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.