R.N. Kinman (1975) & E. Katzenelson, et al. (1974) reported “As temperature increases, ozone becomes less soluble and less stable in water; however, the disinfection and chemical oxidation rates remain relatively stable.  Studies have shown that although increasing the temperature from 0 to 30 deg C can significantly reduce the solubility of ozone and increases its decomposition rate, temperature has virtually no effect on the disinfection rate of bacteria.”

Ozone use for Surface Sanitation

Original page HERE

Food safety is a growing concern worldwide. The CDC (Center for Disease Control and Prevention) estimates that each year one (1) in six (6) Americans get sick from food borne diseases. As illnesses, hospitalizations, and deaths are made more public by the media this is a constant concern for food processors.

In food processing it is important to provide pathogen free food products. Keeping food products pathogen free and reducing the potential for cross-contamination of potentially deadly pathogens is very crucial, and that is why surface sanitation is so important. This page will provide some detail on the potential use of ozone for surface sanitation.

Many processing plants already use ozone-in-water, or aqueous ozone for antimicrobial intervention steps directly on the surface of food products. Due to the FDA and USDA giving ozone GRAS approval for use directly on the surface of all food products the use of ozone has spread dramatically in the last 10 years. Ozone use for surface sanitation is just one more cost saving method that can be implemented by plants already using ozone, or for plants that would like lower cost and have a more effective method for surface sanitation.

One of the major concerns for cross-contamination on food processing equipment is bio-film buildup. Bio-films are layers of microorganisms bonded tightly to a surface. Microbes can attach themselves to a surface and continue to grow layer upon layer of new microbes. The new layer of microbes can provide nutrients and protection against sanitizers to the existing layers of microbes. These layers of microbes can continue to grow, and become more resistant to sanitizers over time making sanitation more difficult if proper sanitation is not achieved on a regular basis. These resistant bio-films are most common in cracks, crevices, and corners of food processing equipment that are only sanitized periodically.

Chemical Drawbacks

A common sanitizer in the food processing industry is chlorine. Chlorine is mixed with water providing chlorinated water to be used as a sanitizer. Some microorganisms such as E.coli and Giardia can build resistance to chlorine over time. This may make chlorine less effective than desired over time. Chlorine residual in waste water can also be regulated and make water recirculation or discharge more difficult due to chlorine residuals in the water.

One more drawback to chlorine and other chemicals is the harsh effect they may have on equipment made of metals and wood. Common issues are steel components that chlorinated water is constantly exposed to, shortening the life of potentially expensive equipment. Wooden wine barrels are also damaged by harsh chemicals. Winemakers take special care to choose high quality wooden barrels to age wine within, this wood can be damaged or altered to the point it no longer serves the original purpose.

Ozone-in-water Application

Ozone can be dissolved into water just as chlorine and other chemicals can be. In many plants ozone injection systems that provided aqueous ozone may already be in place for use on food products for anti-microbial intervention. Aqueous ozone can be sprayed anyway within the plant safely. Equipment, walls, floors, drains, tanks, tubs, racks, knives, and tables can all be sprayed with aqueous ozone. Enclosed piping can also be sanitized with ozone using a Clean in Place (CIP) system.

During sanitation with ozone a two-step process is generally required. Surfaces are cleaned and bio-films are removed with a hot water or cleaning step. Then aqueous ozone is used to sanitize the surface destroying all bacteria, viruses, fungi, and spores. No other sanitation step after the use of ozone is necessary. In fact no rinse step is necessary after ozone as the ozone will leave no residual on the surface. This may lower cleaning time and water usage costs.

Ozone is a powerful sanitizer that leaves no residual on the surface of equipment or materials. This limits the corrosive potential of ozone and provides a more gentle sanitizer than many of the common chemicals used. Ozone will provide great sanitation results without the harmful effects on metal or wood equipment.

Ozone can be used throughout the day during processing. As there is no danger in damaging product with harsh chemicals, ozone can be used to sanitize processing equipment throughout the day during normal processing. This may lower down time, and allow for more production hours.

Results with the use of ozone-in-water

Aqueous ozone has proven an effective sanitizer in many applications throughout the food processing industry.

Below are few examples of result obtained.

