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.
Dissolved ozone test kits
It is no surprise that ozone will neutralize coronavirus. Ozone is well known to be a powerful disinfectant. It is especially effective with small pathogens such as viruses and bacteria. Some of the more recent studies have demonstrated that coronavirus can thrive in the air in the form of aerosols breathed from people. Recent research has demonstrated that low levels of ozone gas effectively neutralizes coronavirus.
Ozone is a simple high-energy molecule of three oxygen atoms and will irritate sensitive tissue such as our lungs when ozone concentrations exceed 0.1 parts per million. The good news is that coronavirus is much more sensitive to ozone than our lungs are. “Scientists at Fujita Health University told a news conference they had proven that ozone gas in concentrations of 0.05 to 0.1 parts per million (ppm), levels considered harmless to humans, could kill the virus.”
The important details are the ozone level and the contact time. Coronavirus exposed to ozone concentrations of 0.1 ppm for 10 hours reduced the potency of the virus 90%. Ozone is not a magic bullet, but it is a valuable tool in our arsenal for fighting the virus. It is a safe, comfortable, and effective tool that can provide secondary benefits. The ultraviolet rays of the sun and lightning naturally produce low levels of cleansing ozone. Well-controlled equipment is already available to bring some of the fresh outdoors into our living and working spaces to stand side by side with others in the battle against viruses.
Oxidation Technologies has worked for years to produce safe and effective ozone generating equipment. We specialize in equipment controls to precisely maintain specified ozone levels for commercial applications. We have the equipment and expertise to maintain safe levels of ambient ozone that will greatly reduce the ability of coronavirus to thrive. We would be happy to assist in your efforts to get employees back into the workplace.
Each year almost a half a million people in the world die because of bacteria, viruses, and other pathogens in the food they eat. https://www.businessinsider.com/annual-food-poisoning-deaths-2015-12 The United States Center for Disease Control (CDC) estimates that 1 in 6 Americans get sick each year from contaminated food, and 6000 die. In addition to the suffering and death caused by the contaminated food we eat, the economic impact of food contamination is in the billions of dollars each year. Ozone has proven to be an environmentally friendly, safe, and effective sanitizing agent for every stage of food processing.
The diligent efforts of government agencies and food production facilities to implement procedures and policies serve to limit and control the potential for contaminated food, but people continue to get sick and multi-state outbreaks of food borne disease continue to increase. New antibiotic resistant strains of bacteria and more centralized food production are only a couple of the factors that may be contributing to the new challenges we face. Of all the strategies to manage food contamination, an enduring and key part of preventing sickness and death from food contamination is careful surface sanitation.
A clean surface is the first step for food safety. https://www.cdc.gov/foodsafety/keep-food-safe.html As our food travels from the field to our table, it comes into contact with equipment that is constantly repopulated with disease causing pathogens from incoming food, food handling equipment, water, air and employees. Unless careful, repeated sanitation practices are maintained, pathogens thrive and multiply on the surfaces of food processing equipment, contaminating food as at passes through. https://www.who.int/foodsafety/areas_work/foodborne-diseases/ferginfographics.pdf?ua=1
Food processing facilities maintain rigorous sanitation procedures to combat the threat of contamination. Physical scrubbing and washing down of surfaces is followed up with sanitation methods that kill the bacteria and microscopic pathogens that remain. Heat and chemical sanitizers are frequently used to eliminate these pathogens, but have their limitations and negative consequences. Ozone is a safe and effective alternative to destroy these pathogens and keep surfaces free of dangerous pathogens.
A growing number of food processing plants are using ozone to eliminate bacteria, viruses and other harmful contaminants on food. When ozone is dissolved in water, the ozonated water serves as a powerful disinfectant that is safe and effective not only on equipment and surfaces, but when applied directly to food products. As the ozone destroys harmful pathogens, it turns back into oxygen and safely disperses, leaving no residue.
