Decomposition is an important part of the cycle of life! When organic material breaks down, important nutrients including carbon, nitrogen, and phosphorus are returned to the soil to be used by growing plants in the future. When food waste goes to a landfill, it’s sealed off from the rest of the environment and can’t decompose into usable soil like it does in nature. Phosphorus and many micro-nutrients are limited resources, and are quickly being depleted. Composting is a natural solution to this problem!
When food waste breaks down when exposed to oxygen in the air, the hydrogen and carbon bonds break, releasing energy for the decomposers, as well as a little heat, and the atoms are released mostly as carbon dioxide gas and water (since the C and H bonds with the oxygen). In a landfill, no oxygen is available, so anaerobic (meaning non-oxygen breathing) organisms break down the food waste and release CH4, or “methane”. Methane is highly flammable and an extremely potent greenhouse gas that can be very dangerous when it builds up in a landfill. If all food waste was composted, methane buildup would be a far less serious and costly issue.
The most important elements to consider in composting are carbon and nitrogen. A simple way to look at your compost is a mix of “green” and “brown” compost. This isn’t directly a measure of color, but more a measure of hydration. Freshly tossed food waste is “green.” It’s still strong and full of water, and will break down much slower than “brown” waste. “Brown” waste is old, dry, and falling apart. Usually brown leaves and other soft (not sticks) yard waste are considered the ideal brown waste. “Green” waste is much higher in nitrogen than “brown” waste, and a proper combination of the two leads to a healthy balance of carbon to nitrogen (The C:N ratio). The ideal C:N ratio is roughly 30:1. This balancing act can be very complicated, but a simple rule of thumb could be roughly half “brown” and half “green” waste, erring towards more “brown” material when in doubt.
As the microbes break down the compost, heat will build up, and water will be lost. It’s important to keep rotating the compost in order to release some of the heat and to get oxygen to all the material. The ideal temperature for the reaction is around 120-140 degrees F, and rotating helps regulate that. It’s also important to keep the compost damp, around the consistency of a wet sponge, both to regulate temperature, and to prevent drying out and slowing the reaction.
There are alternatives to simply traditional composting that can supplement the early stages of composting, which can be quite slow. Anaerobic composting in a controlled environment can actually help create a more concentrated material that can be moved to a traditional compost pile. Bokashi bran is a common medium for anaerobic bacteria that can break down food waste quickly in an air-tight container. Red worms can also be used to speed up the breakdown of food waste to be moved to a compost pile, in a process called “vermicomposting.” These techniques are discussed under the “advanced techniques” tab.
Helpful links for further learning
Chemistry of Composting:
- http://compost.css.cornell.edu/chemistry.html
- https://web.extension.illinois.edu/homecompost/science.cfm
Nutrient cycles:
Cincinnati At-Home Composting 