Ozone dosage =the amount of ozone applied to the water
Dissolved ozone =the amount of ozone measured in the water
Ozone dosage into water does not equal dissolved ozone in water. Ozone is generated as gas and must be dissolved into water in many applications. As ozone is only partially soluble in water mechanical mixing equipment is necessary to dissolve ozone into water efficiently. There are no systems that will achieve 100% mass transfer of ozone gas into water, therefore the dissolved ozone levels will always be lower than the applied ozone, or ozone dosage rate.
Final measured dissolved ozone levels in water will be affected by water quality contamination, water temperature, and the efficiency of your mechanical mixing equipment used to dissolve ozone into water.
To achieve a specific, targeted dissolved ozone level the oxidizable compounds in the water must be overcome along with any other ozone scavenging conditions, also keep in mind the ozone half-life may come into play depending upon the duration of time used to achieve your target dissolved ozone level.
The quantity of ozone you attempt to put into the water will always exceed the amount of ozone actually absorbed into the solution.
Due to the low solubility rate of ozone gas into a liquid and due to system inefficiencies, a portion of the ozone off-gases without being absorbed into the water. This off-gassed ozone must then be vented outside or destroyed with an ozone destruct unit.
The ratio of ozone gas dosage to the final dissolved level is commonly referred to as the mass transfer rate. This refers to the amount of ozone gas that was measured as dissolved vs the ozone dosage rate. This is commonly referred to as a percentage. Such as a 90% mass transfer rate of ozone would indicate that 90% of the ozone dosage, 1ppm for example, would result in 0.9 ppm of ozone measured in water.
Different methods of ozone injection will achieve different dissolved ozone levels into water due to different efficiencies and mass transfer of ozone into water. A few examples of these options are shown in the images below:
How much ozone do I need to destroy pathogens? The question is similar to asking “how much heat do I need to cook an egg?” This question is more easily answered when put in terms of time and temperature. Five minutes in boiling water can produce a softboiled egg. Ten minutes in boiling water will produce a hardboiled egg. The ozone question can be answered in a similar way: About three seconds of exposure in 0.5 ppm ozonated water can destroy 99% of E.coli bacteria. Six seconds of exposure in 0.5 ppm ozonated water can destroy 99.99%. Time and ozone concentration are the two main factors needed to how much ozone is needed.
If the ozone concentration is lower, it takes longer to destroy the bacteria. In a similar way, it takes longer to cook meat when the temperature is lower. A higher temperature cooks faster, but can also have undesirable side effects. Higher concentrations of ozone destroy pathogens more quickly, but also can have undesirable side effects. When cooking a piece of meat, the goal is to reach a particular internal temperature. In the disinfection industry, the goal is a particular Contact Time or CT value. The CT value is often given in units of mg/min -1 which is equivalent to ppm x time in minutes.
The CT disinfection value is a number that tells you when a particular type of pathogen has been “cooked” or inactivated to the desired level. The numbers come from a CT value chart. For example, the chart here gives a set of CT values for inactivating cryptosporidium. The CT value needed to inactivate 99% (2 Log) of the cryptosporidium at 15 degrees Celsius is 12. If my ozone concentration in the water is 2ppm, then I need to maintain that level of ozone in the water for 6 minutes. Ozone concentration (2ppm) x Time (6 min) = 12.
Another chart gives the CT values for inactivating 99% of a variety of different pathogens at 5 degrees Celsius with four different kinds of disinfectants. E.coli bacteria have a very low CT value of 0.02 with ozone. A 0.5 ppm concentration of ozone requires only 0.04 minutes (2.4 seconds) of contact time to inactivate 99% of E.coli. Chlorine is also an oxidant, but it is not as strong an oxidant as ozone. The chart shows the CT values of three different forms of chlorine. All of them have a higher CT value and therefore require a higher concentration or a longer contact time for the same level of disinfection.
