Commercial, Farm and Municipality Composting

Composting is the accelerated biological decomposition of organic matter under managed aerobic conditions resulting in a stabilized product that can be used as a soil additive, fertilizer, growth media or other beneficial use (compost).
Composting is the second most preferred method of materials management in EPA’s Waste Management Hierarchy.

Waste Management Hierarchy, Courtesy of the U.S. EPA Source Reduction & Reuse is Most Preferred, followed by Recycling/Compost and then Energy Recovery. Treatment & Disposal is the Least Preferred. This is displayed in an inverted triangle.

Different types of composting

Aerated Static Pile - Process in which decomposing organic material is placed in piles over an air supply system that can be used to supply oxygen and control temperature for the purpose of producing compost. Piles must be insulated to assure that all parts of the decomposing material reach and maintain temperatures at or above 55°C for a minimum of 3 days.

Turned Windrow - Process in which decomposing organic materials are placed in long piles for the purpose of producing compost. The piles are periodically turned or agitated to assure all parts of the decomposing material reach the desired stability.

In-vessel - Process in which decomposing organic material is enclosed in a drum, silo, bin, tunnel, or other container for the purpose of producing compost; and in which temperature, moisture and air-borne emissions are controlled, vectors are excluded and nuisance and odor generation minimized.

Benefits of Composting

There are a number of benefits to compost that not everyone is aware of. Some examples are listed below:

Organic waste in landfills generates methane, a potent greenhouse gas. By composting wasted food and other organics, methane emissions are significantly reduced.
Compost reduces and in some cases eliminates the need for chemical fertilizers.
Compost promotes higher yields of agricultural crops.
Compost can help aid reforestation, wetlands restoration, and habitat revitalization efforts by improving contaminated, compacted, and marginal soils.
Compost can be used to remediate soils contaminated by hazardous waste in a cost effective manner.
Compost can capture and destroy 99.6 percent of industrial volatile organic chemicals (VOCs) in contaminated air.
Compost can provide cost savings over conventional soil, water and air pollution remediation technologies, where applicable.

Science

Ingredients

All composting requires four basic ingredients:
- Browns - This includes materials such as dead leaves, branches, and twigs.
- Greens - This includes materials such as grass clippings, vegetable waste, fruit scraps, and coffee grounds.
- Water – Composting organisms need a moist environment.
- Air – Air circulation in the pile will allow the composting organisms the oxygen they need to live and keep the pile from producing a foul odor.

Parameters

Initial Parameters for Composting (preferred ranges)
- Moisture: 50-60%
- Carbon to Nitrogen: 25:1-40-1
- Oxygen: Greater than 10%
- Temperature: 120-150°F (49-60°C)
- pH: 6.5-8.0
- Particle Size: the preferred range depends on feedstocks and use of compost, but a reasonable range is 1/8-2 inches
- Porosity
  - Bulk Density: 800-1000 lbs/yd³
  - Free Air Space: 50-60%

Compost vs. Mulch

Mulch IS NOT Compost

Compost	Mulch
Organic in nature	Organic or inorganic in nature
Processed to reduce pathogens	Not processed to reduce pathogens
The process often requires a Solid Waste Permit	The process does not require a Solid Waste Permit
“Earthy” smell (usually)	“Woodsy” smell (usually)
Final C:N ratio should be less than 20:1	No ideal C:N ratio, but usually carbon-rich if organic
Applied at 2" or less depth or can be incorporated into soil	Applied at least 2-3" deep and not incorporated into soil
Can be used as mulch	May turn into a carbon-rich compost-like product if organic