Concerns over chlorine could lead to bullish UV, ozone markets.
By Matthew Barker
From the June 2002 edition of Water Technology magazine. For a free introductory subscription, click here.
The most widely used method of water disinfection for swimming pools, principally thanks to its cost, the ease of use and the huge range of products that are available.
However, many believe it would be desirable if chlorination of water could be phased out because of the known health and environmental risks. Chlorination byproducts have been linked in some studies to cancer risks, and chlorine might be corrosive to some types of swimming pools.
High THM levels
Recently, researchers at Imperial College London said they found levels of trihalomethanes (THMs), a byproduct of chlorine, in
Studies from the
The presence of chloroform and other THMs in water has been blamed by some experts. The
To reduce THM formation, scientists recommended making sure people clean themselves before swimming and filtering the water.
Additional links
September 2001 also saw high levels of THMs linked to lung damage. Children who swim in a chlorinated pool once a week scored the same on one measure of lung damage as adult smokers, announced Belgian researchers.
The team took blood samples to measure levels of three surface proteins that indicate lung damage resulting from exposure to a high level of oxidants. They found the level of the proteins increased with higher exposure to chlorinated water.
This oxidative damage also increases the amount of 'surfactant' proteins, which the team measured after the children had been swimming. The highest levels detected were similar to those seen in adult smokers.
UV makes for a clean, fresh-smelling pool. |
The bottom line is that although chlorine is still an essential step in the pool disinfection process, levels in pools can be decreased significantly.
This can be achieved by using low chlorine doses in conjunction with ultraviolet (UV) or ozone treatment.
Ultraviolet
disinfection in swimming pools is an emerging market.
In the past, it gained a somewhat tarnished reputation, because it was badly maintained and wrongly sized in many installations. However, UV is starting to emerge as a very competent piece of equipment for treating water safely and effectively.
The main reason UV is growing is that when used in conjunction with chlorine in the pool, it can lower the chlorine dose by between 75 and 95 percent.
It also destroys chloramines, which give pool occupants red eyes, and create the familiar smell in the pool atmosphere.
Ozonation
Ozone has been used as a treatment for swimming pool water for over 30 years. It is a very powerful oxidizer of most organic materials, including swimming pool contaminants such as soaps, body oils, perspiration and chloramines.
In the presence of halogens such as chlorine, ozone will also oxidise ammonia, urea and amino acids. Therefore, it is also extremely effective for killing bacteria, viruses, spores and cysts.
Considering its powerful qualities as an oxidizer of a broad range of waterborne contaminants, ozone is more effective than chlorine. It also helps to add great clarity to the water, as it acts as a microflocculent, enhancing the pool filter system.
Frost & Sullivan expects as that the public will push commercially owned pools to invest in systems that ensure that they have the safest pool conditions.
Future years will see continued investment in chlorine dosing equipment, but the increased use of alternative techniques such UV and ozonation will become far more popular to both the domestic and commercial customer.
From the June 2002 edition of Water Technology magazine. For a free introductory subscription, click here.
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New Advances in Ultraviolet Light Disinfection Technology
Waterborne diseases have been of concern to man since the causes were discovered. The Western world has been using a variety of methods to combat this problem. Chlorination has been the standard method of treatment in
During the last decade, however, ultraviolet irradiation has emerged as a leading contender in this field. The following is a brief treaties on the state of the art of ultraviolet fluid treatment equipment. The many advantages of this method of disinfection over standard chemical treatment are outlined, as well as the limiting factors.
The Concept
Scientists have known for almost a century that ultraviolet light of certain wavelengths is an effective germicidal agent. However, production of ultraviolet rays in the proper range was expensive. With the development of the low-intensity, long-life lamps came renewed interest in the use of ultraviolet as a disinfection agent for a variety of liquids, but primarily water. Now, with the recent development of reliable, long-life high intensity lamps, a further dimension has been added to the existing application spectrum.
Over the last thirty years, extensive experimental work has been carried out by numerous researchers in an effort to determine lethal ultravolet dosages for a variety of mico-organisms. Pathogenic microbes were generally the number one target. The data is now available to enable us to design ultraviolet irradiation equipment to meet virtually any disinfection requirement.
The Mechanics of Disinfection
Ultraviolet radiation is actually high energy light composed of photons vibrating to produce a narrow band of wavelengths. These wavelengths in the ultraviolet spectrum are too short for the human eye to resolve and are therefore invisible.
Studies show that the DNA and RNA molecules in the nucleus of micro-organisms absorb this radiation. The organism may not be killed instantly, but it is rendered non-viable. The disruption of the bonds results in a scrambling of the genetic messages, and prevents reproduction. This is termed induced lethality. The amount of ultraviolet energy required to produce this effect is normally referred to as lethal dosage.
