Compost and Composting: The Basics

Chart and diagram on compost and composting
Thermal phases of composting and what this bioprocess implies

What is Compost?

Compost is a type of organic fertilizer that is produced from organic waste, such as food waste, pruning and garden waste, harvest waste, animal manure or pet excrement, among others.

Compost is a material rich in humic substances, which are what give soils a dark color and improve their fertility.

What is composting?

It is a process by which compost is produced. It consists of the transformation of organic waste under aerobic conditions, that is, in the presence of air. This process is carried out by microorganisms such as bacteria and fungi, including yeasts, lactobacilli, actinomyces, and many other bacterias.

During composting, microorganisms decompose and transform organic waste into simpler substances, and then a new formation of substances such as humic substances and other beneficial compounds for the soil and plants growth.

Diagram of the implications of composting

Composting History

The word composting comes from the latin compositus (ppart. componos) which means “to put”, “to put together several things”. Surely, the first composting occurred accidentally when people out of habit piled up food waste, collected fruit scraps or animal manure as a way to get rid of them.

The process itself is a millenary practice associated with the first historical stages of agriculture in Mesopotamia.

Justus von Liebig (1803-1873) was a chemist of German origin, considered one of the first people to study in detail the phenomenon of how organic remains were transformed into compost for plants. His knowledge of organic chemistry allowed him to describe biochemical changes that the residues undergo when they were put together, and then he applied this knowledge in agriculture.

What are the types or techniques of composting?

We can say that the types of composting refer to the technique, the nature and condition of the process itself, referring to the phenomena of how waste is transformed into compost. The different types are:

1. Microbiological composting

It is the composting itself in which the transformation of organic waste is carried out by aerobic microorganisms. Some people speak of cold composting and hot composting to refer to the increase or not of the temperature of the waste mix during the process.

1.a. Thermophilic Composting

It is composting itself, and we could point out that it is traditional composting; also called active composting or hot composting.

In this type of composting, the transformation of waste goes through different temperatures, with four phases, called the thermal phases of composting.

Phase I – Mesophilic Phase 1: It occurs at the beginning of composting when the temperature begins to rise above ambient temperature until reaching 40°C. This phase is also known as the initiation phase.

Phase II – Thermophilic Phase: It is the second phase of the process and begins when the temperature has reached 40°C and could increase to 60°C or 70°C, after reaching a peak it begins to decline.

Phase III – Mesophilic Phase 2: Known as the cooling phase. Starts when the temperature is dropping below 40°C until it reaches room temperature again. Mesophilic phase 2 ends once the composting temperature remains equal to room temperature for at least three consecutive days.

Phase IV – Maturation phase: This phase is very important for the stabilization of the newly formed compounds during composting. The maturation phase begins once the process has reached room temperature and remains the same for at least three consecutive days. This phase can last a long time, but it is recommended that it be at least 30 to 60 days.

Thermal Phases of Composting
Graphic of the Thermal Phases of Composting
The four thermal phases of composting. In phase II, the thermophilic phase, composting can reach different temperatures depending on the type of organic waste, initial additives and/or aeration processes. Some composting processes do not reach high temperatures above 40°C. The mature compost is obtained at the end of the maturation phase, phase IV. [Image designed by Oswaldo Páez]

1.b. Mesophilic Composting

The transformation of the waste occurs under conditions of room temperature or the temperature increases very little and does not exceed 40°C throughout the process. This type of composting is also known as passive composting or cold composting; and it takes longer to generate the compost since the transformation of the waste is slower.

It is commonly used to compost organic waste that does not tend to compact or does not pile up in large quantities, and maintains good aeration.

Passive or cold composting is common to occur when small amounts of waste are composted as in home composting.

2. Vermicomposting

It is composting in which the transformation of organic waste is carried out by earthworms. In the process, the worms feed on organic waste, degrading it into a compost called vermicompost.

On many occasions, for the vermicomposting process it is recommended that the organic waste first go through a precomposting process (semi-decomposed state of the waste), before giving it to the worms. However, worms also crave some fresh organic waste such as fruit and vegetable peelings that are soft, low acid, and of intermediate moisture.

The red worm, of Eurasian origin and scientific name Eisenia foetida, is the most commonly used worm species for vermicomposting in Costa Rica and the world, since it is one of the most efficient, voracious to degrade organic waste and very well adapted to different environmental conditions.

