Backyard Aquaponics
A place to discuss aquaponics

I wanted to start a thread that focuses on home made / DIY fluidized sand bed filter ideas. Please post pictures of you're attempts and share ideas! On the third page of this thread I posted my DIY LDPE FSB.

Some notes I have gathered:
1 kg / 2.2 pounds of fish feeding produces about 37g ammonia per day.
1 square meter surface of bacteria can convert .9g .2 being more real.
1 mm sized(medium) sand has S:V ratio of 3141 per cubic meter to 1.
Very Fine sand can have a S:V ratio of 10,000 to 1
Fluidized sand filter gives most surface area for bacteria
Takes longer to get bio started in FSB filter.
*Water flow to high and bacteria will not work and ammonia goes up
To Little flow and sand will not fluidize properly and may channel.
Best operated with only enough flow to fluidize all of the sand
FSBs work well with shock load changes
FSBs have been use for 15 years now in large systems
FSBs have been used in fresh water aquariums for 8 years
FSBs operate best in a starved mode. More bacteria vs ammonia
FSBs are extremely efficient at converting ammonia to nitrites/nitrates
FSBs need to be pre-filtered to remove solids, to prevent foaming

Starved operation allows for rapid adjustments in fish load
Water should be going through FSB at all times.
Long power failure can cause anaerobic conditions.
Anaerobic conditions can generate hydrogen sulfide, dangerous to fish
Air stone in bottom of FSB can prevent anaerobic conditions.
When calculating ammonia load add 25% for ponds in full sun; algae ect
It us best to have a cone to make sure sand settles back down.
Sand should all be round and the same size to prevent caking/sticking.

Fine even graded sand can be bought in 50 pound sacks as sand blasting sand. There are several sizes to choose from. It cost $8 for 50 pounds here at a local equipment rental.

If the medium sits in the bottom of the cylinder for an extended period, it may start to pack or compress, forming a column of hardened filter medium that is resistant to refluidization. Refluidization of the hardened bed could require forces in excess of what are normally required in an active system. To assist in breaking the resistance that may result from this settled medium, release holes can be bored into and positioned along the hollow delivery tube. Release holes will normally be positioned below the level of the fluidized bed and often below the level of the non-fluidized bed. Water exits these release holes to break the settled bed in layers.


Other notes:
Shreded "ester grass" has a 800:1 ratio; AKA bio bale.
http://www.spring-fill.com/cello.html
Pastic pot scrobbers 330:1

Pro:
FSBs pack more biologically active surface area into a given volume than any other type of biofilter. They have a small foot print for a given capacity. They are self cleaning and relatively tolerant of different nutrient loadings.

Con:
The fluidized bed sand filter has a relatively high energy requirement because of the high pressure drop necessary to fluidize the sand. The other main problem with sand filters is that the pressure required to fluidize the bed varies depending on the amount of biofilm on the sand particle. As the biofilm builds on the sand particle the size of the particle increases while the density of the particle decreases. This means that the depth of the bed will tend to increase as the bed ages. It also means that the bed depth will fluctuate as the loading on the bed varies. In order to prevent blowing the sand out of the tank, the tank must be oversized or the flow of water needs to be regulated.

Another potential problem is the uniformity of the water flow. In order to completely fluidize the bed, the water needs to be evenly distributed across the whole bed. One possibility is that the water will channel and short circuit though the bed. This means that the treatment capacity will plummet.

Fluidized bed sand filters are limited to the oxygen carried in with the water. This means that the water entering the filter should have a high level of oxygen in order to insure a good level of treatment.

A do it your self acrylic FSB


A High tech patented filter that measures 62" tall and 16" x 16" at the top of the filter box. The filter holds 75 lbs of media—over 5,000 sq.ft. (464.5 square meters) of biological surface area. Maximum flow rate is 25 gpm, but the filter can be operated at a lower flow to promote nitrate removal.


An Idea I have to prevent hard starting. The sand is venturied up a tube that is always clear and the sand circulates up the pipe, exits via holes, then falls back onto the pile and slides down the 'funnel'/cone. The inner tube is attached to the lid.

Large cone shapes are expensive or impossible to find. So what about making our own cones? You can buy a 48" by 96" sheet of PVC for $80, and smaller sheets cheaper. Why not make our own cones so that we have the best possible FSB?