The term dosage is used to describe the total amount of energy absorbed by the micro-organism. It is the product of intensity and time. There are some limits to the two factors involved. Neither low intensity for very long periods of time, nor very high intensity for micro-second time spans are useful, even though the product of the two may be greater than the lethal dosage. However, these limitation are, in all cases, outside the design parameteres of practical systems.
It has been found that most pathogens are inactivated by ultraviolet light at 2,537 Angstrom units wavelength at a dosage of about 8,000 microwatt-seconds per square centimeter. Since the dosage is a product of ultraviolet radiation intensity (as given by the lamp) and time (determined by the time the pathogens are exposed to this intensity), it becomes apparent that the capacity of any ultraviolet unit can be calculated. Since dosage is cumulative, the pathogen accumulates the lethal dosage by passing though the various intensity levels given by the lamp. The time to acquire this dosage is controlled by its passage through the intensity levels, and hence the way in which the fluid flows through these regions is of importance. Maximum performance is given by shortest travel time through maximum intensity levels. By optimizing these factors in a design, the manufacturer is able to provide the proper unit for a given application.
There are two distinct types of lamps. Low-intensity lamps are similar to fluorescent lamps in size, shape, and output, and are cheap. They should be used where only low-intensity ultraviolet treatment is required, such as in sterilization of fairly clear water. These low-energy lamps are efficient producers of ultraviolet rays in the germicidal range. About 50% of the input energy is converted to ultraviolet rays having a wavelength of 2,537 Angstrom units. This wavelength is very effective in the destruction of all known micro-organisms. High-intensity lamps are small and compact, and 20 to 30 times more intense than low intensity lamps. They are more expensive, and used where large volumes of dirty fluid are to be treated, such as sterilization of wastewater and sewage effluent, etc. About 25% of their input energy is converted into germicidal ultraviolet rays.
In the disinfection of water and wastewater, etc., a glass tube is normally used to protect the mercury arc lamp. Since normal glass is opaque to ultraviolet, all lamp sleeves are made of fused silica or quartz. These materials readily transmit germicidal ultraviolet rays.
Design Criteria for Ultraviolet Sterilizers
There are many factors that influence the final design of an ultraviolet sterilizer. The special design factors the company has incorporated into its equipment are briefly described below.
It is absolutely necessary to control the flow to provide maximum treatment efficiency in an ultraviolet treatment system. This means, in most cases, the need to eliminate channeling flow in an ultraviolet sterilizer chamber. The lethal dosage is calculated using the actual dwell time of the fluid elements in the chamber, and the ultraviolet light intensity a pathogen is exposed to on its flow through the unit. If water is allowed to pass directly from inlet to outlet, the unit will be performing as its lowest efficiency. Fluid control is best effected at the chamber inlet by using the company's patented fluid flow diffuser plate. This device has been found to provide the correct flow control and give the laminar plug flow required for optimum fluid passage through the chamber.
Quartz sleeves are used in the design to isolate the ultraviolet lamps from the fluid to be treated. These sleeves protect the lamps from direct contamination, and the influences of heat or cold. It is important for the lamps to be able to maintain their optimum operational temperature of about 40 degrees Celcius (104 degrees Fahrenheit). Although ultraviolet sterilizers require a minimum of care, consideration have been given to ease of service. The lamps are readily accessible, and the quartz sleeves do not require any special skills or tools for cleaning or replacement.
The "Fail-Safe" System
Since the effectiveness of an ultraviolet sterilizer is governed by the amount of ultraviolet light that actually penerated the fluid being treated, it is imperative that a monitoring device be included as an integral part of the system. The company's systems provide various forms of ultraviolet sensors and monitoring units. The company's sensing circuit design incorporates a narrow band detector that is sensitive to the germicidal wavelength. The sensor is mounted at the point of lowest ultraviolet radiation intensity - in a single-lamp design, this would be at the wall of the chamber. The sensor measures the intensity of germicidal ultraviolet light that has penetrated the water. When the sensor does not receive the minimum required intensity related to the equipment's design dosage, the monitoring system goes into "Fail-Mode." In potable water units, a solenoid-operated water shut-off valve is de-activated and the water flow is interrupted. Thus, insufficiently treated water cannot pass into the distribution network. The user is thus assured at all times that the water has been disinfected by the sterilizer, as long as the system remains in an operational mode. No user involvement is needed. In wastewater treatment systems, the monitoring system adjusts the lamp intensity upwards to counter the reduced ultraviolet light penetration, but should the lamp limit be reached, warning signals are activated.
