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Water Treatment Handbook: A Technical Guide to Water
This book is the international reference work in the field of water treatment. This new version, completely revised and updated, incorporates major technological advances of these last fifteen years: membrane separation, development of fixed and mixed cultures, sludge drying and incineration, and reduced sludge production. Without forgetting automation-related issues, such as control-regulation and maintenance assistance. A total of five chapters are dedicated to treatment channels. The aim was to offer engineers an everyday aid by summarising the basics in water treatment.
The Water Treatment Handbook assembles the sum of Degrémont know-how to date and takes into account changes in new problem areas in water treatment such as conservation of fresh water resources, health safety and waste management.
Ozonia ’Tip of the Month’ Articles
These requirements, in conjunction with improved analytical methods that cast some doubts on the established ways of doing things, are the reasons why food and beverage companies are being forced to find treatment systems to raise their product quality and, at the same time, remain competitive.
One of the many problems in the food-stuffs industry that requires very close attention is disinfection. Here, careful selection is essential because the method chosen can easily affect the product quality and storage life. Chlorine, or its derivatives, is the most commonly used disinfectant. However, with limited effect on bacteria and the increased awareness of chlorinated by-products and associated health risks, a chlorine alternative is widely sought.
Ozone gas is a very strong oxidizing agent, with an extensive track record in municipal drinking and bottled water disinfection all over the world. Given GRAS (Generally Recognized As Safe) status in 1997 as a food disinfectant (by EPRI), the unique disinfection properties of ozone are perfectly suited to applications in the food-stuffs industry.
Ozone is the triatomic form of oxygen that has been generated by recombining highly excited oxygen atoms and molecules with one another. It is a virtually colorless gas with an acrid odor and very strong oxidizing properties.
The ozone molecule is only moderately stable and decays quite rapidly to form diatomic oxygen. This property makes it ideal for use in products for human consumption because it results in a product that is not only better in quality with regard to taste and smell, it is actually healthier for the consumer.
Ozonia, and its wealth of experience, with more municipal drinking water plants high-purity water installations and general industrial clients than any other ozone manufacturer, is an ideal partner to assist clients with ozone application and disinfection problems.
To ensure that operators get the best possible performance and results from their state-of-the-art OZAT ozone generators, Ozonia offers complete systems as well as standardized injection skids perfectly matched with the clients’ requirements.
Micro-organisms proliferating within a potable water distribution system can cause taste and odor problems, trihalomethanes and general poor health effects from water-borne pathogens. To remove these potential health hazards from within the system invariably results in higher-than-anticipated operating costs and customer-related concerns.
- Small and medium sized communities often rely on water wells or surface water sources for potable water needs
- Water treatment and distribution systems are designed to meet specific water quality standards and community requirements
- The water treatment system may be publicly or privately owned and characteristically will have a limited customer base
Consequently, there are normally limited financial resources available and this may restrict the investment required to expand or upgrade the water treatment system to meet the standards now set for potable water.
The encysted bacterium Cryptosporidium is of particular significance in potable water treatment due to its virulent nature and resistance to chemical treatment. Medium-pressure UV irradiation is one proven technique for inactivating this organism.
Ozonia provides a complete range of medium pressure UV for a variety of water and wastewater treatment applications. Primary features and benefits include:
- Ultraviolet (UV) radiation is a simple, convenient, and environmentally acceptable process for treating potable water
- UV units can readily be fitted to new or existing water treatment facilities. Strategic placement of properly designed and sized UV systems can solve and prevent many microbiological problems associated with potable water distribution systems
- The UV process disinfects the source water by non-chemical means and this both minimizes microbiological contamination and enhances the efficiency of the subsequent chlorination system prior to distributing the water to the community
- Medium pressure reactor designs are more compact than low pressure reactors, resulting in considerable space savings
- Medium pressure systems offer high reliability due to minimal internal components and fast lamp replacement reducing system down-time during maintenance
In addition to UV, Ozonia is world’s leading supplier of ozonation equipment to satisfy all your disinfection needs.
