Ok, this is not a FSB (fluidized sand bed) filter. Its bead clarifier filter which is only fluidized during cleaning. Its a DIY homemade bubble washed bead filter.
I copied the design from
http://www.vcnet.com/koi_net/BubbleBead.html only in a miniature fashion using 3 inch PVC.
Here are the basic of operation:
Quote:
Theory of Operation
Bead filters function both as a solids capture device and a biofilter. They operate very much like a submerged rock bed or undergravel filter except that they are designed to facilitate cleaning. Bead filters dramatically simplify operations by providing two of the most important water reconditioning processes, clarification and biofiltration in a single unit. Clarification is the process of removing suspended solids from water. Suspended solids in a pond consist of small particles of partially digested food, debris, algae, bacteria, clays, and silts, which are small enough to stay suspended in the water column for an extended period of time. Fine suspended solids tend to make the water opaque, interfering with the clarity of the water. The larger organic particles, on the other hand, represent a serious wasteload problem and can consume tremendous amounts of oxygen while adversely impacting the hygienic pond ecology. Bead filters are considered excellent clarification units, capable of maintaining display quality water at high waste loading rates. Bead filters remove suspended solids by four different mechanisms as the recirculated pond water is passed through the plastic bead bed. Physical straining is probably the most dominant mechanism for the larger particles (>80 microns). The bulk of the suspended particles (20-80 microns) are probably removed by interception, a subtle process caused by collisions between the particle and the bead media surface. The finest particles (<20 microns) are removed by bead filtration, but at a slower rate. It is believed that bioabsorption, the capture of particles by the bacterial biofilm, is the dominant process attacking these fine particles.
Biofiltration depends on the development of a filter bed that encourages the growth of beneficial bacteria, which extract dissolved chemicals from the water and convert them to particulate biomass or harmless dissolved compounds. Given the proper encouragement, the bacteria grow in a thin film, coating the surface of each of the 600,000 beads contained in every cubic foot of media. There are literally hundreds of species of bacteria at work in a biofilter. Most of the bacteria fall into the category of "heterotrophic" bacteria, which actively break down organic materials into carbon dioxide and water. The most critical however, are broadly described as nitrifying bacteria, consisting primarily of the genera Nitrosomonas and Nitrobacter. Nitrifying bacteria are responsible for the conversion of the toxic nitrogen forms of ammonia and nitrite to the relatively harmless nitrogen form of nitrate . Success and a wide variety of parameters that influence bead biofiltration have been identified. The pond hobbyist should be aware of these factors. However, the pond itself generally contains a very active population of nitrifying bacteria, so optimization of the filter's operation can be relaxed.
Backwashing
Bead filters spend most of their time in the filtration mode (Figure 1). As the recirculating pond waters pass through the bed, solids consisting of fish feces, algae, zooplankton, debris, and biofloc accumulate, gradually clogging the filter. For most pond applications, the clogging process generally occurs over a one to two week period.
Bubble-washed bead filters are designed to be self-washing when drained. The discharge of the filter is equipped with a valve (or check valve) that prevents the backflow of air into the filter when the sludge (or drain) valve on the bottom is opened. This causes a vacuum to form within the filter housing. An air valve on the side of the filter is opened so that air can be sucked into the filter as it drains (Figure 2). This air injection line is located below the washing throat, in the middle of the filter. This constriction is critical to the washing operation. Water dropping out of the filtration head causes the beads to fluidize downward and pass through the narrow throat where they are scrubbed further by the rising bubbles. The washing process is complete once the filter is drained and all the beads have dropped into the expansion chamber (Figure 3). The next filtration cycle is started by readjusting the valves and refilling the filter with the The energy for backwashing is generated from the hydrostatic pressure stored in the filtration chamber. Draining alone is not sufficient to wash the beads; so, the bubble-washed filter is configured to release waste while sucking in air below the washing throat. The rate at which the water stored in the filter is drained, and thus the vigor of the washing, is controlled by the siphon head formed between the elevation of the internal end of the air injection line and the elevation of the first air break in the sludge discharge line (Figure 6). Typically, hourglass filters are designed with a minimum siphon head of about six inches, which is sufficient for most applications. If the filter is mounted 12 to 24 inches above the ground, then a drop pipe can be attached to the sludge discharge line and the siphon head can be increased to 12 to 18 inches, doubling or tripling the rate of draining. This increased siphon head will translate into a quicker and more vigorous wash. Drop pipes dramatically increase the filter's resistance to clogging. Their use increases the amount of fish the filter can support without shortening the backwash interval.
I did use my $29 harbor freight plastic welder for the project. Still, it was a simple 2 hour project. The cost came out to $69 with all new parts.
I looked every where for media and could only find a source of food grade LDPE beads from the makers of the poly geyser bubble wash system. The price would have been $31 delivered for 8.25 pounds (.25 cubic feet media). Well, being that I was in a hurry and my fish needed clean water asap I found rolls of .25 inch LDPE tubing precut to 25 foot at Lowes.
Each roll weighs about .25 pounds. I cut up 3 rolls and it weighed about a pound. First I thought I would cut it in short 1/8 inch sections.
But then I decided to splitting the tubing in half to avoid the possibility of anaerobic spaces in tubes.
Here is 1 25 foot roll cut up and put in a 16 oz solo cup.
Next, I cut up my pipe making the top section longer to hold more water for the purpose of getting more bubbles through the media during cleaning. I only added enough filter media to fill the bottom chamber below the washing throat. I drilled holes and welded the pipes into place after drilling some extra holes in the inlet and outlet pipes. I glued a union in the middle for later access to the inside of the filter.
Next, I set some screens in place to keep the filter media in. I used fiberglass screen. At the top I cut out a disk that overlapped the pipe and the cap was forced on pinching the screen between the cap and pipe all the way around.
For the bottom I just used a stainless hose clamp to hold a screen over the inlet pipe.
Notice the air inlet tube in centered under the 1.5 inch washing throat.
For the bottom cap I could not find a flat one so I used a "test cap" with lots of glue. I hope this will be fine, there will not be any real pressure on this anyway.
And so I finally got it all together in about two hours.
After letting the glue dry for 13 hours I hooked it up to my dirty little fish tank and is at this moment filtering out the junk from my tank.
I used a couple 3 way ball valves that way I have the ability to go into bypass mode during cleaning letting water continue to be pumped through the FSB filter. I can also run it in a backwash mode to remove that extra junk if I get to busy to clean it every day or two.
I talked to the people who build the polyGeyser and bubble wash filters. They said that after a good bio film is in place their filters would remove particles down to 5 micron; by sticking action. They use 1/8 inch LDPE beads.
Backyard Aquaponics