Recent FDA approval for using ozone directly on food and improvements in ozone equipment have opened the door for the use of ozone to combat food born illness. For many years, food processing plants have been restricted to using heat, pressure, and chemical methods of disinfection, even though ozone has been used since the early 1900’s in water treatment plants for disinfection. In August 2, 2000, the Electric Power Research Institute (ERPI) petitioned the FDA to approve of using ozone directly on food to reduce the level of harmful pathogenic microorganisms. In addition to providing a wealth of technical information about ozone, the 380 page petition cites over 80 studies of ozone and food sanitation conducted over the past 60 years. https://ioa-pag.org/resources/Documents/Applications/Food%20Additive%20Petition.pdf The following year, the FDA granted GRAS (Generally Recognized as Safe) status to ozone as a food additive. https://www.federalregister.gov/documents/2001/06/26/01-15963/secondary-direct-food-additives-permitted-in-food-for-human-consumption Since then, ozone use has increased dramatically in food processing.
Chlorine has been a common sanitizer in the food processing industry. It is a simple and convenient sanitizing solution. The convenience of Chlorine comes with the problem of residual chemicals in waste water and a building of resistance to Chlorine of E.Coli and Giardia microorganisms. Chlorine and other chemicals can also react with metals and wood equipment used in the food and beverage industry causing damage and flavor alterations. Concerns about water contamination with residual chemicals, food quality, and equipment maintenance make ozone an attractive option for sanitation. https://www3.epa.gov/npdes/pubs/ozon.pdf
Ozone is a gas that is made from oxygen, and turns back into oxygen as it breaks down. Ozone is responsible for the fresh smell generated in lightning storms. Two oxygen atoms bound together form the stabile oxygen molecule. Passing oxygen through an intense electrical field breaks this oxygen bond, and energy is stored in the three-atom arrangement called ozone. The sanitizing power comes from the energy stored in the ozone. Ozone gas is a highly energized form of oxygen composed of three oxygen atoms instead of the more stabile combination of two atoms. This gas readily dissolves into water to provide a powerful disinfecting solution. The energy is released as contaminants are broken down, and the oxygen atoms return to the lower energy form of O2.
Unlike a chemical sanitizer that can be stored in a barrel and added to water when needed, ozone cannot be generated in a factory, concentrated, and stored in a bottle or barrel to be sold to the end user. The ozone would all turn back to oxygen before it could be used. Instead, ozone is generated with electricity on site when needed and injected into a water stream to be used immediately. As ozone makes contact with contaminants, the energy is released, destroying the contaminants and returning to the two-atom low energy state of oxygen.
A reliable industrial ozone water injection system will often pay for itself after a year of reduced chemical costs. Chemical disinfectants may be needed to provide some residual protection, but the bulk of the disinfection can be achieved with ozone. The system in general does not take any more space than the totes of chemicals it can replace. The electrical and preventative maintenance costs are well worth the improvements in food quality and zero chemical footprint in wastewater.
A little bit of ozone goes a long way in disinfection power. A small ozone generator using a couple hundred watts of power is capable of making enough ozone to turn 20 gallons per minute of water into a 2 ppm dissolved ozone sanitizing solution similar to using 200 ppm Chlorine in water. Ozone decomposes rapidly, but in exchange, it provides a more rapid rate of disinfection. The precise ozone concentration and contact time will vary with the particular application and pathogen.
Given the mountain of evidence that ozone is a quick and effective destroyer of viruses and bacteria, why is there so much hesitation to champion ozone as a key weapon against the spread of Covid 19? The EPA has a list of 478 different products and 30 active ingredients that officially kill the Covid virus, but ozone is nowhere to be found in the list. The closest thing to ozone that is on the list is hydrogen peroxide. Have all these products actually been applied to the virus and proven to destroy or inactivate it? How can you tell if a virus is dead or inactive? Given what we are gradually learning about the virus, how it spreads, and how it infects our bodies, how effective are these disinfectants in preventing infection?
Dr. Chedly Tizaoui, a professor of chemical engineering at Swansee University has taken a rather novel approach in an attempt to answer some of these questions. Instead of conducting statistical analysis of thousands of people or trying to count dead viruses after applying a particular disinfectant, Dr. Tizaoui has applied molecular modeling to evaluate the effect of ozone on the molecular structures the virus. He shares his results in the International Ozone Association research journal “Ozone: Science and Engineering” https://www.tandfonline.com/doi/pdf/10.1080/01919512.2020.1795614?needAccess=true
Molecular modeling is an especially useful tool for studying viruses because viruses are so small they can’t be seen with a standard light microscope. Their shape and structures are defined on a molecular level, so understanding the types of molecules making up their structure allows us to make an accurate model. The model not only evaluates the shape and function of corona virus anatomy, but it also evaluates the bonds holding these molecules together. Understanding the relationships between these molecules and how they function together to make the Corona Virus so sucessful provides important insight in the weaknesses and vulnerabilities of the virus.
