Ozone used to remove micropollutants

Wastewater treatment for micropollutants is becoming more popular and important worldwide. As the concerns of pharmaceuticals in water comes to the forefront, the desire for cleaner, safer water is understood. This leads to the implementation of systems to remove micropollutants from wastewater during the treatment process. Ozone is one technology that has proven effective to remove micropollutants and pharmaceuticals from wastewater. Article below gives some great information on another new plant upgrading to ozone use.

Learn more about ozone use for wastewater and micropollutants HERE

Full news article HERE

Swiss wastewater plant chooses Xylem’s ozone tech to remove micropollutants

Swiss wastewater plant chooses Xylem’s ozone tech to remove micropollutants

SCHAFFHAUSEN, Switzerland – Xylem (NYSE: XYL) has been awarded a contract to provide advanced treatment technology to the Werdhölzli wastewater treatment plant in Zurich, the largest wastewater treatment facility in Switzerland.

The European Union (EU) has published a list of prioritized substances that pose a threat to ground and surface water sources. To adhere to the environmental standards set by the EU, the member countries have to regularly monitor the occurrence of the listed substances.

In Switzerland, a 20-year process to upgrade major wastewater treatment plants is underway to tackle such pollutants, which currently remain in treated wastewater and are released into surrounding lakes and rivers.

As part of this agenda, new legislation came into effect on 1 January 2016 requiring wastewater treatment plants to implement an additional treatment process, specifically for the removal of micropollutants.

Xylem said its ozone technology will enable the plant to meet new Swiss regulations regarding the protection of water bodies and specifically, the removal of micropollutants.

Eight Wedeco SMOevo ozone systems will be supplied to the Werdhoelzli wastewater treatment plant as part of a 50 million CHF (51.17 million USD) upgrade project.

Once operational, the plant will be able to produce 153 kilograms of ozone per hour (kgO3/h)  to treat a  flow of 6,500 liters per second (l/s), making it the largest ozone plant for the removal of micropollutants in the world.

Growing concern about micropollutants – contaminants that are released from everyday products such as industrial chemicals, pharmaceuticals and personal care products (PPCPs), pesticides, and hormones, and cannot be removed with conventional wastewater treatment technologies – is leading many countries to consider more rigorous treatment solutions.

Peter Wiederkehr, chief operating officer (COO) Entsorgung + Recycling Zürich, said: “Wastewater treatment plants serving a population of 5,000 or more must be equipped now with a new treatment stage which ensures that up to 80% of pre-selected micropollutants are removed. Extensive research has confirmed ozone as a preferred technology for this stage. Xylem’s Wedeco SMOevo ozone systems will enable us to meet the new treatment regulations with a reliable, environmentally-friendly and cost-effective solution.”

Florian Milz, key account manager with Xylem added, “The elimination of micropollutants from wastewater is a challenge which more and more facilities must address. While conventional treatment processes do not remove them completely, oxidation with ozone is proving to be one of the most efficient methods for reducing these contaminants. Pollutants, colored substances, odors and microorganisms are directly destroyed by oxidation, without creating harmful chlorinated by-products or significant residues.”

Construction on the Werdhölzli wastewater treatment plant upgrade began in 2016 and the plant is expected to be operational by 2018.

Ozone Equipment Service and Repair

Here at Oxidation Technologies, we have the know-how and the tools required to help you with whatever Ozone issues you may be having. Whether it’s generator repairs, system services, or simple preventative maintenance, we are here to help. Our technicians have experience working with most ozone generator manufacturers and we have all the equipment needed to either keep you running, or get you back up-and-going as soon as possible. We offer comprehensive service contracts for ozone systems as well as for the water treatment industry. Follow below to see just how Oxidation Technologies can help you.

Ozone Generator/System Repair:

  • We can repair your ozone generator on-site or here at our location in Inwood, IA
  • We have repair technicians that we work with, and trust throughout the USA
  • Most ozone generators use common components, even if your ozone generator is obsolete, it may be repairable
  • New ozone generators may cost more to purchase than to repair your existing ozone generator, call us for a quote today!

