While all biological filters rely upon the same species of bacteria for ammonia and nitrite removal, it's how the filters operate that sets them apart. It's very helpful to remember that in biological filtration, it's actually the bacteria that do the work; the filter itself only provides a suitable "home" for the bacteria to colonize. Trickle filters can best be described as open containers filled with various forms of solid media. As water enters the top of the filter, it drains down through this media in a random, cascading fashion. Since the media is stationary, it relies upon the changing water currents to keep the bacterial surface area moist. Fluidized bed filters, on the other hand, are flooded cylinders or tanks partially filled with a granular media, such as white quartz. Water upflows through this media bed, causing it to expand and fluidize. The large numbers of bacteria that colonize this expanded media serve to remove the nutrients that are present in the flowing water. What results is a highly efficient filter bed that is no longer solidly packed, but is in dynamic motion. It is this combination that is the key to the fluidized bed filters’ success.
While trickle filters may have relatively large amounts of surface area (up to 200 square feet per cubic foot of media), it is virtually impossible for bacteria to colonize all of it. This is because water will take the path of least resistance as it moves down through the media, often leaving dry areas and low flow, anaerobic pockets. Another serious problem with these filters is called "bio-fouling". This occurs as particles of organic material lodge within the filter bed. Once clogged, you have no choice but to tear the system down and clean it. This is not a pleasant job; but if left unattended, your water quality will rapidly degrade.
Fluidized bed filters, by design, do away with this problem. The most obvious benefit is that all of the filter's large surface area is available for bacterial growth. With more than 6,200 square feet of surface area per cubic foot of media, you can quickly understand why fluidized bed filters don't need to be nearly as large as comparable trickle filters. Since the water is evenly distributed as it flows through the cylinder, there are also no anaerobic pockets of bacteria developing. The water that reaches the media is oxygen rich and very conducive to rapid bacterial growth. Also, these filters are almost impossible to clog due to the constant motion of the media. The filter bed is a mildly abrasive environment that is constantly cleaning and renewing itself as it moves quietly around inside the cylinder.
COMMON QUESTIONS
What happens when the power goes off?
Some bacterial die off occurs within 2-4 hours and probably at about 30 hours, the filter should be considered biologically dead. But, similarly, all biologicals have this attribute. The unique feature of the fluidized bed is that since they depend on a small power head for their operation you can obtain a small power pack from a sporting goods store, or a UPS for a computer which will keep the filter going. Or you can take the fluidized bed filter with a bucket of water to someone’s house that has power and keep the biological alive. P.S.: try doing that with a trickle or undergravel filter!
Will my fluidized bed filter clog?
The early models did have a clogging problem. A minor design change has eliminated this problem and we currently have not heard of this problem occurring.
How much will my filter system cost?
Fluidized bed filtration will cost you less than you think. In many cases you can keep an older, out designed hang on or canister filter which can be retrofitted as a pure mechanical/chemical filter for your system then simply add the fluidized bed to act as the sole biological filter. |
