Marshall University Molecular and Biological Imaging Center

Whether a facility uses cartridge or sand filters, one essential consideration is the use of an antimicrobial treatment.

From the perspective of microbial life, the filtration area represents a proverbial cesspool where it can gather, reproduce into colonies, seep back into the mainstream pool, and create increasing pressure drops across the filter media. The normal sanitary mechanism that works in the main pool rarely makes it back to the filter, and most pool makers agree that hypochlorous (or hypobromous) acid should not be added to skimmers, lest it compromise the integrity of piping and filtration materials. Always keep in mind that the water that passes through the filter area eventually ends up back in the mainstream pool — where your guests swim!

What can be done about this? The answer: Purchase antimicrobial-treated media, whether in the form of sand beds or cartridge filters. Microbial build-up found in untreated media can come in the form of bacteria, protozoa, fungi, algae, and viruses.

By their very nature, antimicrobial ingredients interact with microbial life, or they wouldn’t function in their role. Destruction occurs when the antimicrobial ingredients pierce cell walls, interrupting the ability of the species to reproduce, disturbing the species DNA, electrocuting the species, and through other modes.

Treatments are applied at small concentrations, just sufficient to perform their task while avoiding health risks.

There are several common antimicrobial tests in use today depending upon the type of media:

• ASTM E2149 (used for granule media or non-regular media)• AATTC 100 (used for fabrics)
• ISO 20743 (used for antibacterial activity of textiles)
• ISO 22196 (measurement of antibacterial activity on plastic surfaces)

Your filter manufacturer should have aged testing data to demonstrate how well their media works in practice. If they haven’t tested the species of your concern, most manufactures will upon request.

Antimicrobials operate through two modes. The first is a diffusion mechanism whereby the treatment diffuses to the outer surface of a coating. A microorganism then picks up the typically cationic, or positively charged, metal ion off the surface. That metal ion could be copper, silver, zinc or another metal. As the microorganism attempts to absorb the metal ion, it is destroyed. The outer media surface automatically refreshes until the antimicrobial treatment runs out. Through the laws of diffusion, higher concentrations of a substance always migrate to lower concentrated areas, with the only secondary consideration of electric charge when present.

The second system employs a non-leaching antimicrobial system whereby the antimicrobial agent is permanently anchored to a surface, and it kills through a quat-amine strategy combined with a long alkyl arm that serves as a skewering sword. Negatively charged microorganisms are attracted to the positively charged quat-amine, and as they approach the opposite charge they are skewered by the long alkyl chain. A rough analogy would be like a moth approaching a light. It strives to get closer and closer to the light and along the way a sword penetrates through its belly. When the moth finally reaches its goal, the opposite charge quat-amine short circuits it.

A secondary advantage of a non-leachable antimicrobial treatment is the ability to regenerate the active agent by adding clarifying agents to remove the leftover anionic debris. Clarifying agents also carry a positive charge, so they can swoop in and replenish the used surface.

The effectiveness of the antimicrobial treatment varies with the species, concentration, and the age and various chemical events that the surface has observed. Because of the huge number of different microbe species that exist, it becomes extremely expensive to test for all microorganisms. This is the primary reason why most companies never boldly claim that their treatment kills all microorganism life forms.

Other potential benefits that residential and commercial amusement parks have observed include crystal clear water, reduced backwash cycles, and lower chemical use.


In closing, the World Health Organization continues to identify microbial hazards as a major health risk. Although many outbreaks occurred due to the lack of sufficient chlorination and general hygiene issues, there are several cases that are believed to be a result of insufficient filtration methods.

Keeping your filters clean of microorganisms should not be overlooked! In addition to an extra security blanket for antimicrobial concerns, you may observe many unrealized side benefits in the areas of clear water, reduced backwash cycles, and lower chemical use.