Re: [compost_tea] Question about dissolved oxygen and air stones

From: David Loring <dloring3_at_cox.net>
Date: Tue, 28 Oct 2003 15:17:38 -0800

David - Your friend has a point and personally I'll try to check it out in =
my Sotillo 50 as you suggested but I suspect the info at this link is corre=
ct. http://www.tmc-ltd.co.uk/filtration/essential_equip/aeration_equip.asp=
 

Dave
  ----- Original Message -----
  From: David Hall
  To: compost_tea_at_yahoogroups.com
  Sent: Tuesday, October 28, 2003 10:51 AM
  Subject: [compost_tea] Question about dissolved oxygen and air stones


  I get interesting stuff from the aquarium folks every now and then.
  Recently I got this message indicating that if I took off my
  bubblers I would get better oxygen infiltration to the tea. First
  of all, I pointed out that a good bubbler would add the equivalent
  of 4 million square feet of surface area per day. He blew that
  off. Here is his rationale.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  David - You are absolutely correct on the math, if the majority of
  the gas exchange happened between bubble and water. Here's the
  thing - if you consider the surface area of the container (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 environment of a compost tea with so many dissolved organic
  compounds (which you see from the foam) the surface tension around
  each bubble is not nearly as good for gas exchange as say a soft
  water environment without many dissolved proteins. By violently
  agitating the top you get a lot more oxygen into the mix - the
  amount of air going in through the air pump is tiny compared to the
  amount of air passing over the surface so keeping that tight foam
  (which small bubbles make) off the top and agitating the c*** out of
  it you get better gas exchange - i had the exact same problem the
  first time I heard this and I must have Missouri roots somewhere
  because i said 'SHOW ME!".

  I found this one to be true one summer when it got to about 110
  [degrees F] in my hatchery - had a few thousand dime-sized Angelfish
  in a 500 gallon vat and they were not doing well - the heat had
  lowered the dissolved O2 capacity drastically. So i took off the air
  stones (teeny bubbles) and pumped the air straight in, the dissolved
  O2 went right back up and ammonia down since there was more oxygen
  for the nitrifying bacteria to filter the excrement. I ran the math
  all afternoon scratching my head until i got around to modeling the
  surface disturbance on the 'puter.... yeah, I'm a geek, I admit it.

  Second thing - air stones clog quite a bit over time and by yanking
  them off you get better airflow so while bubble surface area is down
  you go from fizzy surface on top to boiling water turbulence. You'll
  also get more circulation which helps eliminate dead spots that will
  go anaerobic.
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  Okay, quote's over...back to me now. His point on clogging was that
  air stones clog from the inside with dust as it gets picked up from
  dusty garages where the smaller tea brewers usually are.

  But his overall point is that by simply running the air hose wide
  open, you develop a roiling surface with less of that nasty old air-
  blocking foam and more of just circulation within and on the
  surface.

  Still, I believe he is implying that by removing the airstone, he
  was able to inject O2 beyond the saturation point for his 110 degree
  tank. Maybe he was not saturated and removing the air stone allowed
  him to saturate??

  I'm not equipped to test this idea. I would think the simplest test
  would be to run an DO test in a batch of tea with an air stone and
  then unplug the air stone, let the batch run awhile, and test
  again. Has anyone run this test, or are you willing to run it?

  David Hall
  San Antonio, TX


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Received on Tue Oct 28 2003 - 19:05:47 EST

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