Ozone, when properly applied and dissolved at the required residual concentration in water, is a very powerful and effective oxidizing and disinfecting agent. Its properties destroy microbiological organisms and degrade many organic contaminants present in the water.
Ozone is preferred over conventional chemical agents because it is generated on site with limited storage or handling concerns. Additionally, residual dissolved ozone ultimately decomposes into oxygen, making it both process and environmentally friendly.
Ozonation is typically only one step in a chain of treatment processes. As such, it is often removed prior to subsequent unit processes for a variety of reasons.
Unlike bottled water, where a dissolved ozone residual reaching the bottle is desired (or even mandated), production of other beverages may require removal of dissolved ozone to prevent reactions with sweeteners, concentrates or other ingredients.
Similarly, in ultrapure water (UPW) applications, dissolved ozone is removed the majority of the time to prevent contact with ingredients and is periodically allowed to flow through process loops for CIP sanitization.
Municipal water treatment plants use ozone for a variety of reasons, such as, THM precursor control, cryptosporidium and giardia removal, taste, odor and color removal, general disinfection, etc. However, even here the dissolved ozone must be removed prior to the addition of chlorine used for water protection in the distribution system.
Destruction of residual ozone is therefore essential in these and other applications before the ozonated water can be utilized or continue in the treatment process.
The following are some of the ways ozone destruction can be effectively accomplished:
- In purified water systems (UPW for example), strategic placement of properly designed and sized medium pressure ultraviolet (UV) ozone destruction equipment simply and effectively reduces residual ozone to below detectable levels with the additional benefit of TOC destruction. Positioning a UV ozone destruction unit directly before the water treatment components requiring protection from ozone (i.e. DI polishing) maximizes the sanitizing benefits provided by residual ozone up to that point. When loop sanitizing is desired, the UV is simply turned off and any sensitive process step is bypassed for a brief period of time. Medium pressure UV systems in UPW also offer the added benefits of TOC destruction and act as "back-up sanitizers" to ozone.
- In municipal drinking water applications, removal of residual ozone in a contact system can be accomplished with the addition of hydrogen peroxide (H202). Known as ozone quenching, this step is important during plant start-up, performance testing or in general when ozone equipment has to be operated to meet CT criteria and then followed by addition of chlorine or other chemicals.
Other methods used to remove ozone from water include:
- Aeration by cascade, packed column or air diffusion. This method strips off the ozone to the atmosphere, so proper controls and monitoring must be employed for safety and environmental reasons
- Filtering to water through activated carbon adsorbs the dissolved ozone on the carbon and adds the removal benefit of carbon in general. This technique can be employed where water quality is less than ultrapure and the carbon can actually contaminate the water.
Demands of the quality of Ultra Pure Water (UPW) become more stringent as developments across the industrial market require more closely controlled quality procedures. Tighter limits on all aspects of production processes frequently extend to the use of disinfected high purity water.
For numerous applications, this high degree of purity is essential to protect the consumer, prevent product spoilage, to minimize reject levels, or to increase the shelf life of the final product. It is a universal requirement that disinfection be achieved without contamination or modification of the process or product. Continuous, in-line, automatic and fail-safe disinfection techniques with minimal maintenance are essential.
For simple pre-treatment system protection, UV radiation is a viable option. Areas for consideration include the protection of carbon beds, reverse osmosis and ultrafiltration membranes from microbiological fouling.
When a disinfection process, such as ozonation, is not used for loop protection, UV is used to protect against microbial contamination at points-of-use downstream.
Medium pressure UV is an ideal solution to protect mixed-bed polishing resin demineralizers from microbiological contaminants passing into and proliferating within the resin beds. UV is a sure and rapid method of deozonation should electrolytic or corona discharge ozonation be employed for continuous sanitization or a periodic CIP process.
Ultraviolet (UV) radiation is a simple, convenient and environmentally acceptable process that can be readily fitted to new or existing water treatment facilities with a minimum of disturbance of system piping.
- Ozonia UV systems are specifically designed for ultra pure water treatment, utilizing a specially tuned medium pressure UV lamp and a high purity quartz sleeve
- UV disinfects the water by non-chemical means, preventing reactivation in closed water systems.
