Backyard Aquaponics
A place to discuss aquaponics

HI every one i want to know if my radial flow filter idea will work. let me tell you about it.

Its five food diameter and 20 feet deep, the center down pipe will be 24 inches diameter and 18 feet long the flow through the filter will be 400 GPM witch gives me a retention time of about 7 mins.

Can this work? will it remove the solid fish waste.

Why so deep?

It doesn't have to be 20 feet or it could be more. depends on how it would work. I wanna replace a drum filter. i am hooping that the dept will take out all of the solids.

20 feet because that is the standard well locally.(every house has one) it will cost about $500us and 2 days to get that done. Then i will just line it with some kinda waterproofing. A drum filter will run me about 10,000us and weeks of interacting with government.

Do you think this will work? is there a way to calculate what that will happen? What are the possible outcomes?

I had concerns about it all going anaerobic but i think that the retention time of 7min is to short for that.

I could be wrong but i hope not.

(edited to add) My thinking is that it will trap and "fluidize" the solids hopefully down to or less that 30 microns with zero head loss or additional running cost.

No it won't work.

Or at least it won't work as you envisage it.

The effectiveness of an RFF is based on its surface area not its depth. The cross section of the RFF determines the velocity of the water moving up through the RFF.

If the upwards velocity of the water is less than the downwards velocity of the particles then the particles get removed as they settle towards the bottom of the RFF.

If the velocity of the water is greater then the particles get taken along with the water and they don't get filtered out of the flow.

The veloicty of the water is set by the flow of the water through the RFF and its cross sectional area. The velocity of the particles is deterimined by their density and size.

Particles from some floating foods are less dense so they don't settle as well. The smaller a particle is the slower it settles.

It won't.

Solids removal/processing components that rely on gravity settling of solids basically don't work below 100 microns.



There is ALWAYS head loss and additional running costs.

thanks for that explanation Stuart...........i am now off to look for equations to see what will happen, i will post them up here in case anyone get the same idea.

I can't remember off the top of my head but the m2/m3/hr value for a RFF has been posted a number of times on the forum.

It shouldn't be that hard to find.

There is a DIY drum filter thread on here somewhere, it goes through how to make them yourself if you're handy.

I found out from this web site http://www.1728.org/flowrate.htm

That the water velocity down a 2 foot pipe would be 17.021 feet/min
And the flow up the outer pipe would be 3.24 f/m

How do i calculate the velocity of the tilapia solid waste???

edit to add:
i think this calculator should help a stokes law calculator.........any one know the parameters i should use?

http://www.ajdesigner.com/phpstokeslaw/ ... locity.php

The viscosity of water is 0.894 kg/ms
The density of water is 999.97 km/m3
particle diameter is 30 microns

Don't know what is acceleration of gravity and particle density of tilapia waste = if i can get those 2 and plug them into the calculator i would get the settling velocity of fish waste wouldn't i?

Damian I've said this to you before but if you are serious about designing these sort of systems you need to invest the money and buy some appropriate text books.

Also you tend to ignore the information we do provide.

The settling velocity of particles under 100 microns in size is essentially zero. Settling filters don't work with aquaculture waste particles under 100 microns in size.

I've said this before but I don't think people believed me...



Once you get small particles they could be LEAD and they still wouldn't settle.

Using your figures above which I'm assuming are correct plus the G constant 9.81m/s2 gives a settling velocity of a lead particle 30 microns in diameter is 5.67x10^(-6).

So since the settling velocity is more than 0 how big will the outer pipe need to be?

Q=VA

A=Q/V

Q=400gmp=0.025ms/s

A=.025/5.67x10^(-6)

A=4.4x10^3m2

Assuming we ignore the area of the down pipe the diameter of the up pipe would need to be greater than 75m.

You would also need to make sure that there was no turbulence like that induced by the sun shining on the water surface or a breeze strong enough to move a piece of goose down.

Also remember that is for lead. Aquaculture waste is a bit lighter.

So glad I put that caveat in. When I posted those numbers I thought they were a bit out. Re did the calculation for 100 micron particle and the answer didn't make sense.

So....

Dynamic viscosity is actually µ=0.000102.

That gives a requirement for an outside pipe diameter of greater than 0.8m. For lead.

For Aq waste it would be need to be greater than 11.5m

what about if we modify the local gravity field with a dubywhatsit?

As Stu says, the RFF is only for big particles - check out the white paper comparing RFF with swirl for design constants. For polishing out smaller particles something else will be needed, though may not be necessary if you have grow beds... in fact you may not even need the RFF if you have growbeds and low feed rates.

http://www.w-m-t.com/library/pdf/Radial ... epaper.pdf

Thanks Matt

that is the article I think everyone draws their information on RFFs and SF from.

i will never disregard any info offered to me in good faith as you have done today. i just question everything!!!! it actually is a good way to learn. well its the way i learn. i wouldn't be trying to make the filter i just want to know the math involved. i am sure it will help me later in life. Thanks for the explanation once more stuart..