Frequently we are asked how quickly ozone kills or inactivates bacteria within processes. This is an important factor to understand when using ozone for food processing, wastewater disinfection, and other antimicrobial intervention applications.
We performed research and wrote a paper on the effect of various levels of ozone on generic E.coli. This research indicated water containing ozone at levels of 2.0 ppm or higher could kill bacteria at sufficient levels within 1 second of contact time. This research also showed that higher levels of ozone dissolved into water did not achieve any better bacteria reduction, or faster bacteria reduction. See image below:
Click on image for a larger version
This chart shows logs of generic E.coli on the left (Y axis). This shows the pork product started with 6-7 logs of bacteria. This was reduced to a level of about 2-3 log of bacteria. An average reduction of 4 logs of bacteria using ozone.
On the bottom of this chart the exposure of aqueous ozone on the pork product is shown. This shows that at ozone levels of 2.0 ppm or greater only 1 second of contact time will achieve the 4 log reduction of bacteria, with no real advantage of longer contact times.
The great results of this research provide money saving information for many applications. This shows that lower ozone levels (2.0 ppm) can be used with very short contact times. This may reduce overall water use in applications, and lower energy costs required for ozone production.
The handheld C-16 Ozone Detector uses a sample pump with a probe to allow for real time monitoring of ozone in any area. This sensor ensures that fresh air is pulled over the sensor at all times for accurate up to date ozone readings. The C-16 also has an on board data logger and can record ozone levels over time.
The C-16 Ozone Detector is great for finding ozone leaks or pinpointing ozone emissions. The sample pump and probe makes a very simple and easy to use sensor.
The C-16 is battery operated and rechargeable. Shipped with a rugged carry case this is the perfect ozone detector for rugged ozone detection use.
Ozone gas was recently tested by the EPA in conjunction with the Department of Homeland Security to evaluate the effectiveness of ozone inactivating specific anthrax spores. This is potentially very exciting research for the ozone industry. Read excerpt from the EPA website:
Decontamination of Materials with Ozone Gas in the Presence of Vaporous Organic Compounds
The U.S. Environmental Protection Agency’s (EPA’s) National Homeland Security Research Center (NHSRC) helps to protect human health and the environment from adverse impacts of terrorist acts by carrying out performance tests on homeland security technologies. In previous testing for NHSRC, ozone gas (O3) was used for inactivation of spores of Bacillus anthracis and other organisms. Unsaturated organic compounds are known to react rapidly with O3 to produce highly reactive species (e.g., hydroxyl radicals, OH•) and reaction products (e.g., formaldehyde), both of which may be effective sporicides. Consequently, mixtures of O3 and reactive organic compounds may be more effective sporicides than O3 by itself. This study investigated the effectiveness of O3 combined with a reactive gas phase organic compound for inactivating spores of B. anthracis (Ames) and the surrogate organism Bacillus subtilis on three representative test materials.
The use of ozone in milling application has grown substantially since 1997 when ozone was first allowed in food processing applications. There are many areas of use for ozone in the milling industries and as research continues new uses will surely follow.
Overview of ozone use in milling applications
Ozone is an oxidant used for antimicrobial and pathogen control in many food processing applications.
Ozone was first allowed in food processing in 1997 with limited application.
Ozone use in milling has been growing with ongoing research in many areas.
Applications of ozone in milling applications
There are many uses for ozone in the milling industry. While some research is on-going, below is a list of industrial applications where ozone has been used with success.
Aqueous ozone is used in the grain temper process to inactivate mold and bacteria at the first point of the milling process.
Ozone gas is used with dry milled product for antimicrobial intervention in process.
Ozone gas is used for surface sanitation of enclosed equipment.
Ozone gas is used in conveyors and transport equipment in process as an antimicrobial intervention point between process steps.
Ozone use in temper process
The temper process adds water to the grain.
Many grains are tempered to increase the moisture content of the grain prior to milling.
Ozone can be dissolved into the water that is soaked into the grain.
Most pathogens are found on the exterior of the grain.
Fewer pathogens are found within the grain.
Ozone use in the temper process lowers all pathogen levels in the beginning of the milling process.
Details of ozone use in temper process
Water used in tempering process passes through an ozone injection system to provide aqueous ozone at very high dissolved ozone levels. A minimum of 10 ppm of dissolved ozone is used to ensure residual aqueous ozone can soak completely through the outer later of the grain. Ozone half life in water is 20 minutes in 20-deg C water. After 60 minutes ozone level in water may still be above 2.0 ppm. Aqueous ozone at 2.0 ppm is sufficient for antimicrobial intervention. Aqueous ozone at 2.0 ppm will achieve a four (4) log reduction of bacteria in one (1) second of contact time
Ozone gas use in milling (ozone gas used on milled grain products in process)
Sealed mixers can be used to mix ozone gas and milled grains (flour, bran, etc.)Mixers commonly used to inject chlorine gas or other chemicals could be used to apply ozone gas to the milled grain. Contact times greater than 30 seconds at ozone levels greater than 20 ppm will achieve excellent reductions in pathogens.
