Backyard Aquaponics
A place to discuss aquaponics

mmmm

Here goes that conundrum you have discussed, a little change here affects XY and 'Z' over there.

AND funny enough it is the 'Z' measure ment discussed earlier I now fear - Does this vented drain under each grow bed change the measurement of Z?

I do like that model as the beds can be independent of the drain AND there are so fewer fittings to get 80 mm drain line to connect to the 25mm siphon was using 4 separate fittings each.


I have a trick or 2 up my sleeve for that which includes adding a hole to the end at the bottom of the water level. I will also have valves on each GB to be able to adjust the fill rate.


I have 2 inline filters (1 for supply- BIO/MECHANICAL & 1 between the FT and ST- MECHANICAL) I am not expecting too much debris and I am leaving the END with the option to bypass the GBs and flush out (ie whole pump through 50mm pipe)


PS did I mention I am going to use 80 mm drain pipe now
Whats 10 mm really haha

Thank you

Judester, I run a system similar to what you are thinking of doing, and the pipe sizes I chose, based on what looked about right to me, rather than calculations (although I have messed around a bit with pumping and piping before), all work very well.

~4000lFT, 50mm SLO to ST (with parallel 40mm overflow in case the 50mm becomes clogged)
Pondmax8000 pumps via Tee to 2 X 32mm poly pipes to 9* 500l GBs, with 25mm risers and taps on each GB. The 32mm pipes are joined at the far end to form a ring main distributor.

25mm drains from GBs into 3 separate (3GBs each) 32mm main drains back to FT, standpipes with holes, not syphons

I'm running 20min on/40min off 24/7 ATM, but do vary that someties to much smaller or larger duty cycles, up to continuous pumping on ocassion.

Just been running the calcs to determine min velocity to avoid solids settling. I got these results:

D(mm) V(m/s) Q (L/h)
13.00 0.21 98.97
19.00 0.25 255.59
25.00 0.29 507.58
40.00 0.36 1643.63
50.00 0.41 2871.31

Which were surprisingly high to me. My ponderance is, if you have an intermittent pump, what time period can you have with no movement and still flush the pipe with the recommended velocity? I'm currently designing a system with RFF that I want to try to automate flow into a mineralising tank, and then take a certain amount of the flow from the MT back into the system. So will be dealing with solids heavy liquids. However I don't want to be running 500L/h through the 25mm RFF bottom drain continuously!

The velocity needed to re suspend solids is higher. No idea how much higher though.

Yeah, my gut feel is that these figures are conservative. Where does this rule of thumb come from?

Chemical and process engineering handbook I'll let you know when computer is working

Thanks Stu - Given that fish solids have a SG close to water I wonder if a lower flow rate can be applied without settling?

I know this sounds wrong but the formula was independent of particle weight.

sounds totally wrong - so a chunk 1cm3 chunk of lead will settle as easily as a 1cm3 chunk of fish poo! Must be some boundary conditions for its application me thinks.

Yeah I'm pretty sure that is out side the boundary.

From memory it was something to do with the friction forces on the the particle being much greater than the force due to gravity. In turbulent flow at a sufficient velocity particles remain suspended. Once they settle though you need more force to get them moving again.

I would have assumed that bigger denser particles would settle more readily but this may be one of those times that the scientists ran the experiments to confirm common sense and then found the opposite.

sounds logical - would be good to know the boundary conditions and range of SGs that the formula applies to.

Stu, I've just been using the above approach to deisgn a new RAS type system that I plan to enclose in a 3m x 1m x 1.2m enclosure made of 150mm EPS coolroom panels.

It will have 2 IBCs for FTs, a RFF and a MBBR/Sump Combo tank. I'm wondering whether to have a dual drain setup from the IBCs. The IBCs are 1000L approx, so I want to be pumping 1000L through each IBC per hour.

My calcs show that I need 500L/h to avoid settling of solids for 25mm diameter pipe. So if I split the flow so that 500L/h comes from the bottom via a SLO, and the other 500L/h is taken near the top, I would need to have a max slo diameter of 25mm... which seems quite small. Does this seem right?

My calcs also suggest I need around 9cm of head to drive a flow of 500L/h through 3m of 25mm diameter pipe with 2x 90 deg bends, 1 ball valve and 1 exit.

My concerns are, with a square IBC tank will the pull of 500L/h through the SLO be enough to pick up all solids? The dual drain has the advantage of doubling the residence time in the RFF which should improve solids removal, though if they don't get sucked out of the IBC, thats not much use!

Other option is to just have a single drain SLO, running at 1000L/h, and this would need to have a diameter of 33mm. If I went with a 40mm SLO, I'd need a flow of 1643 L/h to ensure no solids settling. This would mean though that I'd be putting 3286L/h through the RFF, giving a residence time of 3.6 mins.

Would welcome any thoughts you have on this proposed design...

I would not suggest using a dual drain in an IBC if you are using aeration. Aeration resuspends solids in the water Colum and you will not get a "clean stream" coming from a surface outlet. It sounds great because you can reduce the size of your RFF BUT dual drain tanks were designed to work with pure O2 that is saturated in the incoming water stream before it ever hits the tank. In tank aeration causes opposing flows and effects the efficiency of the design. I don't know who is telling everybody to start using dual drains In there backyard designs (I've heard this several times recently) but they obviously missed an important aspect of why the engineered design works...

I would just di a center outlet bottom drain or a bottom draw standpipe. Hope this helps Matt!

That might have been started by me in a post I did on tank design a few months ago.

But in my defence some aspects of the design people are talking about taking up but not all. One thing in particular that seems to have been missed in the translation is the ratio of width to height of the FT. The dual drain tanks also work on a minimum ratio of depth to width of 3:1 to 3.5:1 diameter:depth. The friction of the rotating water with tank floor is one of the things that drives their efficiency. This is reduced substantially when the ratio is more like 1:1 like you have in many BYAP tanks not just IBCs.

Thanks guys thats great input.

It wasn't you Stu, it was Swede - its not only RFF filter efficacy, its appealing in terms of reducing RFF size and thus ease of solids removal. Since this will have no GB filters I wanted to make sure the RFF works as effectively as possible. Do you think a residence time of 3.6 mins in the RFF is enough as the only solids filtration, or would additional filtration be required?

Ryan, if I put air stones in the ST would that address the issue? I have seen the issue you are talking about first hand as I have another system with a bottom drain -the heavy large solids go out the bottom drain well (that is a 1:1.3 H/W ratio tank) though the finer solids seem to stay going round and round in the airstone current.