Posts Tagged ‘Biofilm’
Sand Filtration: the GOOD, the BAD, and the UGLY
Anyone who owns, cares for, or cares about pools, spas or any kind of recreational water, knows that water filtration is an integral part of every water system. Using sand for filtration is commonly used on recreational and residential pools and large spas. Here are some of my observations, thoughts and concerns about sand filtration.
The Good
Sand is cheap, plentiful, and when it is a particle, it works well as a filter medium.
The Bad
Sand filters are usually filled, sealed and the sand is forgotten. The commonly held belief is that back washing the sand periodically, “fluffs it up” and returns the sand to a particle state where it can again work its magic as a particulate filter. Some sand filters have never been opened for 5-10 years to inspect the sand.
Back-washing the sand filter is costly. Water lost during back washing needs to be replaced, heated and treated. Ideally, the pool operators backwash often enough to keep the sand working as a filter, but do not needlessly back wash so water, heat, chemicals and time aren’t wasted.
The Ugly
Inspecting and analyzing the sand from pool sand filters in both residential and commercial pools has been enlightening, to say the least. At the bottom and sides of many filters we found sandstone. Actual sand in the process of forming sandstone. It wasn’t the gravel that is often put down underneath the sand, but sandstone. The sand in those filters was anywhere from 2-10 years old. The sand that wasn’t rock was sticky and foul. When we tested it in our laboratory, we found that it was full of biofilm.
The Hypothesis
We know that in an aqueous environment that contains bacteria, biofilm forms on every surface. To be effective, filters have enormous surface area whether they are made from sand, charcoal, paper, glass or diatomaceous earth. The particles become covered with biofilm over time. Biofilm is very sticky so the particles stick together. As time and pressure continue to pack the biofilm-coated particles together they eventually become rock. So what happens during backwashing? The water will take the path of least resistance. We observed in these filters that there were channels in the sand. We think that the water follows channels through the sand that have become established over time.
We know that backwashing will not remove biofilm. In fact there are very few things that will remove biofilm. Strong acid or base solutions work but they destroy the filter, pumps, valves etc. We have demonstrated that a flush used in spas removes 90% of laboratory created biofilm in one hour, and that many other solutions that claim to remove biofilm don’t.
Getting Better Results
We also have observed that sand in filters where the water is treated with PoolNaturally® Plus (the commercial version of the residential product PoolNaturally®) appears to remain as particles. We think this is why we needed to backwash filters with PoolNaturally Plus much less often than those with conventional water treatment.
By understanding the relationship between biofilm, filters and water we are aiming to create biofilm free aquatic systems that require less chemicals, maintenance, and unwanted side effects.
Preventing Biofilm Formation in Spas
Now that you’ve flushed your spa once, twice or as many times as it takes to get it all out, how can you prevent biofilm from forming again?
Remember – biofilm forms when bacteria in solution adhere to a surface, divide and cover themselves with a protective layer of slime (mucopolysaccaride). Learn more at Montana State University’s CBE site.
You could try to completely sterilize your spa and the spa water and keep it sterile; drain the spa and use fresh water every week; use a flush to remove all biofilm once or twice a month and replace the water; OR you can prevent formation of biofilm while killing all swimming bacteria. Let’s look at each one.
The Hard Way:
Sterilize your spa and water
There is no easy way to sterilize every surface in your spa short of sending it to an industrial sterilization facility that uses high power x- rays. Even if that was done, the water placed into the spa would have to be sterilized, and you couldn’t use the spa because the second you stepped into the spa the bacteria on your skin would quickly repopulate the spa water and the spa surface. In my research laboratory, we conduct many experiments under sterile conditions and keep the systems sterile. The amount of work and equipment in addition to training required to accomplish that is enormous.
Drain the spa and use fresh water every week
This is essentially how commercial spa operators try to keep their spas within health department guidelines. They often use a measurement called “total dissolved solids” to determine when to dump the water and start fresh. Depending on the bather load, this could be done twice a week or weekly. The water is then treated with a sanitizer like chlorine to keep the bacteria count in the water within safe limits. This approach uses a lot of water, takes a lot of time, and does nothing to address the formation of biofilm in the spa. With the biofilm present in the spa, any excess bacterial challenge or change in bather load will “tip the balance” of the water and require more frequent water changes.
Use a flush to remove all biofilm once or twice a month and replace the water
As we discussed in my last blog (September 23, 2009), we now have an effective flush system that efficiently remove biofilm from surfaces and keeps it in solution. When the spa is drained, the biofilm goes out with the water. With fresh water and sanitizer in the spa, new biofilm will form over time requiring reflushing and fresh water. Theoretically, the water should last longer between changes than the previous scenario, but with frequent spa use, flushing would have to be done once or twice a month. The same problems as above make this treatment plan a real problem.
The Easy Way:
Prevent the formation of biofilm and control the number of swimming bacteria
This solution is ideal. Up until the discovery that certain species of moss prevent the formation of biofilm, this was a just a theoretical possibility. We know that sanitizers like chlorine and bromine are very effective killers of bacteria that swim. We now know that these same sanitizers are absorbed by biofilm and fail to kill all the bacteria within the biofilm.