Ozone Generator/System Service:

  • We can perform on-site service of your integrated system as needed or set-up a contract
  • We offer monthly, quarterly, bi-annually, and annual service contracts
  • Proper service and maintenance are required for long lasting equipment
  • Many times, preventative maintenance will cost less than costly repairs

Ozone System Preventative Maintenance:

  • Even the best systems require maintenance
  • Poorly maintained ozone systems produce poor results
  • Ozone system maintenance can be simple if it is performed regularly
  • Feed gas systems are commonly neglected
  • Ozone leak sensors require calibration
  • Some corona cells require cleaning
  • Check valve and water traps must be in working condition
  • If neglected, repairs will cost far more than routine maintenance

Ozone used to remove odor from Sports Equipment

One of our customers who uses ozone for a unique application created the following video. This is a great explanation of one of the many uses for ozone.

Ozone has many applications in air treatment. While care and caution must be taken, ozone gas in air is very effective at removing odor, eliminating bacteria, and even prolonging the shelf-life of food. More info on ozone use in air treatment is at the link below:


Ozone Science & Engineering

The International Ozone Association (IOA) publishes a journal called Ozone Science & Engineering. This is a publication issues 6 times per year with great info on many ozone applications.

Ozone science and engineering - the journal of the international ozone assocation

Ozone: Science & Engineering (OS&E), Vol. 42, Issue 5 is now available online. This new issue contains articles about a variety of ozone applications including a molecular modeling study examining potential mechanisms of ozone to inactivate SarsCov1 COVID virus, sterilization of medical devices, pesticide residue removal, ozone in food storage, contaminant oxidation, textile treatment, and cyanotoxin oxidation.

Receive OPEN ACCESS to the entire archive of OS&E by becoming an IOA member at https://lnkd.in/gkk-tq2

View the Table of Contents at the Taylor and Francis website: https://lnkd.in/gGf7pCg

Dissolve ozone in water with bubble diffusers

Ozone gas can be dissolved into liquid with simple bubble diffusers, similar to what is commonly used in the bottom of a fish aquarium for aeration. This is a simple and cost-effective method to dissolve ozone gas into liquid. As ozone is partially soluble into liquid the ozone gas will transfer into liquid immediately at the interface between the ozone gas bubble surface and the surrounding water.

Diffusers implement a gas permeable membrane that will disperse the gas stream into many smaller ozone gas bubbles in the water. As these ozone gas bubbles naturally rise to the surface of the water that ozone will transfer into the water due to contact between the liquid and gas bubble.


  • Low cost
  • Easy to setup
  • Low energy – does not require water pumps or elevated water pressures
  • Simple, reliable operation long-term


  • Generally the least efficient method of dissolving ozone into liquid
  • Diffusers can become plugged and may require periodic replacement
  • Difficult to use in pressurized water flows

Ozone gas is partially soluble into liquid. However, using proper methods and equipment high mass transfer efficiencies can be realized with any method of dissolving ozone into water. Review the tips below for success using an ozone gas bubble diffuser in your ozone application.

Fundamentals of ozone solubility:

  • Lower temperatures increase the solubility rate of ozone gas into liquid
  • Higher pressures increase the solubility rate of ozone gas into liquid
  • Higher ozone gas concentrations increase the solubility rate of ozone gas into liquid

Design considerations for your bubble diffuser and column:

Diffuser micron ratings – smaller is better!

Ozone gas bubble diffusers will be rated in micron size, or resulting bubble size the diffuser will create. The membrane that splits the gas stream into small bubbles will have pore sizes, smaller pores will result in smaller bubbles. This pore size or bubble size is normally referred to in a micron rating.

Micron = micrometer. Equal to 0.001 millimeter, or about 0.000039 inch

Smaller bubbles create more surface area of the gas the ozone is flowing in. Greater surface area will increase the ability of ozone gas to transfer into the liquid. See the example below:

Ozone gas bubble size compared

The image above shows the same gas volume (1 ft3) shown in one bubble, 8 identical bubbles, and 512 (8 tall x 8 wide x 8 deep) identical bubbles.

  • One 1 cubic foot sphere = 4.8 ft2 surface area
  • Eight 0.125 cubic foot spheres = 1 cubic foot = 1.2 ft2 each = 9.66 ft2 total surface area
  • Eighty 0.0125 cubic foot spheres = 1 cubic foot = 0.26 ft2 each = 20.8 ft2 total surface area
  • 512 0.001953 cubic foot spheres = 1 cubic foot = 0.07567 each = 38.7 ft2 total surface area

A bubble size ¼ the size (4.8 / 4 = 1.2) results in 8x more bubbles and double the overall surface area.

