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PostPosted: Sep 28th, '08, 21:12 
Can you post a picture (or diagram) of what you call a "shallow" filter Frank ... so we know what you mean when you say shallow...

Wasn't meant as an assumption... just that all the bio-filtration systems I've seen or seen pictured... are usually much deeper than they are wider.....

And I'd be curious as to what leads you to say ...

Quote:
water that has passed a first "healing" layer of media will be O2 depleted and thus impede the good functioning of below layers.


Given that most bio-filters, other than trickle filters usually work with the media in suspension and "movement"....

And trickle filters and Bakki showers have been employed by Koi enthuasists for donkeys years... with great success, both in terms of filtration and oxygenation....

You certainly seem to challenge a lot of conventional wisedom Frank.... love to see your "bookmarks" and a list of research you've uncovered that lends weight to your suggestions...

Seems we might have to turn a lot of things on their head.... :wink:


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PostPosted: Sep 28th, '08, 21:23 
And isn't it about the "available" surface area of the media rather than the physical surface area of the media container anyway....

Sure you can obtain the same "available" surface area of media for nitrification by a "thin/shallow" layer over a large physical area....

But isn't it the same "available" filtration potential if it's stacked vertically rather than horizontally???... particulalry, (but not necessarily IMO) if the media is in suspension...

With static media like growbeds... or trickle towers ... then depth gives you the same filtration potential in a smaller footprint....

Sure would save space... in fact you could say it was space efficient.... :wink:


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PostPosted: Sep 28th, '08, 21:51 
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Quote:
Seems we might have to turn a lot of things on their head.... :wink:

you finally have understood part of my philosophy, Rupert:
turning things on their head is a hobby of mine :cheers:

most theories can stand a little shaking
but turning them upside down is the ultimate challenge
if the theory can stand that it is probably sound
if it cannot, wide open roads are there for new explorations

Quote:
Given that most bio-filters, other than trickle filters usually work with the media in suspension and "movement"....

is not valid for the subject at hand: growbeds
shows how easily one is confounding one situation with another
(not a criticism, just a motion to be cautious and not fall into concealed traps)
growbeds are static, not moving
so, if you accept that surface is determining for nitrification, it is easy to understand that depth is irrelevant as far as media surface is concerned as it can be compensated by either width or length (media surface = specific surface of media * media volume = specific surface of media * width * length * depth)

But depth TMHO absolutely is relevant on another level: that of aeration and DO saturation or depletion, needed for optimal functioning of the nitrifying bacteria

an example to support this:
a cascade of say 20 m high will certainly be impressive and make a lot of noise
but dividing this same cascade into 2000 small and thin cascades of each 1 cm high will undoubtedly give incredibly much better aeration results
only disadvantage is the footprint needed for filtering and nitrification

but in growbeds that means more planting surface (not necessarily more produce as that depends on nutrients content)

my spreadsheet V4 is ready for posting
it includes a comparative calculation of 10 mm gravel volume demands as biofilter media

thanks Steve for adding the warning

Frank


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PostPosted: Sep 28th, '08, 22:08 
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Nitrification will be limited by the weakest link in the system.
Both deep and shallow will have their own advantages and disadvantages.
All things being equal eg, O2 availability, PH, surface area, temperature swings etc, the choice boils down to weight, cost, size and suitability.


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PostPosted: Sep 28th, '08, 22:23 
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Quote:
the choice boils down to weight, cost, size and suitability

I absolutely agree with you, Hex, but:
Quote:
Nitrification will be limited by the weakest link in the system.

so the first thing to determine is exactly that
once determined it is up to our imagination to find solutions

frank


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PostPosted: Sep 28th, '08, 22:40 
Yeah Frank, I'm aware that the subject is about growbeds....

hygicell wrote:
shows how easily one is confounding one situation with another
(not a criticism, just a motion to be cautious and not fall into concealed traps)
growbeds are static, not moving


I was responding to your statement....

hygicell wrote:
I suggest that with all bio filters only contact surface is all important and depth absolutely irrelevant, even counterproductive: water that has passed a first "healing" layer of media will be O2 depleted and thus impede the good functioning of below layers.

so a shallow biofilter will necessarily perform better than a deep one


And the assertion that once water had passed a healing layer ....