When you start looking at CT charts, you will notice that water temperature has a significant impact on CT values. In cold water, ozone does not react as quickly as it does in warmer water. Keep in mind, however, that the ozone level in warmer water declines more quickly as it oxidizes things. As the ozonated water moves through a pipe or reaction chamber, it may begin at 4 ppm, and end at 2 ppm. (see charts at end of post)
Temperature is not the only factor to consider. Minerals or other organic compounds in the water will be oxidized by the ozone and reduce the concentration. Contact time may also vary depending on water demand. A CT value table provides a solid starting point, but all the other factors that affect ozone and limit contact of ozone with a particular organism must be considered when determining how much ozone will be needed.
A five gallon bucket and a stopwatch will give a fairly good measurement of your water flow in gallons per minute. Ozonated water flowing at 5 gallons per minute through a 10 gallon tank will provide about 2 minutes of contact time. Dissolved ozone test kits are a low cost method of measuring the ozone levels in water. Dissolved ozone sensors that provide a continuous digital reading of dissolved ozone levels are much more expensive. Measuring the Oxidation Reduction Potential (ORP) is a cheaper option, but does not give a direct ppm measurement. However, some sampling with a test kit can provide a fairly accurate correlation chart (see blog post) of ORP and dissolved ozone levels in your water.
Related blog posts and links to products. https://www.oxidationtech.com/blog/measure-ozone-in-water-with-orp/ https://www.oxidationtech.com/blog/e-coli-o157h7-reduction-with-ozone/ https://www.oxidationtech.com/av88-ozone.html
Dissolved ozone test kits https://www.oxidationtech.com/products/ozone-monitors/dissolved-meters/k-7404.html https://www.oxidationtech.com/products/ozone-monitors/dissolved-meters/i-2022.html https://www.oxidationtech.com/products/ozone-monitors/dissolved-meters/i-2019.html
“References: Bader H. and J. Hoigné, “Determination of Ozone in Water by the Indigo Method,” Water Research Vol. 15, pp. 449-456, 1981. APHA Standard Methods, 23rd ed., Method 4500-03 B-1997.
With the indigo method, indigo trisulfonate dye immediately reacts with ozone. The color of the blue dye decreases in intensity in proportion to the amount of ozone present in the sample. The test reagent is formulated with malonic acid to prevent interference from up to at least 10 ppm chlorine. Results are expressed as ppm (mg/L) O3.The CHEMetrics Indigo Ozone Vacu-vials® Kit employs an innovative “self-zeroing” feature to eliminate the need to generate a reagent blank. Each Vacu-vials® ampoule is measured before and after being snapped in sample. The change in color intensity, measured in absorbance, between reagent in the unsnapped and snapped ampoule is used to determine the ozone concentration of the sample.”
The indigo test kit can be purchased at the Oxidation Technologies web store. Indigo test kit.
The I-2022 Dissolved Ozone Meter is designed for accurately and quickly measuring ozone in water levels from 0 – 0.75 ppm. This device uses the Indigo Method for testing. This method is based on the colorization of dye by ozone, where the loss of color is directly proportional to the ozone concentration. The results are then displayed on the monitor in ppm (mg/L) of ozone present.
This device has LED display for precise and accurate readout and is easy to use. Once the I-2022 has been purchased the cost per test is only $1.02.
Next, use the dilute method to measure higher concentrations of ozone.
The Indigo snap method test kits will measure up to 0.75 so a dilute procedure can be used to derive an accurate measurement. The video uses the K-7404 kit which used the DPT method, but the principle can be applied to the Indigo kit as well.
Feel free to contact Oxidation Technolgies with any ozone questions.
A brand new ozone injection system to the market, the OXS-8 and OXS-16.
The OXS-8 will produce 8 g/hr of ozone to dissolve in up to 20 GPM of water. Water flows up to 10 GPM will contain an ozone residual of 2.0 PPM. Sufficient ozone levels for surface sanitation, most food processing applications, and other point of use (POU) ozone applications.
Review diagram below for complete breakdown of components and operation of the OXS-8 Ozone Water System.
The OXS-8 Ozone Water System will produce ozone from oxygen, via the integrated oxygen concentrator. Ozone will be dissolved into water efficiently using a mazzei injector, dedicated ozone injection pump, and ozone mixing tank.
All components necessary for operation are installed on one convenient skid that is ready to use upon delivery. Simply plumb water in, water out, and electrical power.