- Optimal positioning of the UV system depends on the process design.
- The reactor body is manufactured from 316 stainless steel and finished to the highest standards.
- Medium pressure systems offer high reliability due to minimal internal components and fast lamp replacement, reducing system time-down during maintenance.
In recent years there has been an increased focus on food safety and in particular the methods used to reduce and eliminate pathogens from fresh produce. With the rise in consumption of fresh fruits and vegetables, incidents of foodborne illness have also greatly increased in the US, drawing significant attention from researchers and authorities.
Traditional methods revolve around the use of chemicals such as chlorine in the sanitizing of produce, specifically in rinsing and washing. Chlorine is widely used in these processes but it has a limited effect in killing bacteria on fruit and vegetables surfaces. There is also wide concern with regards to the by-products of chlorine and its effects on health and the environment.
Ozone is becoming a popular alternative solution to traditional sanitizing agents and providing additional benefits. Ozone is an oxidizing agent, 1.5 times more powerful than chlorine and effective over a much wider spectrum of microorganisms. Ozone kills viruses and bacteria such as Escherichia coli and Listeria much faster than chlorine and other chemical agents and is free of chemical residues as it decomposes into simple oxygen.
To simplify the integration of ozone into an existing or future process, Ozonia has developed a broad range of pre-engineered and pre-fabricated injection skids to fit nearly every application.
There are many different applications in the food industry for ozone. Here are a few:
Disinfection of Process Water
Raw water can contain traces of pesticides and toxic organic compounds which when combined with chlorine can produce harmful chlorinated compounds. Process water may also become contaminated by bacteria in storage tanks or piping. In both cases, poor water quality may have an effect on the overall quality and safety of the final product. Ozone as been proven to be an effective treatment for these contaminants without the formation of by-products. Ozone has also been shown to be effective against chlorine-resistant microorganisms such as Cryptosporidium and Giardia, which have caused several deaths in recent years.
Produce Washing and Rinsing
Spray and fume washing systems using ozonated water can be used to greatly reduce microbial counts on the surface of the produce. Contamination of produce arises in the field as a result of pesticides as well as during storage, transport and packaging. Ozone is particularly effective against E. Coli, the food pathogen of most concern in the food industry.
Process Water Recycling
It is estimated that more than 50 billion gallons of fresh water are used by the produce industry each year in the US. With the increasing difficulty in sourcing large quantities of water as well as wastewater treatment costs, a need exists to decrease the amount of water used. Ozone is very effective in the treatment of water for recycling as it can be used to remove color, odor, and organic load.
Ozone can be applied at low concentrations in the storage of produce to guard against mold and bacteria. One of the most important effects of ozone in storage is that it can slow the ripening process of produce, and extend the shelf life of many fruits and vegetables. Over the years many experiments have shown an increased shelf life in a wide variety of fruits and vegetables including apples, tomatoes, potatoes, strawberries, pears, oranges, grapes, cranberries and corn.
The fundamental purpose of ultra-pure rinse water used in the manufacture of printed circuits, semiconductors and integrated circuits is for decontamination. As such, the water is required to have very low TOC levels measured in the low ppb range.
Ozonia medium-pressure UV TOC systems provide high UV dose throughout a broad spectrum for efficient TOC reduction to low levels. UV irradiation in the UV-C (200-280nm) and V-UV (<200nm) ranges will effectively oxidize the organic compounds constituting TOC by:
- Direct photolysis process, transforming them into ionic entities that are removable by ion exchange resin,
- OH radicals produced may freely react with organic molecules to partially ionize or fully oxidize them to CO2 and water.
An Ozonia UV TOC system positioned directly before a final mixed-bed resin polisher effectively lowers the organic loading that would otherwise consume ion exchange capacity. The UV barrier reduces regeneration and servicing frequencies while extending final membrane filter efficiencies.
All Ozonia UV reactors are 316L stainless steel with a surface finish designed to suit the application. For TOC reduction, the reactor vessel is mechanically polished, electropolished and passivated. The vessel incorporates an internal baffle plate assembly, creating turbulence for radial mixing, ensuring maximum exposure to the UV irradiation.
