[compost_tea] Re: Re: Flow rate for air pumps

From: Kirk Leonard <kirkleon_at_open.org>
Date: Fri, 18 Feb 2005 08:36:52 -0800
Bob and I and others banged on this several times.  Oct 12-15, 2003 and May
15-16, 2004 are two periods of discussion if you want to go back and look
(sorry, I do the digest so I don't get message numbers- it's a tradeoff for
not getting a lot of yahoo...) and there is scattered mention throughout
list archives.  "Air pumps" and "air/water" volumes are good keywords to
find the posts.

I'd do some translating for those who want to figure on their own, using
Bob's post.  He's probably done more looking at this than anyone else, so it
bears repeating.

> Date: Thu, 17 Feb 2005 21:20:16 -0800 (PST)
> From: Robert Norsen <bnbrew_at_yahoo.com>
> Subject: Re: Flow rate for air pumps
>
> A bit more complex. Steve, That air/water formula.  Air is not required by
water.  It is required by the life in the water, how active it is, how fast
it is eating, reproducing, using O2.

> We ran some tests with identical brewers, identical loads, identical
temps, one in 10 gallons, 0.17 CFM/g, one in 50 gallons, 0.034CFM/g. .  O2
readings were the same, hovering between 7 and 5.7, back up to 6+ mg/liter
on the same O2 meter.

Bob's talking about an air/water volume ratio.  Air in cubic feet per minute
divided by water in gallons.  There are 7.48 gallons in a cubic foot.  The
ratio would be the same using liters of air per minute/liters of water (the
metric system is so much easier).

.17 cfm/gal in 10 gallons would be a 1.7cfm air pump.  .034 a/w in 50 gals -
same pump, 1.7.  (Math whizzes probably got this immediately.)  "Linear" or
diaphragm pumps are the best to use here - Alita, Sweetwater, Gast, Thomas,
there are many... aquaticeco.com has a good selection.  Aquarium pumps are
(good) linear pumps but they're usually not big enough for making tea unless
you gang several up.

> A given air volume is just one of many parameters to consider.

> 1- Water volume is usually related to compost and nutrient load so it is a
factor.

> 2 - Efficiency of the Aeration system will vary air volume required.

> 3.- Effectivity of circulation is critical since "dead volumes of ACT can
pollute just as can anaerobic left over crud in dirty brewer.

You want good air movement throughout the tank, so aerator design is
important.  Bubble size is important too.  Smaller bubbles provide more air
for critters, bigger bubbles move the water and support extraction better,
generally.

> 4 - The compost can release little or much life into the brewer depending
on -

>      A - the compost.
>      B - the effectivity of the extraction process of the brewer.

You want good organism extraction, and the better the compost and extraction
action, the more you can get.

> 5 - The kind and quantity of the nutrients included in the "load".

To me this is the most important variable - high nutrient loads will create
greater oxygen demand, compost held constant.  If you use a lot of nutrients
you want a lot of air, but you can do with less air if you use less
nutrients.

> 6 - The temperature of the process. 65- 75 F  moderate air volume is OK

>     If your bewer is gong to run into the 80+F range  expect to reduce the
nutrients or provide    more than minimal air.

> We have tested small brewers where air is as low as .01cfm/gallon
> and with some care to not overload the (small) brewer O2 was held
> above the magic 5.7 mg/l.  ( A safer, excess of air is less expensive than
an O2 meter)

> It is more comfortable in big agricultural models to have  .05 to .1 CFM
per G.

I think Bob thinks of big ag models as starting at 500 gals.  An a/w ratio
of .05 in 500 gals would be a 25cfm pump; .1cfm would be a 50cfm pump.  Most
cost-effective in this range are "regenerative" air pumps, but rotary vane
pumps will do better over time.  There are several ag air options (for
silos, driers) that work well, I hear, usually have separate motors, don't
know much about that.

> At the .1 to .05 cfm range the operator can load the brewer rather heavily
and still hold O2 above 6mg/l.   However the system must be efficient,
circulate very well.  Air must not stop.  The herd is using O2 at a high
rate.   Tests showed that 5 minutes OFF dropped the O2 to 3mg/l.  Air back
ON brought the O2 level back to 6mg/l in 12 minutes.

> The rate of O2 required near the end of the brew cycle when all the
nutrients are used and the herd is asleep - the O2 drops much slower.  This
may allow a short non- aerated time for transporation and application.  We
think and practice that it is safer to keep aeration going ON the brew
until it lands on the leaf or the soil.

KIS machines and many mentioned by OZ folks use much higher air/water
ratios.  I measured a little KIS fresh out of the box at a/w = 4!  That's
Four, not point four.  Another person here measured it at 2 after some use.
It's simply an air blower and wears out relatively fast.  OZ folks seem to
run above a/w = 1, even 2-3.  You can get to the point where you're blowing
tea out of the tank... How much roil is really useful?

I'd repeat what Jeff said, too. Along the way here, I think we've found it
to be a viable, testable hypothesis:  More air is better?

> Date: Thu, 17 Feb 2005 19:39:34 -0900
> From: Jeff Lowenfels <jeff_at_gardener.com>
> Subject: Re: Flow rate for air pumps
>
> Well, all I know about fungi and air is that one of our customers had
> low fungal numbers.  By increasing the air...we were able to get the
> fungal numbers and diameters way up to high levels. We literally had to
> double the pumps. I suppose we should have published the information.
> Unfortunately, all the customerr wanted was higher fungal numbers.
> So, my experience is that when numbers are higher than 6mg/liter,
> tested fungal numbers were higher.
>
> Cheers,
>
> Jeff

And Tom's right, too, more testing is needed.

Kirk




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Received on Fri Feb 18 2005 - 12:21:02 EST

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