Compost is the product manufactured through the controlled aerobic, biological decomposition of biodegradable materials.
The product has undergone mesophilic and thermophilic temperatures, which significantly reduces the viability of pathogens and weed seeds (in accordance with EPA 40 CFR 503 standards) and stabilizes the carbon such that it is beneficial to plant growth. Compost is typically used as a soil amendment, but may also contribute plant nutrients. (AAPFCO definition, official 2018) Finished compost is typically screened to reduce its particle size, to improve soil incorporation. (i.e., compost) Municipal composting programs help residents divert organic materials such as food scraps and yard waste from landfills or incinerators, where they can cause environmental problems, and instead turn them into useful products. Using compost in soil has many benefits, including plant health, drought resistance, and improving the soil’s ability to sequester carbon.
What is not commercial composting
Other forms of organics processing will not be covered in this toolkit:
- Backyard composting
- Chip and Grind Mulch
- On-site pre-processing technology and equipment
While composting leaves and food scraps in homeowners’ back yards is good and part of our national composting infrastructure, it will not be addressed here. Communities should continue to promote and support backyard composting efforts, as more educated consumers are more diligent at reducing contamination and buying finished compost. Organics recycling programs supplement backyard composting. Large scale compost facilities often accept more materials than can be composted in a backyard bin like meat, bones, and dairy products. They also make it easier for residents to compost, as not everyone has the time, space, or interest in composting in their backyard.
For more information on backyard composting, visit the USCC’s Home and School Composting web page.
Often times municipalities and parks departments will chip or grind tree branches and stumps. This raw material can be used either as-is to cover the ground or may be used as feedstock in composting operations. The word “mulch” is confusingly used to mean several different things: coarse tree chips that have not been composted, or it has been used to mean the action ofapplying any type of material to cover the ground in a blanket formation. It may help reduce the
confusion if as an industry this “mulch” word is reserved for tree chips, and covering the ground were instead consistently called “topdressing” with a “compost blanket”.
On-site and pre-processing technology is more commonly used in commercial systems than residential. While these technologies are useful to create feedstocks for composting, they do not fully decompose materials. This Target Organics Hub of Resources aims to help municipalities start composting programs at the household level. Some examples of on-site and pre-processing technology include:
● Liquid aerobic digesters (also called aerobic biodigesters or liquifiers): These use mechanical processes, water, and often enzymes or microbes. Liquid aerobic digesters send slurry to the sewer system.
● Dehydrators: These use mechanical and thermal processes to evaporate liquid in the food waste. The output is a dried food waste, which may be used as a soil amendment, but is not compost.
● Composters: These typically require a carbon source such as sawdust. The output described by manufacturers as compost, but it needs time to cure.
● Depackagers: Depackagers are equipment that mechanically separates packaging from food waste, often using water. These aren’t used at a residential setting, but may be used in conjunction with a large organics recycling program, often for commercial waste.
● Anaerobic digesters: Anaerobic digesters use anaerobic microbes to capture methane from organic materials and produce an unfinished digestate. The by-product (digestate) may be able to be composted, but not all commercial composting facilities accept it.