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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.
Swimming Pools and Asthma
During our test this last summer at the St. Paul, MN outdoor aquatic park we surveyed the swimmers twice a week. One of the most striking findings was that swimmers with asthma did not need to use their inhalers when swimming in the pools that were conditioned with PoolNaturally Plus. We then treated the indoor aquatic park in St. Paul and had similar results.
Able to Swim Again
In fact one lady wrote to me about her inability to swim indoors due to her asthma. She was a competitive swimmer in her younger years and had to stop swimming because of severe breathing problems from asthma caused by the air in the pool. She heard about the sphagnum moss treated pools and how people could swim without using their inhalers so she tried swimming again. She reported that she could do a full workout without breathing problems and thanked me for “giving her back her favorite sport”.
With a little research the relationship between recreational and home water, chlorine and asthma became clear.
The Chemical Reactions
Here is what happens when we use chlorine to sanitize water in a pool or in our municipal water supply. As it turns out chlorine is not the problem. A byproduct of chlorine and biological molecules that contain nitrogen is the formation chloramines. These chloramines come in many different forms such as mono, di, and trichloramines. One of these compounds, a molecule called trinitrochlorine, has been implicated in causing airway irritation.
Trinitrochlorine is a volatile molecule that is extremely irritating to tissues such as your eyes, skin and airways. Because the molecule is volatile, it rises to the surface of water and is easily inhaled. In fact, in a pool, the levels of trichloronitrate are highest in the air right on top of the water. So every time a swimmer takes a breath, they inhale an irritant that causes airway constriction called reactive airway disease. The smell we all associate with a chlorine pool is actually the smell of the multiple species of chloamines, not chlorine. The problem is that chlorine is so reactive, it immediately finds and combines with nitrogen containing compounds to create chloramines..
Correlation between Pools and Asthma
A recent study reported in the pediatric literature, showed that children who are repeatedly exposed to swimming pools have a significantly higher incidence of reactive airway disease or asthma, than those who aren’t exposed to pools.
In our research laboratory, we are currently studying why the pools treated with PoolNaturally Plus don’t cause this reactive airway response, skin irritation, or burning eyes and don’t smell. We know that for chlorine to become trichloronitrate you need chlorine, nitrogen containing biological molecules and a low pH. It could be that the amount of biofilm in the pool correlates with the amount of trichloronitrate because biofilm contains and produces huge amounts of nitrogen containing molecules and it creates a local microenvironment that has a very low pH. It could therefore be the “engine” that drives the formation of these toxic molecules. In the laboratory we know that the moss in PoolNaturally Plus inhibits the formation of biofilm and if our hypothesis is correct it could greatly reduce the formation of chlorine to trichloronitrate by removing the primary nitrogen source, the biofilm . We will find out with further research
Aquatics International recognizes CWS’ Knighton in Power 25 Reinventors
Creative Water Solutions President and co-founder David Knighton, MD has been recognized by Aquatics International magazine as one of their Power 25 Reinventors. Successful testing of sphagnum moss-based PoolNaturally Plus at Highland Park Aquatic Center in St. Paul, MN, during the summer of 2009 marked CWS’ entrance into the commercial side of the aquatics industry. Read more at Aquatics International.
Cyanuric Acid and Last Summer’s Journey
This last summer we added our Sphagnum moss pool product to the Highland Park Aquatic Center in St. Paul. We treated two pools. One was a 430,000 gallon Olympic pool and the other was a 22,500 gallon children’s activity pool. You can read about the results on our website.
One lesson we learned involved cyanuric acid, outdoor pools, and chlorine. The accepted dogma is that cyanuric acid is required for outdoor pools and spas to stabilize the chlorine against UV degradation. In fact, most granular or solid chlorine sold in stores is stabilized with cyanuric acid. Dichlor and Trichlor have cyanuric acid in the formula.
When cyanuric acid interferes with chlorine
We started to try and understand the chemistry and science of cyanuric acid because of its side effects. Cyanuric acid above a certain concentration (which is dependent on pH) inhibits chlorine’s (hypochlorous acid to be precise) ability to oxidize bacteria. Failure to oxidize means no killing.
We also found that cyanuric acid is denser than water so it sinks to the bottom of a body of water. Therefore, the level of cyanuric acid on the surface of the pool or spa is the lowest level in the pool and it increases from there to the bottom. It will be the highest in the deepest part of the pool.
We tested this at the Olympic-sized pool. We sampled water at the bottom, middle and top of the pool. The cyanuric acid was set for 40 ppm. At the surface the level was 30-40 ppm, in the middle it was 60-70 ppm and at the bottom it was 100 ppm. From the middle of the pool to the bottom hypochlorous acid was essentially ineffective.