Please stop treating me like an idiot... address the issues... rather than nit picking a singular point... :x


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PostPosted: Sep 28th, '08, 23:00 
hygicell wrote:
so, if you accept that surface is determining for nitrification, it is easy to understand that depth is irrelevant as far as media surface is concerned as it can be compensated by either width or length (media surface = specific surface of media * media volume = specific surface of media * width * length * depth)


Again Frank... isn't the determing factor the surface are of the media... not the surface area of the "container"....

hygicell wrote:
But depth TMHO absolutely is relevant on another level: that of aeration and DO saturation or depletion, needed for optimal functioning of the nitrifying bacteria

an example to support this:
a cascade of say 20 m high will certainly be impressive and make a lot of noise
but dividing this same cascade into 2000 small and thin cascades of each 1 cm high will undoubtedly give incredibly much better aeration results
only disadvantage is the footprint needed for filtering and nitrification


Here I tend to agree with you somewhat... not that it's been quantified to my knowledge, or any optimum depth determined....

But from observation of the use of Bakki showers in Koi systems... which not only result in great oxygenation, but have proven to be highly effective in terms of filtration.... handling both large numbers of "dirty" koi... and large pond volumes...

Attachment:
bakki_installed (Medium).jpg
bakki_installed (Medium).jpg [ 36.66 KiB | Viewed 8988 times ]


But they all tend to be at least 300mm deep ... or more...

Quote:
but in growbeds that means more planting surface (not necessarily more produce as that depends on nutrients content)


Having a quadzillion narrow, shallow growbeds might mean more planting surface... but as you say might not mean more plant production....

Push the boundaries by all means.... but consistently, growbeds of 300mm depth have been shown to perform reliably in terms of oxygenation, nitrification, solids breakdown, trace element release, plant support, and high plant yield/area....

I'm not convinced as to your argument that oxygenation is restricted/constricted by depth of media....

Show me the data.....


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PostPosted: Sep 28th, '08, 23:58 
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I will ignore your snidy remark about idiots, Rupert, keeping in mind your own motto:
"To sin by silence when they should protest makes cowards of men." - Abraham Lincoln
I respect you and have shown that

back to subject:
compare a vertical biofilter to a horizontal one:
where do you think that anaerobic circumstances are most likely to occur?

frank


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PostPosted: Sep 29th, '08, 00:50 
I've seen anaerobic conditions occur in NFT systems Frank... and even you'd have to agree that such systems are horizontal... :lol:

Ive seen/heard of anaerobic conditions developing (through channeling) in other bio-filtration methods as well...

A 25mm layer of sand in a 2mtr trough could develope anaerobic conditions... just as a 2mtr sand filter in a 90mm pipe could....

The question is why did anaerobic conditions develope....

The accepted 300mm depth, which has never been postulated as the "one and only" depth for flood and drain... as the myriad of different systems here attest...

With correct and simple design, flow rates etc... has proven to be to work and maintain aerobic conditions...

Anaerobic conditions almost always arise as a result of system imbalance... over feeding, over stocking, lack of oxygenation, incorrect pH etc...

Or when people either fiddle with a system or system inputs without understanding the varibles involved...

Or again, through lack of knowledge, or willingness to ask for advise, design or manage their systems with points of failure...


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PostPosted: Sep 29th, '08, 01:59 
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The absence of oxygen causes anaerobic conditions :wink:


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PostPosted: Sep 29th, '08, 03:43 
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how can I take the sting of enmity out of this discussion if you don't help me, Rupert?
and please without having to concede on the discussion at hand?
I have no problem with a growbed depth of 30 cm
you seem to have one with lesser depths
there could be lots of reasons for this
but I believe biofiltering capacity not to be one of them
you ask me to support that with data
I have gathered most data I have found in a spreadsheet and posted it for all to see, use and criticize
they seem to confirm my suspicion that a thin layer of water holds more potential for aeration than a thick one
I constantly adjust this spreadsheet with new data found
please help me with this so we can together find what is best
either by informing me of contradicting data
or of confirming data

frank


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PostPosted: Sep 29th, '08, 06:02 
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Seriously, this cant be healthy.
Seriously, this cant be healthy.
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Quote:
how can I take the sting of enmity out of this discussion if you don't help me, Rupert?


What I do Frank is treat it as a tongue in cheek comment and ignore any nastiness that might be perceived...seems to work for me :flower:

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PostPosted: Sep 29th, '08, 06:06 
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ignore any nastiness that might be perceived

you are perceiving nastiness where there is none, Rupert
please consider this as established

frank


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PostPosted: Sep 29th, '08, 06:11 
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you are perceiving nastiness where there is none

sorry, should have been addressed to you, LKB, not to Rupert
but it also counts for Rupert
I have nothing but the best intentions
and I do my best to prove that

frank


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PostPosted: Sep 29th, '08, 06:14 
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so much for impulsive reactions, LKB
it has just now downed on me that you were actually coming to my defense

thanks

frank


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