Relating this to your ozone gas flow. A 25 micron diffeser will create bubble sizes ¼ the size of a diffuser rated for 100 micron therefore creating more than 2x the surface area of gas contacting the water at the same flow-rate of gas flowing into water.

Smaller really is better!

Tank design – skinny is better!

Gas bubbles will naturally rise to the surface of water due to buoyancy. Therefore, the taller your tank, column or ozone tank is the longer your gas bubble will remain in the water increasing the opportunity for the gas to transfer into the liquid.

Taller tanks will also increase the water 

pressure at the bottom of the tank where the ozone gas diffuser will likely be placed. Greater water pressure will increase the natural solubility of ozone gas into liquid. For example:

11.33 feet of water = 5 PSI

5 PSI = 34% increase in ozone solubility vs 0 PSI

Increasing your water column by 11.33 feet will increase your solubility of ozone, or your mas potential ppm of ozone in water by 34%.

1 ppm becomes 1.34 ppm with no other changes.

A great example of separate columns is shown in the image and dimensions below. Both columns are 3 liters in volume, with a change in diameter from 2” to 4” the height is increased from 12” to 58”

If you have the opportunity when desiring your tank or reactor, choose the smallest diameter possible.

Skinny really is better!

Counter Current Flow

Ozone contacting basins can be designed with counter-current flow, where the water flows counter-current to the gas bubbles. While gas bubbles will naturally rise to the surface of the liquid due to buoyancy liquid can be forced into the path of the gas bubble to create additional turbulence. The diagram below shows a simple contactor basin design using baffles to create counter-current and con-current flows of ozone gas to liquid

Ozone gas countercurrent flow with bubble diffuser

This same technique can be applied to any column in flowing water using piping water flowing down a column that ozone gas is rising within. Consider this simple technique when designing your tank or piping system

Full page info on ozone diffusers HERE

Fundementals on ozone solubility into liquid HERE

Understand dissolved ozone vs ozone dosage

Purchase ozone diffusers here

Ozone Dosage vs Dissolved Ozone

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:

Ozone dissolved into water with bubble diffusers
Ozone dissolved with a bubble diffuser is simple and cost effective. However, in most cases offers the lowest mass transfer efficiency of any method used and therefore the greatest difference between ozone dosage and measured dissolved ozone in water.
Ozone dissolved into water via pump and venturi
Ozone dissolved with a pump and venturi injector is simple to set-up and fairly efficient. This will mix water in the tank well and achieve higher mass transfer of ozone into water than a typical bubble diffuser due to the forceful mixing action of a venturi.
Ozone dissolved into water via an ozone injection skid
Ozone dissolved into water with an ozone injection skid. In this application a dedicated, pressurized ozone mixing tank can be used to increase mass transfer of ozone into water as ozone solubility increases as water pressure increases. A system like this will have the lowest difference between ozone gas dosed into water and resulting measured dissolved ozone in water.

More info ozone solubility found HERE

Full Webpage on this topic HERE

Ozone used to purify Ethanol

There has been a great deal of interest recently in the use of ozone to purify ethanol products to achieve a higher grade of ethanol or alcohol products. We have performed a great deal of bench-testing and pilot testing with companies to assist and achieve these goals. We have found that ozone is very effective at reducing certain undesirable compounds from ethanol along with improving the color and odor of the ethanol.

We thought it might be helpful to assist with promoting this application and the original research that brought this application to light. Right here in Iowa, at the University of Iowa research was done on the purification of Ethanol. See link below and summary for details:

Link to full paper HERE

Purification and Quality Enhancement of Fuel Ethanol to Produce Industrial Alcohols with Ozonation and Activated Carbon


