By Ed Knueve, CWS-VI, and Ted Rich
Summary: Since ozone was first used for treating municipal drinking in Europe over a century ago, information about the technology has emphasized its commercial applicability. This article suggests ozone can be very versatile in residential applications and outlines more common uses in water treatment as well as lesser-known air purification systems.
The benefits of using ozone in a water treatment system can be maximized by learning as much as possible about the water being treated and knowing the properties and capabilities of ozone. Water treatment professionals should understand what ozone does—and doesn’t do—so it can be applied properly and efficiently with satisfying results.
Ozone is one of the more traditional pre-filtration water treatment oxidizers, which also include chlorine, oxygen, potassium permanganate and peroxide. Generally, the use of ozone can be considered for problem water applications where multiple treatment challenges exist, equipment such as water softeners are doing double duty as iron filters, or existing chlorination systems aren’t meeting expectations in terms of overall water quality.
Ozone effectively oxidizes a variety of waterborne contaminants without leaving an undesirable residual, adding to total dissolved solids (TDS) levels or causing radical shifts in pH. Ozone is used to achieve a number of water treatment goals including disinfection, oxidation of inorganic contaminants like iron and manganese, and oxidation of organic micropollutants.
Ozone may also be effective as a pretreatment to improve the performance of subsequent water treatment processes. For example, ozone’s ability to coagulate particulate matter has been used successfully in modern water treatment plants. The introduction of ozone can have a wide range of secondary effects on coagulation, including improved total organic carbon (TOC) and turbidity removal during subsequent treatment and a decrease in required dosages of the traditional coagulant (see EXTRA).
What it doesn’t do
Ozone isn’t effective in removing such constituents as calcium, magnesium, potassium, sulfates and nitrates. These are better handled by brine regeneration systems such as cation or anion resins in ion exchange. Small amounts of sodium, arsenic and chlorides are also treated more effectively by reverse osmosis (RO) or distillation.
A typical problem water system—Depending on treatment goals and the type and amount of contaminants to be treated, a typical residential problem water system using ozone will also include a booster pump, contact tank, filter, water softener and an undercounter RO system.
In a typical home system, the water flows from the well through the pressure tank and to the ozone system. A time delay may be included, allowing the ozone generator and circulation pump to run for a specified amount of time after the well pump shuts off so ozone-treated water is always available when the well pump re-starts.
From the ozone system, the water flows through a filter; filter size and configuration are dependent upon water chemistry and flow rate requirements. The water then passes through a water softener and on to the house service lines. Finally, an undercounter RO unit may be installed for all drinking water needs.
Swimming pools & spas
Concerns about both personal health and the environment have prompted a demand for alternatives to the more traditional halogen compounds used for pool and spa water sanitation. Ozone is effective in oxidizing many swimming pool contaminants including bacteria, viruses, soaps, body oils, perspiration and chloramines. Also, in the presence of halogen-type oxidizers like chlorine or bromine, ozone can oxidize ammonia, urea and amino acids (however slowly). Since it also acts as a microflocculant, ozone can actually enhance the performance of the spa or pool filter system, improving the aesthetic quality of the water.
A typical aquatic ozone system—Proper installation is critical to maximizing the benefits of ozone in a swimming pool application. A basic ozone system will include the ozone generator, air preparation, booster pump and ozone injector. A more sophisticated system may also employ an automated chemical controller (to monitor and control pH and ORP, or oxidation-reduction potential), a contact vessel, and an interface device to control the ozone generator. It’s especially important to locate the point of ozone injection downstream of the filter and upstream of the point at which the residual sanitizer enters the return water. This helps minimize the load on the ozone and allows the ozone to do its oxidation work without “fighting” the residual sanitizer.
Since ozone is corrosive to some metals (including copper and iron), careful consideration must be given to the type of plumbing materials used—particularly in retrofit situations on older pools. Also, if the ozone injection point is upstream of the pool’s heater, it should be plumbed into a sidestream that bypasses the heater. Injecting ozone into the coolest possible water enhances its solubility, but sending ozonated water straight into a heater will wreak havoc on internal components.
A properly sized and installed injector is also critical to ozone system performance. For safety and efficiency reasons, most ozone systems work under a vacuum. Using the suction created by a pressure differential across the injector’s venturi, ozone is drawn into the water rather than pushed into it.
Because ozone is a very unstable gas, its half-life is comparatively short. Therefore, the use of a more stable residual sanitizer is recommended for complete swimmer protection; however, the required amount of residual sanitizer required is significantly reduced when ozone is employed as the primary oxidizer.