We may not yet know all the complex interactions of the virus with people, or exactly how the virus infects, but we do have a pretty clear understanding of the molecular structure of the virus. It is also clear that the unique shape and structure of the molecular structures on the outer shell play a key role in the success of the virus. Molecular modeling is a tool that helps us see how this structure is altered when a molecule like ozone comes into contact with it.
Ozone is like a molecular hand grenade in the virus world and has the power to change the shape of the virus’s “arms” and disable them. Various kinds of molecules behave and react in predictable ways making it possible to use molecular modeling to study what happens when something like ozone molecules interacts with the structures on a virus.
Ozone is an exciting molecule to model because it packs a lot of energy. The molecule is very sensitive and quick to unload its energy on nearby molecules. It has a very positive 100 year track record for effectively destroying viruses and bacteria. The water treatment industry has grown to appreciate the value of ozone for destroying pathogens in water. The food industry is also learning how to harness its power for sanitation and shelf life extension. Ozone has also been used extensively in medical treatment, but faces an uphill battle against the pharmaceutical and chemical industries.
After applying the science of molecular modeling to Corona Virus anatomy and ozone, Dr. Tizaoui concludes, “The results show that ozone is able to attack the proteins and lipids of the virus’s spikes and envelope, particularly the amino acids tryptophan, methionine and cysteine, and the fatty acids,varachidonic acid, linoleic acid, and oleic acid. Ozone also attacks the N-glycopeptides of the spike protein subunits 1 and 2, though at lower reactivity. Disruption of the structure of SARS-CoV-2 could inactivate the virus, suggesting that ozone could be an effective oxidant against COVID-19 virus.”
Thank you, Dr. Tizaoui, for sharing this research. Now it’s our job to safely get the ozone where it needs to be to do its work.
Is there a way to measure dissolved ozone (0.5 to 3.0 ppm) in water with a high chlorine level. Yes, there is a way to to this.
First, be sure to use the Indigo Method.
The Indigo Method
“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.
Thought I would share my quarterly maintenance report for an ozone iron removal system serving a hog farrowing operation. Iron in the water had been causing high maintenance costs on the power washing equipment used to maintain a sanitary environment. We sized an ozone well water treatment system to remove the measured iron levels at a rate of 20 gallons per minute. The system injects ozone with a venturi, circulates it through a contact tank, and filters the oxidized iron with two sand filters. It has been running for a year and a half now and continues to provide excellent iron removal results. The picture shows two water filters, grey one with clay silt from the well water prior to entering the system. The red one is a post system filter to remove any iron the sand filters missed. I used the Chemetrics iron test kit we sell to verify results. The clear ampule reflects a post-filtration reading of 0.2 ppm total iron. The medium colored ones reflect a pre-treatment sample of 1 ppm iron. The dark-colored one was a test of the backflush water indicating what the sand filters are removing. Overall, the system is operating very well. I changed filters and check valves, measured system performance, and prepared a report for the customer. This summer the demand will be higher on the system, so I will try to get there a little before the next scheduled visit. Ozone can provide excellent results when properly applied and maintained. We are happy to provide quarterly maintenance to keep your ozone system operating at peak performance. Give us a call at 515 635-5854. We’d be happy to provide service for any ozone equipment on the market.
The Coronavirus pandemic has sparked an exponential increase in interest in ozone as a disinfectant. The phones at Oxidation Technologies have been ringing non-stop with people looking for answers and looking for help with their grand ideas for ozone as a silver coronavirus bullet. Our ozone specialists have been working hard to provide accurate information for those looking for answers. Ozone has been a powerful tool for over a hundred years, but misinformation is dangerous in a climate of desperation and hype. Our goal throughout this health crisis has been to educate our callers about safe and unsafe uses of ozone, effective and ineffective applications of ozone, and the facts and false claims people make about ozone.
