Spinning water

Gardening continues very slowly at Ligaya Garden as I’ve been focused on policy and planning and helping folks get fed during a food shortage. The biting cold doesn’t help gardening much either.

That all led to me going stir crazy and getting stuck into a new project. Athena and I decided, on an overcast, bitingly cold day, to make up a vortex brewer for our microbes and fertilizers.

The idea is really simple. An air-lift pump lifts water and pumps it into the top of the bucket. The water flows out and runs around the edge of the bucket and spins the water. An outlet at the bottom lets the water flow out and back into the pump for redistribution. The spinning water and the outlet at the bottom form a vortex or whirlpool and this sucks further water down.The water becomes super oxygenated. The air lift is just a bubbler at the bottom of a pipe. The bubbles lift water up to the outlet, mixing it with air. The circulation of the water in the bucket mixes in further air and the walls of the vortex increase the surface area available to absorb oxygen. The continual breaking of the surface tension of the water allows more gas exchange and Bob’s your Uncle, highly oxygenated water!

How and air lift pump works.

The heart of this system is an air lift pump. It’s a simple thing that works by pumping bubbles of air into a vertical pipe in which water flows. The bubbles expand to the diameter of the pipe and lift the water immediately above them as they rise.

For this small setup, a 380 litre per hour aquarium air pump is just adequate to get things working. When I scale up the system, I’ll swap this out for a more powerful, commercial one. Conventional air compressors don’t work well because, although you can get the flow rate, they are only designed to run in short bursts and overheat easily.

We found a few variables that need to be tweaked to reach perfection but we’re not far off. A second try with a larger diameter pipe allowed more constant flow and smoother and faster vortex formation.Our biggest problem was thinking that we could get a massive whirlpool going in a 10 litre bucket using an aquarium pump. We did get it working though and are really happy about that.

Some of the variables that make a difference to vortex formation and size are –

• Pipe diameter
• Pipe length
• Number of jets
• Width of bucket
• Depth of liquid
• Flow rate of water
• Flow rate of air
• Diameter of outlet

So, you can see that there are plenty of things to tweak but I think, ultimately, its a balance between the diameter and depth of the bucket and the size of the outlet. Once the vortex gets going it is pretty easy to keep it spinning but the diameter of the hole in the middle is what is interesting me.

Most of the systems you see online make more than 60 litres at a time but with our fertilizers and small space, we don’t need a lot. When I have a good brew going, we can do the whole block with one bucket so I will try and find a shallower, similar capacity container with a wider diameter.

What good is swirling water, you may ask?

This brewer doesn’t just mix oxygen into water, it will be used for much more. When I brew up any of our liquid fertilizers or additives, such as worm casting tea, Nettle tea, chook poo tea or anything else, I can strain the liquid and add it to the brewer, often with a teaspoonful of molasses and let it do its thing.The microbes will be well fed, mixed around a lot to allow a bigger, healthier population and of course, well oxygenated. This will give us a very healthy garden additive, full of life and vitality.

After running the original design, I tried a two jet version with a second air pump added to make a second air lift. The results are less than spectacular with the only change being that the vortex forms earlier after starting it up. I don’t think that that is worth the extra investment, especially now that pipe fittings have doubled in price!