How to avoid microorganisms in compressed air

Hygiene-sensitive applications used in food and beverage companies are trying to reduce the risk of microbial growth in the final product, thus eliminating potential contamination sources from utilities such as compressed air. Food companies today are rightfully concerned about food safety. Ambient air itself is far from sterile — outdoor air typically contains hundreds to thousands of bacteria and fungi per cubic metre, and under favourable conditions these organisms can proliferate once they enter a compressed air system, making proper system design and maintenance essential from the intake stage onward.

To prevent the growth of microorganisms, it is necessary to eliminate the conditions that allow the organisms to reproduce.

Suitable temperature

High temperatures are deadly to microbes, but each species has its heat tolerance. Fungi and mesophilic bacteria prefer moderate temperatures, between 25 and 40°C. Thermophilic or heat-loving microorganisms grow at temperatures between 45 and 90°C. The destruction process depends on the temperature and the time required. High temperatures (>180°C) in oil-free compression elements are sufficient to reduce existing microorganisms significantly. However, because this temperature does not last long enough, the process cannot be considered sterilization. Given that ambient intake air may already carry a substantial microbial load, this partial reduction at the compression stage is only one layer of protection and should not be relied upon as a standalone safeguard.

Moisture

It depends on how much water a particular type of bacteria or fungus needs to grow. However, they all require some form of water to reproduce. Generally, they require a relative humidity (RH) of 75% or higher. Some can survive and reproduce in 50% to 75% relative humidity. Relative humidity below 50% generally does not support microbial growth. In other words, lowering temperature and humidity (RH) reduces the likelihood of creating a hospitable environment for microbes.

Pressure dew point (PDP)

The dew point is the temperature at which air must cool to reach saturation. When discussing compressed air, the term is designated as pressure dew point or PDP. This is critical because changing the pressure of a gas also changes its dew point. 

PDP is the maximum water content of compressed air under pressurized conditions. If the air comes into contact with the product after expansion (which is the case in most cases), the dew point or moisture content will decrease significantly. In this case, the atmospheric dew point or ADP is more relevant. Different technologies can be used for low dew point requirements, such as a heatless double-tower adsorption dryer, thermal compression twin tower, thermal regeneration blower dryer, thermal compression drum, refrigeration dryer, etc. 

Some drying technologies are designed for a fixed and very low dew point and can consume 10% to 20% of the power of their connected compressor. The annual energy costs required for these drying technologies can be as high as EUR 13,000 per 100kW of installed compressor power. In most cases, a maximum of 10% to 20% relative humidity is low enough to avoid the growth of organisms. Using relative moisture in compressed air codes instead of PDP on temperature scales helps achieve hygienically safe and energy-efficient installations.

The danger of microorganisms and bacteria in the compressed air

Microorganisms and bacteria present a unique set of dangers. Bacteria, viruses, and bacteriophages can contaminate an air compressor via spores, water droplets, biofilm shedding, and airborne aerosols. Bacteria are generally the main concern, since they can survive and reproduce on their own if conditions are favorable, while viruses need a living host to multiply.

Ingesting certain microbes through food, medicines, or the air can cause serious problems. Foodborne bacteria such as E. coli can disrupt the digestive system and, in extreme cases, cause death. Toxins in the air can cause allergy-like symptoms and long-term respiratory problems.

Go through narrow spaces

Microorganisms are tiny – small enough to pass through many filters. Bacteria can be 1 to 3 microns, small enough to penetrate a basic filtration system easily.

Because of their size, they can be challenging to catch. They can live in small, hard-to-reach spaces, hidden from sight. That is why taking preemptive measures to limit their spread even more is so important.

Multiply from within the system 

Because they are living things, microbes reproduce under the right conditions. Although they are individually microscopic, they can accumulate and become increasingly dangerous over time. They tend to thrive in high humidity and warm environments — moist, warm environments that allow microbes to multiply quickly, and biofilm buildup inside piping or fittings can further shelter them from cleaning efforts.

Cleaning oil, water, and other substances from the air compressor will reduce the chances of bacteria surviving.

Spread disease and toxins

If certain bacteria come into contact with food or drugs, they can cause illness or death. The eradication of these microbes is crucial for human health and well-being.

Even if contaminated compressed air is unlikely to enter food or pharmaceuticals, limiting the spread of these microorganisms is still essential. They reduce air quality and cause short- and long-term symptoms in people who breathe the air.

Prevent microbial growth with environmental factors

Because microbes are so tiny, they can be challenging to find and address. Preventing them from building up in the first place is the most vital thing you can do. Create an optimized environment to reduce microbial growth. To prevent microbial growth, you should:

Fixing leaks in your air compressor system

You can detect leaks by listening for a hissing sound or by using an ultrasonic frequency reader. You can also apply soapy water to the suspected leak — if there is a leak, air bubbles will form. Beyond wasting energy, leaks also serve as entry and multiplication points for contaminants throughout the system, so repairing them promptly is essential.

Food

When we think of bacteria, we might not think of them as living organisms that need to eat, but they are! Bacteria need nutrients like all other living things. Oil is a particularly common concern in compressed air systems, as it acts as a food source that promotes microorganism multiplication when left to accumulate. Limit potential microbial food sources in your facility, including residual oil, to reduce this risk.

