The Science of Composting

While Composting is a "Natural" process of microbes breaking down organic matter, and, essentially the source of all of our topsoil, a process that has been going on in nature for millions of years; we can help the process.

On the forest floor the leaves are deposited by nature in a thin layer each year, so there is not the oxygen limitation that can occur in larger piles of organic matter.  Also, in nature, turn around time is not an issue.  Because the material is so spread out, there are not the foul odor issues that can arise in more concentrated composting.

Foul Odors are the number one complaint about composting; and they are avoidable, when the facility is properly designed, and the operating team is committed to preventing the foul odors. 

The above chart shows data from a passively aerated windrow just one hour after building the windrow.   At all six cross section profile monitoring locations the oxygen was seriously below 15%; and it got worse as time went on.  Lack of oxygen is a primary complicator, though not the only one. 

Many people believe that compost placed in windrows will aerate by convection.    We've done over a thousand oxygen monitorings, using an oxygen meter, and our data, from monitoring real windrows, built of real compost, indicates that aeration by convection simply is not good enough.  The microbes, just like you and I, need oxygen, on a full time basis and 5 or 10% oxygen is apparently not good enough for them, based on our assaying the population of active bacteria in our own lab.

Though the microbes are the primary workers at a composting facility, maybe because they are far too tiny to see without a microscope, they have generally not been given the consideration that they deserve.   Though it is hard for us to comprehend, bacteria are so tiny that it takes about 25,000, 'shoulder to shoulder' to span a single inch.  Furthermore, the bacteria in a single teaspoonful of compost, if lined up 'shoulder to shoulder' would span over 0.4 of a mile, assuming a reasonable population density.  That is based on microbial assays that we have had done on compost samples. 

At least in theory, turn around time, how long it takes to turn new feedstock into mature compost is largely a matter of how many active bacteria and active fungi are working to achieve that goal.    Given favorable environmental conditions, these microscopic critters are very prolific.  

What are the critical environmental conditions that will enable the microbes to get the job done most cost effectively?  Oxygen, moisture, temperature, and a 'balanced diet are a few keys.   Our extensive oxygen monitoring has convinced us that forced aeration is essential.  Furthermore, our research composting restaurant organic residuals has demonstrated that, when providing ≥ 17% oxygen, adequate moisture (≥ 40% by weight), and plenty of food for the microbes, that the microbes can generate incredible 'surplus microbial metabolic heat', and that a lot of forced aeration is necessary to provide cooling, to hold the temperature below 160°.  We want it to be ≥ 131°F for at least 3 days, to kill pathogens and seeds, like the seeds from that tomato that was part of the waste that we were paid to accept.   The cooling is evaporative, thus, it causes significant drying, and that moisture has to be replaced, to provide the microbes with adequate moisture.  The microbes work in a film of moisture on the particles of composting material.

To optimize the composting process, we have to be able to check up on our microbial workforce.  Because bacteria are so small, and we want to be able to differentiate between total bacteria and active bacteria;  doing the microbial assays (direct estimates) requires a differential interference contrast microscope with fluorescence observation and 1000X magnification.  Dr. Elaine Ingham developed the procedure for doing the assaying while she was at Oregon State University.

We have developed our own QuattroPro spreadsheet templates for doing the 'number crunching' for total and active bacteria and fungi direct estimating.

While the microscope and other lab supplies represent a significant investment, and understanding the protocol for doing the assaying is vital, without being able to get this sort of hard data, we'd be working 'blind'.  We need to be able to know how well we are managing the composting process. 

We have compost research silos with computerized temperature monitoring.  The silos give us a very good environment for research.   We are now using silos inside, in an enclosed space, where we learned that we must provide bio-filtering.  As quickly as we identified the need, we modified the aeration manifold system, Developing our Dynamic Bio-Filters technology, which proved itself very capable of eliminating all of the odor problems. 

The foul odors were apparently sulfur compounds and ammonia, (NH₄).   Sulfur is an essential nutrient for healthy plants.  It came in the feedstocks, and should be conserved, be part of the finished compost, to provide for plants in the future.  Hydrogen Sulfide, H₂S, may have been a primary culprit. 

The chart to the right is from the composting scientific literature.   It simply suggests that our facility design MUST be able to mitigate the foul odors that can be produced during the very active stage of composting.  Bio-filtering is well established as an effective means of odor control.  Our own silo research has confirmed that we can effectively eliminate the foul odors with bio-filtering.  Our commitment to being good neighbors demands that we release no foul odors.

Ongoing Research and Development are an essential part of good business leadership / management, in our opinion.  We have done extensive research in the field of oxygen in composting, including publishing much of our data on our website, www.magicsoil.com, making the information available to all.  We developed our own compost research silos which have proven themselves a great tool.  In the Spring of 1998 we developed what was apparently the first, and is still the only diesel powered compost aeration blower in the world.  It performed up to our highest expectations, and appears to be far more efficient than electric powered blowers.  We will continue to do research to improve both our composting process and finished product quality. 

In the Spring of 2010 we added our first compost research silo capable of holding compost over 8' deep.  We wanted to know just how much pressure / vacuum it takes to move air through compost 8' deep, at different rates, and moisture content.  We want to know how the population of active bacteria and fungi varies through the compost, and now we have the capacity to get answers to those questions, first hand, including replicating our research.

While research is expensive, ignorance is far more expensive.  We learned that much of what is commonly accepted in the composting industry does not stand up to our testing.  We seek the truth to enable us to better empower the microbes, and remain very good neighbors and environmentally friendly.