[compost_tea] Getting Oxygen into Tea and Preserving Fungi At The Same Time

From: chris reid <reidchris_at_earthlink.net>
Date: Wed, 29 Oct 2003 07:47:24 -0500

With compost tea, there are two considerations: 1) oxygen transfer and 2)
getting oxygen into the water in a way that is not damaging to the
microorganisms. Oxygen transfer efficiency in and of itself is not
sufficient, because the end product you want is not oxygen (such that fish
can live), it's compost tea, filled with a mixture of bacteria AND fungi and
so on. Oxygen is a means to an end here. So there are tradeoffs -- getting
oxygen is good, but getting good tea is better. Suggestions that produce
good oxygen but not good tea have to be discarded in favor sometimes of what
may appear to be a less effective oxygen delivery system per pumping power
used, but results in better tea.

This brings us to ways to get oxygen into water. We are seeing bubbles
discussed as one way, and surface disturbance as another, and in reality it
is probably a variety of combinations of both. So - what combinations work,
and what combinations are disastrous for fungi?

I would find it useful for someone to again comment on oxygen readings in
wider vs. deeper containers, and quality of tea in wider vs. deeper
containers. If anybody understands the physics involved, it would be useful
to understand how much width would make wider better -- if it would -- and
what limits there are on that. I'm trying to clarify the differing
information contained in several posts:

As points of reference:

In David Hall's post, he quotes his aquarium friend as saying:

Here's the thing - if you consider the surface area of the container (NOTE
THIS COMMENT: wider is
better than deep) start with it completely stagnant - say a surface
area of 4 sqft. now add a few ripples from bubbles.... much larger
surface... Now add big violent bubbles that give it that 'perfect
storm' level chop on top and you get a LOT more surface area.

In the link about air stones posted by David Loring, the author of the
linked material says:

The efficiency of bubble diffusers will depend largely on two factors:-

1. The size of the bubbles that are liberated - the smaller the bubbles, the
higher the surface area to volume ratio, and hence the more efficient the
gas transfer. (MY QUESTION: at what point do small bubbles damage fungi?)

2. The contact time that the bubble has with the water - i.e. the depth of
the tank.

A medium sized air bubble of 3mm will rise at a rate of 1 ft/sec and hence,
a bubble released from a depth of 3 ft will have a contact time of 3
seconds. Air injected at depths greater than 4 ft can lead to excess
nitrogen dissolving in the water. This can result in what is commonly known
as 'air bubble disease'.

MY OBSERVATION: I don't know the size of the larger many hundreds of
gallons brew tanks, but would wonder if the increased nitrogen levels at
depths greater than 4 feet begin to affect the bacterial numbers of the tea
(not sure the form of nitrogen (nitrate?) but the thinking would be, more
dissolved nitrogen equals more food for bacteria).

Bob Norsen says:
Stuart the absorption rate at higher pressures of deeper water drives more
O2 into water at the deeper location. This would allow the slightly less
air cause equal or more aeration in the deeper tank. The longer travel thru
the water would also add to the effectiveness of the air. So if the pump
puts out nearly the same air at the greater depth go for the deeper tank.
If the pump shuts way down at the deeper tank it will be quite reduced in
the shallow tank. Select a higher pressure capable pump. The quiet modest
cost aquarium pumps I use go to 50 " with no measurable change in volume.
X


I cannot relocate a post from Elaine that I seem to recall where she said
that fine bubbles, or a mixture of large vs. small bubbles rubbing against
each other, seemed to be harder on fungi/cause them to break up.

Any clarifications you all can offer would be really welcome.

By the way, I do not get anything close to a perfect storm roiled surfaces
Bob describes in my trash can (dust bin if you're from the UK) brewed tea
using the Bitti. I don't know if the pumps lose steam after Bob tests
them, or they are unevenly quality controlled at the factory, or I'm setting
it up wrong or what. But I ain't got no perfect storm over here.

Chris Reid




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Received on Wed Oct 29 2003 - 10:45:49 EST

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