Chlorine is generally regarded as an effective method of water disinfection. Whilst this is basically a correct assumption, one needs to look at this issue from a holistic standpoint.

If it were true that chlorine was the universal panacea against microorganisms there would surely be no risk of disease or infection from water. This however, is not the case. We are constantly seeing major microbiological contamination issues arising worldwide. Even in advanced countries with modern plumbing infrastructure, the issue of infection is increasing at an alarming rate.

“Microbiologists have traditionally focused on free-floating bacteria growing in laboratory cultures; yet they have recently come to realise that in the natural world most bacteria aggregate as biofilms, a form in which they behave very differently. As a result, biofilms are now one of the hottest topics in microbiology.” (Potera 1996)

As Potera pointed out, a far deeper understanding of the biofilm medium is required before the concept of microbial removal can be meaningfully considered.

Many bacteria exist in two distinctly separate forms. They can live in an attached mode of growth, or, they can live in a free floating (or swimming) “planktonic” life form. In the planktonic phase, microbes are suspended in the water and are highly vulnerable to chlorine and similar biocides. When the organisms are in an attached lifestyle, the opposite is true. Amazingly, science has found that the same bacteria, when attached, has different DNA to when it is free floating!

As part of the attachment process, the cells excrete a slimy, sticky material to bond them to any hard surface they come in contact with. This process is continual and ongoing. It may commence within thirty seconds of the organism coming in contact with a surface. This can even happen with polished stainless steel! Eventually the surface has a significant covering of this material, which is termed biofilm. Biofilm has been metaphorically described as “cities” for microorganisms. In these safe havens, the microbes are safe from attack from potentially damaging environmental components by the slimy film. This slimy barrier also protects them from chlorine.

Obviously, significant effort has gone into researching this phenomena, as it is found throughout nature. One researcher. LeChevallier1 (1988) demonstrated that bacteria incorporated into the biofilm are up to 3000 times more resistant to chlorine than their free-floating [planktonic] counterparts. He stated: “Once the micro-organisms have attached, they must be capable of withstanding normal disinfection processes. Biofilm bacteria display a resistance to biocides that may be considered stunning.”

Just as remarkable was the research of Roger Anderson2 (1990) at the Centre for Disease Research (CDC). In short, Anderson and his colleagues took plastic pipes and filled them with water containing two strains of pseudomonas bacteria. After allowing the bacteria to incubate for eight weeks, the scientists emptied out the infected water and doused the pipes with chemicals, including chlorine, for seven days. They then drained and refilled the pipes with sterile water and took periodic samples of the “clean” water. Astonishingly, the team reported that both strains of pseudomonas survived in the chemically treated pipes and quickly re-established colonies.

Another key researcher, Marc W. Mittelman3 (1986) wrote: It is virtually impossible for microorganisms to develop a general resistance to such compounds (chlorine). However, bacteria in a biofilm can resist biocides because they are shielded in slime. This is the reason for the regrowth as shown.

Biofilm Roger Anderson

The chart shows typical regrowth following chlorine sanitisation. Initially, the bulk water bacteria count dropped to zero after sanitisation, but this was followed by a gradual increase in numbers to levels at or below the pretreatment levels. In this example, regrowth started after 2 days and was back up to previous levels after 20 days.

In later times, other researchers have expanded on these studies. Hsiu-Yun Shih and Yusen E. Lin4 (2010) performed a complex experiment where they built a modelled ‘water distribution system’ akin to what is found in institutional environments.

The study was to determine the efficacy of copper-silver ionisation against the formation of Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Acinetobacter baumannii in biofilms and planktonic phases. These organisms were chosen as they are the main constituents and building blocks of biofilm.

It was determined that copper-silver ionisation, at concentrations below the WHO limits for potable water, was able to control and eradicate the three waterborne pathogens. The synopsis then adds; “(copper-silver ionisation has the potential to control) in addition to Legionella, in hospital water systems for nosocomial infection control.”

This work certainly validates the research of, Yu, Stout and others5 (1996-2003) who studied live instances of copper-silver ionisation installed in hospitals in the United States.

With the impact of airborne and waterborne pathogens having more serious and widespread effects on the population, as antibiotic resistance increases, an effective solution has never been more crucial.

These studies clearly point to the fact that chlorine dosing is not viable for the long-term control of microorganisms in water distribution systems. The only viable solution is Copper-Silver ionisation. Bion Systems AccuionTM technology is the clear worldwide leader in administering copper-silver ions into potable water. No other system has the ability to proportionally dose copper and silver into varying flow rates, whilst at the same time self-compensating for water chemistry and anode wear.

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  1. Mark W. LeChevallier,* Cheryl D. Cawthon, Ramon G. Lee. 1988 Inactivation of Biofilm Bacteria. Applied and Environmental Microbiology 54: 2492-2499
  2. Roger Anderson PHD, Betty W. Holland, Janice K. Carr, Walter W. Bond, Martin S. Favero 1990. Effect of Disinfectants on Pseudomonads Colonised on the Interior Surface of PVC Pipes. Am J Public Health 80:17-21
  3. Marc W. Mittelman 1986. Biological fouling of purified-water systems: Part 3, treatment. Microcontamination 4(1):30-40 · January 1986
  4. Hsiu-Yun Shih and Yusen E. Lin*. 2010. Efficacy of Copper-Silver Ionisation in Controlling Biofilm- and Plankton-Associated Waterborne Pathogens. Applied and Environmental Microbiology 76:2032–2035
  5. Lin, Y. S., J. E. Stout, V. L. Yu, and R. D. Vidic. 1998. Disinfection of water distribution systems for Legionella. Semin. Respir. Infect. 13:147–159.
    Lin, Y. S. E., R. D. Vidic, J. E. Stout, and V. L. Yu. 1996. Individual and combined effects of copper and silver ions on inactivation of Legionella pneumophila. Water Res. 30:1905–1913.
    Stout, J. E., Y. S. Lin, A. M. Goetz, and R. R. Muder. 1998. Controlling Legionella in hospital water systems: experience with the superheat-and-flush method and copper-silver ionization. Infect. Control Hosp. Epidemiol. 19:911–914.
    Stout, J. E., and V. L. Yu. 2003. Experiences of the first 16 hospitals using copper-silver ionisation for Legionella control: implications for the evaluation of other disinfection modalities. Infect. Control Hosp. Epidemiol. 24:563–568.