generated in situ by a discharge were not effective at killing yeast cells, although the H
2
O
2
generated by the discharge added ex situ to a contaminated sample could be used to kill the cells.
Unfortunately, these pulse discharge experiments for decontaminating water employed a high voltage, pulsed discharge which generated filamentary non-stationary discharge channels, resulting in reactions having a very localized character, which tends to limit the effectiveness of the reactions for inactivating microorganisms.
Another approach to the disinfection of microorganism-contaminated water employs antimicrobial nanoparticles. Nanoparticles are important components in the development of catalytic, sensor, aerosol, filter, biomedical, magnetic, dielectric, optical, electronic, structural, ceramic and metallurgical applications. Nanoscale metallic particles exhibit volume and surface effects which are absent in the same material with dimensions in the micron range (i.e., 0.1 micron<particle diameter<1 micron).
The use of colloidal suspensions of silver as antimicrobial agents is well known. Such use is resuming increased importance as antibiotic resistant bacteria become more prolific. Minimizing the silver particle sizes is believed to be important both from the stability of the colloidal suspension and for the efficacy against microbes.
Various processes to produce nanoparticles are known in the prior art. For example, U.S. Pat. No. 5,543,133, issued to Swanson et al., discloses a process of preparing nanoparticulate agents comprising the steps of: (i) preparing a premix of the agent and a surface modifier; and, (ii) subjecting the premix to mechanical means to reduce the particle size of the agent, the mechanical means producing shear, impact, cavitation and attrition.
Likewise, U.S. Pat. No. 5,585,020, issued to Becker et al., teaches a process of producing nanoparticles having a narrow size distribution by exposing microparticles to an energy beam such as a beam of laser light, above the ablation threshold of the microparticles.
Also, U.S. Pat. No. 5,879,750, issued to Higgins et al., teaches a process for producing inorganic nanoparticles by precipitating the inorganic nanoparticles by a precipitating agent for a microemulsion with a continuous and a non-continuous phase and concentrating the precipitated nanoparticles employing an ultrafiltration membrane.
Additionally, U.S. Pat. No. 6,540,495, issued to Markowicz et al., teaches a process for making a powder containing metallic particles comprising the steps of: (i) forming a dispersion of surfactant vesicles in the presence of catalytic metal ions; (ii) adjusting the pH to between 5.0 and 7.0; (iii) mixing the dispersion with a bath containing second metal ions; and; and, (iv) incubating the mixed dispersion at a temperature sufficient to reduce the second metal ions to metal particles having an average diameter between 1 to 100 nm.
CS Pro Systems advertises a high voltage AC processor producing nanoparticles of colloidal silver. The HVAC process is claimed to produce particle sizes between 0.002 to 0.007-9 microns by imposing an AC potential of 10,000 volts across two silver electrodes in a distilled water medium.
The production of large quantities of colloidal silver solutions required for industrial applications, such as water treatment or treatment of biological fluids, are not economical by using the electrolytic approach.
The prior art methods do not provide simple, convenient, low-cost methods for disinfecting water, and other dense media, contaminated with undesirable microorganisms.
SUMMARY OF THE INVENTION
One aspect of the invention provides a method for disinfecting a dense fluid medium, such as water, containing at least one undesirable microorganism. The method uses multiple spark discharges to inactivate the microorganisms in an intensely stirred liquid medium. The method comprises the steps of: providing a reaction vessel for containing a dense fluid medium containing at least one microorganism; charging the dense fluid medium into the reaction vessel; providing a first electrode comprising a first conductive material, the first electrode immersed within the dense fluid medium; providing a second electrode comprising a second conductive material, the second electrode immersed within the dense fluid medium and disposed opposite the first electrode; stirring the dense fluid medium between the first and second electrodes; applying an electric potential between the first electrode and the second electrode to create a discharge zone comprising a plurality of discharges to produce reactive species in the dense fluid medium; and exposing the microorganisms in the dense fluid medium to the reactive species in the dense fluid medium for a time sufficient to at least partially inactivate the microorganisms. The reactive species include electrons, ions, free radicals, and mixtures thereof which are capable of interacting with the microorganism to promote the inactivation of the microorganism. In a preferred embodiment, the first electrode is a rotating electrode and the second electrode is a static electrode. In this embodiment the dense fluid medium is stirred by the rotating motion of the first electrode.
Another aspect of the invention provides a method for disinfecting a dense fluid medium containing at least one microorganism using antimicrobial colloidal nanoparticles generated in a dense medium plasma (DMP) environment through multiple spark discharges in an intensely stirred liquid medium. The steps in this method are substan
Denes Ferencz S.
Lee Wong Amy C.
Manolache Sorin O.
Somers Eileen B.
Foley & Lardner
Lawrence Frank M.
Wisconsin Alumni Research Foundation
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