Backyard Aquaponics
A place to discuss aquaponics

I have air pumps and was planning on using them in the FT. I have 3 so I was thinking about using 2 for the FT, (one a backup) and perhaps one in the sump to help raise the DO. My thought was that DO depends (from what I have read) on surface bubble eruption - I read that hardly any DO is transferred by the bubble in the water and that it occurs as the bubble bursts.

So I have this wide area of water surface in the sump doing bugger all and I figured I could make use of it by starting to increase the DO before the water gets pumped to the FT.

My thought was that if a venturi could run from the water falling back into the sump, it would be another source for DO, but if a short fall isn't enough to do it, I will add the venturi where the water enters the FT instead. Then I can have the active pump on the other side of the FT and use the water entering to swirl the FT water.

Mind you it all depends on what I can set up in the GH - there's been a slight delay in building it while I work out ways to prevent the disaster that happened to another member here recently.

I can list at least three people that will be ROFL @ me.

The theory/myth that aeration only occurs at the water surface is true for ponds where mixing is the critical factor in insuring well aerated water. In FTs where the pumping rate is relatively high (compared to a pond) the percentage of aeration that occurs at the water surface as compared to the water/air interface of the bubbles is debated but there are studies that seem to state that it is somewhere between 30:70 to 90:10. ie some where between 30% to 90% of the oxygen needed by the system is absorbed from bubbles rather than the water at the top of the FT. A lot depends on the design and operation of a particular system but regardless there is a significant amount of gas exchange via the bubbles.

I would not use a venturi to aerate my water unless I did not have another option. Air pumps will get more air into your FT water for less electricity.

If you are using a CHOP 2, couldn't you just use the flow back to the FT for venturi airation? You wouldn't be pumping any less water or using any electricity that you wouldn't otherwise be using. I was planning to use venturi and water fall/jets to airate my 2 grow bed IBC CHOP2 set up.

Indeed you could.... and you might as well....

Hi everyone:

I'm sure you are all familiar with Paul Van der Werf--even though he focuses more on aquaculture.

In the video below he talks about his filtration system but also discuss the venturis that he uses. (I'm designing my big system now.) I know my stocking density is not going to be as high as his (he is basically running an aquaculture system where he uses some of the waste for plants), but I like the idea of a venturi for aeration and air pumps as back-ups.


Of course the venturi he uses restricts the water flow alot (he even says you need a bigger pump), but I can make one that is less restrictive but still takes in a lot of air. My line back to the FT will split into two: 1. with the venturi going into the middle of the FT and causing a slow swirl and 2. the other flowing into the top of the tank unrestricted but still adding aeration. I plan on using web4deb's design, but not having end-caps so their is absolutely no back-pressure on the pump.

https://www.youtube.com/watch?v=NHAbuq8OBUI

What do you all think of my idea?

If your FT is round (cylindrical) then I wouldn't have the venturi disturbing the water in the centre of the tank as this is where the solids will accumulate with the slow swirling action (that's the whole purpose of getting the water swirling, to accumulate the solids in the centre of the tank where a SLO/pickup collects them) In order to generate a swirl, the water should enter the tank close to the wall of the tank and in a direction along the tank wall.

For the spray bars; you can use some of the pump pressure to direct jets deeper into the water, which not only disturbs the surface (breaking surface tension) but air will be drawn into the broken stream as bubbles delivered to depth, so regardless of the arguments about where gas exchange takes place, you're covered. Again, you don't need to direct water into the centre of the tank, you get more "push" from the edge of the tank than from the middle.

If you've got such a powerful pump that you can afford to make flow restricting venturi systems, then I'd be making one kick-ass venturi and delivering this water and air mixture to the bottom of the tank near the tank wall and forgetting about the spray bar idea. The delivery of water containing air under pressure can move the water, the bubbles under pressure have an opportunity for gas exchange, the rising bubbles cause mixing of the water column ensuring there is no stratification within the water column and when the bubbles finally break the surface they break the surface tension with an upwelling action which does not promote water loss through splashing (or increased evaporation/wind loss etc) I didn't use an air injection venturi in my system, but captured air in my gravity GB drain, but the effects are the same and can be seen here :




[edit]

Of for another view of the same idea with a slightly modified configuration:





$0.02c

bunson:

I suppose I should have been more clear in my post. The line with the venturi into the FT would have a 90 degree angle on the inside of the tank--meaning that the water would be forced along the wall of the tank causing the swirl and moving solids to the middle for the SLO to pick up.

As I'm thinking through my purposed design I suspect that my second line to the tank, with the spray bar, would be pushing the majority of the water that comes into the tank because the other line would have the restrictive venturi on it. So I may need to eliminate the spray bar altogether or put a value on it to even out the water flow between the spray bar and the venturi.

I do like stand-pipe idea (I watched your other video on the channel). Would the same design work in a bell siphon? I suspect it may not because the air inside the bell is restricted under pressure.

Thanks for your post.

I added a 3/4 piece on the end of my pipe into the fish tank for $3.00 and it is a perfect venturi and to EB's point I can and will make it a forced air venturi so even if my pump fails there will still be air. You can see it on the video on my thread if you want. But it is used for irrigation as a split for a drip hose. But I am all for venturi's while everything is working they work great to add that much more but I am also about the back up plan too.

Yeah thats right i am sitting on the fence

As I said earlier, I'd be looking to have all of the excess water moving through the venturi, however you could always drill fewer smaller holes in the spray bar and use an end cap to balance the pressure between the two routes. How are you balancing with the distribution of water to the GBs?

You're right, it doesn't work with a properly working bell siphon as for a good portion of time, the bell siphon doesn't have any air in it. If your bell has enough air in it and that air is being drawn into the drain flow then you'd be expecting the siphon action to commence very shortly. If you've got air in your siphon and that air is being drawn into the flow and the siphon action doesn't start then you've got bigger problems!