Additional benefits of Ozonia medium-pressure UV TOC systems include:
- Much higher output of UV energy using a medium-pressure lamp than from multiple low-pressure lamps
- The wide spectrum medium-pressure lamp provides total wavelength coverage at high energy levels to efficiently dissociate water and the complex organic mixtures that constitute TOC.
- Medium-pressure UV TOC also provides radiation in the germicidal range for disinfection.
- The high lower-wavelength range output of medium-pressure lamps provides powerful TOC destruction by both direct dissociation and by intermediary hydroxyl radical generation and subsequent reactions.
- Medium-pressure reactor designs are more compact than low-pressure reactors, resulting in considerable space savings.
- Medium-pressure systems offer high reliability due to minimal internal components and fast lamp replacement, reducing system down-time during maintenance.
Ozone’s growth in domestic drinking water treatment has been dramatic in Europe since the early 1900s and in North America for the past three decades. The many advantages of ozone as a multi-platform treatment technology are well documented, but an often overlooked aspect is ozonation as a cost saving method versus other technologies. Here are some examples:
Ozone as a flocculating agent results in rapid and enhanced microflocculation of raw waters. The net result can be an increase in plant filtration rates, decrease in size of filtration beds and lower chemical costs.
As a pure disinfectant, the higher oxidation potential of ozone versus chlorine results in reduced contact time, which can mean smaller contact chambers (footprint). In fully developed areas, where the cost of land is at a premium, the reduced space requirement is a tremendous savings.
Some pollutants can only be oxidized by ozone. Cryptosporidium parvum, for example, are very resistant to most chemical disinfectants but are economically and effectively destroyed by ozonation. Most other applicable methods act only as barriers to cysts but do not actually destroy them.
Ozone not only has a positive effect on COD removal by breaking down refractory compounds and making them biodegradable but also prolongs the service life of GAC. This feature alone makes ozone economically feasible when GAC is needed. Ozone can totally replace chlorine, chloramines or chlorine dioxide in the preoxidation and main oxidation stages. Although some form of chlorine residual is nearly always required in the distribution networks, ozone can drastically reduce its use, enhance the quality of the water and still be more economical than other oxidants.
With recent advancements in ozone generation technology, the cost of ozone from both capital and operating investment is less than half of what it was only seven years ago. As the cost of ownership goes down and application methods are optimized, ozone will continue to be at the forefront of desirable and economical drinking water treatment technologies. These savings have been demonstrated in many cities around the world, including Los Angeles, Orlando, Mexico City, Barcelona, Singapore, Paris, Shanghai and Zurich.
Modern high purity water networks are mostly constructed as closed loop systems in which the water is pumped through one or more circulation loops to different use points
Water not used is returned to a storage tank located in the system before the distribution pump.
Make-up water from ion-exchangers, reverse osmosis units, etc., is fed directly into the system and is controlled by the level in the storage tank. This arrangement allows the water system to meet peak water requirements from the storage tank and, at the same time, minimize the production capacity and size of expensive pretreatment equipment.
Such networks are susceptible to bacteria growth, especially when production is at a standstill and there is no exchange of water in the system. Measures must be taken to prevent contamination. With this in mind, the proliferation of bacteria colonies can be easily avoided by continually dosing the system with ozone from an electrolytic ozone generator.
Ideally, the electrolytic ozone generator should be connected to the loop system on the return line near the storage tank.
Installation is very simple. A low flow sidestream taken from the return line feeds the electrolytic ozone generator. This water is ozonated via a hydrogen-oxygen dissociation process and then is discharged as pure, ozonated water to the main return line where it is mixed with the bulk of the return line water.
In order to attain maximum exposure, with some pipe diameters it is recommended to install a static mixer or some other means of causing flow turbulence to ensure that the two water streams are thoroughly mixed.
The use of UV technology for water and wastewater disinfection is a well-recognized and accepted technology. Medium pressure UV is a likely choice wherever chemical disinfection would be problematic or prohibited.
