Technical Study Part 2

Reduction of Microbiological Growth

In Air-Conditioning Systems

1 Introduction

Growth of legion Ella in cooling towers and humidifying sections has been a well known problem for many years. But there are more organisms present in several parts of the air-conditioning system. These organisms might not be as lethal as legion Ella but are well capable of creating nasty smell, food contamination, allergies and other unhealthy effects. In this study the microbiological growth and the prevention of growth on the air-cooling heat exchanger are discussed.

Microbiological Contamination

Cooling of air is realized by transporting airflow through a cooled heat exchanger. Due to humidity in the air and the temperature differences, water will condense on the heat exchanging surface. At the wet surface, pollution and micro-organisms will adhere easily. Depending on the temperature present, several organisms will be able to reproduce rapidly under these circumstances. Air-conditioning systems normally re-circulate air from the air-conditioned room to prevent extreme energy consumption. As a result of this, air passing contaminated heat exchangers will be re-contaminated. This re-contaminated air is brought back into the air-conditioned room. This may result into several problems, for example: cross contamination in food processing. Overall it can be said that the air-conditioning system is reducing the indoor air quality instead of increasing it. Types of organisms found in air-conditioning installations: legion Ella, aspergillus, cladosporium, penicillium, staphylococcus, pseudomonas and salmonella.

Microbiological Control

Microbiological growth on cooling heat exchangers needs to be prevented or at least controlled. Simply disinfecting the surface is often considered to be a good way to stop microbiological growth. Thorough disinfecting a heat exchanger is very complicated as surfaces are difficult to reach. Besides that, one must consider the fact that surfaces are only hygienically clean temporarily. The moment air is passing the surface again it will be contaminated with organisms and pollution. Thorough cleaning on a regular base will have much more effect than incidental disinfecting. By cleaning, the pollution on the surface (which serves as nutrition for organisms) is removed.

One of the most important steps in reproduction of airborne micro-organisms is the adhesion/settlement to a surface. As soon as there is some adhesion of organisms to a surface they tend to develop extra cellular polymers. These polymers will create a better adhesion to the surface but even more important to other airborne organisms as well. This way a bio-film will develop rapidly on a surface.

The best way to control or prevent microbiological reproduction is the prevention of this first adhesion of organisms to the surface. Three levels of surface treatment can be used to realize this:

1. Prevention of rough and porous surfaces by using corrosion protection and suitable insulation materials.
2. Creating biostatic surfaces by applying coatings with a low surface energy and a micro-organism repellent surface.
3. Creating bioactive surfaces by applying coating with biocide leaching from the coating to actively kill organisms present on the surface.

Blygold provides coatings to realize option 1 and 2. As Blygold coatings are normally applied in food industry, hospital and offices Blygold does not use coating of type 3 as leaching biocides are unwanted in these environments. Heat exchangers require special coating systems, as they must be heat conductive, flexible and chemical resistant at thin layers. Corrosion protection on heat exchangers can not be realized by just any paint. Blygold developed Blygold PoluAl to create corrosion resistant and smooth heat exchanger fins. This product is developed for aluminum fins but can also be used on copper. For galvanized steel another primer is necessary. To create a biostatic surface on the heat exchanger fins Blygold developed PoluAl MB. This coating is not only creating a smooth corrosion protection layer, the special ingredients make the surface very repellent to mould, yeast and most bacteria as well. In this report the effectiveness and safety of these coatings is discussed.

2 Tests and Methods

In this report different properties of the Blygold PoluAl and PoluAl MB are evaluated.

1. Leaching properties: Samples with the coating to be tested are submerged in water; the water is then checked for residues.
2. Safety in contact with food: Samples are exposed to water at higher temperature for a longer period; the water is then checked for residues. All according EU directive 85/572/EEC.
3. Effectiveness to repel different organisms on laboratory scale: Samples are exposed to different organisms; growth of these organisms on or nearby the coating is a reference for effectiveness.
4. Effectiveness to repel different organisms in practice: Samples are placed at locations in the food industry.
5. Effectiveness to resist adhesion of pollution: Surface energy of the sample surfaces is measured; surface energy can be seen as a reference for adhesion of pollution to a surface.