Other domestic ozone uses
There are a number of other interesting uses for ozone in residential water treatment applications, but most have yet to be commonly accepted. For example, ozone can be used to treat home grey water—wastewater other than sewage such as sink, shower, laundry or dishwasher discharge—that may in turn be used to water lawns, gardens, etc. Such systems may gain popularity as ozone generators become more efficient and less expensive while the cost of potable water (for those tied to municipal water sources) continues to rise. Also, as laws governing wastewater discharge become more stringent, discharge problems play to one of ozone’s greatest strengths—handling organic problems such as biochemical oxygen demand (BOD) reduction and the oxidation of certain pesticides with a minimum of filtration equipment and without adversely affecting water chemistry.
While ozone has shown potential for use in commercial laundries, it hasn’t caught on for home washing machines. The main advantage ozone has demonstrated in commercial applications is in water savings. Fewer rinses are required and during the rinse process, ozone oxidizes bacteria, residual soaps and other contaminants, leaving cleaner fabrics and discharge water.
In the kitchen, ozone can be used to wash fruits and vegetables, sanitize water, clean surfaces, etc. Again, commercial operations are using ozone for produce washing, hard surface cleaning and clean-in-place (CIP) systems as well as water vending machines, water bottling facilities, etc. For home use, appliances are available that allow the user to simply bubble ozone into a kitchen sink for vegetable washing or into a pitcher of water for sanitation. Some home water coolers with built-in ozone systems are also available.
Despite some warnings about exposure to high levels of ozone, the number of air treatment devices using ozone technology has increased significantly in recent years. It’s important to know what the device is capable of delivering in terms of ozone concentration (measured in parts per million or ppm) into the air. Generally, any level below 0.1 ppm is considered non-symptomatic, but higher concentrations can be tolerated. For example, exposure levels up to 1.0 ppm can be non-symptomatic, but only for up to 10 minutes. The 0.1 ppm point seems to be the accepted tolerance level; in fact, the Occupational Safety and Health Administration (OSHA) standard is 0.1 ppm for a maximum of eight hours in the workplace. Anything beyond that level and, depending on exposure time, symptoms include eye, nose and throat irritation, coughing, headache and shortness of breath (see Table 1).
The primary function of ozone in residential air treatment is the control of odors. It effectively oxidizes the organic or inorganic contaminants that cause the odors—bacon or cooking smells, tobacco, smoke, new paint and carpet fumes, etc. Some air treatment devices combine ozone with ultraviolet (UV) light; the ozone for odor control and the UV light for inactivation of a variety of microorganisms. These devices use UV lamps—one (using 185 nanometers, or nm) produces low concentration ozone, while the other produces a wavelength of UV light (about 254 nm) capable of inactivating certain bacteria, molds, viruses, etc.
Residential air treatment devices can be divided into two general categories—room treatment and whole-house treatment. Simply stated, room treatment appliances are comprised of an ozone generator and a fan, and the fan distributes the ozone throughout the room. Whole-house systems are usually installed on the return side of the home’s HVAC system, using the HVAC fan for air circulation. Room treatment devices are limited in the space they can treat, and the ozone levels can rise in the confined area. Whole-house systems treat more air and do their work in the air ducts. While potential exposure to elevated ozone levels is minimized, opening windows or doors “contaminate” the otherwise closed system.
The applications for ozone are many and span a wide variety of markets. Ozone is a very powerful oxidizer, easy to handle and generally leaves no harmful chemical by-products. At the same time, it shouldn’t be viewed as a cure-all in and of itself for any water or air treatment challenge. To be successfully applied, the water/air treatment professional must understand the properties and capabilities of ozone. Armed with accurate information, the dealer will know what ozone does, how much is required for each application, and how to use it in conjunction with other technologies to provide complete, effective treatment systems.
About the authors
Ed Knueve is vice president and water treatment manager for Knueve & Sons Inc., of Kalida, Ohio. Knueve is a Water Quality Association Certified Water Specialist, Level 6, and has 22 years of experience in water treatment. He can be reached at (419) 532-3699, email: email@example.com or website: www.knueve.com
Ted Rich is the marketing director for ClearWater Tech LLC, of San Luis Obispo, Calif. A division of Aquion Partners LLC, the company manufacturers a complete line of mid-sized ozone generators for a variety of water treatment applications. He can be reached at (800) 262-0203, email: firstname.lastname@example.org or website: www.cwtozone.com