Typical UV dose levels range from 30 mJ/cm2 for basic disinfection, to over 100 mJ/cm2 for wastewater reuse such as irrigation. Due to the sensitive nature of the application, equipment and process reliability are of utmost importance.
The term medium pressure UV refers to the mercury vapor pressure inside the UV lamp when operating. UV energy from a medium pressure UV lamp is emitted over all wavelengths from 175 to 300 nm, depending on system design.
The broad energy spectrum allows medium pressure UV systems to efficiently disinfect wastewater and reduce residual organics (TOC), with significantly fewer lamps than conventional low pressure or low pressure/high output UV systems.
The advantages of Ozonia’s medium pressure mercury vapor UV lamp systems include:
- Higher energy density
- Stronger output below 300 nm
- Higher UVC (200-280 nm) efficiency - greater than 18 percent
- Variable lamp power available for those applications where the power needs to be adjusted
- Longer guaranteed lamp life using fewer lamps
- Ability to treat higher flowrates using a small footprint
- Highly efficient for disinfection, ozone destruction, TOC reduction, catalytic oxidation, etc.
Ozonia’s closed-chamber design is ideally suited for both low head and high-pressure effluents, such as from a pressure filter. Available in a variety of configurations, the most popular systems use single or multiple 3.0 or 6.0 kW lamps.
Ozonia UV systems are available in a variety of configurations from basic keypad interface with programmable relay for simple on/off operation, to sophisticated Allen-Bradley® PLC’s with a touch-screen operator interface for numerous logic and control functions such as variable output, data logging and SCADA communication capability.
Ozonia’s closed-chamber design is ideally suited for both low head and high-pressure effluents, such as from a pressure filter. Available in a variety of configurations, the most popular systems use single or multiple 3.0 or 6.0 kW lamps.
All Ozonia UV reactors are made of 316L stainless steel construction throughout with a variety of surface finishes, inlet/outlet connections and pressure ratings, consistent with the application.
In the last several years there has been an increasing demand for drinking water in bottles, cans, etc., around the world. This demand and market growth has drawn manufacturers’ attention to the necessity for specialized filling techniques where product safety and integrity is of utmost importance.
Ozonation of bottling water guarantees a very high product quality resulting in a long shelf life. Experience has indicated that a small dose of ozone, in the region of 0.3 mg/l to 0.5 mg/l, is sufficient to sanitize the product and the product packaging. After filling, the bottles are placed on stock for a few days to allow the ozone to decompose back oxygen and well below the detectable limit. After this period, the ozone will have oxidized the organic substances in the water and any microbial activity will have been reduced to a minimum.
The most effective method of ozonating product water is by the pressurized mass-transfer method. Basically, this is when ozone is applied to a medium under the prevailing system pressure. Not only does this method conserve energy, because the water does not have to be re-pumped to the bottle filler, but ozonation under pressure results in a higher transfer rate.
To meet the demands of the bottled water industry, Ozonia has developed a line of completely integrated ozonation systems called OZFIL® specifically for the bottled and drinking water markets. Basic packages include feed gas preparation, ozone generation and contacting, precise ozone monitoring and control, all prepackaged on a stainless steel skid.
In most cases, a filling station is made up from a mixer and a filling machine. The integration of an OZFIL™ package requires very little installation work on site and virtually no major changes to the existing equipment on site.
When in operation the four main criteria needed to assure product quality are met:
- Ozone is produced to treat the rated flow rate of the filling machine (up to 300 gpm)
- After ozonation the product is exposed to the ozone for at least 4 minutes in the integrated stainless steel contact chamber
- The target dissolved ozone level in the product is established (typically 0.4 mg/l). This value is measured and used to regulate the actual ozone production rate.
- The level of ozone in a freshly filled bottle can be adjusted between 0.2 mg/l to 0.5 mg/l.
Secondary and tertiary effluent from water treatment plants, although relatively low in BOD and suspended solids in efficiently operated installations, contains a number of pathogenic micro-organisms that can cause serious diseases in people and animals.
