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Answering a question regarding the air lifts in my system

Regarding: A question about the air lifts used in my aquaponics/aquaculture system.

The air lifts I use for transferring the solids to the settling basin are powered by one external aquaculture 64 watt air compressor and gravity which continually moves more than 1000 gallons through the basin system at a rate of approximately 3 gallons per minute.

Air lifts are not anything new. Under gravel filters and other forms of air lifts are regularly used in the aquarium hobby. Modern sewerage treatment plants also use these systems. These designs owe their existence to work of engineer Carl Emanuel Loscher who is credited with inventing air lift technology in 1797.

The system I use has a center drain cut in the middle of each of my two circular poly culture tanks. Water and solids use the power of gravity and the properties of both water and air.  These forces send the water out of the bottom of the tanks in search of level. Clean water is returned after making a pass through the aquaponics system where it feeds the plants.

The system can be switched into Aquaculture only mode. It is 100% separated from my aquaponics to overwinter, clean, harvest, etc. Clean water returns from the drain of the bioreactor and from a separate gravity fed filter system, where it is airlifted back into the tank using the same compressor.

The air lifts are made by simply drilling a hole into a 90 degree elbow and attaching an aquarium pump hose fitting to it. I seal it with silicone and allow it to dry fully. The fitting is attached to an aquarium air hose and runs to a manifold that comes off the single air pump used in the process. Once air is supplied to the hose it generates the bubbles necessary to carry the water and solids up the pipe and through a bulkhead to the settlement basin tray. There is an extension on each of the up pipes with a cap that I drilled a hole into. This allows the air to escape. It does drip from time to time so I think the next one I make will be a little taller. I usually attach a pairs of tanks to one settlement basin tray and find the flow rate is perfect.

Can I make my own solids settling basin and how do I size it?

Sure the design is very simple. For those interested in the math it is all based on Stokes’ law. The system uses the power of gravity and reduced velocity. In simple terms, for the solids to settle out the sinking force (gravitational pull on the solids) must be greater than the horizontal velocity (water flow). The larger the waste the faster it will fall. Smaller particles have less gravitational attraction. Smaller particles therefore require a longer basin and slower water flow.  By playing with these parameters you can select for the size particle you wish to remove. It is easy to visualize, especially if watching Gold Rush is one of your guilty pleasures.

The balance of solids will be sent to your grow beds for the worms and/or skimmed with filters (also using gravity). I will discuss this in a future blog.

A homemade settling basin/tank made from Dura Skrim or a similar product should work just fine. It is a great way to get those solids out. It is especially helpful if you plan to use them elsewhere. (I use them in Vermiculture and for BSF feed). It will also keep your system cleaner much longer than any other method I have tried.

Thank you for taking the time to read this. If you are interested more in the math, send me an email and I will jot down the formula for you or post it in the future.

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Comment by George on February 12, 2016 at 10:52pm

Glenn at Olomama Gardens described such a scenario, stating that it is possible to pump 10 stories high.  Perhaps if you contact him, he can tell you how to do it..  Check out the videos and good luck.

Comment by Mykl Winn 13 hours ago

Is there a practical limit to how high an air elevator can lift water?

I am trying to design an aquaponic system on a mountain side with a 200 foot elevation difference between the bottom sump and the top/beginning bed.

Comment by John Stevenson on February 12, 2016 at 2:40pm

I suppose the real question is how you define practical? I am sure there are many others here with more experience and on a much larger scale. But, here is my two cents. 

As I understand it, the air lift height and the capacity of the airlift depend on two major factors. The depth of the water where the air is supplied and the amount of compressed air provided. I have never experimented with any great height so I am afraid I do not have any first hand advice to share. 

If you look at my system you will see the main line rising up from the ground and emptying into a settlement basin. The other end of the line is connected to the bottom of a full culture tank. The tank’s resting water level is at a depth that is greater than the distance the water needs to travel upwards above the resting water level in the tank to my settlement basin.

My compressor pumps air to a fitting at the lowest point on the line rising to the settlement basin. The air/water mix has a lower density than water (nearly half) so it travels upwards. It is my understanding the air carried water will continue to rise to a height above the tank water level equal to approximately the depth of the tank. I will be extending the line in the near future but have not tested it any higher than it currently sits.

 I would surmise you would need a well or sump tank at least 200 feet deep to lift the air/water mix to a height of 200 feet using a system similar to mine on a larger scale. I have heard from others that it is recommended to use a sump twice the depth of the resting water level. That sounds like a lot of work.

I wish I knew more about Geyser Pumps and Pneumatic Ejector Pumps but maybe someone on the forums has some experience with them and can tell you if they are a more realistic solution.

I would also like to ask if the water in the “hot pools” is too hot or if it is conducive to culturing fish in. Setting systems horizontally on several levels may be easier than pumping all that water vertically up the mountain in one system.

Is any excess flow coming from the pools above (springs/stream/etc.)? If so and you don’t need to capture a high percentage of it to send back up consider a Hydraulic Ram Pump. Again, I do not have personal experience but I have seen them in action and with a 200 foot fall you may have quite a powerful pump that runs entirely on kinetic energy rather than electricity.

I hope many others comment as my experience is limited to residential systems and I would love to hear what they have to add.

I am very interested in your project and would like to hear more. Thank you for sharing.

Comment by Mykl Winn on February 12, 2016 at 8:38am

Is there a practical limit to how high an air elevator can lift water?

I am trying to design an aquaponic system on a mountain side with a 200 foot elevation difference between the bottom sump and the top/beginning bed.

Parallel to this is a series of ho

t pools that flow down into a pond where the water is filtered and moved back up to the top pool to cycle again.Thanx.

Comment by George on January 22, 2016 at 8:11pm

It's difficult to catch everything.  I've become a big fan of airlifts.

Comment by John Stevenson on January 22, 2016 at 12:20pm

Hi George,

Thanks for catching that. I really should proof my posts before I submit them. It should have said "must". I will correct the typo.

Comment by George on January 20, 2016 at 8:07am

See below -  shouldn't the underlined word be must, instead of cannot?  

The answer to your question is, of course, yes.  As to size, if you are not restricted by space, then more water volume in the settling basin is better, in my opinion.  This is something I've been thinking about for a while. For my relatively small system (400 gal fish tank), I'm thinking of using a 60 gallon blue barrel radial flow filter with air lift flow rate of about a gallon per minute.  My fish tank is in the ground and is the low point of the system;  therefore, the blue barrel settling tank/filter will be a high point and will gravity drain to either the fish tank or a gravel bed, probably a gravel bed.  

In a concept commercial system I've been mulling over, the flow would be gravity from fish tank to radial flow to gravel bed to DWC to settling tank.  Air lift from settling tank to fish tank.  Settling tank would gravity drain from near the top of the tank to a lower point where the air is injected - see air lifts at Olomana Gardens.  The goal of this settling tank is to capture the smallest particles which have no plant food value - they've already passed through the entire system.

As to volume of settling tank/basin, this is determined by water flow so another way to size is by adjusting the flow.  Larger settling tank = more flow and visa versa.  

thanks - this is food for thought

quote below

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In simple terms, for the solids to settle out the sinking force (gravitational pull on the solids) cannot be greater than the horizontal velocity (water flow). The larger the waste the faster it will fall. Smaller particles have less gravitational attraction. Smaller particles therefore require a longer basin and slower water flow. 

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