This month’s featured article from
Steve’s Pool Service
How clarifiers work to polish pool water
Though it’s often hard to describe, you know when you have pool and spa water that has that something extra – a polish or “snap” – that sets it apart from the rest.
If your water has it, great. If not, hours can be spent adjusting the chemical balance on a pool, brushing the walls, scrubbing the tile, vacuuming and backwashing the filter. But if, after all this work, the pool water isn’t sparkling clear, you may wonder, what causing the water to be cloudy? How can that perfect “snap” be acheived in your pool?
Good questions. First, let’s look at the cause of the cloudiness.
Even when you have a circulation system that is running at optimum capacity and a filter is doing its job, we know that at best, a filter can remove particles down to a few microns.
A micron, as you may or may not remember from your high school chemistry class, is a scientific term for a unit of measurement that equals one millionth of a meter – in other words, really small. To give you an idea how small, the human eye can recognize things a small as 35 microns. A single grain of ordinary table salt measures about 90 microns across.
So if your filter is working like it’s supposed to and filtering out all of the particles larger than that which can be seen only with the aid of a microscope, what’s the problem?
Well, these tiny particles – called colloids – are so small that they often lack any real gravity and usually become suspended in the water. And when you get enough of them in the pool, they are a real pain the neck when it comes to maintaining water clarity.
Because they are so small, they can pass right through any pool filter. Because they are not affected by gravity, they generally will not settle out – they simply remain hanging throughout the water. And because they reflect light, they make the water look murky even though you can’t actually see them.
One more thing about these tiny colloids. Nearly all of them are negatively charged, which is important because that means they repel each other. They simply can’t combine or neutralize one another.
Colloids are not the only things making the water murky. While your sanitizer kills bacteria, once you’ve successfully killed these organisms, you’re still left with their tiny skeletons that float in the water.
And then there are all the things that are brought in to water by bathers, or blown in from the surrounding environment. This stuff includes body oils, deodorant, hair spray, lotions, makeup, sweat, spit, urine, insects, grass clippings, pollen, smog, acid rain – you name it.
Most of it can be filtered or swept out of the water. But some of it can stay around to help cloud or discolor the water, making it, let’s just say less than desirable.
OK, we now know that the cloudiness is being caused by all these tiny particles floating around the pool that cannot be filtered out. But what can we do about it?
One suggestion would be to somehow glue all of the particles together until they formed a larger unit, capable of being trapped by the filter. And this is actually the principle behind water clarification.
While it’s an idea that has been perfected by modern science, it is far from new. Mankind has been trying to clear murky, cloudy water for thousands of years. In fact, in the early days of recorded history, various materials – such as crushed almonds and beans in ancient Egypt and nuts in India – were used to clarify turbid (cloudy) water.
These early people would store their drinking water in metal or clay pitchers, throw in some nuts or beans and wait for the impurities to glom onto them, then skim off the added material and drink the water.
This form of clarification used is a principle now callagglomeration, because the impurities glommed together before they settled. Individually, the particles were not heavy enough to be affected by gravity. But once they were agglomerated, they became heavy enough to settle.
This process is also called coagluation, because the dissolved particles form a clot and fall to the bottom of the water.
The ancient Chinese found that they could clarify water effectively using a natural chemical salt, which scientists in the 19th century identified as aluminum sulfate, more commonly known asalum.
Though it was first used to clarify municipal drinking water in England as early as 1843, the first municipalities to use it in the United States were in New Jersey in 1885. The same technology is still in use today by water companies throughout the world.
The swimming pool industry has used alum as a water clarifier since the 1920s, and while limited, many service technicians continue to swear by its effectiveness today.
The ancient Chinese didn’t know how alum worked; they just knew that it did. Today, we know how.
When alum is added to water, it forms a gel-like precipitate – aluminum hydroxide – that bridges or sticks together, forming small bundles that trap suspended particles as they fall through the water. These bundles are called flocs, and this process is today calledflocculation.
What is created is a large amount of sediment on the bottom of the pool, which is made up of both the gel-like alum precipitate and all the suspended particles and oils that were in the water. This is usually vacuumed rather that filtered out, because it tends to be more than the filter can handle.
Scientifically, a polymer is a huge molecule chain that contains many repeating parts. Wood, hair and rubber are natural polymers, but scientists have imitated these natural polymers in synthetic polymers that have many uses in the modern world.
Synthetic polymers were first used as a water clarifier in 1945, but it wasn’t until about 1970 that they were first introduced in the pool industry.
The key to understanding why they work as a water clarifier is that each link in the polymeric chain takes on an electrical charge. If you remember back to our discussion about colloids, we said that they carried a negative charge. In fact, most all dirt particles in water are negatively charged.
A polymer-based water clarifier carries positively charged ions that are added to the water. One of the first rules of chemistry is that opposites attract. So we have all the negatively charged dirt particles attracting themselves to the positively charged polymer molecules, which get together to form coagulated clumps or flocs.
Whether water is cleared by flocculating, coagulating or agglomerating, what is accomplished is the gathering together of suspended particles to produce an object that the filter is physically capable of capturing in its media. In many cases, this is the exact technology needed to restore pool and spa water to a state of crystal clarity – the “snap” that every pool owner wants.
Excerpted from the September 30, 1998 Service Industry News
Story by Doug Walsh
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