Disease can be transmitted orally by ingestion of infected water or by consumption of contaminated shellfish, or merely as a result of contact with the skin when swimming in contaminated water.
The risk of disease is increased by the discharge of infected water close to swimming areas, drinking water intakes, and shellfish-farming locations or when used for agricultural purposes in the interests of water conservation.
The incorporation of a medium-pressure, broad-spectrum germicidal irradiation system after final filtration of treated waste water can provide an economical means of disinfection to meet the microbial standards required for safe discharge or re-use without the use of additional chemicals, which could add to the contamination load.
Design of the UV system must consider the minimum UV transmission value of the effluent and the peak flow.
Industrial wastewater treatment plants may incorporate a medium-pressure UV system in conjunction with ozone. This advanced oxidation process offers a powerful water treatment combination both for disinfection and for reduction of difficult organic compounds.
Consider the following additional advantages of medium-pressure systems:
- Compared with conventional low-pressure mercury lamp systems, the use of high intensity, medium-pressure models results in a dramatic reduction of number of lamps, space requirement, maintenance time, and installation and lamp replacement costs.
- UV radiation of broad germicidal action applied at the correct dose rate destroys the ability of pathogens to metabolize and reproduce and is successful against viruses and bacteria.
- Medium-pressure UV systems with high energy output per unit size are particularly applicable in this respect, being specifically designed for this purpose. Some units incorporate an automatic wiper with interval control to suit effluent quality.
- UV irradiation treatment eliminates the need for chemical handling and storage on site, or systems for dosing chemicals into the treatment stream.
- There are cost savings for smaller waste water treatment installations when compared with open channel technology.
A GAC (granular activated carbon) filter after an intermediate ozonation has many purposes:
- To remove chemical compounds or ozonation by products by adsorption.
- To degrade such substances by biological activity on the surface of the GAC by bacteria.
- To destroy the residual ozone in the water fed to the GAC filter – this takes place in the top few centimeters of the GAC bed
In a GAC filter different competitive processes take place simultaneously:
- fast adsorption;
- slow adsorption;
- biological effects; and
- biological effects enhanced by ozonation.
Between the fast and the slow adsorption there is competition. New GAC will first adsorb a lot of weakly adsorbed compounds, e.g. alcohols, ketones, aldehydes, acids, aliphatics and colloids. These compounds will then be displaced from the active carbon surface by more strongly adsorbed pollutants, e.g. aromatics, chlorinated, non-aromatics and high molecular weight hydrocarbons.
The displaced, weakly adsorbed material will be readsorbed further down in the filter. This phenomenon is called the “chromatographic effect.”
A look at adsorption
Three types of adsorption can be distinguished for a GAC filter:
- Exchange adsorption (electrical attraction of the solute by the adsorbent).
- Physical or ideal adsorption by weak van der Waals forces.
- Chemisorption or chemical adsorption (chemical reaction of the adsorbate with the carbon).
In water treatment application is the primary mechanism is the physical adsorption, which is reversible followed by the chemisorption, which is generally considered as irreversible.
A GAC filter offers an excellent surface for biological activity. The rough surface provides numerous good places for attachment. Such biological activity has become evident in full-scale plants, showing that the amount of organic carbon removed is far beyond that, which can be removed by adsorption alone.
Removing bacterial nutrients
It is well established that an ozone step will produce aldehydes and ketones by oxidation of the carbon double bonds. These products are nutrients for the bacteria, which are always present in a distribution system, If these nutrients are not removed during the treatment process, they will promote rapid and dramatic growth in the distribution system. This situation has to be avoided and is done by the introduction of an appropriate biological treatment step, e.g. GAC filter or slow sand filter. If such biological filters are present after the main ozonation, the organic compounds will be biodegraded on the surface of the filter media.
An additional measure to avoid a bacterial regrowth problem in the distribution network is the dosing of a disinfection agent at the end of the treatment plant, e.g. chlorine dioxide or chloramines.
With a new GAC filter, rapid adsorption is dominant and nearly all-organic material can be adsorbed. According to the adsorption capacity of the filter and with increasing running time, the rapid adsorption will decrease in favor of a slow adsorption. At the same time a biological activity is started and will additionally reduce the organic matter.