Ozone tests at fruit and vegetable pilot plant

Tests conducted in 1999 by Polytechnic State University at a pilot plant showed the effectiveness of ozone in reducing microbiological loading. The Ozone System in use provided a 2.0 ppm dissolved ozone level that was sprayed on the surfaces to be sanitized. No other cleaning methods were used with the ozone to ensure all reductions in bacteria were attributed to the aqueous ozone. The table below shows the results from this test.

Surface	% Reduction in Plate Count
Stainless Steel Kettle	89.7-98.2
Stainless Steel Tabletop	98.9-99.7
Stainless Shroud	63.1-99.9
High-Traffic Floor	67.0-95.6
Low-Traffic Floor	84.3-99.9
Floor Drain	–
Floor Drain 2nd Attempt	77.5
Plastic Shipping Containers	96.9-97.2

Ref: Use of ozone for winery and environmental sanitation
By Brian Hampson, PhD, Food Science and Nutrition Dept
California Polytechnic State University, San Luis Obispo, CA
http://www.practicalwinery.com/janfeb00/ozone.htm

Results from tests at a Fortune 50 Pork Processing Company

Tests were performed at a Fortune 50 Pork Processing Company to determine the effectiveness of aqueous ozone for sanitation of hard surfaces, meat cuts, and knife dips. These tests were performed in a working plant in normal working environments. Samples were sprayed with aqueous ozone ranging from 1.1 – 1.4 ppm for about 10-15 seconds. All tests compared microbiological counts on samples before and after ozone, ozone vs 180-deg F water, and ozone vs 180-deg F water and cold water.

In these tests, ozone performed very well as a sanitizer. Ozone showed a consistent reduction in microbial loading on each material tested. In all tests ozone performed at an acceptable level for sanitation. In many tests ozone outperformed 180-deg F water. As these tests were performed in real world environments with fairly conservative ozone levels (1.1 – 1.4 ppm) these results are very realistic and show the potential for ozone use as a surface sanitizer.

Results from tests at a Fortune Fifty Pork Processing Plant 4/09/02. The Effectiveness of Ozonated Water for Hard Surface Sanitation, Meat Cuts and Knife Dips-Microbial Kill Results http://www.ozonesafefood.com/Ozone_Report_1.pdf

White Paper Abstract

Decontamination of a Multilaminated Aseptic Food Packaging Material and Stainless Steel by Ozone

Authors: Mohammed A. Khadre, Ahmed E. Yousef

Abstract

A multilaminated aseptic food packaging material and stainless steel were treated with ozone to inactivate natural contaminants, bacterial biofilms and dried films of Bacillus subtilis spores and|| ||Pseudomonas fluorescens. Sterility of the multilaminated packaging material was achieved when 1.0 x 2.0 cm-pieces of the naturally-contaminated material were treated with ozone in water (5.9 µg/mL) for 1 min. Dried films of spores (108/6.3-cm² surface) were eliminated by 13 µg/mL of ozone in water for the multilaminated packaging material and 8 µg/mL in case of the stainless steel. Ozone inactivated Pseudomonas fluorescens in biofilms more effectively on stainless steel than on the multilaminated packaging material. Repeated exposure to ozone of Pseudomonas fluorescens in biofilms on the multilaminated packaging material eliminated up to 108 cfu/12.5 cm². In conclusion, ozone is an effective sanitizer with potential applications in the decontamination of packaging materials and equipment food-contact surfaces.

Click here for the abstract

Studies on the disenfection and removal of biofilms by ozone water using an artificial microbial biofilm system http://www.tandfonline.com/doi/abs/10.1080/01919510802586566

Gaseous Ozone Applications

Ozone can also be used in the gaseous form to disinfect and sanitize areas. While actual bio-films will not be removed with gaseous ozone, there are applications where this may be a suitable solution. Many applications do not allow for water to penetrate locations where bacteria may reside and cause future cross-contamination. Gaseous ozone has been used for many years for odor control, mold remediation, and other disaster restoration services. The same action used to remove odor and mold spores can be used to kill bacteria and mold in industrial settings.

Results from gaseous ozone applications

The use of gaseous ozone has been tested in various forms for many applications. A wide variety of applications from hospital rooms to sports gear, such as hockey equipment, have used gaseous ozone for disinfection. When using aqueous ozone for surface sanitation the two main variables that affect the success of ozone are contact time and ozone levels. When using gaseous ozone a new variable, humidity, will dramatically affect the results. The level of humidity in the environment will affect the ability of ozone to penetrate and destroy microorganisms. The following research will show a new variable affecting the results of microbiological reduction with ozone.

