Frank wrote:
For first you insist that a floating raft part is incorporated in my concept.
That is only fruit of your own imagination: the bottom bed is a growbed filled with media.
I have never and nowhere suggested otherwise.
Nowhere in this thread have you said that the bottom growbed is filled with media Frank
Perhaps an oversight.... but your diagram doesn't show any indication of it either...
As such I "postulated", on more than one occasion, that it appeared to be operating as a DWC tank... presumably with floating raft...
Up until know you have never corrected that impression....
Perhaps as you say... it's clearer in your mind than you have presented it .. or than I have interpreted it... and I tend to write as I'm "thinking"... perhaps leading to a mis-conception of my "mood"...
And I accept that the design is being "tweaked" as the discussion progresses...
Lets us then accept that it is indeed a media filled growbed.... running, neither as a continuous flow system.... nor flood and drain... but possibly a slow (depending on pump) drain....
Some people maintain a continuous flow system (with high flow rates) provides good results... however... you have indicated this is not the case....
Frank wrote:
There is no growbed drain. All there is is a compartment in which the pump is located. The pump is controlled by level switches, so it would not run continuously. It is not intended to run continuously. It is intended to provoke an ebb and flow effect.
Flood and drain growbeds provide a high degree of oxygenation.... while some oxygenation may occur through the series of NFT pipes.... IMO... this could be minimal depending on "flood" levels, rate of flow and period of "ebb"....
You've postulated that the initial pipe would effectively be flooded to near overflowing...
... and that subsequent pipes would also be ....
Frank wrote:
Plant root aeration is ensured not by the water (which might be O2 poor depending on settling tank draining frequency) but by ebb and flow in both NFT and growbed(s) as already explained.
And it is not a "trickle flow".
and it is not slow either:
each time the pump starts the gutters are quickly filled to overflow. If you want to limit flow in the gutters, put overflows on both sides of the gutters.
With the only aeration occuring...when the pump cycle stops... and the water drains from the NFT pipes... how quickly this occurs is dependant or various factors... as you noted...
Frank wrote:
Each time the pump is stopped, the gutters start to drain.
Draining speed is determined by drain hole size and number.
Draining height is determined by drain hole position.
Aeration is ensured each ebb cycle.
Flow cycle aerates the water.
How often this "ebb and flow" occurs in the NFT section is dependant on how long it takes to "drain" down the growbed to lower switch level... or timer...
Frank wrote:
ebb and flow frequency is determined either by growbed size and pump capacity if regulated by level switches or can be regulated by a timer.
Which then reactivates the cycle, beginning by pumping to the tank... the major point of oxygenation...
Now .. to my mind the pump capacity may not need to be that large... it certainly can't have a flow rate any more powerful than what capacity the solids settler and top NFT pipe can handle without overflowing...
So the question in my mind is then... would the rate of flow being pumped from the growbed be sufficient to lower the level such that the pump is switched off.. hence the growbed drained down...without overflowing the settler and/or the NFT...
Or would the flow rate end up effectively being continuous and maintaining a certain level in the growbed???
As suggested this may possibly be overcome by the dimensions of the growbed...
Frank wrote:
Of course fast enough water access to the pump compartment must be ensured. This is easy: make the compartment big enough and the connecting faces permeable or else lay some drain pipes along the bottom of the growbed leading to the pump compartment.
But, by making the growbed large enough to ensure enough water access to the pump... requires that it be exactly matched to the outflow from the NFT.. so as to not overflow
Probably not impossible, but I suspect it would require a fair amount of "fine tuning" to get the dimensions of the component parts and pipe sizings right...
Obviously, the flow rate of the pump could be modulated, possibly even to incorporate an extra oxygenation affect...
And you have incorporated an additional overflow from the solids settler to allow for some of these factors...
Another possible means of inducing more oxygenation might be to incorporate a "venturi" straw into each of the NFT elbows between rows... to draw more air in..
Frank wrote:
Having a second overflow on the solids settling tank draining directly to the pump compartment or growbed distribution pipe allows for adjustable flow to both the NFT and the growbed(s) or directly to the pump compartment if one of both overflows is adjustable
I'm still unsure though Frank... as to whether or not the system will drain down the growbed... or just find a balance that matchs the pump flow rate, and maintains a constant height in the growbed...
Regardless , I still feel that the (possible) slow "ebb" of both the NFT and more particularly the growbed... wont provide very much oxygenation to either the water or the plants....
It might be that it's a matter of build it and see....
To me it seems somewhat complicated and finely "balanced" in terms of setting it up... although I do see your "simplicity" in terms of water flow...
With regard to blocking/clogging/water channeling...
Frank wrote:
The combination of all the above would reduce clogging to the utmost minimum if not completely if you remember to cover up unused holes to avoid algae growth.
No blocking, no "subsequent loss of water" at all (which would not get lost anyway -don't know where you fished this idea- : even in case of -extremely unlikely- blocking, any blocking, partial or not, would drain the water back to the growbed(s).
I think that you have totally underestimated the amount of root growth that can occur in NFT pipes Frank.... and IF any NFT pipe was to block... then surely it must overflow...
Not lost as such ... if you connect tubing from each pipe overflow to return to the growbed... and if the tubing has sufficient capacity to cope with the inflow from the settler tank, or previous NFT pipe...
Frank wrote:
At higher densities, I would drop some floating beads under a screen in the solids settling tank to also eliminate floating debris and ensure nitrification in all circumstances even if recirculation is not over the growbeds (I have calculated that you need 5 l of beads per m³ of fish tank at a fish density of 100 kg/m³ at a feed rate of 1.5% = 1.5 kg/day/m³).
Then to stock at those densities... usually only achievable in the most sophisitcated aquaculture facilities.... according to my aquaculture course notes..
1.5kg of feed would require 0.33kg of oxygen just for metabolism....
1.5kg of feed would produce 0.0375kg of ammonia....
Densitites above 40Kg/m3 are only achievable with the use of direct O2 injection and high flow...
I would certainly query you figures regarding bead/feed rate capacities Frank...
Specs for Kaldness media... recognised as the "bees-knees"...
Quote:
50 Litres of K1 media will handle up to 250 grammes of food per day and for K3, 225 grammes of food per day.
So to process 1.5 kg of feed would require 300ltr of kaldness K1 media..
You'd need a fish tank of at least 2000ltr... with your figures...
And a settler tank of a fairly reasonable size...to house the beads and solids inflow...300ltr of beads by your calcs...
Typically such a filter would be nearly a m3 itself... and contain up to 1000ltr...
So fish tank at 2 tonne and settler tank at 1 tonne... all raised... would require significant structural strength... engineering... and cost...
Most other "bead" type filters require daily cleaning, usually by backwashing... the kaldness technology is self-cleaning, but benefits from periodic backwashing....
All up Frank.... I do see some nice design points.... but I also see impracticalities in terms of cost, access, maintenance, plant capacity...and oxygenation...
Combined with the degree of fine tuning required.... doubts over bio-filtration as you propose....
Sorry... I'll go for a more standard, tried and tested "flood and drain" growbed system to deal with the solids... and then utilise NFT as an addon...
And there's no way I'll push much beyond 40kg/m3....
But best of luck to you Frank.... look forward to seeing your implementation and wish you success...
And I'll supplement both with additional oxygenation....
Backyard Aquaponics