3 Results

Test results from different reports and cases are summarized in this report, original data can be found in the original reports (see references)

3.1 Safety, Leaching

Blygold PoluAl MB coated test samples were submerged in water at 40 °C for 60 minutes. The water is analyzed for any residues of the coating material. This way the leaching of elements from the cured coating system can be determined. Levels of possible residues in the water were below the detection limit of 0,1 mg/l. Under these circumstances no significant amounts of materials are leaching from the coating. [Ref: 2.1]

3.2 Safety, Contact with Food

Microbiological growth control is needed in several industries. Hospitals, food and beverage, clean room but also office climate installations may suffer from micro-organism growth on heat exchangers. The conclusion from paragraph 3.1 can be that coated samples submerged in water do not show any detectable leaching of coating ingredients. Coatings on air-cooled heat exchangers are only in contact with air and condense. If located in food processing facilities there will never be a direct contact between food and the coating. Still official approval for food contact is sometimes asked for although it is never required by law. Blygold PoluAl MB was approved for contact with food according European regulation EU directive 85/572/EEC. If no harmful ingredients leach out under given test circumstances then one can be absolutely sure that it is safe to use the product on air-cooled heat exchangers in any application [Reference BIREF2.5 and 2.6]

3.3 Effectiveness on laboratory scale

To determine the effectiveness of surfaces in reducing or prevention of microbiological growth, several tests can be applied. Bio active surface Biostatic surface (PoluAl MB)

One of the most commonly used test methods is the agar diffusion test. In this test method a small piece of the tested surface is placed into a petri-dish filled with specific agar medium for optimal micro organism growth. In this medium some specific micro-organisms are inoculated which will start growing rapidly. If the growing bacteria will keep distance from the coated surface than ingredients are leaching from the coating and the surface is bio-active. If the organisms grow next to the coated sample but not on the sample itself, the surface is biostatic. If the organisms grow next to and on the coated sample than there is no bio-effect of the surface. [reference 2.2 and 2.3]

3.4 Effectiveness in Practice

To determine effectiveness of Blygold coatings against micro-biological growth several tests in practice are applied. Every location has it’s own specific environment with temperature, organism species, pollutants and cleaning procedures. These circumstances are very difficult to imitate in a laboratory so effectiveness tests are best done in practice.

Soprof, Food Consulting Agency:

Uncoated and coated test samples were placed in food processing facilities. Blygold PoluAl MB was tested under the name Blygold PoluAl F. Presence of micro-organisms was measured at a set time interval. [Reference 2.6]

Conclusion In Vivo test (page 37):

“For both the plates treated with Blygold PoluAl and Blygold PoluAl F. , a development of
aspergillus’s species was determined at below 1 %. We are therefore able to conclude that the Blygold PoluAl F. is eminently suitable as a preventive means against fungi which appear in the food sector.

Area’s are amongst others:
Food processing industry: canneries, industrial bakeries, dairies, cheese dairies, company kitchens, slaughter houses, fisheries, jam producers and fruit storage. Agriculture and horticulture, animal husbandry: Potato silos, vegetable and fruit halls, greenhouses, stables

Drinks industry: Breweries, soft drinks producers.
Also in sanitary installations (amongst others bathing establishments, washing and changing rooms and shower areas), cleaners, tanneries, companies processing cellulose and producing paint, fungi are often a problem”

Covee, Instant Meal Processing Factory, Belgium

Covee is a producer of ready for use meals, selling these products throughout Belgium in their own shops. Covee also supplies meals for other companies such as aero plane charters. This means that Covee is processing different products, like meat and vegetables, etc in their factory. Different processes are applied that finally result into frozen meals. These processes are very critical for the quality (taste, hygiene, appearance) of the food. Big cooling capacity is required to execute all these processes in hygienic circumstances. To prevent contamination of food with micro-organism strict quality procedures are followed.

Those procedures comprise of:

• Low temperatures
• Temperature control
• Employee instructions regarding dressing, washing and disinfecting
• Strict cleaning program using aggressive cleaning chemicals
• Independent hygiene checks

The galvanized steel walls at Covee are provided with a skin plate. This skin plate is a synthetic layer that is glued to the surface. The ceilings are painted with a thin paint layer. The wall and the ceiling show deterioration of the surface. Corrosion, mould growth and blisters with water are found at most surfaces in the factory. This problem must be solved to come to strict hygiene regulations. Corrosion and microbiological problems. Hygienic surface with Hygicoat 2000 MB.

