BioFilm: The Hidden Accomplice


Biofilm: The Hidden  Accomplice

     So many times when I hear the  word biofilm all I can conjure is the movie BioDome and how much the two are  alike.  They are two protective enclosures with living organisms that can  contain within themselves one or many different types of living organisms.  But  they are also different in that BioDome  was many organisms working for a common good and being self sufficient  where as biofilm is a nuisance due to its ability to harbor bacteria, fungi,  algae and protozoa.  Of course the movie did portray Pauley Shore to be a  nuisance and example of what can go wrong.  The same is true of the hidden  accomplice of biofilm.

     Biofilm is formed by the  combination of water, a surface to grow on, and microorganisms. The water needed  can be as little as high humidity and can be fresh or salt water.  Surfaces can  be solid where most types grow but also biofilm can grow on biological surfaces  like organs.  Microorganisms such as algae, bacteria, protozoan, fungi or a  combination of such can be present in biofilm.  Some are harmful that can cause  illness such as Legionnaires disease, Pseudomonas rash, and intestinal illness  as with giardia, e-coli, and cryptosporidium.

     In our swimming pool environment  we encounter water everywhere.  The outside environment including the deck,  chair and bench surfaces to of course inside surfaces of the pool including the  piping.  The moist outside areas out of the pool can harbor microorganisms that  can be transferred into the pool. 

     Biofilm that is attached to a  surface is more resistant to disinfection. In the pool there are areas of poor  circulation or dead zones that will allow the microbes to attach themselves to  the surface easily. In pools where the circulation is stopped such as in use of  a timer, biofilm can began to grow easily.  This is not an area that can be  brushed.  In circulation piping if the velocity of the water is fast the biofilm  experiences erosion and it becomes smooth creating a strong biofilm harder for  chemicals to penetrate.  If the velocity is slow the biofilm will be rough and  have an uneven surface creating an unstable biofilm. [Klueger and Meyer] Biofilm  that has broken off and is free floating is more susceptible to  disinfection.

     Microbes are smart.  They can  talk to each other through chemical signals and know when to colonize. Once the  microbes attach and start to colonize they secrete an Extracellular Polymeric  Substance otherwise known as EPS or that slimy, sticky covering that protects  the colony from normal levels of sanitizer and algaecides.

      Then they invite their friends.  So many different living organisms can be in the biofilm.  They release part of  the colony to find new areas to grow and find more friends. Also any harmful  microbes can be released and cause a recreational water illness.  The CDC has  found that 65% of RWI involve a biofilm. [NSPF Pool & Spa Handbook, 2011  Edition]. The microbes can wait around in a well maintained pool or spa for an  opportunity to get established again like when the sanitizer or algaecide level  is low.  Once treated for biofilm it is important to keep a higher than normal  sanitizer level so they don’t come back again and again.


    The conventional methods of  microbe control for swimming pools have proven inadequate when associated with  biofilm.  Biofilm prevention is recommended as it is much harder to eliminate  once allowed to establish.  However there is evidence of less to no occurence and ease of removal in salt water systems.  See Mixed Oxident Solution for further information and pictures.

     Dental plaque is a type of  biofilm.  We brush our teeth to remove the biofilm and prevent dental decay, bad  breath and such.  The same is true in our pools and spas.  If we perform regular  brushing of all surfaces in the pool we can dislodge the biofilm that may be  present so that it becomes free floating and more able to be disinfected by the  sanitizer and algaecides we keep in our pools.  Brushing the walls, skimmer  throats, under ladder treads and around lights and fiberglass steps is a must to  prevent biofilm from forming.  As these can form on decks and be introduced into  the pool it is wise to also periodically use bleach and scrub the deck area as  well.

        Keep an optimum level of  sanitizer in the pool at all times not just when it is being used.  This  includes the off season of pool and spa use.  If a spa is drained there are  usually wet surfaces in the pipes that can form a biofilm.  The majorities of  spas are “wet tested” after manufacture and then may sit for long periods of  time before having water introduced for use.  This is why many spa manufacturers  recommend that the spa is filled, super chlorinated, jets run and spa circulated  for a few hours, drained and then refilled.  I have found that when this is not  done within a couple of weeks the water turns cloudy due to biofilm and cannot  be cleared up with conventional methods. 

      If a pool is winterized the  same can happen in the plumbing.  Water mold although a different structure uses  biofilm to adhere and during these dormant times is easily established.  I have  found that raising the chlorine to a minimum of 10ppm or more upon pool opening  after a winterization has decreased the number of spring water mold and algae  complaints.  I use this method for chlorine and biguanide pools. 

     Cleaning of the filter is very  important to discourage biofilm as well.  If a filter is acid washed only but no  degreaser type cleaning done the biofilm will not be removed.  [Biofilm: That  Gooey Stuff,  Connie Sue Centrella]

     Brushing of surfaces, keeping  sanitizers in the recommended range at all times, weekly chlorine treatment of  10ppm, regular testing, chemical filter cleanings and the use of algaecides and  enzymes are the best tools for combating biofilm.

     Many pool and spa owners do not  want to add more chemicals than necessary for fear of bad chemical  implications.  It is important to educate these owners that improper chemical  levels and poor housekeeping is more of a hazard to their health. 

     Just like in the movie BioDome when it looked like all life  had been destroyed one green leaf of vegetation started growing again.  And in  pools/spas you may think the biofilm is gone but one microbe that has survived  can start the biofilm again.

Research materials used:

Understanding Biofilm in Recreational  Water Environments, James J. Miller  MS

Biofilm: That Gooey  Stuff, Connie Sue  Centrella

Understanding and Combating  Biofilm, Todd  Klueger & Ellen Meyer; Arch Chemicals

Miox Corporation: Biofilm Removal

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  • Fantastic article, Wendy!!  Great info as well, Richard

  • Yes an interesting article and as Richard has noted the count in the filter (219 cfu/g) is a really good reason to use a self sterilising filter media rather than filtration types that provide the perfect growing environment.

  • Great information...I don't think we emphasize enough how important the regular brushing is.  Dental plaque is a biofilm so maybe if we let the consumers know this, they will think of brushing their pool when they brush their teeth!  This is to me the most important benefit of using a robotic wall climbing cleaner, it may be hit and miss but at least a majority of the surfaces get cleaned.

  • Thank you for the great article.  It may not be necessary to shock weekly to 10 ppm FC if proper chlorine levels are consistently maintained, but "proper" does not mean industry-standard recommendations since they have absolutely no recognition of the details of the chlorine/CYA relationship.  There is a long Biofilm thread that includes a reference to this paper which described how shocking for 16 hours weekly to 10 ppm FC eliminated the buildup of biofilm.  However, a closer look at the amount of biofilm when maintaining chlorine levels without shocking (from this same paper) is instructive where this maintenance alone reduced biofilm formation by a 5.53 log10 reduction on coupons and a 6.70 log10 reduction in the filter.  After 30 days there were 3.7 colony forming units (CFUs) per square centimeter while in the filter it was 219 cfu/g.  So shocking probably makes more sense for sand filters, but for pool surfaces it doesn't seem to be required, especially if regular brushing is performed.

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