No backwashing required
What makes RMF systems unique is they do not require backwashing. Depending on the aquatic facility’s size, this can save hundreds of thousands, even up to millions, of litres of water annually. Operating expenditures can be reduced significantly when considering costs for make up water, sewer discharge fees, in addition to chemically retreating and/or reheating the new water.
RMF’s ‘regenerate’ the media within the filter by going through a daily ‘bump’ cycle—an automatic function that shuts down the pump and closes the necessary valves to isolate the filter. During normal filter operation, flex tubes, which are attached to a tube sheet at the top of the unit, are held in place via air pressure. During a bump cycle, air pressure is quickly released and the tube sheet drops slightly, agitating the tube elements, which release the media into suspension within the tank. The cycle will occur 10 times and take approximately 10 minutes to complete before the pump comes back on. When it does, water is recirculated around the filter through a pre-coat loop in the piping and the filter media is redistributed onto the tube elements to create a new outer layer.
Due to the large amount of filter area and what is considered ‘void space’ in the media, it takes a long time before the filtration media becomes saturated and needs replacement. A typical filter cycle runs an average of 30 days.
When the influent vs. effluent pressure differential is achieved, this indicates the end of the filter cycle. Spent media, water and particulates are merely drained from the tank via gravity through the drain connection on the tank bottom. The tank is then refilled to rinse the flex tubes and drained again—it only takes two tank volumes of water to clean the filter. Once the filter is clean, the drain valve is closed and new filtration media is introduced via a vacuum transfer system, starting the whole process over again. As RMF systems use less water when being cleaned, these filters are being utilized on more facilities around the world, as water conservation is a huge issue in many countries.
The space needed for a RMF system in an equipment room is typically one-fourth to one-sixth of the space required for a similar-sized sand filter. With current construction costs, the ability to reduce the equipment room space requirements and the facility’s overall carbon footprint, can represent significant savings for a facility.
Filter media comparison |
|
|---|---|
| Perlite advantages | Diatomaceous earth (DE) disadvantages |
| · Nuisance dust (same as kitchen flour); | · Carcinogen (causes cancer); |
| · Amorphous (uncrystallized) silicate (containing less than .001 per cent crystalline); | · Crystalline silicate (can cut the throat and lungs if inhaled); |
| · Can be discharged into sanitary sewers (holding tank not required); | · Must be disposed of as a hazardous waste (holding tank required); |
| · Lighter weight (4.03 kg/m3 [0.25 lbs/cf]); | · Heavier weight (6.8 kg/m3 [0.42 lbs/cf]); |
| · Use less (0.41 kg/m2 [0.08 lbs/sf]); and | · Use more (0.75 kg/m2 [6.8 lbs/sf]); and |
| · Lighter and less volume of media ensures even distribution. | · Heavier weight and increased volume of media causes frequent clogging. |
Bob Hawken is vice-president/sales manager for Neptune-Benson Inc., in Coventry, R.I. He has worked in the pool industry for 40 years, the last 26 of which in commercial pool construction and equipment sales. Hawken specializes in competition pools, waterparks, aquariums and other large aquatic facilities. Most recently he was involved in some of the world’s largest facilities, including Great Wolf Lodge Resorts, The Georgia Aquarium and the Atlantis Resorts in the Bahamas and Dubai.