Check out this cone pattern application http://66.76.55.66/news/setup-cone205.exe

You can type in what you need to build and it makes a 2D pattern that can be printed out and then scribed to a sheet of pvc. Then just cut out and roll your cone up, apply some pvc glue and clamp in place for a few hours and WA-LA you have a custom cone of any size you need! Note, the program is a 30 day trial version. I use altiris to virtualize the install allowing me to "reset" the trial at will. You may not be able to reinstall the cone application so you may want to save out all the cone patters you think you might need using a PDF printer of some type (there are several free ones). If you want to altiris before they start charging for it download it. Software_Virtualization_Agent.zip
Make sure you check all the boxes during setup! You can PM we if you need help with this.

I thought the FBFs were operated in a continuous flow?

They are continuous running , my notes are mixed with other info I found

I have created a PVC tube FBF, but I'm having a challenging time mounting it in a vertical orientation. It's a 3" PVC pipe, pretty simple.

Would a horizontal flow work, or would the sand just settle in the bottom portion? I have about a 1:3 sand:total volume ratio.

Unless the water is moving upward keep the sand "up" then I bet it would settle if horizontal.

I edited the first post to fix the error.

This is a link to a DIY FBF that was put up many months ago and then revisited by Rope recently, thought it a good idea to put it here...might add some ideas for others

DIY FBF

Trialling the RSG filters, I found that sediment settling on the top of sand very effectively blocks the water flow after a month or so, pre-filtering is needed as you suggest, although the link suggests that with the sand fluidized then any fish poo would be crunched up by the sand and spat out with the water flow.

I think laying down a pipe would allow the water to flow over the sand and thus it would not be fluidized, hence no filtering as such

im curious as to the purpose of these, we offten use sand filters in water treatment but we WANT the bed to commpact this is what gives us our bed depth for filtration, generaly we use quite coarse sand so as not to cause a total blockage when filtering dirty water

the other thing that happens is it gets a periodical back wash flowing to drain,

i dont really see how a FSB would filter anything unless its just a large surface area for the bacteria and thus nitrate removal all the solids would
be lighter than the sand and just pass though it

Please enlightnen me
Cheers
Pete

delgrade the purpose of thses is to provide a filter that with a relatively small footprint can cope with an ENORMOUS ammonia load. picture a bucket of sand, then pick up each individual grain of sand and lay it next to each other one grain high side by side...................got an idea of the surface area available? now multimply that image by 3 and you have the effective surface area of a bucket of sand in a fluidised bed.

short answer: its a bioflter not a mechanical filter

I think the main differences between the water treatment type sand beds and the fluidized sand beds are
1-direction of movement.
2-purpose

It looks like the FSB are arranged with fine sand and water inlet at bottom so sand gets all stirred around (like fluid) to work with aerated water and provide lost of media surface area to do the Ammonia/nitrite/nitrate conversions. As the solids can just flow right through and out the top with the water to be captured by some sort of mechanical filter like a gravel grow bed. The outlet for the water at the top needs to be quite a bit higher than the sand level or sand would come out all the time.

The settling pond type sand beds with coarse sand that are fed water from the top and drain or leach out the bottom are more like what I think of when talking about water treatment.

Just another way of saying what Steve is saying.

I just read about slow sand beds today. A slime layer forms at the boundary of the sand and the "effluent", and this is where all the magic happens. Periodically they scrape off or otherwise remove the slime layer to get the bed flowing well again.

Sounds like the RSG was working like a slow sand bed as the slime layer established itself.

BTW, The word of the day is: "Schmutzdecke"

http://en.wikipedia.org/wiki/Slow_sand_filter

After testing today, my conclusion is that tubes are really unstable mechanically .

Which, I suppose, is why so many designs are barrels, top in, top out.

tamo,
when you say unstable mechanically, do you mean as in difficult to keep from knocking it over or as in it is difficult to keep the sand fluidized?

I think in those that look like top in top out the in actually goes all the way to the bottom so though the input enters the vessel from the top, it actually feeds at the bottom of the bed. Otherwise the sand would just sit there at the bottom doing little.

Some of the tube designs actually are kinda like the top in top out too.

A rather interesting hybrid http://www.freepatentsonline.com/20070264704.pdf

Unfortunately I do not appear to be able to attach pdf's.