Results from study on ozone use for surface disinfection

This study investigated the potential of gaseous ozone to inhibit growth of microorganisms on surfaces. This study evaluated the effectiveness of ozone at varying ozone concentrations, for various contact times, at varying relative humidity.

The effect of ozone on Apergillus niger, Pseudomonas aeruginosa, and a mix of microorganisms was tested. Highly contaminated surfaces were exposed to ozone gas at various levels ranging from 0.1 to 5,000 ppm in these tests. Exposure times from 20 minutes to 120 minutes were used at low ozone levels, while exposure times of 0.33 minutes to 20 minutes were used at 5,000 ppm. Humidity showed a great affect on the reduction of bacteria in the presence of ozone gas. Altering the humidity level from 15-25% to 85-95% showed a greater change in bacterial reduction than altering the ozone level in some tests.

http://www.rentforum.se/Prod/Rentforum/sajt.nsf/wwwpages/10D011244DA8DAC6C1256D5B0042A28E/$File/ICCCS%20Ozone%20article.pdf

White Paper Abstracts

Inactivation of Vegetative and Sporulated Bacteria by Dry Gaseous Ozone

Ozone: Science & Engineering, Volume 32, Issue 3, 2010, pages 180-198

Authors: Ahlem Mahfoudh, Michel Moisan, Jacynthe Séguin, Jean Barbeau, Yassine Kabouzi & Danielle Kéroack

Abstract

Inactivation by gaseous ozone of different types of microorganisms is successfully achieved provided, as is well known, the gaseous phase is strongly humidified. The inactivation mechanisms and species involved in this process are, however, not yet clearly identified. To gain insight, we considered exposure of bacterial spores to dry rather than humidified ozone, a less complex chemical environment. In contrast to most of the published literature, it is shown that, under strict dry ozone conditions, bacterial spores can be inactivated, but to a degree that is largely dependent on the spore type and substrate material. In this case, the O₃ molecule is determined to be responsible for the inactivation process through its diffusion into and oxidative action within the spore, as no outer erosion of the spore is detected. With humidified ozone, a higher inactivation efficiency is observed that is most probably related, in part, to the swelling of the spore, which facilitates the diffusion of oxidative species within it and up to the core; besides O₃, these oxidative agents stem from the interaction of O₃ with H₂O, which in the end leads to a heavily damaged spore structure, in contrast to dry-ozone exposure where the spore integrity is maintained.

http://www.tandfonline.com/doi/abs/10.1080/01919511003791971

An Evaluation of the Antimicrobial Effects of Gas-Phase Ozone

Ozone: Science & Engineering, Volume 31, Issue 4, 2009, pages 316-325

Authors: M.Y. Menetrez, K.K. Foarde, T.D. Schwartz, T.R. Dean & D.A. Betancourt

Abstract

This project evaluated the effects of exposing a variety of microorganisms on porous and non-porous materials to elevated gaseous ozone concentrations ranging from 100 – 1000 ppm. Gypsum wallboard (porous) and glass slide (non-porous) building materials were used. Two fungi organisms, two bacteria organisms and two levels of relative humidity (RH) were tested. Increased humidity and non-porous surface exposure were found to increase the biocidal capability of high levels of ozone. The results of this study indicate that even at relatively high concentrations of ozone, it is difficult to get significant reductions of microorganisms on surfaces, especially on porous materials.

http://www.tandfonline.com/doi/abs/10.1080/01919510903043772

The Practical Application of Ozone Gas as an Anti-fungal (Anti-mold) Agent

Ozone: Science & Engineering, Volume 31, Issue 4, 2009, pages 326-332

James B. Hudson & Manju Sharma

Abstract

We evaluated the ability of a portable ozone generating machine (Viroforce 1000) to inactivate 13 different species of environmental fungi. Samples, prepared as wet or dried films, were subjected to one or two cycles of treatment (35 ppm ozone for 20 minutes, with a short burst of >90% relative humidity), and measured for residual viability. Treatments could inactivate 3 log10 cfu (colony forming units) of most of the fungi, both in the laboratory and in simulated field conditions, on various surfaces. We conclude that the ozone generator would be a valuable decontamination tool for mold removal in buildings.

http://www.tandfonline.com/doi/abs/10.1080/01919510903043996

Conclusion

Ozone has a bright future in surface sanitation. The use of ozone for surface sanitation in process using aqueous ozone, CIP, and gaseous ozone will continue to grow. If you have an application that you would like to evaluate the potential of ozone, give us a call. We would be glad to discuss your application and provide the technical support necessary to implement ozone as a solution.