Other earthworms that can be used in vermiculture are: Eisenia andrei, Glossoscolex spp., Dendrobaena veneta, Amynthas ssp., Pheretima ssp., Polypheretima elongata, Perionyx excavatus, Eudrilus eugeniae (Lombriz africana), and Lumbricus rubellus.

3. Larvicomposting

It is composting in which the transformation of organic waste is carried out by insect larvae. The most commonly used larvae are the larvae of the Black Soldier Fly (Hermetia illucens – Diptera), and the larvae of the King Worm beetle (Zophobas morio – Coleoptera). The compost from this bioprocess could be called larvicompost.

As in vermicomposting, there may or may not be a microbiological precomposting of organic waste before providing the waste as food for the larvae. Or, at the end of the degradation of the waste by the larvae, a microbiological maturation process is carried out.

How many types of compost are there?

Although each type of compost should come from a type or a composting technique like the ones we saw in the previous section, the truth is that we can get different names of compost referring to various recipes and modification of composting procedures, as well as do reference to the type of organic waste that originated them, to the person who designed the method or to the type of organism that degrades the waste.

Technically, according to the types of composting, we would have three types of compost:

1. Microbiological compost

Which was formed by a composting process with microorganisms and where there was or not an increase in temperature.

2. Vermicompost

It is the compost from the vermicomposting process, in which the transformation of the waste is carried out by earthworms.

3. Larvicompost

It is the compost from the larvicomposting process, in which the transformation of the waste is carried out by insect larvae.

Which organic fertilizers are not considered compost?

For an organic fertilizer to be considered compost, it must have undergone a complete composting process. So all semi-decomposed organic fertilizers, fermented or not, that have not yet reached a final compost state, should not be called as such and should simply be considered organic fertilizers.

Among the organic fertilizers mistakenly called compost we have:

Bocashi

It is a semi-decomposed fermented organic fertilizer, partially stable and maintains a slow decomposition.

Manure

They are all those herbivorous animal droppings used as compost, either fresh or semi-decomposed. These generally receive the name depending on their origin, for example: chicken manure, swine waste, horse manure, cow dung, and slurry, among others.

How many types of compost bins are there?

The type of compost bin refers to the different types of piles or mounds, devices, class and size of facilities, structures or procedures that allow carrying out some of the types of composting. This means that there are a large number of compost bins with very different names, and sometimes, little or very related to each other.

There is no consensus standard to classify all compost bins. However, each one is named according to its most outstanding functionality or characteristic. For example, a rotating composter will have a device that rotates in order to mix the waste and generate aeration.

The pile or mound compost can be identified as the oldest and most traditional type of compost since it only consists of making a mound with the organic waste, mixed or in layers, it is turned over with the help of a shovel to aerate the mixture and then rebuild the mound or pile.

The vermicompost-bin are also a very particular type of compost bins since they are exclusive when referring to the fact that the composting is done with worms. We have, for example, box or bucket vermicomposters, all of these for a small scale and process a few kilos of waste. When it comes to a greater amount of waste, we can point out the bed-type earthworm bin.

When is the compost ready for use?

From a holistic point of view that includes the greatest environmental and agricultural benefit, the compost should be used when the process is completely finished, that is, when the maturation phase IV reaches its end and the compost already remains mature. In this way, we ensure that the compost compounds have greater stability and produce the greatest benefit in the soil, providing better nutrients for the plants, conditioning the soil more adequately for micro and macro-organisms and fixing carbon in the soil itself for much longer.

From an agronomic point of view, on many occasions the use of compost is recommended before reaching the maturation phase, especially when it is used on adult plants such as grasses, lawns, trees and shrubs or vegetable crops that are already adult. Although, this practice contributes nutrients to the soil for a better growth and development of the plants, the general benefits of the compost diminish, especially those that have to do with a medium and long-term effect such as carbon fixation and permanent increase in humic substances.

Using immature compost could further decrease your benefits in the soil when compost use is infrequent and applied in small amounts.

What are the benefits of composting and compost?

Benefits for the Environment

Organic waste while composting can reduce its emission of greenhouse gases (GHG) by up to 90%, compared to if it undergoes an anaerobic fermentation process that would occur when it is accumulated without any treatment or is buried.

