Settleing tank in place of filter socks

[Chris Abbott]

Just brain storming ideas for my next system an d was thinking of using a cone bottom tank as a settleing tank n place of socks. I currently have a simple system with a bare bottom sump and I siphon the bottom once a month when I don't use socks. Has anyone ever tried this? I am sure it has been done and somebody can post a link to a thread. Please share your thoughts on the idea

 

[stephenhall1987]

A lot of aquaponic systems use swirl filters to prevent sediment from getting into the grow beds. If i had room, I would set one up on my saltwater tank.

Youtube aquaponic swirl filter

 

[SoloGarth]

Sounds like a good idea to me.

 

[spamreefnew]

In home brewing beer,they sometimes use a conical fermenter to accomplish the same thing,I'm sure it would work in an aquarium as long as it had low flow.

 

[Chris Abbott]

Yes this it the type of tank I have been looking at for the project. I think they also use them for biodiesel production. I thought wouldn't it be cool to just turn a valve and flush the bottom gallon out of that cone every few days than clean a sock.

 

[Chris Abbott]

Just didn't know if somebody had tried it out on reef tanks yet

 

[ecotanker]

Adey talk about settling tanks in his book 'Dynamic Aquaria' so yes people have thought out this before, but not in the shape of a cone.

 

[drauka99]

In fermenting you are letting gravity settle out the fines. The filter socks catch 1 or 2 micron pieces of sediment. you would have to have an ULTRA low flow sump to accomplish any sort of settling of this size particle IMHO, for the larger particles such as leftover food and large pieces of algae and waste then you could collect that and be easier to vacuum out with a separate chamber, I just don't see it as being as effective as filter socks

 

[karimwassef]

I'll definitely use on my next build. I wonder what the size to flow ratio needs to be?

For example, if the total is 12,000gph, does it need to be a 4' diameter x 2' deep or bigger?

 

[karimwassef]

I did find this...
http://www.w-m-t.com/library/pdf/Radial_Flow_Settler_Diagram.pdf
http://www.w-m-t.com/library/pdf/Radial_Flow_Settler_Datasheet.pdf
Looks like a combination of sump baffles (up, down, up) with a settling cone - but this is radial flow, not spiral flow... still looking

Oh - the koi pond guys seem to be deep into this (bigger poop, I guess)... and the hydro/aqua-ponics guys (need cleaner water with less solids to grow vegetables)

http://www.koiphen.com/forums/showthread.php?141689-DIY-Radial-Flow-Settler

 

[karimwassef]

Woohoo... found the math that works -

http://www.backyardaquaponics.com/forum/viewtopic.php?f=8&t=16296
Here's what I got out of it

Q = flow rate
A = surface area
D = depth
V = volume = A x D
Vp = particle settling velocity (finer particles settle slower than big particles)

Hydraulic Loading Rate HLR = Q/A
Detention Time = Hydraulic Retention Time HRT = V/Q
Settling Time tp = D/Vp

For a particle to be caught in the filter, Detention Time = Settling Time
V/Q = D/Vp
... that gives the surface area needed as a function of flow rate and particle settling velocity & vice versa
A = Q / Vp
Vp = Q / A (which is also the Hydraulic Loading Rate HLR)

So the depth is not a significant variable, the surface area is. The missing step is determining what the settling velocity or a particle size would be.

 

[karimwassef]

this is close... https://en.wikipedia.org/wiki/Terminal_velocity#/media/File:Settling_velocity_quartz.png

so for something like a sand grain.. if I want to settle out anything bigger than 0.7mm, it would have a settling velocity of 0.1m/s (just a convenient point for an example).

Then with a flow rate Q = 2400gph = 154 in3/s ... and a particle size of 0.7mm with a settling velocity of 0.1m/s = 3.9 in/s,

I need a container with a surface area of A = Q / Vp = (154 / 3.9) in2 = 39.5 in2

The diameter would be ~ 7 in ... that's smaller than 5 gal bucket top (assuming I did all the math right).

 

[karimwassef]

working it from the bucket size up.. a 5gal bucket has a diameter of 11.9" = area of 111 in2

the settling velocity at Q = 2400 gph = 154 in3/s would be Vp = Q / A = 154 / 111 in/s = 1.4in/s = 0.036m/s

the smallest sand-like particle that would settle would be 0.25mm

I think this is very doable in a real reef setup.

 

[JamesHolt]

Oh dear he found a formula..... Look Out, Its on now....:spin3:

 

[karimwassef]

Ha Ha Ha...

I was actually working on a way to separate large solids without mechanical filtration when I saw this thread. It's just one of those perfect timing things.

I'm a big believer that planktonic life as well as pods, worms, and living sponges are killed by filter sponges or socks or any kind of mechanical filtration media. So I have almost none. The pumps have intake covers with slots that are 1/8".

However, this means that I've gotten small fish, shrimp, crabs, snails, urchins, starfish, anemonae, and pieces of macro algae along with other large particle solids (I have sand) flow straight against the grates on my return pumps... with consequences over time.

A settling tank should allow the separation of large solids without causing the stagnation and planktonic trap effect of filter socks.

I don't see a downside yet!

 

[JamesHolt]

From the above videos it seems to work,, just a matter of room....

 

[karimwassef]

That was my concern too. That's why I was worried about how big it needs to be and needed the math to validate that it's not unreasonable relative to the tank size and flow.

If it had turned out that running a 55g tank running 800gph needed a 4' circular settling tank, then the discussion would be moot...

But I'm cautiously optimistic now... this looks like a viable alternative (or addition) to the traditional baffled sump design.

 

[karimwassef]

pretty easy math ....
circular tank diameter in inches = 0.0456 x sqrt (Flow in gph / Particle settling speed in m/s).

Still need to use the chart to go from desired filtered particle diameter to settling speed though... :rollface:

 

[karimwassef]

rough approximation

settling speed in m/s = 0.13 x sqrt (d) where d is the particle diameter in mm (works for >1mm)

settling speed in m/s = 0.83 x d^2 where d is the particle diameter in mm (works for <0.1mm)

So the diameter of the tank in inches ~

0.046 x sqrt ( flow in gph / 0.13 sqrt (d) ) for big particles with d>1 in mm
-OR-
0.046 x sqrt ( flow in gph / 0.83 d^2 ) for small particles with d<0.1 in mm

That's as easy as I think it gets. If you're looking to filter in the 0.1mm - 1mm range, I'd take the biggest diameter from either equation and just add 20%.

It's all approximate with tons of assumptions, but that's what ballpark is.

 

[stephenhall1987]

Thanks for the math Karimwassef

.1mm is equal to 100 microns
Most common aquarium filter socks are 100 or 200 microns.

How big would you need to filter out 1 micron particulates (.001mm)?