While composting can be used as a blanket term, there are several methods that are best for certain environments. For example, an at-home compost bin and one that serves an entire community are not going to look or function the same.
There are five main traits that must be “controlled” in any kind of composting system, similar to a science experiment. These include the following:
1. Feedstock and nutrient balance
As mentioned in the previous blog post (link), composing requires a balance of green and brown organic materials, which ensures equilibrium between carbon and nitrogen rich substances.
2. Particle size
Grinding, clipping, and shredding compost materials increases the usable surface area on which microorganisms can feed, which helps to produce a more homogeneous mixture. However, if the particles are too small, this can prevent air from flowing freely through the pile.
3. Moisture content
Having water in the pile is essential, as the microorganisms require a moist environment to survive. This can be derived from the materials, but often requires additional water through rainfall or intentional watering.
4. Oxygen flow
Having a consistent air flow can help decomposition occur at a faster rate. However, there should not be excess air, as this can dry out the moisture that is also necessary for healthy organic decomposition.
5. Temperature
Microbial activity within the compost pile can increase the core temperature to at least 140 F. Without this, anaerobic decomposition (i.e.. rotting) can occur. By controlling the other four areas, optimal temperature is usually achieved.
Going beyond these basics, there are more specific titles for different kinds of composting: onsite composting, vermicomposting, aerated windrow composting, aerated static pile composting, and in-vessel composting.
Onsite Composting can be utilized by organizations and groups that generate small amounts of wasted food and/or yard trimmings, greatly reducing the cumulative amount of waste. However, animal products and larger quantities of food cannot be used for onsite composting.
Vermicomposting is a bin of red worms that live in bins and feed on discarded food scraps, yard trimmings, and other organic matter. The worms break this material down into castings, a kind of high quality compost.
Worm bins are easy to put together and can be purchased, making it ideal for those in smaller living spaces. One pound of mature worms can eat up a pound of organic matter in a given day. Typically, it takes 3-4 months for the worms to produce usable castings that can be used as soil. Another valuable byproduct of vermicomposting is “worm tea”, a high-quality liquid fertilizer for houseplants and/or gardens.
Aerated windrow composting is suitable for compost generated by entire communities and/or collected by local governments and high volume food-processing businesses. This yields significant amounts of composting.
The process entails forming organic waste into rows of long piles called “windrows” and aerating them periodically by turning the piles manually or mechanically. The “ideal pile height” is between four and eight feet, and is about 14-16 feet in width, giving it the size to generate adequate heat, while still allowing oxygen flow to its core. As mentioned at the beginning of this article, a balance of the correct temperature and oxygen flow is necessary in successful composting. A larger variety of wastes can be composted through this method.
In-vessel composting is best suited for schools or restaurants, as it can process large amounts of waste without occupying too much space. This can accommodate most varieties of organic waste, including meat and biosolids. By the in-vessel composting method, organic materials are fed into a controlled environment which regulates extremities such as temperature and airflow. The material is then turned and mixed to aerate, producing compost in as little as a few weeks. However, it cannot be used for a few weeks/months, as the microbial activity needs to balance and cool.
Let us know in the comments which composting method you are most familiar with, and which you learned more about through this article!