Composting explained by Guilford College’s Dining Service

Guilford College Composting (credit)

Guilford College Composting (credit)

Food that doesn’t go through the food Digester is added to the Guilford College composting process. Food waste is combined with a balance of wood chips, leaves, and sawdust all of which is put into Earth Tubs. Earth Tubs speed up decomposition by keeping out rain and wind which can disrupt the composting process. After the compost maintains a certain temperature consistently for a few days, the bad pathogens in the compost have been killed because they can’t survive in the heat .All the good aspects of the compost which make up healthy soil remain in the compost. Once the compost reaches this stage, we move it into what we call a windrow, stage two of the process.

In Depth:
Approximately half of all the food waste generated through dining services is used in on-site composting. The word compost comes from two Latin words: com meaning “to bring” and post meaning “together.” When we bring together nitrogen, protein, carbon, moisture, and air, compost happens. Composting, then, is a controlled effort to manage what occurs naturally during the rotting process of all living matter. Civilizations have been composting for thousands of years. The composting process occurs through the work of billions of microorganism (mostly bacteria) breaking down proteins. Carbon is the energy source for the microbes. They work best with adequate moisture and plenty of oxygen, just like a fire. The bi-product of their activity is heat. As the temperature increases during the process, different types of microbes come into play. These microbes can be classified into three major groups: psychrophiles, that work at lower temperatures, while mesophiles work in warm temperatures, and thermophiles in hot temperatures. All three groups of microorganisms can, and often are, working in the compost pile simultaneously.

The result of these microorganisms efforts in the compost pile is humus. The final product does not in any way resemble the initial components. Humus is rich in organic matter full of helpful microorganisms, it holds moisture and soil nutrients well, and is very beneficial to plant growth and overall health. Humus allows us to replenish the earth with much of what we reap while growing plants.

Guilford uses two Earth Tubs to compost food waste. Food waste is our source of nitrogen. We add sawdust, leaves, and compostable paper products as a carbon source. Leaves are very plentiful on our campus, and our Theater Scene Shop produces sawdust. Also, our dining services purchased compostable food service paper products for most of the catered events across campus. Moisture is controlled by lids on the Earth Tubs and oxygen is encouraged by use of an auger that rotates around the EarthTub stirring its contents. It generally takes about six weeks to produce quality humus using our Earth Tubs.


The idea of a windrow is to take healthy compost that has reached a minimum of 140 degrees from our Earth Tubs, taking about a week, then putting the material into an environment that still allows the compost to thrive while also helping to decompose other carbon products like leaves. A windrow consists of a row of leaves holding actively composting material in the middle and then covered with more leaves. This keeps the compost insulated and hot enough to keep composting at a fast rate but also allows more air to draw into the compost and help feed it like a fire. Because of this set up, the leaves around the compost will begin to rapidly decompose and produce humus. By adding the humus produced by the EarthTubs into a larger carbon source, we are able to generate a large quantity of humus by having the EarthTub material rapidly breakdown the leaves added to the windrow. After sifting the humus for large particles such as wood chips, the humus is ready for use. Our humus is used in Guilford’s farming operations to enrich the soil. It is also used during our turf renovations as a top-dressing. The result is healthier grass and trees all over our campus with a significantly reduced carbon footprint. [Guilford Dining]