Swimming Pool Scene INDUSTRY NEWS
the backwash process is just as important as is achieving an efficient filtration speed. Whatever the media used, it’s important to get fluidisation of the media bed in order to release all the captured debris. According to German DIN standard, where sand is used as a filter media, the required speed for backwash is 60m/h (m3/m2/h). This requires a lot of water and also will not guarantee a break-up of the ‘mud-balling’ than occurs in sand. The result of an insufficient backwash is the reduction of filtration efficiency. Captured debris remain in the filter, harbouring bacteria and increasing the demand on the disinfectant used. It’s at this point that the water quality starts to suffer.
A more efficient backwash can be achieve at a slower backwash speed when glass media is used instead of sand. This stands to reason as glass is lighter than sand in weight so, less forces are required to achieve the same lift. We would recommend a speed of 45m/h to get the required fluidity. However, not all glass media will give the same filtration and/ or backwash performance.
The shape, size and colour of glass media available on the market vary considerably. Some are very round, almost sphere like. I liken this spherical media to the plastic balls you find in kids play pits. You can quite easily push your hand right through them. This demonstrates a lack of mechanical performance although I understand that it works well at very slow speeds in grey water applications. Other glass media are quite flat, a bit like piling coins on top of one another and
will block up a filter very quickly resulting in the need for more frequent backwashing. Most will still be prone to ‘mud balling’ and encourage bacteria growth but, not to the same extent as sand.
TOP PERFORMANCE
AFM (Activated Filter Media) has been engineered to a specific shape and size and is available in various grades. It has been independently tested by IFTS (Institut de la Filtration et des Techniques Séparatives) out-performing all other medias. Because it is made from specially selected green and brown glass, the raw material already has a certain ionic charge to it. No other coloured glass carries an ionic charge at these levels.
The charge is enhanced with further heat treatment and chemical processes. As a result, the surface of AFM is bio- resistant. No ‘mud balling’ can occur and bacteria cannot reach its surface. Captured debris is released very quickly during even the shortest of backwashes, resulting in huge reductions in water consumption and savings on heating for replacement backwash water.
Disinfection demand is greatly reduced thus resulting in less disinfection by-products which, in turn results in a safer, more pleasant environment for bathers.
So, just like in the ‘pyramid’ of pool water treatment, if you get the foundation correct in the first instance with the correct dimensioning of the filter vessel, the correct flow rate, correct backwash speeds, the best filter media and you simply eliminate future water quality problems significantly. ■
ABOVE: Correct flow rate, backwash speeds and filter media results in eliminating future water quality problems significantly. Swimming Pool Scene INDUSTRY NEWS 53
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