Trash Talk #10: The Dirt on Composting
Everything we consume either returns to the earth as food or as poison.
Composting refers to a microbial process that converts plant materials, such as vegetable trimmings or grass clippings, into a more usable soil amendment. Gardeners have used compost for centuries to increase organic matter in soil and supply essential nutrients for plant growth. In fact, compost has so many benefits for a garden that it is often referred to as “black gold”!
Types of Composting
There are two main categories of composting: Aerobic (requires oxygen) and Anaerobic (does not require oxygen). In both cases, microorganisms break down organic material.
Another third category of composting, Vermicomposting, is technically aerobic as well, but depends on special species of worms rather than microorganisms. Below, we’ll break down all three types.
1. Aerobic Composting
Aerobic composting requires inputs of air, water, and nutrients (aka food/plant scraps), and it releases outputs of carbon dioxide, ammonium, and heat as the microorganisms digest the material. In order to break down properly, the ideal mix of food/plant scraps would strike the right balance of “green” and “brown” materials — aka the right balance of nitrogen and carbon:
- “Greens” are high in nitrogen — for example, kitchen scraps, yard trimmings, plant leaves. Typically this means things that are “fresh.”
- “Browns” are high in carbon — such as dead leaves, untreated wood chips, and paper.
Each of the molecular components has a role to play:
- “Oxygen oxidizes the carbon, which sparks the process.
- Carbon produces the energy and heat needed.
- Nitrogen encourages the growth and reproduction of microorganisms.
- Water maintains the microbes needed to decompose.”
Aerobic composting works quickly but requires active management through regular aeration and watering. The majority of small-scale composting is aerobic, but aerobic composting is also suitable for large-scale operations. It is an accommodating option though, as it can vary from something as small as a compost box in a living room to a setup as large as windrows on a farm.
2. Anaerobic Composting
In anaerobic composting, food waste is put into an oxygen-free environment. In these digesters, microorganisms break down material to a pre-compost state (called digestate) and release biogas, a mixture of methane and carbon dioxide. The digestate is a sludge-like, highly acidic material that then needs to be “finished” off by aerobic composting before it can be used.
Because of its longer timeline and tendency to be accompanied by strong odors, anaerobic composting is typically used only in large industrial or municipal operations. Additionally, industrial operations can capture the output methane to use as a source of energy (otherwise, it releases into the atmosphere and has a 20x effect on trapping atmospheric heat compared to CO2).
The benefit of anaerobic composting is that it can not only process plant-based food waste, but also meat, bones, and dairy, all of which are not recommended in aerobic composting.
3. Vermicomposting
Vermicomposting leverages a unique kind of worm, called “Red Wigglers”. These worms live in “worm bins” and feed on organic matter, turning it into a high quality compost called worm castings.
Worm bins are easy to construct or are also easily available for purchase online. “One pound of mature worms (approximately 800–1,000 worms) can eat up to half a pound of organic material per day. The bins can be sized to match the volume of food scraps that will be turned into castings.” Many home composters find vermicomposting an attractive option for at-home use due to their ease of maintenance, low-odor, and fun “science project” appeal.
Lastly, a Mythbuster:
A common misconception around food waste is that because it is biodegradable, it will eventually decompose in landfills. However, now that you know a little more about how composting works, you’ll realize that organic materials can only break down in landfills anaerobically due to how tightly packed the conditions are. Any biodegradation that takes place does so very slowly, and leads to the release of methane. As mentioned above, methane induces even more intense heat trapping effects than carbon dioxide.
By diverting your food waste from landfills, either by setting up home composting options or seeking out composting options in your community, you can greatly and easily reduce your greenhouse gas footprint.