The total ethanol production capacity in the US just passed 6 billion gals/year. The production process of ethanol from corn includes corn milling, cooking, enzymatic starch conversion, fermentation and distillation.Food-grade alcohol production requires more care and undergoes costly additional purification to remove volatile organic impurities. These impurities could be of health concern and/or impart unpleasant tastes and odors to beverage alcohol. Multiple distillation steps are usually employed. The additional purification of ethanol to obtain food-grade alcohol adds at least $0.30 per gallon in processing costs. In this research, we tested a novel approach to purify fuel grade ethanol to pharmaceutical and beverage grade. The cost of the proposed treatment process is expected to be less than $0.01 per gallon. We have shown that ozone can oxidize a number of undesirable compounds in ethanol. Furthermore, it was demonstrated that adsorption ongranular activated carbon can remove many of the ozonolysis byproducts. All chemical and sensory analyses were completed using solid phase microextraction (SPME) to extract volatile organic compounds from ethanol samples and a multidimensional GC-MS-Olfactometry system to identify impurities and the impact of odorous compounds. To date, we confirmed a significant reduction of some impurities with ozone alone.Ozone and granular activated carbon are very effective in purifying fuel ethanol. Also, we designed a pure ozone generating setup. This setup can provide further purification efficiency on this research. This technology will help the corn milling and ethanol industry and provide an opportunity for improving the long-term sustainability of corn growing and processing.

If you have any questions on this application, or would like help performing your own testing, please let us know. We would be glad to help.

Ozone disinfection of respirator masks for front-line workers coping with COVID-19

Great article on the use of ozone to disinfect respirator masks. See original article HERE.

Researchers at Yale School of Medicine and collaborators have successfully used ozone to disinfect the respirator masks used by healthcare workers to protect against respiratory diseases such as coronavirus disease 2019 (COVID-19).

The development could be used to address a shortage in the availability of this critical piece of personal protective equipment, caused by the COVID-19 crisis.

The authors say that, to their knowledge, their study is the first to report successful disinfection of the masks with ozone and the first to identify the conditions necessary to do so, without damaging mask function.

A preprint version of the paper is available on the server medRxiv*, while the article undergoes peer review.

Supplies of the masks are dwindling

Supplies of the NIOSH-certified N95 filtering facepiece respirators (commonly shortened to“N95 respirators”) have dwindled with the increasing strain placed on healthcare systems due to the COVID-19 pandemic.

This had prompted front-line medical workers to resort to reusing the respirators and experimenting with their own methods of disinfection, which some researchers have described as generally ineffective and damaging to filter performance.

What does the CDC say?

The Centers for Disease Control (CDC) has recognized that the reuse of personal protective equipment such as N95 respirators may be necessary to protect healthcare personnel and to lower the risk of transmitting infection in the workplace.

However, the organization says four essential points must be addressed when considering potential ways to achieve this. The method must be effective at killing the organisms being targeted; must not degrade the function of the equipment; must not introduce new risks to healthcare workers and must be practical in the setting of emergency pandemics such as COVID-19, where resources may be too limited to ensure adequate supplies of the equipment.

Some organizations have described potential protocols, including disinfection with dry heat or using vaporized hydrogen peroxide (VHP) and UV-C light.

Ozone is an appealing option

However, Manning and colleagues were interested in the possibility of disinfecting the respirators with ozone as an alternative for healthcare personnel who may not have access to VHP or other disinfection devices.

The team says that not only is ozone attractive as a potential disinfector because it is a strong oxidant that can deactivate viruses, but it can be generated from air, can quickly be destroyed, and does not leave any residue.

Now, the researchers have tested using ozone to kill Pseudomonas aeruginosa on three types of N95 respirators, namely the 3M 1860, 3M 1870, and 3M 8000.

They point out that P. aeruginosa is a bacterium that the CDC has previously referred to as more difficult to kill than viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Top row: cultures from respirators inoculated with bacteria culture, exposed to 400 ppm ozone 80% humidity for two hours, and incubated for 24 hours. Bottom row: cultures from respirators inoculated with bacterial culture, exposed to ambient air 35% humidity for two hours, and incubated for 24 hours. Columns are labeled to identify respirator types tested. Tests were performed in duplicate for each respirator type. Serial dilutions were performed to enumerate the numbers of live bacteria.
Top row: cultures from respirators inoculated with bacteria culture, exposed to 400 ppm ozone 80% humidity for two hours, and incubated for 24 hours. Bottom row: cultures from respirators inoculated with bacterial culture, exposed to ambient air 35% humidity for two hours, and incubated for 24 hours. Columns are labeled to identify respirator types tested. Tests were performed in duplicate for each respirator type. Serial dilutions were performed to enumerate the numbers of live bacteria.

The ozone disinfector the team used

The device comprised an airtight chamber than could generate ozone from ambient air at a concentration of 500 parts per million (ppm). This ozone UV analyzer could accurately determine ozone levels in the chamber and an ozone destruction unit.