If there is so much interest in ozone as a powerful and chemical-free disinfectant, why do we read so much about ozone as a very bad and deadly pollutant? For example, the American Lung Association says “Ozone (also called smog) is one of the most dangerous and widespread pollutants in the U.S.” On the other hand, the Food and Drug Administration (FDA) approved the use of ozone as an antimicrobial agent for the treatment, storage and processing of foods in gas and aqueous phases.” For years, now, we have recognized the value of an atmospheric layer of ozone that shields “living things from too much ultraviolet radiation from the sun.” Ozone sterilization of water has made the bottled water industry possible providing billions of bottles of safe drinking water. The answer to this paradox is not difficult or mysterious, but does require some ozone education. We hope you take some time to explore the wealth of ozone information on our website.
Ozone has been used to disinfect water for over 100 years. Many water treatment plants throughout the world not only use ozone to disinfect water, but also remove organic compounds and improve taste and smell. Ozone is an attractive alternative to chemical treatment because it is very effective and does not introduce any new chemicals to the water you use. The drawback has been a high initial cost and equipment maintenance. Advances in technology have brought ozone within the reach of the average home owner, and small scale reliable ozone generating equipment has stood the test of time. Our ozone water treatment (WT) system is simple to operate and monitor to ensure that it is working properly to provide safe water. Here are five routine, simple, and quick checks of your ozone WT system to maintain your peace of mind.
You will know your water’s staying clean when …
1) The desiccant air dryer feels warm.
Put your hand near the top of the air dryer. Does it feel warm? If it is cold, something is not right. The air dryer contains two cylinders of desiccant material. It is the same stuff you find in little packets sometimes placed in the packaging of sensitive electronic equipment. This material absorbs moisture from the air. Eventually it becomes saturated with water and no longer absorbs moisture. The water is removed by heating the desiccant material. The desiccant air dryer is designed to cycle back and forth between two cylinders filled with desiccant material. When air is flowing through one to remove the moisture, the other is being heated to drive off the moisture. If the outside of the box feels warm, this is a good sign that all is well.
2) The moisture indicator is blue.
The moisture indicator provides additional assurance that your ozone equipment is getting dry air. This little viewer contains crystals that change color in the presence of moisture. When it is blue, you can be sure the air feeding your ozone generator is dry. If it is not blue, it could mean that the dryer is not working properly, the crystals have been contaminated in some way, or the crystals need to be replaced. Don’t become alarmed right away. The dryer requires a good six hours of uninterrupted operation to stabilize. If the location is excessively warm or humid, the dryer will not perform well.
If you continue to suspect that the air dryer is not performing as it should after a number of checks over the course of a few days, try to determine what has failed. If the dryer feels warm but the moisture indicator is not blue, it may be that the moisture indicator is contaminated. New moisture indicators are available from our store. It is also possible that the desiccant material has been contaminated or worn out. In that case, you will need one of our desiccant refill kits. If the air dryer feels cold, check the power connections. We also sell replacement heater tubes that contain the desiccant. If you are unable to verify that the air dryer is working, it may be time for a new dryer.
The only part of the treatment system that is active 24/7 is the desiccant air dryer. All the other components wait until the well pump turns on.
3) The little silver ball in the flowmeter jumps up and hovers when the well pump turns on. (Newer models have a digital reading of air flow)
The flowmeter is a simple device telling us how much gas is flowing through the system. Air is pulled through the air dryer and ozone generator by suction produced by the black plastic venturi. Suction is created by the flow of water through the venturi. When the well pump turns on, water rushes through a narrow passage in the venturi. With sufficient flow, the water pressure differential between the input and output of the venturi creates air suction. Air flows through the tubing as it is pulled into the venturi. The little silver ball is lifted by this gas flow giving a visual indication that air is flowing through the system.
If no air flow is created when the water pump turns on, remove the ozone tube connected to the black venturi. Place your finger over the hole to see if suction is created. As long as the pump is running, the venturi should create air suction. If there is no suction, remove the check valve that is threaded directly to the venturi. Clear out any rust or mineral deposits. If the pump stops, water will squirt from this port, so try to open enough faucets to keep the pump running. If you are unsuccessful with getting air suction from the venturi, it could mean that the well pump is not pumping enough water through the venturi to create suction, or the venturi has worn out.
If you do have air suction at the venturi, but still no air flow indicated on your flowmeter, it may be that a check valve needs to be replaced or something else is blocking the flow. The source of blockage needs to be found and cleared before ozone generator will operate. The ozone generator turns on when it senses a sufficient flow of air. Most ozone generators will have a blue light indicating that the ozone generator is running.
