Composting

Compost is a collection of organic materials such as leaves, twigs, soil, and food scraps among other materials that is turned into fertilizer. Compost has to go through a composting process before it can be useful. This process requires organic material, water, bacteria, and sometimes oxygen.[4] Composting is final once the material is completely broken-down with the help of microorganisms. There are two forms of composting: anaerobic and aerobic.

The Importance of Composting

When organic material is sent to landfills, that could otherwise be composted, it contributes to methane emissions in the atmosphere and takes up land space.[3] Food waste is a major issue and 30-40% of the United States' food supply ends up as waste.[7] Although reducing waste from the start is crucial, compost can be used as a means to combat this issue.

Anaerobic Composting

Anaerobic composting does not require any oxygen. This process is comparable to the breakdown of waste in landfills, however this process emits much less greenhouse gases.[3] Anaerobic composting is also known as cold composting. Cold composting doesn't generate the heat that aerobic composting does.[9] This type of composting can be expensive because of the machinery that is needed to compost correctly. Cold composting needs a closed system so that any methane that is released can be trapped, stored, and later used for energy. This closed container is known as a digester. Although cold composting is more expensive, it requires less maintenance since it does not need to be churned.[3] Cold composting, in return, can take up to 2 years to fully breakdown and decompose.[9] Most municipal waste compost facilities utilize this method of composting.[12],[13] Pathogens can still be left in cold compost since it does not reach high enough temperatures to rid the organic material of pathogens.[9] Pathogens can occur from fungi or bacteria, and common pathogens in compost include Aspergillosis, farmer's lung, tetanus, and E. coli. Aspergillosis is a fungus that can affect the lungs and is found in rotting plants. It is typically not life threatening, but can be if an abundant amount of spores are inhaled. Farmer's lung can occur from bacteria or fungus and has similar symptoms to pneumonia. Tetanus is common in soil bacteria and can affect the central nervous system.[2] E. coli is a bacteria and affects the intestines.[6] To avoid contracting these pathogens, it is important to wear protective gear such as gloves and masks when spinning or working with compost. You should also always wash your hands after working with compost.[2]

Aerobic Composting

Aerobic composting works at a much faster rate and is considered hot compost because of the high temperatures it can reach.[9] This type of composting requires oxygen, and therefore must be spun every few weeks or when new organic material is added. Aerobic composting is much more common for household-use because it is fairly in-expensive. Compost bins can be easily created at home or purchased.[3] With hot composting, it is important that moisture and oxygen level are kept balanced. Hot composting will not easily spread pathogens because they are killed off from the heat. By spinning the mixture and balancing the oxygen and water intake, microbial activity will increase and reach, at minimum, 60° C(140° F)[14].

Making Compost

Compost is very versatile as it can be made with many different organic waste materials, such as food, green, and manure waste. Food waste is most common for at-home-compost and consists of food scraps. Green waste comes from plants and manure-based compost as it’s gathered from animal fecal matter. The carbon to nitrogen ratio is important in making compost. Therefore, it is necessary to alternate between the "browns" and "greens" layers. The browns include dead leaves, soil, and twigs. This layer supplies the carbon needed and the greens layer supplies nitrogen. The greens layer can consist of plant material and food scraps. The layers should be 1:1 to produce the best compost. Increasing the surface area of the organic material, by chopping up or breaking into small pieces, speeds up the decomposition process.[4] Aerobic compost needs to be turned every few weeks or when new material is added as it supplies oxygen. Moisture is also key to a good compost mixture. Moisture creates a livable environment for microorganisms to thrive as water transports material around in the mixture so that it is accessible to microorganisms. If a mixture is too dry, water can be added manually or with rainfall.[14] If the mixture is too wet, spinning or adding more browns can improve it.[4] Meat scraps and animal feces should not be added to at-home compost since it creates pathogens that can not be dealt with by the generated heat and it can also attracts pests.[9]

Types of Compost

Benefits	Disadvantages
Easy to accomplish	Only ideal for small scale waste
	Requires a great deal of time

Onsite Composting

Onsite composting requires little effort and should only be used for small amounts of yard or food waste. It is a longer process than most other types of composting, and it can take a few years to fully decompose. Most onsite composting is anaerobic, but can be aerobic if it is spun.[13]

Vermicomposting

Benefits	Disadvantages
No spinning required	Worms require maintenance
	Only ideal for small-scale waste

Vermicomposting uses worms to break down simple food scraps like food and vegetable scraps, coffee grounds, and tea leaves and tea bags. Food waste that is thick or high in fats and oils is not good for vermicomposting. The composting bin should not be made out of metal because it can get too hot for the worms. Red wiggler worms thrive on this type of compost-soil and are great for vermicomposting.[8] Using a pound of worms can create castings or quality compost when they break down the material. These castings can be used as potting soil or plant fertilizer.

Aerated Windrow Composting

Benefits	Disadvantages
Great for large scale waste	Requires a large amount of land
Animal byproducts can be composted	Requires spinning

This type of composting is typically used by large organizations or local governments because it requires a lot of land space where windrows or rows of organic waste can be turned and aerated. Windrows should be large enough to create enough heat but small enough for oxygen flow (about 4-8 ft. high and 14-16 ft. tall). This is one of the few methods of composting where animal byproducts can be used along with grease.[14]

Aerated Static Composting

Benefits	Disadvantages
Great for large scale waste	Requires expensive equipment
Does not require spinning

Aerated static composting is when organic material, excluding animal byproducts and grease, is piled and layered using bulking agents. Bulking agents such as wood chips and newspaper clippings can help with aeration. More expensive forms of aerated static composting use air blowers or fans for aeration.[14]