The team reports that exposing the respirator to ozone at a concentration of 400ppm at a humidity of 80% over two hours successfully killed bacteria on all three types of respirators.

Image of N95 respirator after ten treatments with 450 ppm ozone for 2 hours at 75-90% humidity. There is little noticeable wear on the respirator after extended exposure to ozone.

Furthermore, exposure to ozone at this concentration with a relative humidity of 75-90% at room temperature did not degrade the filtration capability of the 1860 and 1870 type respirators for up to 10 cycles of two-hour treatments.

A practical way to decontaminate the respirators

Manning and colleagues advise that ozone disinfection using the small devices could serve as an effective way to decontaminate N95 respirators, especially in rural areas and in cases where healthcare workers and institutions have no access to large-scale disinfection facilities.

Ozone used for wound care

Another great paper has been released for the use of ozone in the medical industry. See below, or click link HERE for original paper.

Wearable and Flexible Ozone Generating System for Treatment of Infected Dermal Wounds

Wound-associated infections are a significant and rising health concern throughout the world owing to aging population, prevalence of diabetes, and obesity. In addition, the rapid increase of life-threatening antibiotic resistant infections has resulted in challenging wound complications with limited choices of effective therapeutics. Recently, topical ozone therapy has shown to be a promising alternative approach for treatment of non-healing and infected wounds by providing strong antibacterial properties while stimulating the local tissue repair and regeneration. However, utilization of ozone as a treatment for infected wounds has been challenging thus far due to the need for large equipment usable only in contained, clinical settings. This work reports on the development of a portable topical ozone therapy system comprised of a flexible and disposable semipermeable dressing connected to a portable and reusable ozone-generating unit via a flexible tube. The dressing consists of a multilayered structure with gradient porosities to achieve uniform ozone distribution. The effective bactericidal properties of the ozone delivery platform were confirmed with two of the most commonly pathogenic bacteria found in wound infections, Pseudomonas aeruginosa and Staphylococcus epidermidis. Furthermore, cytotoxicity tests with human fibroblasts cells indicated no adverse effects on human cells.

Ozone for wound care


Skin and soft tissue infections (SSTIs) are a major health and financial burden for millions of people worldwide. In 2016, SSTIs comprised 3.5% of all emergency room visits (Niska et al., 2016). Furthermore, the average cost of a hospital visit resulting from an SSTI is about $8,000 (SSTI, 2018). These numbers are only expected to rise in the years to come due to the aging population and the increasing prevalence of diabetes associate non-healing wounds and bedsores. To complicate the issue even further, many of these infections can be caused by bacteria that are resistant to common forms of treatment. Infections caused by drug-resistance bacteria have become a significant problem and now affecting over 2 million people in the US each year (Centers for Disease Control and Prevention, 2018). For instance, methicillin-resistant Staphylococcus aurous (MRSA), has been noted to kill more Americans every year than HIV/AIDS, emphysema, or homicide (Federal Bureau of Investigation, 2017; CDC, 2018; Kourtis et al., 2019; Lei et al., 2019). This alarming decrease in antibiotic efficacy has been brought on by a number of factors, but a primary culprit is the commonality of antibiotics usage in society today, especially for inappropriate or unnecessary indications (Ventola, 2015). Simultaneously, major drug companies have reduced the number of antibiotics they are developing. This is mainly due to a significantly reduced return on investment for antibiotic research and development compared to the drugs for chronic conditions such as diabetes, heart disease, and cancer (Ventola, 2015).

