recycled glass is being used to filter pool water instead of tried and trusted media like silica sand
Chris Carr, Fellow of the Institute of Swimming Pool Engineers
We all like new ideas, especially ground-breaking inventions that save us money, improve efficiency and make life easier. Such an invention has hit the commercial and private swimming pool industry – recycled glass is being used to filter pool water instead of tried and trusted media like silica sand. But are all the positive claims about glass media true? There is a heated debate within the industry about the effectiveness and, more importantly, the safety of recycled glass being used in pool filtration systems.
Having been involved in the pool industry for over 30 years, I have extensive knowledge and experience of filter media such as silica sand and zeolite and run filtration workshops on behalf of the Institute of Swimming Pool Engineers. It is, therefore, important to keep abreast of new developments that affect the way trainee pool engineers are educated. So, on hearing negative industry comments, I investigated the use of recycled glass as a filter media.
To get an objective view I talked to installers - those on the frontline - to find out what the problems are for both installer and swimmers and discover any limitations glass might have for the use in filtering swimming pool water.
I spoke with pool installers who are regularly installing pumps and filters and change filter media. There were a range of concerns including the cost, the fact that glass expands more than traditional media resulting in a loss of glass particles when the filter is backwashed, glass migrating across the filter and a loss of quality water. Additionally, glass is more abrasive than sand and can have a detrimental effect on the inside of the filter. Others expressed concern about the claims of the longevity of recycled glass as a filter media; fearing that its lifespan is much shorter than sand which could lead to performance problems.
Some installers said they had used glass on several installations and had not seen any significant improvement in the water quality compared to using sand. Furthermore, there was no real reduction in chemical consumption either. On a more positive note, some installers had used glass on domestic pool installations and seemed fairly happy with the result. However, no formal monitoring seems to be taking place.
Several installers said they had experienced problems with glass. One commercial installer found that after a time, the glass started to clump together and no matter how he tried he could not eliminate this problem without changing the media completely – a costly exercise.
Another installer showed samples of glass media being used in a commercial pool in the South East. The support media looked like pieces of shattered glass similar to that of a car windscreen smashed by a major impact. The main difference was that unlike a car windscreen, this glass was multi-coloured and looked quite attractive, rather like uncut semi-precious stones.
One could imagine if a young child got hold of this they might think it something to play with or even sweets! More worrying, these glass fragments have very sharp edges - if you were to run your fingers through these fragments, you would most likely suffer from lacerations. The main media, although a fairly uniform size, are also multi-coloured and appear to have sharp edges similar to the support media.
I was shown fragments of glass which had been collected from an in-line strainer protecting the dosing equipment probes. These fragments ranged in size around: 5 to 20 thousand of an inch and were of a shape that would pass easily through the slots in a typical under-drain system. These glass shards are probably formed from the sharp edges of the support media which may be breaking off when the filter is rinsed.
On the installation from which these samples came, it would appear that there is a continuous stream of glass shards being emitted from the filter which float around the swimming pool, invisible to the eye.
When preparing a risk assessment for a pool, one of the key rules is to ensure that all items made of or containing glass are kept well away from the pool area. In a pool environment, glass can be lethal. Apart from the obvious risk of cuts, glass shards can be ingested or become embedded in a swimmer’s eyes, ears, nose and other vulnerable parts of the body.
Such risks need to be properly considered. What would be the consequences if a filter charged with this type of glass media had a fault with its lateral system and lost its contents into the pool? If this happened suddenly with a lot of young children in a pool, would they play with the media before the supervisor/life guard had a chance to get them out of the pool?
As mentioned, the samples examined were multi-coloured, but other suppliers are providing single colour, clear or slightly green-coloured recycled glass, which is equally problematic. Imagine if a filter fails and empties its contents of ‘clear’ glass into the pool, how could a swimmer see it? The pool would have to be closed and drained in order to vacuum out the glass. In addition to the obvious health and safety risks, there would be substantial cost to rectify the problem.
On viewing the samples, two senior health and safety advisors acknowledged that there are potential risks.
There are now several companies offering recycled glass as an alternative type of filter media. Some of these companies and their products appear to be of a physically superior quality than the problem samples observed so it would be unfair to tar all of them with the same brush.
My advice to anyone contemplating using recycled glass as a media is to consider all the potential risks if a fault arose. Examine the product carefully; check its sharpness and its visibility in a depth of water. And ask about written guarantees from the supplier - who is liable if an engineer or swimmer is injured by a glass fragment and who would cover the cost if a pool hand to be drained and cleaned of glass that escaped from the filtration system.
Ultimately, we want swimmers and engineers to be safe rather than sorry!
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