4) You can smell ozone from the off-gas vent
But can you be sure that that sufficient ozone is being generated to disinfect your water? When your system is operating properly, left-over ozone that does not get dissolved into the water is vented from the top of your contact tank. If you remove the tubing from the off-gas vent, you should smell ozone when the system is running. It might take a little while for enough ozone gas to build up for venting, but when it accumulates at the top of the tank, it will be vented, often in short spurts.
5) Testing your water for dissolved ozone levels.
Ozone is a more powerful disinfectant than Chlorine. It destroys, inactivates, and prevents growth of bacteria and viruses with very low levels of dissolved ozone in water. As little as .3 ppm dissolved ozone for contact time of 5 minutes provides a 5 log (100,000 bacteria reduced to 1, 99.999% reduction) reduction of most bacteria and viruses. Contaminants are exposed to much higher levels of ozone when it passes through the venturi. By the time the water leaves the contact tank, any contaminants have been in contact with ozone long enough for most of them to be destroyed. The ozone has done its job and very little is left in the water that is distributed to your home. Enough will be left over to prevent growth. As little as 0.01 ppm will prevent growth. These low levels of ozone leaving your contact tank can be measured with our low cost K-7404 dissolved ozone test kit. You don’t want much ozone left in your water. Too much ozone left over in the water can lead to irritating ozone off-gas at the point of use.
A Not-So-Lazy River Circuit Analogy
Our journey to the center of an ozone generating plasma cell begins with a ride around a not-so-lazy river. Perhaps you’ve enjoyed floating in a raft around a lazy river at a hotel or water park. Picture these rafts as electrons flowing through a circuit. Moving magnetic fields are pushing electrons through the fluid media of metal atoms. They follow the circular paths of circuits like rafts floating around and around the lazy river ride. A pump continually pushes the water along.
Unlike the continuous flow in one direction of direct current (DC), alternating current continuously reverses the flow of electrons. Imagine the lazy river model constantly changing direction. The electrons first flow one way, slow, reverse, and rush the other way. The electric supply to your home goes through 60 cycles per second. Our lazy river model begins to defy imagination at this rate of change. You can think of electrons as virtually weightless, unlike all the water and rafts in a lazy river. Electrons are quite capable of reversing direction very quickly.
The flow of electrons through a wire might be apparent from the glow of a light bulb. As electrons squeeze through a resistive part of the circuit, the wire heats up transferring energy to heat and light. Other things are happening outside the wire. Hold a compass near a wire in which current is flowing, and the needle is pulled away from North. Whenever an electric current flows, a magnetic field develops around the wire. Stop the flow, and the field collapses.
Wrap this conductor into a coil, and the magnetic field is intensified. Add an iron core, and a magnet is born. A continuous flow supports a useful magnetic field, capable of pushing the rotor of a motor or the lever of a switch. Again we notice a transfer of energy, this time from electric current flow to some mechanical motion. Energy transfer doesn’t stop there.
Energy transfer is reversed in a magnetic field when the electric current stops. When current stops or reverses, the magnetic field collapses. The collapsing magnetic field gives electrons a push in the coiled conductor. This phenomena opens up the possibility of generating a flow of electrons in a second circuit that is isolated from the first circuit. It also introduces radio waves. Imagine a second lazy river next to yours. It doesn’t have a pump, so the water is still. But imagine an invisible force generated by the flowing of the first river pushing the water along in the second. Such a transfer of energy happens with the flow of electrons and is essential to ozone production within a plasma cell.
A Dam in the River: The Plasma Cell Heart
A dam in the lazy river brings the rafts to a halt, but build two Olympic sized pools on either side of the dam. Now the river continues to flow awhile even with a dam because it takes time to fill the pool. Depending on the strength of the pump, the water flows for a while as one pool gets a little deeper while the other is drawn down. If you can pump one pool much deeper than the other, a significant stress builds on the dam. Our lazy river could get exciting if the dam were to burst. We are getting closer to the center of a plasma cell.
In your mind you need to convert the Olympic sized swimming pools in our lazy river circuit to large flat pieces of metal. In the electron world, the dam between these two plates is an insulator, a material that prevents the flow of electrons. Electrons pile up on one side while they are drawn down on the other side. Electrons are the negative charge. Pulling electrons away leaves one side with deficiency of electrons: a positive charge. If the insulator were breached, a powerful surge of electrons would create a dramatic spark. It would be equivalent to the deep swimming pool emptying to the shallow one in milliseconds.
