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Understanding the Science Behind Ozone Laundering

It seems like such an elementary question when one talks about the addition of ozone (O3) to a laundry facility. Many ozone system providers discuss the benefits of ozone laundry systems, but fail to mention what ozone is and how it works. The following will provide the tools to become a more informed purchaser by understanding the chemistry of ozone, ozone’s creation and characteristics, and how it can improve the operation of a laundry facility.THE NATURE OF OZONE
Ozone is a gas made up of three oxygen atoms. It can be created naturally (by a lightning strike) or synthetically with an electrical or coronal arch from an ozone generator. Ozone is the result of high electric voltage being passed through oxygen (O2) molecules. When this occurs, it breaks the molecular bond of the O2 into single oxygen atoms. These atoms then bond to remaining oxygen molecules (O2), creating ozone (O3). It’s the third oxygen atom in ozone’s molecular makeup that makes it such a powerful cleaning agent.
With oxidizing power 3,000 times more effective than bleach, ozone is the second most powerful oxidant in existence (deadly fluorine gas is first). When ozone gas is introduced to an environment with bacteria, mold or any other organic material, it readily donates one of the oxygen atoms in its structure to oxidize or destroy that material.
Ozone can also oxidize some inorganic materials like calcium and arsenic and a number of trace metals, such as iron. Once the third oxygen atom is used to oxidize an organic or inorganic contaminant, there is only an oxygen (O2) molecule left. This is one reason why ozone is preferred as an oxidant to various chemicals, because it does not leave any type of residual chemical.
As a result, ozone gas is used in mold remediation, air sanitizing, equipment sterilization, water purification and commercial laundering. Ozone attacks soils and greases the same way it attacks bacteria and mold. This means that as soon as ozonated water comes in contact with linen and fabrics, it begins breaking down these contaminants so they can easily be removed from the fabric by detergents.
Ozone achieves all of this with an increased level of cleaning power and without damaging linen.
In the application of ozone systems for commercial laundries, an ozone generator is utilized to create ozone by using either ambient air (the air that we breath), or an oxygen concentrator (usually found within the generator) and a series of plates that produce high electric charges. By using an oxygen concentrator, the generator can produce higher concentrations of ozone with less risk of nitrogen-related acid erosion of the equipment. This equates to a reduced generator size needed for a particular application and consequently lowers equipment and energy costs.
The generator takes the ambient air and passes it across the charged plates. Ozone molecules are formed through the separation of oxygen molecules and reformation of oxygen atoms. The ozone gas that results from this process is then discharged through an exit port. It’s introduced to the supply water or directly to the washer, depending upon the method utilized by the ozone system manufacturer.
Although ozone is a powerful oxidant, it’s unstable. The half-life of ozone in water is only about 15 to 20 minutes under normal conditions (75 F with no contaminants). In other words, 15 minutes after generation, the ozone level will normally be reduced to half its original concentration.
Factors affecting ozone’s half-life include the temperature of the water into which the ozone is introduced and the concentration of contaminants within the water. If the water temperature is 90 F or greater, it becomes more difficult to dissolve ozone. Water molecules become more widely spaced (less dense) as temperature increases and the heat energy in turn stretches the ozone atomic-bonding.
Because ozone bonds are unstable to start, any stretch due to temperature serves to hasten its reduction back to oxygen. Other factors affecting the concentration of ozone include chlorine or any other contaminants in the water. This impacts a system’s ability to produce the needed levels of ozone because a portion will be used to reduce the contaminants (chlorine, bacteria, etc.) in the water instead of the soils on the linen.
Any of these factors found in the supply water for a laundry facility could negatively affect the designed levels of ozone achieved by any ozone laundry system. These are the reasons why introduction of the proper concentration of ozone in the supply water is essential to taking advantage of the cleaning power that ozone has to offer.BREAKING IT DOWN
Ozone concentration in water is usually measured one of two ways: with an ORP (Oxidation-Reduction Potential) meter or a direct-read measurement in ppm (parts per million).
ORP utilizes a scale of measuring the free available electrons (which would produce a negative number) or a deficit of electrons (producing a positive number). This translates to a reading of oxidants in the water and may not be specific to ozone gas alone (i.e., chlorine, iodine, bromine, etc.). The main disadvantage to using ORP is the customer has no way to tell if the reading truly reflects the ozone levels or if it’s a combination of oxidants. Because the system cannot provide an exact reading, it’s difficult to know how much ozone is actually being delivered to the washers.