The carbon that the plants have absorbed and then is part of the organic waste, constitutes the main component of the mature compost. Most of this carbon is sequestered in mature compost and becomes part of the carbon in the soil. Thus, we contribute to the decarbonization of the atmosphere and the carbonization of the soil.

Benefits for soils in the agricultural and urban sectors

  • When mature compost is frequently added to the soil, it improves the pH and increases its fertility, improves its permeability and water retention, allowing greater infiltration.
  • It is a source of microorganisms and creates a favorable environment for a more effective interaction in the rhizosphere.
  • The mature compost in the soil also favors the activity of fungi, bacteria and other forms of microflora and microfauna in the soil, increases its genetic diversity and, due to the increase in beneficial soil microorganisms, they counteract pathogens.
  • In addition, it provides mineral nutrients and other substances that stimulate the growth and development of plants.
  • It is an excellent microbiological additive to be used as an initial inoculum (Source) in composting processes; it becomes an ideal inoculum for decomposing microorganisms.

Health benefits

Composting at home and at work can help improve health by reducing stress and increasing physical activity.

Likewise, composting is perceived as a healthy habit that strengthens awareness about environmental care and food waste.

What organic solid waste can we compost?

As a principle we can say that all waste that comes from a living being or is part of a living being can then be composted since it is organic in nature. From the excreta of any animal to the corpses can be composted.

However, some organic waste will be easier to compost and others more difficult. There is organic waste that will have to be composted under certain health and legal standards, and there will be other waste where greater safety care must be taken to reduce the risks of plant pathogens or animal pathogens.

On the other hand, there is waste that we can easily compost without any risk to human or animal health.

Next, I present a table with the most frequent organic solid waste:

SawdustPeels and fruit scrapsLow ink paper
Compostable bagsLegume and vegetable skins and leftoversUsed paper towel
Paper bags and tea bagsAsh and Charcoal - use as additivesCooked Fish and Seafood
Coffee wasteLawn, pruning and yard wasteCompostable plates and cups
Human and animal hairCoffee maker paper filtersPens
Egg cartonGrains and seedsCheese, Kefir and other dairy
Brown cartonsGreen or dried leavesRemains of orchards and crops
EggshellsCooked bonesUsed napkins
Citrus and pineapple peels and remainsOld breadCut nails and hoof debris
Manure:
Herbivorous animal excrement such as chickens, rabbits, goats, sheep, cows, horses and pigs, among others.
Leftover cooked meats and cooked food in general:
Yes they can be composted. Be careful with the amount that is added to the compost bin.
It is recommended to add small amounts per day.
This type of waste requires more attention when composting. Consult a technician.
Raw meat, fish and seafood leftovers, and raw bones:
Yes they can be composted. Be very careful with the amount that is added to the compost bin and give a good management of the composting process.
It is recommended to add small amounts per day.
This type of waste requires more attention when composting. Consult a technician.
Cat and dog droppings:
Yes they can be composted. It is recommended to use a compost bin separate from the other organic waste.
Maintain adequate hygiene and excreta handling care.
The compost produced should not be used in vegetables but it can be used in fruit trees, lawns or ornamental plants. Consult a technician.

What solid waste can we not compost?

All waste that is not organic in nature cannot be composted. Even waste whose composition is a mixture of organic with non-organic cannot be composted either. An example of the latter case are laminated cardboard with a layer of plastic material.

Non-compostable waste:

Aluminum, iron or other metalsSausage, pepperoni, or other sausage casingsWaxed paper
Popcorn BagsExpanded Polystyrene Foam (EPS)Paper with excess ink
Juice or milk boxesChewing gumPaints (waxes), enamels or glues
Tetrabrik boxesNon-compostable biodegradable materialsPlastic of any kind
Cardboard with excess inkMedicinesSynthetic fabrics / Polyester
Scotch tapeDisposable diapersReusable kitchen towels
Cigarette buttsAdhesive paperSanitary towels
Synthetic ropes or ropesAluminum foilWet wipes

General recommendations

  1. Always apply mature compost to the soil.
  2. Do not use immature compost, especially those that have the smell of ammonia or other strange odors.
  3. Use suitable additives at the beginning of composting. A simple additive as a microbial inoculant is the same mature compost.

Note: This article is constantly updated.

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