It is here at the “dam” where we discover the center of a plasma cell. When the distance between the two electrically charged plates is made smaller, the electrostatic forces between them grow exponentially. In other words, a thinner dam makes a more powerful electrostatic field. But a thin dam is also weaker and more susceptible to failure. The goal is a material that is strong and a good electrical insulator. Ceramic and quartz serve well for this purpose. But without some oxygen present in this high electrical pressure environment, we only have a capacitor and no ozone production.
We need to introduce one more element: a thin layer of oxygen as part of the “electron dam.” We can think of the dam as a sandwich of two insulators with a very thin slice of oxygen between them. When oxygen is exposed to the tremendous electrostatic forces found within this space between highly charged surfaces, the oxygen molecules are pulled apart and re-combine in highly energized forms. I would like to zoom in for a closer look at this sliver of space.
A Peak Inside the World Between Dielectric Barriers
Photographs of this space between the two insulators reveals what appears to be a mini, but intense electrical storm. We are used to thinking about lightning bolts jumping from one charged conductor to another, but in this electrostatic microcosm, the mini “bolts of lightning” are jumping from the surface of one insulator to the surface of the second insulator. In the presence of the strong electric field, the molecules within the insulator become polarized. This means that the electrons are pulled by the positive electrode toward one end of the molecule that make up the insulator. Even though electrons are unable to flow through the insulator, the polarization sets up “pools” of electrons on the surface. We call the insulating material used in in this application a “dielectric.” The type of ozone generator we are entering here is a dielectric barrier discharge (DBD) generator.
Exactly what is happening in this high electrical pressure world between dielectric barriers has been and continues to be a topic of considerable research and study. Already around 1897, John Townsend discovered that the strong electric field in the oxygen space between dielectrics initiates electron avalanches. A free electron among the oxygen atoms accelerates very quickly because it is attracted to the positively charged plate (anode). When it reaches a high enough velocity and collides with an oxygen molecule, it knocks off another electron, turning the molecule into a positively charged ion. This ion begins to move in the opposite direction toward the negatively charged plate (cathode) while the two electrons further accelerate toward the anode and collide with more oxygen molecules. As the growing electron cloud races toward the anode, it leaves a trail of positively charged ions in its wake.
This trail of ions and free electrons is conductive, and allows for a discharge of electric current through the oxygen. The discharge is the flow of electrons that has gathered on the surface of the dielectric towards the positive charge on the other side of the oxygen gap. It is this discharge of energy that breaks the oxygen molecule bonds releasing free oxygen atoms. Some re-combine with single atoms, and others combine with pairs to form highly energized ozone molecules made of three oxygen atoms. The world here at the center of an ozone generator is a stormy one swarming with surges of electrons.
DBD: A Specialized Form of Corona Discharge
The discharge is similar to a spark, but not nearly as hot. It does not result in a discharge of the electrodes. Only small areas of the inside surface of the dielectric discharge with each electron avalanche. The strong electric field induces a secondary, high voltage mini-circuit within the oxygen gap. Thousands of these discharges can be repeated as long as the voltage supplied to the anode and cathode continues to increase.
The power supply for an ozone generator alternates this electric field thousands of time each second. When the pressure (voltage) rises through the threshold that sets off electron avalanches, the discharge storm erupts. Since the electric field changes thousands of times each second, the oxygen gap experiences thousands of storms each second. The optimal frequency and voltage depends on the gap size and oxygen pressure. The electronics controlling the voltage need to be tuned to match the particular dielectric arrangement for optimal ozone production.
The benefits of setting off thousands of mini discharges in a space between insulators instead of simply allowing a spark to ark between the positive and negative electrodes are the following: 1) an arc generates so much heat that it melts most materials. Such an arc is useful for welding or plasma torches, but would destroy an ozone generator. 2) Ozone production is minimal with an arc. Most of the energy is converted to heat and the heat destroys ozone. 3) Producing many small discharges from dielectric surfaces within a strong electrical field stays cooler and yields more ozone.