Ozone can be introduced into pneumatic or mechanical conveyors to disinfect grain in processConveyers that are used to transport milled grains from one location to another can be used to apply ozone gas to the grain. This is an efficient and convenient method of applying ozone gas to the grain.
Equipment can be sanitized by ozone gas disinfectionMilling equipment can be sealed and exposed to high levels of ozone gas. Ozone gas at effective levels for pathogen reduction can be used in these applications to safely reduce pathogens without the use of chemicals or residuals.
Ozone gas requires more contact time and higher levels than aqueous ozone.
The use of ozone in milling has shown increased reduction of bacteria, yeast, and mold reduction over time.Due to cross contamination, residual mold spores, and residual pathogens; mold and bacteria counts in the final product are not dramatically improved immediately. However, over time the mold and bacteria counts are lowered with the use of ozone in process.
Customers have commented on reduction and complete elimination of mold growth in sifters and other equipment throughout the milling process.
Shelf life of of some milled products has increased dramatically due to lower bacteria and mold counts.
IOA User Success Report — Harvest States Amber Milling, Huron, OH
Ozone was used in temper process to replace chlorine.
APC bacteria reduction of 75-80% using ozone, compared to chlorine.
After months of operation further reduction of bacteria (up to 95%) was achieved.
Influence of Tempering with Ozonated Water on the selected properties of wheat flour — Dept of Food Engineering, Univ of Gaziantep — Senol Ibanoglu (Oct 14, 2000)
Aqueous ozone at 1.5 and 11.5 ppm were tested.
No physical properties or baking quality changes were found.
Statistically significant reduction in total bacteria and yeast/mold population was found at both ozone levels.
A Comparison between Chlorinated Water and Ozonated Water as an Antimicrobial Treatment during Tempering of Wheat — ASABE Meeting Presentation
Ozonated water did not have any effect on the color and germination capacity of wheat grains.
Ozonated water significantly lowered the yeast/mold counts in durum and hard red spring wheat.
Ozone Solutions has recently added a new ozone generator to our product line. The NANO Ozone Generator is manufactured by Absolute Ozone and is perfectly suited for lab applications where high concentrations of ozone are required.
The NANO Ozone Generator can produce ozone concentrations greater than 9% by weight from oxygen at flow rates of less than 1 LPM. When lab tests are performed on a small scale it is imperative to have ozone generated at the concentrations possible. Ozone solubility is dependent upon ozone concentration, this makes high concentrations of ozone extremely beneficial in any application.
The NANO Ozone Generator can be used for small industrial applications where the small size will come in handy. With the great efficiency of this ozone generator very low oxygen flow rates will still produce great ozone outputs. At only 3 LPM of oxygen 15 g/hr of ozone is produced with the NANO Ozone Generator.
With easy to use controls and a small compact size the NANO Ozone Generator can be useful for many applications. The low price of the NANO Ozone Generator opens up an entire new world of possibilities for our customers on a budget who demand the highest ozone concentrations possible.
A fairly new ozone monitor to our website is the Honeywell GAXT-D-DL Ozone Monitor, or better known as “The GAXT”. We have found this to be a great handheld Ozone Monitor for daily safety use and spot checking of ozone levels. Watch video below:
There are many practical uses for ozone in the world today. While no one ozone company can be experts at every ozone application we can try to provide useful information on many applications, and possibly point visitors in a direction to find the information they are looking for.
For information on the use of ozone for any of these applications or any others please contact our application engineers today. If we do not have the information you are looking for, we will be glad to point you in the right direction.
Ozone is dissolved into water to create aqueous ozone for many applications. This page is a general overview of the methods and devices to dissolve ozone into water, along with a few helpful tips for the novice ozone user.
Ozone cannot be stored, therefore it must be generated on-site and dissolved into water on-site at the rate of consumption. Ozone is generated as a gas that must be dissolved into water. A mixing device will be necessary for ozone gas to dissolve into water efficiently. There are many variables to consider when determining the proper mixing device for a given application. The information provided below serves to provide a better understanding of the variables that may affect your application.
Bubble diffusion is the oldest and simplest method for dissolving ozone into water. This is essentially a porous device used for breaking the gas into small bubbles at the bottom of a water column to allow the bubbles to slowly rise to the top of the column and dissolve into water.
