by Rob Cox, October 29, 2010
Regenerative Pool Filters - Eco-Friendly Filtration for Large Pools
In the commercial world of waterpark management or pools containing hundreds of thousands of gallons, regenerative pool filters have gained quite a foothold. On large commercial pools, the use of traditional sand filters have their drawbacks. Backwashing a set of 3-6 large sand filters can require 30-50,000 gallons of heated and treated pool water.
Regenerative pool filters also have the benefit of taking up less space. Several TR-140 sand filters can be replaced with one 60 inch regenerative pool filter, which use Diatomaceous Earth or Perlite as their filter media.
What do we mean by "regenerative"? From the word "regenerate", these filters are able to increase filter cycles, or time in between backwashing, by recycling the filter media. Basically, the DE powder (or perlite) is mixed up with the dirt every so often, to allow the maximum amount of surface area to be used for water filtration.
In design, these large commercial filters are very similar to the Hayward Perflex pool filter, used on residential pools, which use "fingers" instead of curved or flat filter grids. Hayward calls them flex-tubes, which are slotted plastic tubes covered in a polyester material. Shown at right, these flex tubes hang vertically in the filter, spaced closely together, and serve as the filter septa. When DE powder is added to the filter, the powder (which does the filtering), coats these "fingers" and traps dirt as the water is pushed through the tubes and out the hole in the top, where it exits the filter.
In the residential world, regenerative filters have appeared, most notably in filters by Hayward such as the Perflex filter. These are both small filters, suitable for smaller pools, under 20,000 gallons. Perflex filters have a bump handle on top, which allows the user to "bump" off the DE powder, which falls to the bottom of the tank, mixing with the dirt that has formed a flow-blocking layer on the flex tube. This is where the "regeneration" happens - an extension of the filter cycle. After bumping the filter, and restarting the pump, the DE powder, mixed with some dirt, will recoat the flex tubes and allow for increased flow and decreased filter pressure.
The RegenX filter by Hayward uses a septa that resembles a filter cartridge, although made of a more rigid material. The DE powder will coat the single cartridge, and the regeneration takes place by pumping a piston that removes the DE filter cake, dropping it to the bottom. Mixing with the trapped dirt, turning the pump back on will reset the DE/Dirt mix, reducing filter pressure and increasing filter flow rate. This filter has been discontinued by Hayward, (not sure why), but we still have RegenX parts available.
The benefit to regenerative filters, outside of water savings and smaller filters, also includes the use of a smaller pump. Large sand filters or DE filters that clog easily will require a larger horsepower pump to keep the water moving. Using smaller pool pumps saves energy. Another benefit is that the DE powder lasts longer, so less money is spent on replacing the filter media - and - less DE powder is flushed into the environment. DE powder does not decompose, it's already millions of years old. It's organic - this is true, but DE powder can kill grass, or choke small streams if it makes its way into your local watershed.
Regenerative pool filters are "Green" pool filters in that they save water. It could be said that water is never truly "wasted" - it does not decompose. There is still roughly the same amount of water on this planet that there was 100 years ago. What is wasted however, is the duplicated water treatment. And there is a real cost to purchasing replacement water from the water authority. Some areas of the country need to ration water, due to it's short supply. This drives up the cost of the water, and puts pressure on pool operators to use less water in their pool management.
DE pool filtration is the superior form of pool filtration. It traps particles down to 3 microns, and will remove 99% of pathogens such as Cryptosporidium in a single pass. Sand filters, by contrast, remove only 50% of Crypto on average, and can only filter down to a particle size of 20 microns or so. Regenerative DE pool filters are not widely available in the residential market yet, options are unfortunately limited.
If you have a regular DE pool filter, you can "bump" the filter by doing a short, 15 second backwash, followed by 15 seconds on the filter setting, then another 15 second backwash. However, much of the DE powder will remain trapped between vertical grids, a difficulty known as "bridging". Nonetheless, bumping your DE pool filter will extend the period of time between backwashing, reduce your water usage and DE powder expense, and reduce the amount of DE powder pumped into your local environment.