- Created on Monday, 02 May 2005 17:04
- Written by Jack J. Reiff, President WET-TECH, The Ozone People
With the crack of lightening and the roar of thunder, Mother Nature goes about her job of cleaning up our environment. Step outside after a thunderstorm and smell the sharp, clean crispness in the air. This is carona discharge of an enormous degree in a natural setting. A walk in the Sun, protected by the ozone layer in our atmosphere using some of the suns light waves (UV) to protect us from other more harmful sun rays is another natural way mother nature works with ozone to benefit all living species on Earth.Several methods can produce ozone. Naturally, the carona discharge and ultra violet (UV) light. The UV process, also natural, is also known as the photo chemical process of generating ozone. Both methods can be reproduced by man.
Another method is with electrolysis or electromechanical oxidation of water -- electrodes in a tank of water and an electric charge to excite the molecules releasing ozone and oxygen at the anode terminal. No feed gas is required. A third process for generating ozone is with a cold plasma system. This system involves a glass tube filled with a mixture of inert gases and a small amount of mercury. An energy tube very similar to a fluorescent light runs through the tube of inert gases and causes the gases to ionize at a low energy level and low temperatures.
There are various adaptations, combinations and arrangements of these generators that can enhance their applications in laundry and wastewater treatment as well as keeping them within an efficient and economical operation. Some of these systems have inherent design and operational restrictions that do not make them the system of choice suitable laundry use and wastewater treatment as the corona discharge and UV method.
All of these systems use a method of aggressive agitation in its simplest term to break up the oxygen molecules (O2) so that these molecules temporarily attach themselves to other oxygen Molecules (O2), becoming (O3) – ozone. One method of aggravation, carona discharge, is more aggressive than the UV light wave of ozone generation. These two systems almost establish the parameters for the present day systems of ozone generation for our industry.
Benefits from using ozone extend to healthcare, water treatment, waste treatment, and laundering. Documented data establishes the benefits of ozone oxidation and sterilization resulting in a quick return on investment (ROI) for ozone equipment.
Some pollutants can only be oxidized by ozone. Cryptosporidium Parvum, a drinking water pollutant is very resistant to most chemical disinfectants but are effectively destroyed by ozone. Some disinfectants act as a barrier to cysts, but do not destroy them where ozone eliminates them.
Flocculation is greatly enhanced; BOD, COD, FOG and other benefits abound with the use of ozone. It is important then, to understand the manufacturing processes of ozone and making the application fit the product.
This two part series on the science and technology of ozone will deal primarily with the manufacture of ozone through the use of the UV light, (photochemical process) and the carona discharge methodology.
UV light (Photo Chemical) process Light comes in various colors based on the specific wavelength that we can see. When atoms are exposed to high energy from any source, they tend to become very excited and give off energy in the form of radiation. The nature of the radiation depends on the source, the excitation energy used and the media through which the radiation is traveling. The wavelength is measured as the distance between the peaks of a wave (angstroms) and the amplitude (Height) of the wave. Light waves are measured with a nanometer and are read in nm units.
The generation of UV radiation is through the use of discharge lamps placed in a glass tube with an inert gas much like the Cold Plasma generators. The construction of the unit and its performance depends on several factors. The type of glass has one such effect on the wave. The glass can restrict the flow and intensity or distort the wave in some other way as it travels through the glass. The inert gases are another factor and are selected for the job at hand as well as the metallic substance, usually mercury, to achieve a specific wave of light.
Visible light is at a wave length of above 400 nm’s. UV radiation, which for practical purposes, can be divided in to four general intensities are below 400 nm’s. The categories of the UV light are UV-A which is between 400 and 315 nm. UV-B is between 315 and 280 nm, UV-C runs between 280 and 200 nm while the vacuum UV is below 200 nm. Vacuum UV is strongly absorbed by air; the UV-C is primarily used to destroy organisms. The level of nm’s in the UV-C range that inactivates organisms is in the range of 253.7. It is interesting to note that the Ozone forming and the Ozone destroying wavelengths of UV light coexist at approximately 254 nanometers It is for this reason that UV generators are also used as Ozone destruct units.
UV generators are rated by their capacity to treat water at specific flow rates. The UV dosage is the major consideration and is the product of the radiation intensity and the exposure time as is expressed in microwatts per square centimeter. It is this dosage that determines the unit’s effectiveness and not the watt input or the radiated output of the UV lamps. The dwell time (exposure time) of the contaminants in the reactor determines the elimination of the organisms and not just the general exposure. The dwell time can be varied based on water flow in volume and or velocity. The organisms to be eliminated must be in the conveying fluid and reside in the radiation zone long enough to absorb a lethal dose of UV light. For this reason most UV Ozone systems must have a treatment chamber so that exposure to the UV is controlled. The UV lights are housed in a sleeve or jacket that is transparent to the UV radiation but acts as protection for the light source as well as an insulator for the light to control the heat buildup.
The life span of the light source (the bulb) varies with age and the film buildup on the shell of the lamp. These two factors impede the proper generation of the UV light and interferes with the extinction of organisms. It is quite possible for a UV sterilizer / ozone generator to lose its intensity when the sleeves that are used for protection get cloudy from the mineral content or particulate matter that is in the water. It is for these reasons that the FDA and other agencies are specifying in line UV intensity meters for output verification. There are various lamp sizes, intensities, internal pressure levels and outputs that can be matched to the design demand of a particular situation. Energy in is energy out so check the design specifications to determine if it fits your needs.
UV light works quite differently than corona discharge generation of Ozone. The method of operation with a UV light is to continuously expose the medium to be processed, whether it be air or water, through the high intensity light contained within the reactor tube. The light permeates through the medium and shines through any organisms that are in the air or water stream. The intense UV rays impact on the sensitive RNA and/or DNA of bacteria preventing the organism from reproducing. Bacteria, having a short life span and relies on rapid reproduction to flourish is essentially prevented from further growth or activity. Unfortunately, since the UV light is only used within the small contact area it does not provide residual disinfection in the water or air. One can see that the use of UV light is an effective tool but one that does not prevent growth of bacteria unless it provides constant exposure. The Ozone that is generated oxidizes the bacteria and particulate soil destroying the bacteria cells preventing reproduction of the bacteria. The Ozone also oxidizes the soil or particulate matter changing or destroying the chemistry of the soiling materials such as organic compounds. It is for these reasons and others that necessary steps be taken to insure the purity of the UV generators so that you insure the desired results.
Some real world uses of UV (Ultraviolet) technology as written about in High Purity Water Preparation by Theodore H. Meltzer and Water Quality Products by Adam Donnellan of Sunlight Systems are well established in UV technology. The use of UV in destroying water Borne diseases is well established. It’s use in the pharmaceutical, food, beverage, cosmetic, healthcare, manufacturing, high tech manufacturing, waste water treatment, cooling towers and laundry processing are also well documented.
Although UV is used to generate ozone it is also used as on off gas control and ozone destruct unit controlling the ozone use to those areas of need. Food and Beverage manufacturers use the Ozone to destroy the organisms that grow around these products. TOC (Total Organic Carbon) reduction is quite popular along with dye stuff removal, chlorine neutralization, the processing of fresh food, drinking water, air conditioning cooling towers, and heat exchangers also benefit from UV light and ozone use. Most of all the laundry and wastewater generated by the laundry through wash processing is altered in so many ways that the benefits to the industry are prominent.
The second part of this series on the Science and Technology of Ozone discusses the Carona Discharge process in Ozone generation and its available in our June 2005 edition,
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