The pore size of the diffuser will affect the size of gas bubble that is created with the bubble diffuser. Two smaller bubbles will have greater surface area than one bubble of the same gas volume. Greater surface area will achieve improved contact with the gas bubble and water, therefore increasing the rate of mass transfer of ozone into water. It is important when choosing a bubble diffuser to find the smallest pore size possible.
Water Column Height
The height of the water column that ozone is bubbled into will affect the mass transfer efficiency greatly. The diffuser should be placed at the bottom of the column, this way the gas bubble must travel the greatest distance within the water column prior to escaping into the head space. Taller columns will lengthen the time duration that the bubble is in contact with the water and can dissolve into the water. More importantly, taller columns will create a higher pressure at the bottom of the column. This high pressure will exert greater force on the surface of the bubble and force more gas into solution.
Bubble diffusers can dissolve ozone into water efficiently; however, a fine pore diffuser must be used with a very tall water column. Water columns shorter than 10 feet typically achieve less than 50% mass transfer efficiency. Water columns 20 feet tall can achieve mass transfer efficiency up to 90%. This may not be practical in a given application. Fine pore diffusers can also plug with contaminates easier and cause poor long term performance. When designing a water treatment system using bubble diffuser keep safety in mind as high levels of un-dissolved ozone may escape from the head-space of the water.
A venturi injector is a very common method of ozone injection in industrial application. A venturi injector combines a method for ozone injection and provides good mass transfer efficiency in one device. A venturi injector requires a pressure differential across the device to create a vacuum to pull ozone gas into the device. Then, using mixing vanes the gas is thoroughly mixed with the water.
A venturi injector creates the very small bubbles desired for great mass transfer, and a violent mixing action to dissolve gas into water. Using a ventui injector alone may achieve mass transfer rates of 90%.
For a Venturi Injector to work properly there must be a pressure differential between the inlet and outlet of the device. This usually requires a separate water pump to increase the water pressure at the inlet of the venturi injector. It is then important that the outlet of the venturi injector is not obstructed or impeded in any way.
We suggest placing pressure gauges directly at the inlet and outlet of the venturi injector. This will help with troubleshooting and determine the effectiveness of the device.
Using a venturi injector will require a method of removing the un-dissolved oxygen and ozone from the water. Unlike the bubble diffuser where the bubbles will naturally rise to the head-space and escape the piping system used with a venturi injector has no method of removing this un-dissolved gas, one must be provided. A contact tank is a popular method, there are also de-gas chambers and columns that can be used. Ozone compatible air vents are used to remove this gas and vent to a safe location or to an ozone destruct unit.
If an off-gas system is not used the excess gas bubbles that may carry residual ozone can off-gas in undesirable locations causing safety concerns. Also, this excess gas may volatilize some of the dissolved ozone back into the gaseous form.
By-pass and plumbing
Venturi injectors become an integral part of the plumbing system in use. A pump is commonly placed prior to the injector, a tank after the injector. A by-pass loop is also commonly used to allow regulation of water flow through the injector and greater flexibility. Follow this link to the Mazzei website for some great examples of these plumbing options.
Venturi Injector Performance and sizing
Venturi injector sizing is a function of the water flow rate through the device. Water pressure will also play a factor in the determination of the venturi injector sizing. Each venturi injector is supplied with a performance chart illustrating the water flow, pressure, and gas suction provided by that venturi injector. Follow this link for extra guidance on this issue.
Water back-flow prevention
When using a venturi injector it is necessary to use a device to ensure water cannot flow from the venturi injector to the Ozone Generator. There are many devices used for this task: check valves, water traps, and shut-off valves are all used. We have found the best success using a quality water trap in conjunction with a check valve to prevent all water back-flow.
Diagram of system using a venturi injector, pump, contact tank, and air vent.
Static mixers are any static device designed for the sole purpose of mixing two flows together. In our application we are mixing ozone gas with water, therefore the same principle of breaking the bubbles up into the smallest possible bubbles is the goal with the static mixer.
There are a variety of static mixers on the market, some go by trade names. For example Mazzei markets a static mixer under the name “Flash Reactor”. While there may be a variety of static mixers on the market they all serve the same function, dissolving ozone gas into water.
Sizing a static mixer
A static mixer is sized based on the velocity of water through the mixer. Each static mixer has vanes or mixing devices inside that require a specific velocity of water past those devices to achieve the desired results. This sizing will translate to water flow rate for our purposes. Each mixer should be sold and marketed with a range of flow rates that the mixer will work well with.
Ozone can be injected upstream of the static mixer using a tee or any other device to force ozone gas into the water stream. Then, the static mixer can be used to break up the gas into small fine bubbles to dissolve into water efficiently. Essentially a static mixer can be used in place of a venturi injector, this can be helpful when energy savings are desired due to the lack of necessary pressure differential.