This circuit board is the driver board for a car coil type transformer as seen in the image above.  This is a great example of how simple the circuitry may be in a typical medium frequency ozone generator.

This is the power supply for a larger (up to 450 gram/hour) high frequency ozone generator.  This power supply can supply an output of up to 30,000 Hz, or as low as 1,000 Hz.  As you can see this power supply is much more circuitry and components are used to achieve these higher frequencies and flexibility.

This power supply is for a larger (up to 400 gram/hour) medium frequency ozone generator.

Putting it all together

There are many different types of ozone generator power supplies for many different applications.  Each serves a unique purpose in the ozone generation world.  Each has advantages and disadvantages.

Line Frequency Ozone Generators (50-60 Hz)

Line frequency ozone generators commonly use larger transformers and voltages from 10,000 – 20,000 volts.  The only other electrical component for operation is a rheostat as pictures above.  These are very simple and reliable setups that perform well for many years.  Absolutely nothing beats the reliability of a line frequency ozone generator.

As the components on most line frequency ozone generators are larger to achieve the same ozone output the costs for the transformer and rheostat are higher than the costs for the smaller transformers and simple printed circuit boards used for medium frequency ozone generators.  Also, line frequency ozone generators cannot achieve near the performance as the higher frequency ozone generators.

Medium Frequency Ozone Generators (100 – 2,000 Hz)

Medium frequency ozone generators are most common today.  These ozone generators may produce 1 gram/hour to thousands of pounds/day of ozone.  The image above is a simple printed circuit board to increase line frequency to about 1,000 Hz, this board is attached right to the transformer that increase voltage to about 1000 volts.  This is an older design with a oil filled automotive style coil. however this is a good example of the typical size of power supply for a 5 – 20 gram/hour ozone generator.  There may be multiple power supplies powering multiple corona cells in one ozone generator to produce more ozone.  This is a very compact, cost effective, and efficient method to produce ozone.

While medium frequency ozone generators are fairly simple there are still more components than a line frequency ozone generator.  This means there are more things to fail and cause problems.  Due to the elevated frequency these generators also produce more heat, both in the electronics and corona cell.  Heat is the enemy of ozone.

Medium frequency ozone generators are also louder than others.  While this may not be a large concern in every application, at some frequencies there is a high pitched whine that is not acceptable in some occupied spaces.

High Frequency Ozone Generators (5,000 – 30,000 Hz)

High frequency ozone generators offer very compact designs due to smaller transformers and corona cells.  As the spark/corona is occurring up to 30,000 times per second the need for a large air gap and high voltage are alleviated.  In return the electronic circuit board becomes the largest, and most expensive component of some high frequency ozone generators.  This is illustrated very well in the above image.  This shows 3 power supply circuit boards with the small transformer mounted right to the circuit board!

High frequency ozone generators may be very energy efficient and compact in size allowing for a very flexible platform to either use multiple cells for redundancy or other configuration changes.  Many high frequency ozone generators are very cost effective as the large parts that carry a higher price (transformer and corona cell) are smaller, while the circuit board and electronics are more elaborate.

High frequency ozone generators contain many components that may fail.  They also produce a great deal of heat due to the high frequency.  However, with the very high frequency there is no audible sound from the ozone generators, they are the most silent of all types.  Many manufacturers have just begun implementing more high frequency components in the last 5 years.  Expect big changes in the future in this area of ozone generation.

This covers the basics of ozone generator power supplies.  I promise the following editions of How Ozone is Made will be shorter and less technical.

The next edition of How Ozone Is Made will cover Corona Cell design in Corona Discharge Ozone Generators.

If you have any questions about ozone generators, or what may be best for you, call our application engineers today!  We are glad to answer questions, dispel myths, and be a general information source for your ozone related questions.