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

From: Stuart Baxter <stu.baxter_at_virgin.net>
Date: Wed, 29 Oct 2003 00:59:55 -0000

Whoa! Another can o' worms :o)

I was sort of trying to feel my way around this a while back when asking ab=
out wide tanks rather than deep. The link talks about 'air bubble disease' =
at depths of 4 feet or more caused by nitrogen. I remember saying that air =
is 70 odd % nitrogen with oxygen rating only 20 odd %. I have a sneaking di=
strust of DO meters too - mainly because I don't know how they work! What d=
o they actually measure in the water and then scale it to DO?
But compost tea isn't just water, and air isn't just O2.

It would be useful to try a bubbler in water with and without a diffuser to=
 see how the DO reads, but the acid test would be a compost brew. Or even t=
wo brews (with and without diffuser) with SFI results.

Something I've wondered about for a while is a volunteer fund (I suppose I =
could afford a dollar or two a month - anyone take paypal?) for basic proof=
s just like this. I'll wait for comments about it although I foresee proble=
ms with regard to funding decisions, fundholding, accounts.....

Be well

Stuart
bits an bobs
UK


----- Original Message -----
  From: David Loring
  To: compost_tea_at_yahoogroups.com
  Sent: Tuesday, October 28, 2003 11:17 PM
  Subject: Re: [compost_tea] Question about dissolved oxygen and air stones


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

  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



    To unsubscribe from this group, send an email to:
    compost_tea-unsubscribe_at_yahoogroups.com



    Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.


        Yahoo! Groups Sponsor
              ADVERTISEMENT
             
       
       

  To unsubscribe from this group, send an email to:
  compost_tea-unsubscribe_at_yahoogroups.com



  Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.




Received on Tue Oct 28 2003 - 22:09:31 EST

This archive was generated by hypermail 2.3.0 : Tue Feb 07 2012 - 14:14:50 EST