It is important to note that an additional role of ozone in this process is the dramatic extension of the life of the GAC filter. By creating a more biologically active bed, the subsequent life is extended many times over.
If a pre and/or main ozonation is introduced before GAC filtration, a further enhancement of the biological activity takes place. A further reduction of the oxidizable carbon will be achieved while a part of the byproducts will be absorbed on the GAC and/or consumed by bacteria.
Such a combination dramatically improves the final water quality.
Even though the bacteria counts in a well-designed water treatment plant may be very low, in most cases, disinfection of closed systems is still necessary. This is especially the true when a system is not continually replenished with fresh make-up water, such as overnight or weekends, when the water is stagnant in a tank or circulates in a system. At those times during periods of low or no flow, disinfection is essential to avoid the proliferation of bacteria colonies.
There are several processes that can be used for the disinfection of pure water systems, however, each of these have distinct limitations or disadvantages when compared to ozonation with an electrolytic process:
Shock disinfeciton with chemicals
- Interruption of operation
- Work intensive
- Waste chemical problems
- Water quality fluctuations
- Chemical traces
Shock sterilization with steam
- Interruption of operation
- Costly installation
- Uncontaminated steam required
- Water quality fluctuations
- Disinfection not always 100 percent
- Only localized effect
- Sterile filter required
- Sterilization and replacement required
- Danger of bursting
Ozone itself is a virtually colorless gas with an acrid odor. It is one of the strongest known oxidants with an electrochemical oxidation potential of 2.08 V. The ozone molecule is only moderately stable and has a half life time of some 20 minutes in pure water at service conditions.
In the absence of oxidiziale substances ozone decomposes to form oxygen - in the presence of oxidizable substances traces of CO2 will also form.
Used for a broad range of applications the advantages of ozone are numerous, however, the most important of these are:
- There are no objectionable by-products or residues when water is disinfected with ozone.
- No chemical traces.
- The transport and storage of potentially dangerous chemicals is not necessary because ozone is produced on site where and when it is necessary.
- The ozone production rate can be controlled by the process parameters, i.e. the required amounts of ozone are generated in order to avoid under or over dosing.
- Experience, gained over many years, shows that an average ozone concentration of ca 0.1 to 0.2 mg/l. is sufficient to keep the germ count in pure water systems below 1 per 100ml.
Interest in health and exercise activities has led to an increase in the number of health and leisure facilities operating worldwide. One popular aspect of these facilities is the health spa or hydrotherapy pool. These facilities by their nature experience much heavier bather loading than larger pools, which in turn results in an increase in the microbiological and chemical hazards associated with the running of a safe and pleasant spa facility.
Due to the small volume of water in spa systems and the increased temperature of the spa water, spas are highly susceptible to proliferation of bacteria. Adenoviruses, Shigella, Escherichia coli 0157, Giardia lambia and Cryptosporidium parvum are all common enteric organisms from fecal matter that must be controlled in spa environments.
The most common disinfectant used is chlorine. This readily reacts with urea and other organic molecules deposited in the spa water by bathers to form disinfection by-products (DPB’s), which can represent a health risk by ingestion, inhalation or adsorption via skin contact.
Of the most common species of bacteria found in spas, many show resistance to chlorine-based disinfectants when dosed at practical levels. Most commonly used chlorine-based systems are difficult to operate in a manner that is reliable and efficient. Instances of detrimental effects on bather health would be catastrophic for the operation of a commercial spa facility.
One novel and extremely effective type of treatment easily adapted to commercial spas is an advanced oxidation process, combining ozonation followed by UV irradiation resulting in the formation of hydroxyl radicals, which have a powerful oxidation potential. The production of hydroxyl radicals results in the oxidation of combined chlorine species within the spa water, producing carbon dioxide and water as harmless by-products.
A system manufactured by Ozonia Triogen Ltd., which incorporates both technologies was installed at a test facility in March of 2002.
