Getting the Recipe Right – A Dead Cow Versus Industrial Perfection


by Craig Coker, Chairman at Virginia Composting Council

In this blog post, Craig Coker shares two illustrative stories that marked his career and describes a few basics of the composting science – or art?

Just about anything that was once alive can be composted.  The simplest compost pile I’ve built was at a farm by covering a dead cow with hay and sawdust.  Six months passed and voila, I had compost!  On the other hand, I’ve built piles at an industrial composting facility that came from fifteen different contracted materials, varying from sewage sludge to food processing scraps to wallboard.  In both situations, it was absolutely critical to get the materials proportioned properly which we will delve into.

First, a little on the science:  composting parameters include chemical concentrations of carbon, nitrogen, and soluble salts, along with physical characteristics of moisture content, bulk density and volatile solids.  These are the very factors that go into how I build my recipes. I am fond of saying that composting is like baking a cake; if the ingredients for the cake (flour, sugar, eggs) are not in the right proportions, the cake will not rise or it will not taste good. It is the same in good composting. If the ingredients are in the wrong proportions:  the carbon-to-nitrogen ratios will be off, the moisture content will be incorrect, there won’t be enough volatile solids to fire up the biological reaction, the free air space might be too low to allow good air flow, or the soluble salts might be too high to be ideal for plants.

While composting sewage sludge with wood chips and many other materials was not a revolutionary equation, it was very precise from strict parameters. At an industrial composting facility, an aeration system was utilized to blow air into piles that were 30’ wide by 100’ long by 10’ high. Composting under this forced aeration system lasted for 21 days, then the piles were broken down and moved outside for curing. Waste materials were delivered to the receipt area next to the mixing hall, where they were stored in separate piles. The loader operator working in the mixing hall had to know how many loader buckets of each material he needed to add together to make a good composting recipe. I used an Excel spreadsheet to develop his recipe. Samples of each waste material were analyzed in a qualified laboratory and then put the values for carbon, nitrogen, moisture and bulk density into the spreadsheet. I adjusted the weights of each ingredient until the spreadsheet model indicated I had a carbon-to-nitrogen ratio of at least 25, and a moisture content of at least 55%. I used the bulk density values to convert the weight to volumes.

I climbed up into the loader operator’s cab to show him the recipe. He said he had a 6 cubic yard bucket on the loader. In sum, we were able to figure out he needed to take so many buckets from this pile and so many buckets from another pile, which he fed into a mechanical mixing system. The properly-mixed ingredients were moved into the composting hall by a conveyor. Perhaps this is sounding a little too precise and calculated. And to that end, you might be wondering:  how did I have such luck with composting the dead cow?

I was running a dairy manure and sawdust composting facility at a farm in western North Carolina. One of the cows had died overnight and the farmer was planning to dig a hole in the fields to bury it. I suggested he let us compost it instead. Agreeing, he brought the animal in the bucket of his tractor and laid it down on a 12 inch thick bed of sawdust we built. I realized that the high nitrogen content of the body coupled with the large size of the cow would slow the process and risk odors, as well as vectors. I punched a couple of dozen holes in the body with a pitchfork to allow access for the bacteria and covered it with an 18 inch-thick layer of hay which gave the pile good bioavailable carbon. We watered the hay until it was damp to improve the moisture content and finished by covering the hay with 8 inches of sawdust to discourage birds and other vectors from poking around. We kept the outer layer of the sawdust wetted down when it wasn’t raining to keep it from blowing around. After 3 months, we dug a hole in one end of the pile and found a leg bone.  We left the pile in place for another 3 months, and when we dug into it, found just a few bone fragments and lots of dark brown compost… Voila!

Is compost a haphazard event?  It can be, but regardless, composting is both a meticulous art and science.  

 edited by Rachel Chibidakis



Piles, Pitchforks, and Perfect Learning Opportunities: Why Colleges and Universities Should Choose Small-Scale Composting

Composting at Pomona College

By Jen Schmidt and Adam Long, Farm Manager at Pomona College, California

In this blog post, Jen and Adam describe the composting program in place at Pomona College and shares their vision on low-tech campus composting.

Shiny, expensive mechanical composters are increasingly popular at colleges and universities that want to compost their food waste, and rightly so. They offer a number of benefits, including reduced labor, minimal odor, and short composting times. At Pomona College, though, we have done things differently and we have come to believe that small-scale, low-technology composting is the way to go. A simple compost pile may not be glamorous, but the educational and environmental benefits of this method are more than worthwhile.

Starting in the mid-1990s, Pomona College students and staff members worked together to compost food waste by hand, that is, manually mixing leaves with food scraps and turning it with pitchforks on an abandoned patch of land on campus. When a formal composting program was finally established in 2009, Pomona College has composted its food waste at the on-campus organic farm. Rather than using expensive, cutting-edge composting machines, we use the simple pile method and do much of the work by hand. This is how simple we do it.

Compostable food scraps (pre- and post-consumer vegan food waste) are picked up from the dining halls by a student worker and transported to the Pomona College Organic Farm on an electric cart. At the “Farm” these food scraps are layered with mulch, leaves, and other campus green waste in a series of three piles, which can be up to six feet tall, ten feet wide, and fifteen feet long. Older compost is mixed in with fresh scraps to introduce the aerobic microorganisms required for composting to occur. The piles reach temperatures of up to 185 degrees Fahrenheit on their own simply from the microbe activity. A small diesel skip-loader (tractor) is used to turn and aerate the piles as they undergo the composting process, providing much needed oxygen to the organisms. After six to eight weeks, the piles begin to cool down and the finished compost is sifted and used to prepare beds for vegetable and fruit production at the Farm. Some compost is donated to community organizations and used in landscaping around the college.

At this point, you might be thinking that this sounds like a lot of work. Why choose such a smelly, dirty, labor-intensive method over a mechanical composter?

Consider the educational opportunities offered by this method. The vast majority of the composting program is run by students, and the physical work of maintaining the piles offers a valuable opportunity to see natural processes of decomposition and nutrient cycling in action. Observing the steam rise off a freshly turned active pile and sifting compost at various stages of the decomposing process with your hands teaches how microorganisms recycle nutrients in a way unmatched by any classroom lecture. Nutrient cycling (or recycling) is what makes compost so popular in organic farming, that is, returning minerals from green waste to the soil, making nutrients available to future crops. That is sustainability. Students who have worked with the compost program at Pomona College come away with a deeper understanding of what sustainability in agriculture really means thanks to their hands-on application of these principles.

Free-standing compost piles use a fraction of the energy of electric composting machines. Small diesel tractors are highly efficient and can run for months on only a few gallons of fuel. Everything else is manual labor.

Though compost piles have their drawbacks, high labor investment chief among them, it is sustainability in its essential and purest form. Our experience with small-scale, low-technology composting has been positive and iconic, and we suggest that other colleges and universities think twice about the educational and environmental potential of the lowly compost pile.