The other fact about cyanuric is that it is nonvolatile. That means as you add more and more to your pool or spa the concentration continues to increase. The only way to decrease the concentration is to empty some water and replace it with fresh water without cyanuric acid so you dilute out the chemical. In places where the spa or pool is full all year long, the concentration of cyanuric acid can increase to the point where the pool has no effective chlorine. I think this is why most pools have algae outbreaks starting in the bottom of the pool. The high cyanuric acid levels inhibit hypochlorous acid so no killing of algae occurs.
The experiment
So, after we learned this, I decided to decrease the cyanuric acid level in the pools gradually to see if it is really needed. The pool engineers told me “if you do that there will be no free chlorine in this pool in the morning.” We agreed to decrease cyanuric acid by 10 ppm each week and monitor the results. The free chlorine levels never decreased and the combined chlorine remained at 0. We decreased the cyanuric acid to zero and never added any more for the rest of the summer. The levels slowly decreased to zero as makeup water diluted out the cyanuric acid. The children’s activity pool behaved exactly the same.
In another pool we treated we were able to manage the large pool all summer without any cyanuric acid and maintained free chlorine levels from 1-3 ppm with no combined chlorine all summer.
Water treated with moss doesn’t need cyanuric acid
The bottom line is that with moss treated water, cyanuric acid is not needed. The mechanism for this probably centers around biofilm. I don’t think that cyanuric acid prevents chlorine from UV degradation or the free chlorine levels would have decreased in the outdoor pools we treated. We know the moss inhibits biofilm formation in the laboratory and know that biofilm absorbs chlorine. We know that free chlorine levels skyrocket when moss is added to the pool and to maintain a level of 1-3 ppm free chlorine, the chlorine added to the pool decreases by over half. So a pool with moss doesn’t need cyanuric acid. That allows the chlorine added to the pool to remain active providing effective microbial control.
Salt Water Pools, Chlorine and Moss: the naked and not always green truth.
In my continuing travels to dealers, shows and meetings I am frequently asked, “Does the moss work in a salt water pool? “ Or “why do I need moss since my pool doesn’t need chlorine since it is a salt pool?” So this blog is about the science and chemistry of salt-water pools.
First, definitions: I’m going to talk about pools where the sanitizer is made from salt by a generator – not about the very few pools that actually have salt water similar to that in the ocean. Second, when I talk about green pool products I’m using the word to describe a product that is sustainable, with no artificially made chemicals, that doesn’t introduce toxic chemicals to the air, water or ground.
How does a salt water pool work?
Salt is usually sodium chloride or potassium chloride. When these chemicals are in water they become positively charged sodium or potassium and negatively charged chloride ions. In a salt pool, solid or crystalline salt (like table salt) is passed through a generator that produces hypochlorous acid and delivers it to your pool.
This is the exact same chemical that results when you place chlorine in your pool. Salt generated chlorine doesn’t add cyanuric acid in addition to the chlorine, which is added when “stabilized chlorine” such as dichlor or trichlor are used.
So a salt pool is simply a different way of delivering chlorine to your pool to make hypochlorous acid. It is no greener or different than using liquid or solid chlorine. Again, the end product that works to kill bacteria in water is hypochlorous acid and whether you produce this from salt, or deliver it to the water as chlorine, it is all the same thing.
Is a salt pool greener?
The short answer is no. People who sell salt generators want customers to think it is green since it uses salt that doesn’t have a bad name vs. chlorine that had a bad reputation. The end result of each method is the same production of hypochlorous acid that causes the exact same problems with pool water regardless of how the chlorine is delivered to the water. Salt-water generation of chlorine is no greener than adding bleach or granular chlorine to the water.
Does moss work in a salt-water pool?
The short answer is yes. It works the same way whether the sanitizer is added chlorine, bromine, cooper or silver salts, or ozone. It has the same positive effects with all types of sanitizers (except biguanides).
In our customer’s experience using moss with a salt generator, the amount of salt consumed by the generator decreases by 80-90% to keep the free chlorine in the pool between 1-2 ppm. This puts much less strain on the salt generator and results in less chlorine being added to the environment. The other effects of moss, such as pH stabilization and biofilm effects are the same.
Will Getting Rid of Biofilm Get Rid of Crypto?
Biofilm
A couple of weeks ago I attended the World Aquatic Conference in Atlanta that focused on health and safety issues in aquatic recreation. There were a few sessions on Cryptosporidium and pool contamination.
A long time ago I spend three months in rural Ivory Coast in Africa and saw the effects of parasites on health. There it is a daily, widespread and often fatal problem. Trying to eradicate the parasites is impossible, so most of the medical effort centered on treatment. Luckily, we have very few parasitic diseases so general knowledge about parasite patterns of transmission and growth are widely known.
