Backyard Aquaponics
A place to discuss aquaponics

Small windmill running an air pump?Been toying with the idea for quite a while but done nothing about it yet!

That was my original approach, but I can't afford the windmills I've been able to find! So, I think I'm going to start with the air pump I already have and then try and build a windmill to mechanically turn a paddle wheel aerator mounted just above the water surface.

I don't wish to start another 'non friendly' discussion however something has been puzzling me. Rather than creating bubbles or using paddle wheels does anyone think that using a bell fountain head would allow for efficient gas exchange. Besides looking attractive the thin film of water of the bell looks to be a good gas exchanger (sort of a reverse bubble).

Got a solar powered fountain running in the pool. I think it adds to the amount of o2 but don't know how much. Does look good.

Yep, I reckon they would do well - I've got something a bit similar - on the left:



But I really think the 'shower' effect of a flood and drain growbed is more than enough to keep O2 at, or close to 100%.

Nice bit of reuse of a vacuum cleaner head Myles, or is someone running round the house going "I'm sure we got one of those tools, just can't seem to find it"?

I think it would have good oxygenating properties.

The thin sheet of water has a very high surface area to volume ratio (compared to a solid flow from a pipe)

interesting thread indeed, Steve
but there is one thing missing, and it is the most important element:
when discussing efficient aeration, the first thing to consider is power consumption.
That factor is completely missing here.
Just like it is on almost any paper defending diffusers and airlift pumps

to summarize what I have distilled and concluded from this thread (and some others):
to be efficient for aeration, bubbles must be as small as possible and be injected as deep as possible in the water (>5 m!), if possible in a counter flow (U-tube) to further increase contact time.
bottom water is more O2 deficient than top water
bottom water is cooler than top water, so O2 exchange will be more efficient
very small bubbles could be unhealthy for your fish
so the diffusion of bubbles best happens in a confined space to which your fish have no access
this can be a screened wide open ended tube from just above bottom to just below water surface

diffusers that produce small bubbles are expensive and need to have a big surface which makes them even more expensive
diffusers that produce small bubbles are more prone to clogging and need more maintenance
to produce these bubbles you need a blower or air pump
pumping air is by definition less efficient than pumping water because air is a gas and can be compressed
compressing a gas means part of the energy is transposed into heat
the further down you need to pump the air, the more you need to compress it
fast removal of the solids out of the fish tank is imperative as these solids consume a lot of O2.

Any AP system needs a pump
The average head this pump needs to overcome is between 0.3 and 1 m.
at these heads a centrifugal pump is known to be more efficient than an airlift pump

jetting water is an efficient way to increase aeration, but only if you compare it to a badly designed gentle inflow system
a well designed gentle inflow system i.e. cascades and waterfalls will save energy and perform just as well if not better
jetting requires extra pressure
all unnecessary pressure in a system is a waste of energy
all unnecessary pressure will reduce flow and thus eliminate every advantage you thought to gain by the jetting

to calculate a pump's efficiency you need to calculate pump effect and divide it by power input.
the equation for that is: pump effect (Kw) = head (bar) x flow (l/min) / 600
an exaggerated example to visualize this:
for 1 Kw of pump effect, you can either pump 2 liters of water per minute to 300 bar or pump 300 liters of water per minute to 2 bar
Both require the same energy
but the result is very different:
at 300 bar 2 liters of water will shatter into tiny droplets (this technique is used for airless painting)
at 2 bar and 300 liters per minute the fire brigade will blast the windows out of a building

while fish can survive at a DO rate adapted to their species, all fish will do better with higher DO up to saturation: they will be happier and livelier, feed better and convert this food better

now for a well designed gentle flow setup:
any AP system consists of different elements, each one lower that the previous
in each of these steps there is ample possibility of incorporating passive aeration enhancing devices like cascades, waterfalls (or a succession of them), open gutters instead of closed pipes, anything to expose more water surface to air surface.
Try to make the water sheet as thin as possible everywhere.
A sideways overflowing gutter to the growbed will create much more surface than some holes drilled in a pipe.
An ebb and flow system (not present in all AP systems) ensures further aeration.
these all work for free by gravity as you already have invested the energy into pumping the water to the highest point.

make the inflow into the fish tank axial to create a rotating movement - an eddy - to gather all solids in the center for faster removal

All of the arguments above lead to the conclusion that in a well designed system, the pump will take care of all pumping and aeration needs at only the necessary head, with no need at all for extra pressure.
so it is very well possible and even easy to make energy gobbling air stones and diffusers and airpumps redundant in AP at no extra cost and to the benefit of fish and plants.

Friendly greetings

frank

Here we go again.

+1

I have a couple of questions. Does still water lose oxygen? If oxygen, small molecules, transfers by simple diffusion should they not stay at air concentration unless actually consumed?

Perhaps pressure is a factor I have not seen discussed yet.

novaris, i'd assume it would stay constant once saturated all thing being equal...........but there are many demands on O2 in a real world situation. Biological demad, chemical demand etc........

add stratification to that. water will form layers (more so with fresh water i think) so the lower colder layers will have oxygen consumed by the factors mentioned above, but never make it back to the surface to be re-oxygenated.

Re:still water.

Thats not fair noely and c1.

Franks post summarised all the points very well.

A well written post, thank you.

thanks Ozzie

really appreciated

Some people seem to misread my intentions as being offensive
we should come to each others support more often

even if not completely agreeing:
a sentence like: "Ozzie(Frank) has a point there, but ..."
is a far more gentle way to continue a discussion than making someone look ridicule
which only shows a lack of arguments

thanks again

Frank

Actually I think it shows too much argument.
But hey I'm an Aussie so what do ya recon...
we are a lazy bunch eh!
Go for it Frank