COMPOSTING 101

What is composting?
What can be composted?
Composting technologies
What's so good about compost?
EPA Region IV overview

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Nature recycles plant and animal matter through the process of decay.  Microbes responsible for biodegradation fall into two camps:  anaerobic (without air) and aerobic (with air). 

Anaerobic systems work well, but they’re not very people-friendly.  Anaerobic microbes are responsible for the smells emanating from rotting food and manures, and anaerobic environments are often wet and sometimes ooze an undesirable liquid called leachate.  But pump air into that same decaying mass, and the odors disappear[1], a sign aerobic microbes – the composting microbes -- are now in charge.

The spongy layer of decaying leaves underfoot when you tromp through the woods?  That’s humus.  The dark, fragrant dirt farmers once shoveled every spring from the middle of a big manure pile that steamed like a boiler during the coldest days of a sub-zero winter?  That was compost.

What’s the difference?  Not much.  It's not the product but the process that differs.  Natural biodegradation is a spontaneous-though-systematic reduction of complex compounds into molecules and atoms.   Composting is controlled biodegradation.  The result, whether it’s called humus or compost, looks and smells about the same.

Composting is like driving.  Mini or Mac, the same principles apply.  Master the basic operation of one, and with some minor adjustments, you can drive the other.  Pop the hood, and you’ll find science is the engine that drives a successful composting operation, but you don’t need to be able to tear it down and put it back together to drive one.  However, you do need to know how to choose the model that’s right for you and keep it humming with the correct fuel, proper fluid levels, and regular maintenance.

Like all creatures, microbes have a comfort zone, a finite set of variables creating a range of moisture, temperature, oxygen, and nutritional conditions within which survival is possible.  Outside of these preset limits … microbial genocide.

In nature, a frenzied period of microbial activity is indicated by ever-increasing temperatures.  But unchecked biodegradation gets too hot and kills off the microbes.  The system crashes, and there is a period of relative inactivity while populations rebuild.  Eventually, the microbes get busy again, the environment gets too hot, the system crashes, etcetera, etcetera, etcetera.  In the wild, this cycle may be repeated many times before the leaves, or log, or dead animal becomes humic material.  

But unlike microbes, humans aren’t particularly patient.  “Letting nature take its course” is evolutionary, not revolutionary, and we like to push the envelope. So while the words composting (the process) and compost (the product) may be relatively new to mainstream waste management, truth is, humans have been making compost for a long time.  

The word compost first appeared in a dictionary in 1388, and certainly, that ubiquitous manure pile was a crude demonstration of the composting process.  But it wasn’t until researchers began tweaking Mother Nature’s system in the middle decades of the 20th Century that the process began to receive serious consideration as a technology for managing large volumes of biodegradable by-products and residuals.

Modern composting applies natural laws, scientific principles, and manufacturing methodologies to the stabilization of organic materials.  During composting, microbial populations (like fungi and bacteria) excrete enzymes as they feast on the proteins and sugars in dead tissue.  Enzymatic activity breaks molecular bonds, releasing energy and elements back to the air and soil to feed and sustain another generation of plants and animals.

But, there is a point between the yuck and the ether when the process of decay slows down a bit and stabilizes.  Why is stability important?

A raw egg, cracked open and dumped into a cold fry pan, is not stable.  It is hard to handle and could harbor harmful bacteria.  Except for people who like to slurp ‘em raw, that ovum is garbage.  But, expose the slime to some heat, and it becomes the Incredible Edible, easily handled and ready to be eaten as-is or blended with any number of other ingredients.  The cooked egg is more stable than the raw egg.

Similar changes happen to organic matter when it’s composted.  When stable, the material can be handled without nose pins or rubber gloves, deposited neatly and cleanly into bags or walking floor trailers, and shipped elsewhere for beneficial reuse.

But unlike that egg, compost isn’t cooked in the traditional sense.  In composting, heat is a by-product of microbial activity, not a catalyst used to induce molecular change.   But both lay and professional composters often refer to the process as cooking, just as some say compost is pasteurized.  While neither is technically true, the results are the same.  The composting process does generate heat, and if temperatures hit certain points and are held there for specific time periods, pathogens and weed seeds are killed, a process that mimics pasteurization. 

Modern composting systems are designed to maximize biochemical and physical conditions to create and maintain an environment that will encourage the proliferation of specific microbial populations responsible for biodegradation. 

Successful composters are successful because they’ve learned how to create the perfect world for their micro-stock:  never too hot or too cold, always enough oxygen, a moisture level that’s constantly just right.   They go to all of this trouble because it results in an accelerated, predictable rate of decay. 

Speed and predictability may not be big concerns for Mother Nature or most backyard enthusiasts, but for large commercial and municipal composting operations, the ability to understand and control these factors is critical since they determine rate of through-put, which impacts the size of the operation, technology selection, labor requirements, and a myriad of other production and cost issues.