Parasites in Pools and Lakes
Cryptosporidium, or Crypto for short, can be a serious health problem from pools and lakes. Giardia in lakes is a type of Crypto. Both parasites set up home in the intestines of mammals and cause diarrhea with the accompanying dehydration.
Contrary to most people’s belief, these parasites do not proliferate or “grow” in the water – only inside mammal’s intestines. They can live in the water for long periods of time waiting for an unsuspecting mammal, maybe you, to swallow the water. Then they set up shop and start to divide causing intestinal disease. Huge numbers of Cryptosporidium parasites can reside in every stool from an infected animal or human. As few a 10 ingested organisms can cause serious disease. Read the rest of this entry »
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.
How do I make my spa biofilm free? ‘Flush’ and Moss!
In my last blog we discussed biofilm and how it affects your pool, spa, home, really anywhere water, bacteria and a surface come in contact. It is an important new discovery that is helping us understand how to keep water clean, safe, crisp, clear and provide a pleasant experience. You can see a newly posted, short video about biofilm and sphagnum moss on our website.
How do I get my spa, or pool to be biofilm free and keep it that way?
So the question remains, how do I get my spa, or pool to be biofilm free and keep it that way? First, if you haven’t done anything to remove the biofilm or keep it from forming, then be assured you have biofilm on every surface. It is very difficult to remove biofilm once it has formed.
The best example of how difficult it is to remove biofilm is the tartar on you teeth. That is biofilm and all the brushing, flossing, and mouthwash use will not remove the tartar. Your dental hygenist has to scrape it off with sharp (an often painful) tools. It would take toxic acid to remove the biofilm. That would destroy your teeth and gums along with the biofilm. Scrubbing the surface of your pool or spa might remove some of the biofilm, but not all of it. If it isn’t totally removed, any remaining will re-infect all the surfaces and restore the biofilm in hours. All the interior surfaces of your spa or pool are impossible to clean.
Spa System Flush
I know of one chemical that is EPA certified to remove biofilm. We tested it. It did remove some of the biofilm, but it off gassed a chemical or chemicals that were very toxic to my lungs and all those in the same room. We found a spa flush that claims to have an effect on biofilm and it does break biofilm free from the spa and doesn’t cause any severe side effects. This is supplied in our SpaNaturally kit (Spa System Flush).
Soon we will be releasing a new solution that is even better at removing biofilm with no side effects. We test these products in our laboratory on biofilms grown in cultures and then also test them in the field.
The bad news for spa owners is that they need to flush the spa to remove biofilm whether it is new or old.
Here’s the problem: When spas are made at the factory they are tested for leaks by filling them with water from tanks in the factory. Biofilm grows in these tanks so the water transfers bacteria and biofilm to the new spa. It is impossible to remove all the water from the spa. It is then shrink wrapped and stored. Everywhere there is water there is biofilm that dries and hardens as the spa is stored.
brand new spa being flushed!
When you refill your new spa the dried biofilm comes back to life and spreads throughout your spa water. Another fact is that the more jets in your spa, the more biofilm there is also. Each jet is fed by a tube made of plastic that comes from a manifold. The more jets, the more pipe, the more places where water collects and forms biofilm.
I proved this by using a long scope like those I used to use for colonoscopy. In a new spa, the tubes leading to the jets were clean until they curved. Along the bottom arc of the curve the biofilm started and continued until the tube curved back either up or down.
Another place where biofilm forms is in the housing of pumps. These are wet tested in the factory and have the same problem as the spa jets. In fact, I recently had to replace my circulation pump in my own spa that is biofilm free. Three days later the water became cloudy and started to foam. I flushed the spa and black biofilm came out with the flush. After flushing the spa returned to crystal clear water, with no foaming. I then checked other pumps and found black biofilm in the pump housings.
Heat also affects biofilm formation. Bacteria and biofilm are very temperature sensitive. The closer the temperature of the water gets to 100°F the higher the bacteria growth rate and therefore the more biofilm forms. Lower temperatures inhibit (but don’t stop) bacterial growth.
How much flushing is needed?
Depending on the amount of biofilm in the spa, more than one flush may be needed to completely remove all the dried biofilm. I needed to flush my new spa seven times (using our current flush) before it stayed clean and clear.
You are probably asking the same question I did while this problem was being understood and researched. Could the spa manufacturers make a biofilm free spa? I know they can. We have been working with spa manufacturers to flush their water tanks and treat the water with moss so they don’t transfer biofilm to the spa when it is wet tested. So far, the results are very encouraging. When we flush the new spas, very little biofilm is removed even after months of storage.
In review. Biofilm coats all spa and pool surfaces in contact with water. It is very difficult to remove. Using the right chemicals and system can remove biofilm. All spas, new and old must be flushed. On the horizon, biofilm free new spas are possible.
Next, I’ll talk about pools and preventing biofilm from forming.
David Knighton, MD