Recently, there has been increased effort toward the development of alternative (non-antibiotic) materials and treatments for bacterial infections (Kowalski et al., 1998; Laroussi et al., 2000; Fridman et al., 2005; Fontes et al., 2012; Guan et al., 2013; Korshed et al., 2016). For example, metallic nanoparticles of noble metals such as silver have shown to exhibit antimicrobial properties for a wide range of bacteria and utilized in various advanced wound dressings (Maneerung et al., 2008; Rujitanaroj et al., 2008). Despite having effective antimicrobial activity, many studies have also shown that silver nanoparticles are cytotoxic, and cause damage to cellular components such as DNA and cellular membrane (Korshed et al., 2016). Other materials include polyvinyl-pyrrolidone, a non-ionic synthetic polymer, which allows for gradual release of free iodine with antimicrobial effects. Yet, povidone-iodine and its different complex forms have also been shown to delay wound healing by inhibiting fibroblast aggregation and leukocyte migration (Álvarez-Paino et al., 2017). Free radical and ionized gasses generated by cold atmospheric plasma (CAP) have also shown to be an effective alternative therapeutic tools, providing both antimicrobial properties and help promoting wound healing, and tissue regeneration (through activation of growth factors and stimulation of angiogenesis) (Laroussi et al., 2000; Fridman et al., 2005). Although a promising approach, only a few devices and systems using CAP for wound treatment have been adopted by the patients or their caregivers. One major impediment of their widespread adoption is the system cost and complexity. These devices (e.g., Microplaster from Adtech Ltd) use plasma gun/torch that require high voltages, carrier gas (typically argon) and need to be operated by trained personnel in an outpatient setting. Similarly, smart wound dressings have been developed to help increase wound healing through delivery and sensing of factors such as oxygen, as well as drug delivery and providing optimal wound healing conditions (Gupta et al., 2010; Mostafalu et al., 2015; Ziaie et al., 2018).


Antibiotic resistant infections are a growing public health concern. A promising alternative to antibiotic therapy is utilizing the antimicrobial properties of topical ozone treatments. Developing a portable system designed to apply ozone to a targeted area will increase the options patients have in fighting infections that may otherwise be difficult to treat. In this work, we developed an ozone-releasing wound dressing consist of a disposable gas permeable hydrophobic patch with a reusable and portable ozone-generating unit. The patch incorporated a hydrophobic and highly ozone permeable outer layer and an inner dispersion layer for increased gas distribution uniformity. The antimicrobial effects of the system were tested against common antibiotic resistant strains of bacteria. The results indicated complete elimination of P. aeruginosa and significant reduction in the number of S. epidermidis colonies after 6 h of exposure. These tests also showed a high level of biocompatibility (low cytotoxicity) with human fibroblast cells during the same duration ozone treatment. The described patch is a promising tool in the management of chronic infected wounds.

Ozone in Aquaculture

Here is a great open article on the use of ozone in aquaculture. Full article here:


What’s the optimum ozone level in RAS facilities?

Scientists have determined that salmon post-smolts tolerate similar levels of ozone in brackish water – which is increasingly used in RAS facilities – as they do in freshwater.

Kevin Stiller was the lead author on a paper defining the threshold of ozone in brackish water. Here he is at the control room of Nofima’s RAS facility at Sunndalsøra © Terje Aamodt, Nofima.

Ozone is a strong oxidant, commonly used for improving water quality and disinfecting pathogens in freshwater fish farms. When ozone reacts with certain constituents of seawater, however, toxic byproducts can severely impact the health of fish populations. As brackish water is increasingly introduced in farming post-smolt salmon, thresholds for the safe use of ozone need to be established. Suppliers of recirculating aquaculture systems (RAS) are looking for safe, cost-efficient and reliable ways to maintain optimal water quality in brackish water RAS, and with this research they are now a step closer.

Scientists from Nofima and The Conservation Fund Freshwater Institute (TCFFI), both central in CtrlAQUA (Centre for research-based innovation), wanted to determine if ozone is safe for salmon in brackish water, and what the safe limits are for post-smolts.

The scientists carried out a trial determining the ozone limit in a flow-through system. Atlantic salmon at 100 grams were reared in brackish water of 12 ppt (parts per thousand) salinity for 12 days. They were exposed to ozone levels of 250 (control), 280 (low), 350 (medium), 425 (high) and 500 (very high) mV (millivolts). They identified ozone levels up to 350mV as potentially safe and 300 mV as safe for the health of post-smolts in flow-through brackish water.

In a follow-up study by Nofima that is not yet published, the identified threshold was confirmed for RAS. Carlo Lazado, fish health researcher in Nofima, will present the results at the digital conference “Smolt production in the future”, on 21 October.

Chris Good, scientist at TCFFI, reports that even lower ozone dosages are sufficient to improve water quality.

“This would depend on the quality of water being treated but in our experience in replicated freshwater RAS, a lower ozone level of 290 mV still resulted in significant improvements to water quality in general, including reduced biochemical oxygen demand and increased UV transmittance,” Good says.

Here is a great open article on the use of ozone in aquaculture.

Full article here: