6 August 2019

How Microbiological Filters Work

Understanding the Basics of Microfiltration

Hospitals and healthcare facilities are becoming more aware of the dangers of waterborne pathogens that can exist in their manmade plumbing systems. With growing concern of preventing infections, point-of-use (POU) filtration has been more frequently used in the healthcare market to aid in reducing bacteria counts found in water. However, not all filters are created equally, and it is important to understand the basics of microbiological filtration.

The drinking water that is provided by municipalities is used to supply ice machines and other consumable areas. Typically, facilities filter their water with common commercial carbon filters for the taste and odor. Carbon is the most common substance found in standard filters and meets the majority of industrial requirements to remove volatile organic contaminants (VOCs) and other chemicals that are typically found in water. Carbon’s effectiveness is largely due its greater surface area. Physical adsorption is the primary process by which carbon will filter out a given substance. As water comes into contact with activated carbon, intermolecular forces draw molecules into the millions of pores and pockets on the surface of the carbon. When chlorine comes into contact with carbon, both molecules react to form chloride ions; effectively removing chlorine from water. Removing chlorine from water for taste and odor comes with a price as the filtered water is left untreated and is now susceptible to bacterial growth. Carbon filters are not considered a microbiological filter as they do not have the capability to remove small particulates like waterborne pathogens.

Internal Design

Filters utilize different types of membranes to capture particles in water that would otherwise pass through. The two most common styles of filters used are: hollow fiber and surface.

  • Hollow Fiber:  Comprised of tiny straw-like tubes that have been bundled together. Each tiny tube has thousands, or even millions, of pores (or holes) that are manufactured to a specific size. These pores are sized to keep particles from flowing through the hollow-fiber tube walls.
  • Surface:  Sheets of filter material are pleated together to create layers that will provide a filtration area. Particles in water will get trapped at the surface and allow clean water to pass through.

Both styles of filters have done exceedingly well in removing particulates that are commonly found in water.

Pore Size

Filter membranes contain thousands to millions of tiny pores that keep particles from passing through. Unfiltered tap water can have a tremendous amount of particles in it and still not be seen by human eyes. Nanometer and micrometer are used interchangeably when describing pore sizes, but typically sizes are referenced in “microns” (short for micrometer). To put it into perspective, a human hair has a diameter of 50-100 microns. Current EPA regulations ensure that city water does not contain particles larger than 1 micron for human consumption. Smaller particles may be 5 times smaller than the allowed limit by the EPA, including some waterborne pathogens (e.g., Legionella 0.3 microns). This is why the majority of microbiological filters on the market have pore sizes starting at 0.2 microns. Even at that size, particulates in water can still manage to pass through. No matter what type of media is used, its effectiveness is influenced by how well it can filter the smallest of particles.

Where Should the Filters Go?

Everyone is potentially vulnerable to waterborne pathogens found in water systems at one point or another, depending upon health status. However, immunocompromised individuals are at greater risk, such as infants, elderly, smokers, chronic disease sufferers, or patients undergoing treatment where the immune system is lowered. Various precautions are already taken to protect these at-risk patients from acquiring a healthcare-associated infection. Water that can come into contact with these patients should be no different. At minimum, care should be taken at sinks and showers of higher risk patient area rooms where overnight stays are frequent.

The Chem-Aqua Water Risk Management Group specializes in assisting customers with their domestic and non-domestic water system issues. Managing your facility’s water systems is a task that shouldn’t be done alone. Contact your local representative to ask about our services.

Writen by: Angel Rodriguez

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