Our Non-unionized microbes are
working 24 hours a day, day and night, 7 days a week, Sundays and holidays included.
They want fresh air, oxygen, on the same schedule.: The least we can do is provide
them with fresh air, oxygen, on a full time basis. If we don't, they may raise a big
stink.
We believe that compost still needs to be
turned, for multiple reasons.... to fluff, homogenize and even out the porosity, and
microbial distribution. During the turning process the compost can be re-hydrated as
necessary. Often re-hydrating is needed in less than 18 hours after turning, and can
be accomplished with overhead irrigation. The microbes need adequate moisture in
order to do their work.
Our first diesel powered
blower worked like a charm. We estimate it to have a capacity of about
10,000 cubic feet per minute. It works on the same schedule as our microbes, full
time. We shut it down twice a week just long enough to check the oil, and once every
five weeks to change the engine oil and oil filter which takes about 11 minutes. The
engine was connected directly to a 500 gallon fuel tank. These pictures of the
blower and manifold show a system that has since been retired, being replaced by newer
versions.
This blower proved to us that diesel powered blowers of
this type are a very cost efficient way to provide the microbes with oxygen and also for
limiting the temperature to not higher than 150° F.
Fuel consumption was less than 10 gallons per day.
We estimate that electric blowers would cost more than twice as much to operate.
Hayward 4" PVC True Union Ball
Valves are our choice for new valves. The tower with the blue fluid in it is a manometer,
telling us just how much pressure is in the system at the point where it is
installed.
The blue fluid is common automobile windshield washer fluid.
The valves enables us to control the air flow into each vane,
thus enabling us to control the amount of cooling and also oxygen level. Our own
standards call for maintaining oxygen at 15% or higher, as determined by using an oxygen
meter.
Also, from experience, we learned that aeration vanes in a
concrete composting pad is the best way to go. Turning is essential for responsible
composting, for multiple reasons. In ground aeration vanes and a concrete pad
simplify turning.
WHY go to the work of providing
Forced Aeration?
The most effective microbes for converting organic
residuals (wastes) to premium top soil and soil conditioners are aerobic
microbes. "Aerobic" means they work in
the presence of oxygen, that they consume oxygen. In the absence of oxygen the
entire chemistry changes and foul odors and phyto-toxic VFA's are produced.
The data on the above chart is from The
Practical Handbook of Compost Engineering by Roger Haug, page 123.
Preventing Foul Odors:
Many of the chemical byproducts of
Anaerobic conditions are foul odor gases.
Thus the key to preventing foul odors and
VFA's is to maintain oxygen levels greater than 15% throughout the
composting mass.
We spent thousands of hours turning compost
under the illusion that turning would keep compost aerobic. Then we invested in an
oxygen meter and discovered that the microbes can exhaust the oxygen in 15 minutes or
less, crashing the oxygen level down from 19% to 2%.... in just 15 minutes.
This is research that we did
at Mother Nature's Farms on forced aeration piles that were over 200 cubic yards, over 35'
long, 35' wide, 7' high with 4" diameter aeration vanes under the pile with aeration
pressure of 2/3". That aeration pressure is about the same pressure you use
when you blow out the candles on the dinner table. It is very low pressure and
massive volume.
We expect that when we
repeat this research with more dynamic compost feed stocks that the oxygen depletion will
be much faster, maybe as quick as 2 minutes.
Turning compost
is still important to homogenize and fluff the material. Turning will facilitate
more uniform air flow through the compost with a lower air pressure and thus less energy
to drive the blowers.
Short Circuiting:
Our research to date suggests that the
people who allege that forced aeration is ineffective because of short circuiting may have
little first hand experience with adequately sized / designed forced aeration
systems. Even when we open up an unused vane valve, creating a 4" wide open
unrestricted air escape the pressure in our main manifold drops very little. When we
monitor the oxygen level at dozens of different places in the pile of compost we continue
to find our oxygen levels greater than 15%.
Passive Aeration by Convection is
nice "Theory",
but our oxygen monitoring doesn't support
the theory.
Within 46 hours after this passively
aerated windrow was built the oxygen level at all 5 monitoring points was critically low,
and the CO2 levels were far too high; even though the temperature was quite
acceptable. Temperature alone does not provide enough information. Monitoring
point "C" is where we expected to find the best oxygen level, but it is still
below our minimum of 15%, and all the other points were below 5%. While this suggests that
there is some aeration by convection, it is massively inadequate.