Install multiple filters

Implement multiple filters in your system, including particulate and absorber models. It’s essential to purchase air compressor filters and install them where the air enters the system, you should also have filters on the pipes.

Clean and replace the filter regularly

You should clean and replace the filter regularly, especially if the filter becomes wet. Clean the filter by blowing away dust, dirt, and debris. Regularly replace old or damaged filters — filters that are not replaced on schedule can become an ideal breeding ground for microorganisms even if they appear visually clean.

Make sure the ambient air is dry and cool

Put your air compressor in the proper environment. Desiccant dryers can dry compressed air to a super-dry level that inhibits microorganism growth, unlike refrigerant dryers, making them a useful option when moisture control is a priority.

How to identify bacteria in an air compressor

To check for the presence of bacteria, you need to perform regular air quality tests. Certain areas in your compressed air system are most likely to harbor microorganisms. These areas are most susceptible to condensation buildup and foreign particle buildup. Plan to sample and test these areas at predetermined intervals. The most common places where microbes are found include:

• Dead end
• Compressed air coils
• Drains
• Leaks
• Filters

Decide when and where to sample your compressed air system

Collect samples close to high-risk points to detect microorganisms such as bacteria, mold, and yeast. When deciding where to sample, you can use a percentage-based system. For example, if you have 24 points to sample, choose eight different points to test each year—after three years, you’ll have sampled all of them. It is wise to select sampling locations along the compressed air system to see if the air quality drops as it passes through. This way, you can identify problem areas.

Regarding frequency, you can choose to test annually, semi-annually, or quarterly. Check the standard requirements in your industry – food processing, medical and pharmaceutical facilities often have to test for microbial life more frequently than other facilities. Whatever schedule you choose, remember that the reliability of your results depends on the sampling equipment itself: many manufacturers recommend periodic calibration—often annually, to ensure accurate results. In addition to scheduled testing, you should perform testing before and after making changes to the system. Test the system after cleaning any components, including filters, valves, or piping.

When you perform these tests, you must look for any potential contaminants. These include rust, dirt, water vapor, condensation, oil vapor, and liquid oil. Check for microbial contamination using a sample test kit.

How to take a sample using a compressed air microbiological testing device

When using a compressed air microbiological testing unit (CAMTU), the sampling and testing process follows 11 defined steps:

• Wear gloves and a mask to keep you safe and limit exposure to microbes.
• Connect the inlet tubing with the sample port.
• Open the compressed air valve to the sample port.
• Open the shutoff valve.
• Purge the sample port.
• Close the shutoff valve.
• Connect the inlet tubing to the test unit.
• Place the petri dish inside the test unit.
• Close the test unit.
• Open the shutoff valve and let it run for 20 seconds.
• Close the lid, remove and incubate the petri dish.
• After completing these important steps, microbial organisms will become visible over time.

How to remove contaminants from an air compressor

If you find microbes in your air compressor, remove them and prevent regrowth. Several tools will help reduce the chance of microbial buildup and remove microbes from your air compressor system. Learn what these sections do and your role in keeping them effective. Follow the steps below to remove contamination. Modern air compressor technology helps minimize these pollutants, but ongoing maintenance is still required to keep microbial growth in check.

Use filters and change them often

A visual inspection of your filters may not indicate that you need to replace them. After all, microbes are invisible to the naked eye. In addition to looking at filters, monitor differential pressure—a significant drop can alert you to a problem. Check these gauges frequently and replace the filter if there is a problem.

Also plan to change filters at predetermined intervals, whether they appear effective or not. Replace filters at least once a year regardless of how they look, and more often depending on how heavily your system is used.

Use an aftercooler to reduce the water content

Compressing air generates heat. Keeping the system temperature down is essential since warmer temperatures help microbes thrive. You can achieve this with an aftercooler placed directly after the compressor. It captures the condensate that flows through the system.

Use a mist eliminator filter

Using a mist eliminator with a large capacity tank and built-in differential pressure gauge will make a big difference in removing microbial contamination. Such filters remove oil, water, and other particles from compressed air. While it won’t wipe out the tiniest microbial life, it will limit the water and oil microbes needed to survive and reproduce.

Use zero-loss liquid drain with electronic controls

Compressed air system lines can accumulate condensation. Since microorganisms need water to survive, draining condensation from the system is crucial. Some air compressors have a manual valve to release the condensate, which allows the compressed air to escape and go to waste. Internal floating drains that open when water builds up can jam either open or shut, undermining reliable drainage.

Your best bet is a zero-loss, electronically controlled drain. These drains will sense the condensate level and open the valve when needed. Before any compressed air is wasted, the valve closes. One of these zero-loss drains may be even more expensive than manual or internal floating drains, but they are more efficient.

Properly dispose of condensate

Always dispose of condensate properly – never pour it down the drain. It is considered hazardous waste due to its potential oil and contaminant content, and it must be processed through a purifying device that separates the oil from the water before disposal. Use a condensate cleaning unit for this purpose. This device separates the oil from the water so you can dispose of the oil as hazardous waste.However, because this temperature does not last long enough, the process cannot be considered sterilization.