Here’s how we now think this works: Combining the moss with sanitizer solves the problem. The moss prevents biofilm from forming, allowing the sanitizers to efficiently do their work on planktonic (swimming) bacteria. The moss also inhibits bacteria from dividing, so there are fewer swimming bacteria to kill. Combined with the moss’s ability to remove heavy metals from water and stabilize pH, the spa water becomes stable, clean, clear and safe. See the video on our website for more information about biofilm and moss.
What’s Hiding in Your Showerhead?
Great podcast from National Public Radio’s “Science Friday” about biofilm in another water environment in your home — your showerhead! Listen here. Originally aired September 18.
Biofilm, Medical Devices, Your Pool or Spa
Last week we talked about biofilm, the microscopic colony of bacteria that lives where water, bacteria and any surface meet. Scientists who study bacteria in the laboratory have known about biofilm for 10-15 years. It has taken that long for the laboratory bench research to impact our daily lives and biofilm impacts just about everything. Think about it: combine water, a surface and bacteria and you have instant biofilm.
Biofilm: A Slime City
A recent article in the July/August 2009 issue of Discover by Wendy Orent called “Slime City” talked about biofilm and its impact on medicine and implanted medical devices. She did a great job describing what is known about biofilm and how it causes serious diseases and problems in the body. View the article: http://discovermagazine.com/2009/jul-aug/17-slime-city-germs-talk-each-other-plan-attacks/?searchterm=Slime
The same biofilm that coats medical devices, your teeth, or an infected bone or wound covers every surface of your pool or spa. All disinfectants such as chlorine, bromine, ozone, cooper or silver are effective killers of bacteria that swim in the water. Unfortunately, that’s only 1-2% of the bacteria that populate a pool or spa. The rest are safely protected from the disinfectants by biofilm.
The colony in biofilm is static. It is alive just like a city. The bacteria move, send off microscopic streamers of biofilm containing bacteria to settle on other surfaces, send off microscopic balls of biofilm to roll along the surface to start a new colony, and provide a nursery for bacteria to multiply and replace those that die off.
A Slime City in your pool or spa?
You see the effects of the biofilm streamers when your spa forms foam on the surface of the water. Biofilm free water in a spa doesn’t foam. The air bubbles injected into the water from the jets come to the surface and pop. Biofilm in pools and spas cause the rings and scale on the pool sides. It also causes cloudy water.
Recently, the scientists at the Center for Biofilm Engineering at Montana State University (http://www.erc.montana.edu/) discovered that biofilm causes corrosion of metals. At the interface of the metal surface and the biofilm the pH is around 1 and there is a small electrical current produced by the bacteria. The combination can cause electrolysis of almost all metals.
Think of your spa or pool’s heater cores, motors, seals and metal fittings. The microscopic biofilm is slowly eating the metal causing mechanical failures that are costly to replace.
The take home message is that biofilm is a major contributor and cause of most problems in pools and spas. So, how do you get rid of it? Tune in next week for more.
Thoughts on the Moon Landing and Biofilm
Where were you when the first human foot made an imprint on the moon 40 years ago?
I was in Ferkessedougou, Ivory Coast working at a mission station for the summer between my sophomore and junior year of college. I spent part of my time doing maintenance and the other helping with surgery. I remember listening to the short wave radio as we heard Voice of America describe the landing. It was night and there was a bright African full moon. After they landed I went outside and looked at the moon marveling at the advances in technology that allowed that human footprint on the lunar surface.
The next morning I excitedly told my co-worker, in my broken French, what happened the night before. He asked me “How long did it take them to get there?” “Three days was my answer.” He thought a while and then said, “The moon is as far away as Buoake.” Buoake is a three-day walk from the mission station.
His frame of reference was completely different than mine and in a way both were accurate.
A Different Understanding
That experience is very similar to what is happening in the understanding of how bacteria live in pools and spas. The old, accepted model says that bacteria like to swim and remain suspended in the water. We now know that 99% of bacteria in water swim to the nearest surface, attach themselves, and set up a microscopic colony that is protected by a layer of sticky protein and sugar molecules we call biofilm.
The biofilm protects the bacteria from chlorine or other chemicals put into the pool to control bacteria. In fact it absorbs chlorine, bromine or ozone so a lot has to be added to the pool to maintain proper levels. As we study biofilm in our laboratory and more fully understand how it affects pools, spas and any other system where water, bacteria and a surface are present, we are convinced that most of the water problems plaguing the recreational water experience are due to biofilm.
The bad news is that bacteria protect themselves with biofilm and that all the chlorine, bromine, ozone, cooper, silver, UV light or other systems that only affect bacteria suspended in water are totally ineffective against bacteria protected with biofilm. The good news is that we are discovering that the sphagnum moss in SpaNaturally and PoolNaturally may be nature’s answer to controlling biofilm.
While this research may not compare with the accomplishment of Apollo 11, in the future we’ll know that cleaner, safer water with fewer chemicals was a dream fulfilled through the scientific effort of hundreds of scientists who transformed our understanding of how bacteria live and protect themselves.
