Re: [compost_tea] Flow rate for air pumps

From: Robert Norsen <bnbrew_at_yahoo.com>
Date: Thu, 17 Feb 2005 21:20:16 -0800 (PST)

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.

Expect the 10 gallon brew to be more concentrated than the 50. Both brews tested in the SFI excellent range.

Many tests were run at different loads and volumes, observing the O2 levels.

Conclusion: 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.

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.

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

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.
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. This entails the brewer going to the application and forming the application system or transferring to an aerated tank. So we made brewers that can do that.
 
 
This brings us to air for the CACT cycle, Steve, but maybe this is more than you wanted to know about AIR already. Grin, Bob
 
My friend once described HIS long winded friend: He hated to ask him what time it was because his friend always had to "build a clock".

Steve Diver <steved_at_ncat.org> wrote:


I've received several inquires lately on
suggested air pump flow rates per volume
of water.

While 6% dissolved oxygen is the established
parameter to monitor oxygen level during
the tea brewing process, what are the guidelines
for matching flow rate of air pumps to tank
volume to achieve this optimum aeration level?

For example, how do you match air pumps (measured
in CFMs - cubic feet per minute?) for 50-gal,
100-gal, 500-gal, and 1000-gal volume tanks?

Are there particular brands or suppliers
of air pumps known to be especially useful
in compost tea brewing?

Thanks,

Steve Diver







Yahoo! Groups Links














Received on Fri Feb 18 2005 - 01:00:28 EST

This archive was generated by hypermail 2.3.0 : Tue Feb 07 2012 - 14:15:47 EST