How much aeration does my compost tea need? How do I provide it?

Question

I've decided to try out active aerated compost tea but I'm unsure of how much aeration to provide, and how. I've seen that I should target 5.5+ ppm oxygen in the liquid, but I have absolutely no sense of how quickly oxygen will be consumed or what putting it back in the tea would look like.

Some online guides show 5 gallons of tea aerated by a 1-gallon-per-minute aquarium air stone, and others pump tens of gallons of air per minute for the same amount of tea. Sometimes they pump the air through an air stone, sometimes through something more sophisticated. I see that the size of the bubbles has a big impact how effectively they oxygenate the water, so it's more than knowing what volume of air to pump through for a given amount of tea.

So my question is, for a given amount of compost tea, how do I aerate it adequately and economically?

Answer 1

Fish stuff will be the most economical method for any reasonable home scale, or you can go to pond fish stuff for unreasonable home scale.

You can pump air into the bottom, using an airstone or bubble wand, or you can pump water (tea) up and let it fall back into the container. Both will keep the fluid circulating, which means it will come into contact with the air at the surface as well as any bubbles involved - so the air exchange is not entirely dependent on the bubbles. If and only if you have trouble with the airstone/bubblewand clogging, you could remove it and use an open air tube.

Unless you invest a rather large amount of money into an oxygen meter which probably won't much like (and therefore may expensively expire from use in) tea, just choose an air or water pump as if it was an aquarium of the volume of your tea, and it will likely be fine. There's probably very little if any practical benefit to massively overscaling the amount of air pumped, but extremism sells on youtube.

Pumping air into the tea will be less affected by particles of compost than pumping the liquid will be.

If you want to delve into the science of biochemical oxygen demand in aqueous solutions, there's a massive amount of data from wastewater treatment - but applying that to a 5 gallon bucket is generally impractical.