To force ozone gas into the water stream the ozone gas must be at a higher pressure than the water stream. Usually a pressure of 10 PSI or greater is necessary to achieve gas flow into the water stream. This may eliminate the option of using only a static mixer and may require using a venturi injector to inject the ozone into water. The option of placing a static mixer in-line after the venturi is also an option.
Plumbing and piping
A static mixer can be placed anywhere in a piping system intended to mix ozone gas with water. The best location when using a venturi injector to infuse ozone with the water is a few feet downstream of the injector. If using a contact tank or off-gassing column place the static mixer directly at the inlet of the tank with the venturi a few feet (as far as practical) upstream from the static mixer.
Tips for dissolving ozone into water
Below are some helpful tips and guidelines to take into consideration when dissolving ozone into water.
The solubility of ozone into water is temperature dependent. Lower water temperatures will achieve greater dissolved ozone levels due to a higher solubility rate. The solubility rate is the maximum ration of liquid to gas achievable for a given gas. While there are many other factors that will affect your mass transfer of ozone into water, it is very simple to understand that lower water temperatures increase solubility, if the solubility rate increases the mass transfer of ozone into water will increase.
Solubility of ozone gas
Temp deg C
At atmospheric pressure
Water pressure will play a role in the solubility of ozone into water. When ozone gas is injected into water at higher pressures more force will be placed on the wall of that gas bubble. This force will allow ozone to dissolve into water more efficiently. Any of the ozone injection methods will be more efficient when the entire system is operated at an elevated pressure. For example, water pressures of 35 PSI will have about twice the solubility as water pressures of 10 PSI.
Ozone gas is normally measured in g/hr, however this is only a measurement of how much ozone is generated. Another method of measuring ozone is the concentration. More ozone in a given gas volume will mean that the gas has a higher concentration of ozone. This is normally measured in % by weight, or g/m3.
Ozone at higher concentrations will dissolve into water more efficiently than ozone at lower concentrations. See chart below for details.
Chart shows the saturation point of ozone in water based upon ozone concentration and temperature, at atmospheric pressure. Dissolved ozone level shown in mg/l
Any contaminate in the water that may affect water quality may also consume ozone, this will lower the dissolved ozone levels in the water. While this may be a desired effect due to the purpose of the ozone in water, it is important to take water quality into consideration when attempting to achieve a specific dissolved ozone level in the water.
A good example and often overlooked factor is chlorine in the water. Most city water supplies will have a chlorine residual in the water. When dissolving ozone into this water the ozone may react with the chlorine and consume some of the ozone.
Dissolving ozone into water for any of the various applications listed above may be very simple, or could be extremely complicated. This will be depending upon the application, and the variables working within that application. This information should only serve to offer guidance on this process, for additional information refer to the great resources below, or contact our office and speak with one of our Application Engineers.
Ozone in Drinking Water Treatment — Kerwin L. Rakness pg. 47 & 48
Ozone in Water Treatment Application and Engineering — cooperative research report — Bruno Langlais, David Reckhow, Deborah Brink: pg. 24-27, 139-142,
A popular page on the Ozone Solutions webpage is the ozone properties page. Recently the Ozone Solubility chart on this page was expanded. The chart below shows what we now have on our website. This data replaces the old chart with only 9 data points that were a little more difficult to understand due to the units used.
This new chart shows the huge difference in ozone solubility based on water temperature and ozone concentration. This data is very helpful when designing a new ozone water treatment system, or troubleshooting existing ozone systems. This data shows that if your water temperature increases the resulting dissolved ozone level may change dramatically. Or, if ozone is generated at only a slightly lower concentration dissolved ozone levels will be dramatically lower.
The solubility of ozone depends on the water temperature and the ozone concentration in the gas phase: Units in g/m3.
This Ozone Journal is a blog managed by the employees of Ozone Solutions. The purpose of this blog is to inform and educate the readers about the world of Ozone, provide news about the ozone industry, and have an easy opportunity to inform about new ozone products.
Check back often, ask questions, and let us know if there is anything you would like to hear about.
What is ozone?
Ozone is an oxidant. Ozone (O3), sometimes called “activated oxygen", or "triatomic oxygen", contains three atoms of oxygen rather than the two atoms we normally breathe. Ozone is the second most powerful oxidant in the world and can be used to destroy bacteria, viruses, and odors.
Ozone is a gas at ambient temperatures and pressures with a strong odor. Ozone can be produced as a gas from oxygen in air, or concentrated oxygen. This ozone gas can be dissolved into water, or used in the gas phase for a variety of applications discussed in this Journal.