This form of ozone generation is called “Dielectric Barrier Discharge” (DBD). DBD belongs to a category of corona discharge. Corona discharge was observed by ancient sailors on the masts of their ships as a flare of luminous plasma at the tips of the mast and other pointed parts of their ship when the atmosphere is highly charged. The phenomenon occurs when strong electrostatic forces concentrate at sharp points and break down air to form plasma. You can observe this phenomena with an electrostatic generator in a dark room. Many of the small ozone generators sold for home use rely on a form of corona discharge from sharp points. Higher quantities of high concentration ozone used in commercial applications often use DBD type ozone generators.
Ozone can also be produced with ultraviolet light and radiation bombardment. The ozone layer which protects earth from harmful radiation is produced by ultraviolet light with a wavelength less than 200 nm. Ultraviolet light between about 200 and 300 nm destroys ozone. The ozone layer is maintained with a balance of ozone generation and destruction with ultraviolet light. Ozone can be created in water with electrolysis. Passing an electric current through water breaks the water molecules into hydrogen and oxygen. Using specific electrodes results in oxygen combining to form ozone.
Here at Oxidation Technologies we do not build DBD plasma cells, but we rely on companies who continue to research and build quality generators for a wide range of applications. We specialize in integrating the right ozone generators into specific applications. Dissolving ozone into water requires ozone generators that make higher concentrations of ozone. Many applications can utilize low pressure or even slight vacuum to minimize the danger of ozone leaks. Sometimes controlling precise levels of low ozone concentrations can best be attained with an ultraviolet ozone generator. Whatever your application, we have the expertise to integrate the right ozone generator to your process.
Ozone: Science & Engineering The Journal of the International Ozone Association Volume 41, 2019 – Issue 1Ozone Synthesis and Decomposition in Oxygen-Fed Pulsed DBD System: Effect of Ozone Concentration, Power Density, and Residence Time Sławomir Jodzis &Tobiasz Barczyński From https://www.tandfonline.com/doi/abs/10.1080/01919512.2018.1506317>
IOP Science publication: Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments From <https://iopscience.iop.org/article/10.1088/1361-6595/aa6426>
Journal of Physics B: Atomic and Molecular Physics Electron impact dissociation in oxygen B Eliasson and U Kogelschatz Journal of Physics B: Atomic and Molecular Physics, Volume 19, Number 8
Plasma Chemistry and Plasma Processing, Vol. 23, No. 1, March 2003 ( 2003) Inûited Reûiew Dielectric-barrier Discharges: Their History, Discharge Physics, and Industrial Applications Ulrich Kogelschatz1 Receiûed April 5, 2002; reûised May 7, 2002 https://www3.nd.edu/~sst/teaching/AME60637/reading/2003_PCPP_Kogelschatz_dbd_review.pdf
Very clear and graphic explanation https://www.plasma-school.org/files/lectures/2016/Guaitella16.pdf
Every day, pharmaceutical companies around the world produce tons of products that people use to enhance their quality of life. This realm of products has been lumped into a category called “Pharmaceuticals & Personal Care Products,” (PPCPs). These products and drugs do not disappear, but are found increasingly in the water being discharged from wastewater treatment plants. The impact that this cocktail of chemicals has on the animals and people dependent on this water is not fully understood, but the evidence is clear that it is not good.
Ozone is a powerful oxidant capable of breaking troublesome molecules. What impact does ozone have on PPCPs? A recent laboratory study published in the engineering journal of the International Ozone Association (IOA) exposed water containing thirty seven different PPCPs to investigate the degradability of these chemicals.
Eight of the thirty five were very quickly degraded to or below their limit of detection with a dissolved ozone dose of 1ppm within 5 minutes. Five more were degraded with a dissolved ozone dose of 2ppm within 5 minutes. Five more required at least 10 minutes of retention time at 2 ppm.
The other half of the thirty five required more time and a higher dose of ozone. Three of them, (DEET, Ketoprophen, and Primidone) did not degrade below their limit of detection even when exposed to 9ppm of dissolved ozone for 15 minutes.
Ozone clearly has a significant role to play with PPCP cleanup. Further study is sure to discover ways to optimize the process and make it more effective. Oxidation Technologies specializes in integrating ozone into the specific process of diverse customers. We continue to pursue a better understanding of ozone use in a variety of applications.
N. Evelin Paucar, Ilho Kim, Hiroaki Tanaka & Chikashi Sato (2019) Ozonetreatment process for the removal of pharmaceuticals and personal care products in wastewater, Ozone: Science & Engineering, 41:1, 3-16, DOI: 10.1080/01919512.2018.1482456