The direct-read method measures the actual dissolved concentration of a gas in solution. This means that when a direct-read device shows 1.0 ppm (also equal to 1.0 milligrams per liter) concentration of ozone in the water, the customer knows with certainty that there is 1.0 ppm of ozone there.
Another important point to consider is where the ORP or ozone probe is located with respect to water being delivered to the washers. One must make sure the probe accurately reads what is being delivered to the washers and doesn’t simply give an arbitrary reading just downstream of where the ozone is injected.
So, how much ozone is needed to clean laundry? The levels will vary depending on how soiled the linens are. Linens from a healthcare facility need higher levels of ozone than linens from a hotel due to the heavier soiling of the healthcare linen. Typically, a hotel laundry application requires between 1.5 and 3.0 ppm dissolved ozone to achieve the greatest level of efficiency when laundering.
Comparatively speaking, a 1.5 ppm concentration of ozonated water equals a level of approximately 975 ORP, which is higher than the maximum capability of most systems on the market that use ORP to measure the levels of ozone within the supply water for the washers. When inquiring about different ozone systems on the market, a buyer should make sure to find out the level of ozonated water being introduced to the washer. That way, the buyer will know if a system is capable of achieving the results he is looking for.OZONE VS. CONVENTIONAL
Why should anyone consider ozone as an alternative to conventional laundering? What are the benefits to management and the laundry facility’s employees, and its effects on the operating costs of the laundry facility?
There are two major areas of cost savings associated with the use of an ozone system in a laundry facility: utilities and chemicals. The greater of the two benefits is the savings in utility costs.
These cost savings are divided into two major areas: gas or electricity (dependent upon which one the facility uses for the hot-water boiler and dryers) and water/sewer. Because ozone works best in cold water, a laundry facility that incorporates an ozone system can significantly reduce its hot-water usage. This reduces the workload put on hot-water boilers to produce thousands of gallons of hot water on a daily basis to support the conventional method of laundering.
In some cases, certain ozone systems can eliminate the use of hot water completely. This means that an establishment with a dedicated boiler for the laundry facility can simply turn it off.
Laundries with ozone systems recognize the ability to use shorter wash and drying times, thus reducing electricity or gas usage. Due to the use of ozonated water in the washing process, fabrics don’t have heavy chemical residues, which allows them to dry faster. Typically, drying times can be reduced anywhere from 10% to 30% depending on the ozone system used. This reduction means less gas or electricity needed to run the dryers.
Water and sewer costs are also reduced due to shortened cycle times for the washers. Because of ozone’s oxidizing power, fewer steps are needed to achieve the level of quality in the linens comparable to conventional washing. Fewer steps equate to less water usage, thus decreasing the overall water and sewer costs for the facility. Reductions in water and sewer costs can range from 25% to 35% when compared to those associated with conventional laundering.
With energy prices continuing to climb, ozone laundry systems offer efficiency-minded businesses an alternative to help defray rising energy costs without compromising quality guestcare laundering.
A reduction in the chemicals needed for conventional laundering is the other main category of savings when using an ozone laundry system. In most conventional laundries, a wash cycle uses five to six chemicals (alkali, detergent, bleach, antichlor, sour and fabric softener). Depending on the size of the facility, the costs for all of these chemicals can easily reach tens of thousands of dollars.
Most chemicals traditionally used in the washing process are greatly reduced and sometimes eliminated entirely in ozone laundering. Overall, the reduction in chemical costs averages 20% to 30% with different ozone systems.
This also contributes to the decreased washing and drying times needed in a cycle. Some chemicals weaken fabrics, thus requiring linens to be replaced due to fabric degradation. By using cold water and lower quantities of chemicals in the washing process in conjunction with shortened drying times, laundries will see less linen replacement due to fabric degradation. Less chemical usage also means less storage needed at a facility for chemical drums and less impact to sewer treatment facilities.
Other ancillary benefits from using ozone systems are an improved work environment and the ability to increase the efficiency of the facility. By using cold water and by not having to operate dryers as long, the temperature in the laundry facility is lower, making it more comfortable.
Due to the shortened washing and drying cycle times resulting from using an ozone system, some facilities have increased their efficiency to the extent that they’re able to reduce the laundry’s work schedule by an entire shift. Others have chosen to use the time to wash a neighboring establishment’s linens for payment. This option actually converts the laundry facility into a source of income for the business.Ozone laundry systems are intended to help the customer recognize the maximum amount of savings possible while retaining the quality standards that are needed within the facility. The ultimate goal is to decrease operating costs without compromising quality. That’s the goal of every business manager.

Have a question or comment? E-mail our editor Matt Poe at [email protected].