During the first 24 days there were only five backwashes. In comparison to spa operation prior to the test, the combined chlorine level was on average 72.3 percent less, the water was of higher quality and after 24 days of operation approximately 30.0 m3 of water had been used. Over a four-week period an approximate 79.5 percent saving in water will have been achieved.
In addition to the savings in water usage, the reduction in the organic species loading in the water due to the oxidation action of the combined process (SPAZONE 75) reduced the overall chemical required to maintain the free chlorine residual by over 25 percent.
Over the last decade there has been an increased demand for water in bottles, cans, etc. This demand, or trend, has drawn manufacturers’ attention to the need for specialized filling techniques, proper sanitation practices and water disinfection or sterilization, typically by ozonation and occasionally with ultraviolet (UV) light. For maximum flexibility and ease of implementation, complete skid mounted ozone systems for large or small bottling plants are readily available.
Beverage filling plants can be complex, often made up of a variety of unit processes including, but not limited to, influent treatment, product water make-up, syrup/concentrate addition, carbonization, bottle washing, bottle filling, PET blow molding, crating, storage, distribution and more.
Because of the relatively large investment involved, operators are compelled to arrange their facilities so they can fill as many different beverage products as possible. Operators must make the most of the bottling equipment, as well as comply with stringent regulations.
Cleanliness is an important factor to enhance product quality. Most bottling companies rely on the use of ozone to meet the ever-increasing legislative and consumer demands.
There are three reasons to use ozone when bottling drinking water:
- Ozonation of the wash water used to clean the bottles prior to filling;
- Ozonation of the actual bottling water;
- Ozone for Clean In Place (CIP) system sanitation
It is obvious that the purpose of washing is to clean the bottles before filling. There are two basic types of bottles used extensively today:
- PET type bottles, which are freshly blown immediately prior to filling. Although these bottles are new, operators must subject the bottles to washing in order to remove any possible mechanical debris.
- Reusable glass bottles, which need to be intensively cleaned so that all debris and any possible residues from the filling are completely removed.
Typically, the washing process for these bottles involves the insertion of a nozzle into the inverted bottle through which a high pressure jet of water thoroughly cleans the inside surface of the bottle of all mechanical debris, deposits, etc. In addition to the mechanical cleaning, filling companies require that this cleaning also disinfects the bottles in order to avoid microbial contamination after the filling and capping of the product.
As with all ozone applications, special measures must be taken to prevent unacceptable levels of ozone build-up in the ambient surroundings.
Experience has indicated that a small dose of ozone from a high concentration ozone generator in the region of 0.3 mg/l to 0.5 mg/l is sufficient to sanitize the product and the product packaging. After filling the ozonated product, the crated or palleted bottles are placed on stock for several days to allow the ozone to decompose.
After this period, the ozone will have oxidized the organic substances in the product water; the microbial activity will have been reduced to a minimum (or even) sterility; and the remaining unreacted ozone will have decayed to form diatomic oxygen.
There are several ways to introduce the ozone to the water, each of which has its own merits depending on the type of filling plant.
This method has shown excellent results and is particularly suited to smaller applications with fewer plant components. Attention must be given to the fact that the ozone mass transfer takes place in a virtually pressureless chamber that allows inexpensive porous diffusers to be used.
However, it does mean that any pressure in the system before the contacting volume will be reduced and that a contact chamber (approximately 6m high) must be incorporated into the design, followed by pumping to the bottle filler.
A second alternative is ozone injection with a venturi eductor. This system requires a motive water pump, venturi gas injector (eductor) and automatic degassing valve on the contact chamber.
An advantage of this system is the fact that the high contact chamber mentioned in the previous example can be replaced by a unit only 2m to 3m high, which is of particular interest where height is limited.
Complete skid mounted ozone systems including the venturi/pump apparatus for large or small bottling plants are readily available.
Regardless of the method of ozone addition selected, the final bottled product will be dramatically improved with consumer safety and confidence increased.
Triogen Leisure Market UV and Ozone Disinfection Q&A Papers
Have questions about UV and ozone disinfection for pools and spas? Download the PDFs below to see the answers to some common questions about alternative sanitation for pools and spas.