This is from early in 1996, that's my Case 580K (yellow) up on the pile, and you can see a man standing down at the base of the pile.  The cloud is moisture from the hot compost when exposed to cooler air.  I guess there was about 12,000 cubic yards total at this site which I worked from 8/1993 until 1997.  I estimate that I spend about $100,000 of my time and machine time, turning compost, under the illusion that I was making a major difference, keeping it much more aerobic.

That was all part of my learning process, what I refer to as my "compost university". 

It was the fall of 1995 that I started learning about VFA's, Volatile Fatty Acids, which are byproducts of ANaerobic decomposition, what Dr. Elaine Ingham likes to call "putrefaction of organic matter".

This picture from January, 1996, shows our first experiments with forced aeration.  The little blower on the ground in line with the front wheel of the loader, was the cooling blower from my 1981 Data General CS/50 computer which I salvaged in 1990. 

Within a couple of weeks of our starting to experiment with forced aeration, we got an oxygen and CO₂ meter set and started measuring the oxygen and CO₂ levels in our compost. 

What we quickly discovered, from monitoring the oxygen and CO₂ is that the microbes can apparently very quickly consume the oxygen in a pile of compost.  Logically, a key factor is how many ACTIVE aerobic bacteria are present in the pile, consuming oxygen. 

This isn't "theory".  The chart to the right represents data that we gathered, using an oxygen meter in the pile of compost pictured above. 

When we got the microscope and started doing the microbial assays, doing direct estimates of the total and active bacteria and fungi, we started taking our documentation to a new level. 

How much air pressure does it take to keep compost aerobic?  Manometers are used to measure air pressure at low levels.

We made our first manometer in February of 1996.  Being cold weather, we used automobile antifreeze for the fluid.  We quickly found that it takes less than ¼ psi of pressure.  24" difference in the columns of fluid would be 1 psi.  By 2001 we were using a 3 decimal place digital manometer.

By Spring of 1998 our aeration manifolds and manometers had gone through a number of permutations, development stages.  This manifold was 157' long, and was attached to a diesel powered blower that we developed, and which performed up to our highest expectations, and burned only 8.2 gallons of diesel fuel a day, running full time.

this picture shows a system that we developed in the Spring of 1996.   It utilized a 1 horsepower electric blower that put out about 800 cfm.  We used a generator to provide the electric power, and the generator burned about 11 gallons of fuel per day, making it far more expensive to operate than the diesel powered blower which we developed afterwards. 

While our first diesel powered blower may have been a bit crude, the important thing is that it worked very well, and economically.  It was the culmination of three and a half years of experimenting and learning, two years of playing with forced aeration. 

IN 1999 we started playing with compost research silos.  Again, the system shown to the left was the result of having gone through several previous versions, learning along the way.   The aeration manifold for the silos, likewise, was the result of several earlier versions.

Our compost research silos include thermocouples for monitoring temperature, connected to an Omega TempScan, which is connected to a computer in our office. 

The silos have been used for doing extensive research, composting the organic residuals from a local restaurant.  During the Summer of 2000, we worked the silos quite intensively. 

Much time and energy has gone into designing the new composting facility.  Moisture balancing of incoming feedstock is one important consideration.  It was during the late Fall of 2001 that we developed a good working understanding of mass / moisture balancing.

The values in the "Ratio" column are proportions by volume.  Until we test and verify this at the compost research silo level, it is good "theory".  We feel that it needs to be verified.  Extensive compost research silo work since 2001 has reinforced our beliefs, and we still want to do a lot more research.  

Our competitive advantages are the result of our R&D, and we are confident that R&D will continue to provide us with massive benefits.  

In the Spring of 2001 we refined our ability to do compost moisture content testing.  We developed a simple QuattroPro Spreadsheet template, that makes it really easy to 'crunch' the numbers.  We also bought a lab balance that has a capacity of 200 grams, accurate to a hundredth of a gram. 

Basically the formula is:

We weigh the dish, add some moist compost and weigh the combination of the dish and sample.  Then we bake it for 12 hours at about 200°F, to bake out the moisture.  Then we weigh the dish with the dried compost.  Once we have that information entered in the spreadsheet, the formula in the last column determines the moisture content.   Baking in a MicroWave oven does not work well, based on our experimenting. 

Bio-Assaying, Quantifying our Microbial Workforce... "census taking"

In August of 2002 we developed a QuattroPro spreadsheet template for processing the numbers for assaying the total and active bacteria in compost and/or soil.

The data shown is hypothetical, just provided for illustration purposes.  Considerable mind power went into developing this template, including the key formulas.

In the Spring of 2004 we invested in a Leica Microscope with 1000X, including Epi-Fluorescence DIC (Differential Interference Contrast) and started doing our own "census taking" of our microbial workforce.

We feel that to responsibly manage large volumes of compost, we must be able to 'check up on our microbial workers'.   Doing direct estimates, using basic microbial assaying techniques seems at this point the best way to check up on our workers.

Rate of aeration required to hold the CO₂ in the off-gas down between 1 - 2% is also a very good indicator of microbial oxygen consumption, and thus, microbial activity.

Being able to look at the population of active bacteria, from our own assaying, and cross link that to the CO₂ content in the compost has enabled us to confirm that CO₂ concentrations in the off-gas of more than 4% repeatedly are associated with lower populations, and that high populations (> 3.0E+9) are limited to when the CO₂ in the off-gas is ≤ 4.0%.

We've done hundreds of rate of air flow tests, so we've got a basis for knowing what the aeration capacity should be.  We also believe that future research will lead us to discovering how to manage the composting process to achieve significantly higher populations of active bacteria and fungi, and thus, need to have the capacity to deliver that much aeration.  For us, the way we pre-process and manage the compost, including the feedstocks that we working with, needing to provide over 23 times the volume of the compost, in fresh air, every hour, to hold the CO₂ in the off-gas down between 1-2% is common during the early part of the composting process.

Why are we targeting Food Residuals?

By the August of 2006 our compost research silos had evolved significantly.  We have some silos with clamp on lids that can be used in either up-draft or down draft aeration.

We have three compost research silos especially adapted for very effectively capturing the Surplus Microbial Metabolic Heat from the compost process, with the necessary other parts for heating the office and other space with that heat.

We've enhance our ability to, and ease of monitoring the rate of air flow, CO₂ and / or oxygen in the off-gas, the humidity in the off-gas.

We've got some open top silos that are only used in down draft mode.  ALL of the off-gas from our compost research silos on the front end, goes through our Dynamic Bio-Filter silos.

In April of 2009 we found that with 3.0"wc of negative pressure, we can move air through 60" of compost at 118 times the volume of the compost, per hour, and that to move the air at 50X only took -0.960"wc.  This was working with compost that started out being shredded to ≤ ⅛" particle size.

Knowing how much pressure / vacuum and how much aeration is needed is elementary to designing compost aeration systems.

This page was last updated: January 26, 2010 07:14 PM