In critical applications, where individual lamp functions are of significance, a lamp monitoring system is used to augment the chamber mode indicator. Not only is an LED used to identify each lamp mode, but a set of contacts is also included which are activated whenever a lamp burns out. This feature is used particularly in multi-lamp units where the chamber are remote from the control panel. Audio/visual alarms, shut-off switches, etc., can be operated by the Fail-Mode indicators.
Additional Design Features
Every attempt is made to size a sterilizer to match the flow requirements of the user. If a source has the capacity to exceed the maximum operational capabilities of the sterilizer, a positive flow control is installed. This device prevents excessive fluid flow through the unit.
In most applications, a remote electrical enclosure is desirable. This is to protect delicate electronic circuitry from exposure to aggressive environments. The enclosure can be installed in an engineer's office or some other location that has a reasonably warm and dry atmosphere. The treatment chambers may be in a pump room or other humid location. A flexible waterproof conduit is used to connect the chamber to the electrical enclosure, and separations of up to one hundred feet are possible.
Water Treatment Considerations
One of the most common negative comments expressed about the use of ultraviolet as a disinfection agent for potable water is that it does not provide a residual. Separate studies carried out by the
Sewage and Wastewater Treatment Considerations
It has been accepted for many years that low-intensity ultraviolet lamp technology is not a feasible disinfection method for water and sewage effluent at high flow rates. However, the new high-intensity lamp technology has gained acceptance and has led many water and sewage treatment municipal installations being built in recent times. Several fish hatcheries in the
Capital Costs Considerations
Capital costs of ultraviolet systems have been cited as being excessive, when compared to chlorination. Almost invariably the comparisons used are totally invalid. A chemical feed pump injecting some form of disinfectant into the fluid system cannot be compared to an ultraviolet treatment unit. A true comparison would have to include control and monitoring systems for the chlorine injection, and probably carbon filtration or sulphur dioxide treatment for de-chlorination. When all the factors are taken into consideration, the ultraviolet method is by far the most economical and reliable method of disinfection.
Source: http://www.ultraguard.com/technology/considerations.htmUses and Applications of UV Purifiers | |
Application | Explanation |
Air conditioning and heating | 10,15,16 |
Apple and fruit storage | 5,16 |
Ampoules, bacteriological, biological enzyme laboratories | 8,15,16 |
Bakeries, bread, cakes, pies, candy mfg. | 1,2,8,15,16 |
Barber shops | 16 |
Beverage plants (soft drinks), syrups, chocolate concentrates, flavoring extracts, coffee & tea concentrates, maple sugar & syrup, cider plants | 1,2,3,6,8,15,16 |
Blood banks & donor agencies | 1,8,15,16 |
Bottle water plants | 1,4,8,15,16 |
Breweries | 1,3,8,15,16 |
Butter processing | 1,3,5,8,15,16 |
Canning | 1,3,5,8,15,16 |
Cheese processing & packaging plants | 1,3,5,8,15,16 |
Chicken, turkey and game farms | 13,16 |
Cosmetics | 1,2,3,8,15,16 |
Dairy products, ice cream | 1,2,3,8,15,16 |
Drug & pharmaceutical mfgrs., vitamin products, chemical plants | 1,2,3,8,15,16 |
Eggs, canned, frozen, dried | 1,3,8,15,16 |
Electroplating & mirror plants | 8,9,15,16 |
Electronic Equipment Manufacturing Plants | 8 |
Farms | 1,5,13,14,16 |
Food products, fruit juices, fresh/frozen | 1,2,3,8,15,16 |
Homes | 12,13 |
Hospitals, sanitoria, institutions, nursing & convalescent homes | 1,2,3,8,10,12,13,14,15,16 |
Hotels, motels and camps | 12,13,16 |
Meat packing, fish and other food plants | 1,3,5,11,13,16 |
Mines, lumber camps, oil refineries | 8,10,13,14,15,16 |
Nylon & synthetic fiber manufacturers | 1,6,8 |
Office and factory | 13,16 |
Paper mills | 1,8,10,15,16 |
Packaging | 1,3,5,13,16 |
Photograph film and paper manufacturers | 8,10,15,16 |
Potable water treatment plants | 13,16 |
Rest Rooms | 13,16 |
Restaurants | 12 |
Schools, auditoriums, theaters, public buildings, office buildings, factories | 1,3,11,13,15,16 |
Sewage plants | 3,8,10,13,14,15,16 |
Swimming Pools | 14,16 |
Vegetable washing | 1,5,15,16 |
Wineries | 1,2,6,8,15,16 |
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