The final coating layer that is applied by Blygold is the Hygicoat 2000 MB. This is a water based coating with very high qualities. The coating flows very easily and creates the perfect smooth surface required. After curing the surface is not only very tough and resistant against mechanical forces but also resists microbiological adhesion. [reference2.8]

Institute of Technology Alkmaar, Department Microbiology

At the institute of technology in Alkmaar a microbiological problem occurred in the storage room of the microbiological department. Mould was present on the walls, floor, ceiling, and all rubber sealants of jars. After a thorough disinfecting procedure the problem seemed to be solved but re-occurred after two weeks. After Blygold treated the cooling heat exchanger with Blygold PoluAl MB, the mould growth did not occur anymore. [Reference 2.7]

Beer Brewery Germ Tower

A germ tower at a beer brewery is cooled by re-circulating air over heat exchangers. Due to the extremely high concentrations of micro-organisms in the air, the heat exchangers tend to clog rapidly. A cleaning procedure with high pressure water is necessary to keep the heat exchangers open. As the adherence of the microbiological pollution to the heat exchangers is strong, the cleaning process is difficult and expensive. The bio-film can not be completely removed and even with regular cleaning, the pollution is accumulating. After treating the heat exchangers with Blygold PoluAl MB the removal of pollution is much easier as the adhesion of the organisms to the surface is poor. [reference 2.9]

3.5 Pollution Adhesion

Adhesion of pollution (or other materials) to a surface depends on the surface energy of the pollution but mostly on the surface energy of the surface. Special non stick surfaces like Teflon are based upon this principle. The surface energy of Blygold PoluAl and Blygold PoluAl MB are compared to the surface energy of bare aluminum and a non stick Teflon coating. [Reference 2.1]

Application of Blygold PoluAl on aluminum or copper will significantly decrease the adhesion of pollution. Application of Blygold PoluAl MB reduces pollution adherence even more. A non stick Teflon coating will result into the lowest adhesion to the surface.

4 CONCLUSIONS

• Blygold PoluAl MB and Hygicoat 2000 MB are very effective coatings to prevent micro-organism adhesion and thus reproduction
• Heat exchangers of air-conditioning systems are important sources for microbiological reproduction. By reducing the growth of these organisms, problems like dirty smell, allergy, capacity loss and cross contamination can be reduced
• Blygold PoluAl MB and Hygicoat 2000 MB are safe to use in almost every environment; no detectable material leaches out the coatings. There is even an approval for contact with certain types of food. Although there is an approval, Blygold coatings are not intended to be in contact with food
• Blygold PoluAl MB reduces pollution adhesion to heat exchangers.

5 REFERENCES

BIREF2.1 Contact angle measurements Blygold coatings, April 2000, Ir.D.P. Borger; Delft University of technology, faculty of aerospace engineering, HI 2065.

BIREF2.2 Inhibition test Blygold coatings, July 1999, DAM 99373/STF-pua, TNO Nutrition and Food Research institute, Microbiology & Quality Management Department.

BIREF2.3 Inhibition test Blygold coatings, February 1999, DMKM 990275/STF-voi, TNO Nutrition and Food Research institute, Microbiology & Quality Management Department.

BIREF2.4 Overall migration according to EU and Dutch legalization, June 2002, DAM 02-2591/SCHH, TNO Nutrition and Food Research institute, department packaging research.

BIREF2.5 Overall migration according to EU and Dutch legalization, June 2002, DAM 02-2521/SCHH, TNO Nutrition and Food Research institute, department packaging research.

BIREF2.6 Verification study of the effective fungicide action of a Blygold PoluAl and PoluAl F. coating, applied to metal plates of an evaporator battery, SOPROF professional food consulting agency.

BIREF2.7 Reference letter: Alkmaar Institute of laboratory education department microbiology.

BIREF2.8 Blygold Hygiene Concept application at COVEE Kampenhout, diagnosis and preventive measurements, Blygold International and Blygold Belgium

BIREF2.9 PoluAl MB application on cooling heat exchangers in germ tower of beer brewery,

Blygold International and Blygold Netherlands.