Classification of Composting Systems: A Proposal

Classification of Composting Systems
Classification of Composting Systems according to different characteristics.

Composting is a versatile process that can be easily adapted to different conditions to achieve the same result from organic solid waste: Compost. Thus, a composting system can be done very easily or a little more laborious depending on the availability of resources and preferences.

For the composting process, apart from the initial organic waste, what is strictly necessary is an air containing oxygen, aerobic microorganisms and humidity. From there, any system that provides a minimum interaction between these factors will be able to support this bioprocess successfully or not so much.

In this way, composting systems have acquired enormous diversity depending on the convenience in which they must be carried out, from the amount of waste and automation, to the place where they are carried out.

Why classify

As by natural instinct, people tend to order almost anything, either by types, classes or groups, even putting names is a beginning of ordering.

Although there may be many philosophical reflections on why classify and order, order comes before chaos; therefore, an intervention is necessary. The classifications allow ordering and make us have more knowledge, making it easier to interpret what is classified.

Composting Systems Classifications

The following classification proposal is based mainly on common sense, looking for a reasonable way to understand the bioprocess that is composting. It has excerpts from previous classifications made by other authors as systems or types of composting, but supplemented here and with certain modifications.

Classification proposal

1. According to the Exposure

It refers to the type of disposal, the exposure or non-exposure to the outside air of the waste where it is confined for the process. Other authors name it according to its structure.

a. Open → when organic waste are outdoors or indoors.
b. Closed → when organic wastes are inside a container, reactor or any type of completely closed structure.
c. Covered → when organic wastes are covered by some type of material that serves to keep it warm.

2. According to the Movement

It refers to the dynamics of movement or absence of it during the composting process.

a. Static → when the waste is not turned, mixed or agitated during the process.
b. Dynamic → when the waste, by different forms of movements, whether manual, mechanical or automatic, is turned, mixed or shaken periodically or frequently.

3. According to the Aeration

It refers to the way in which air flow is provided or allowed to the waste mass during the process.

a. By turning → when by some manual or mechanical procedure the waste is turned, mixed or shaken to aerate it.
b. Forced → when the waste, being static, air is injected into the composting mass; or when air is sucked into the compost mass and new air enters due to differences in gradient.
c. Passive → when vertical or horizontal “chimney” type devices are used so that gas exchange occurs spontaneously, by convection. Also, when composting in thin layers of waste or these are placed in such a way that aeration is voluntary.

4. According to the place or origin

It refers to the place where the composting process takes place. Also, it can take the name of where the waste comes from.

a. Domestic → when composting takes place at home; or when it takes place in the workplace and the amount of composted waste is small, similar to that of an average family.
b. Community → when the composting unit is located in a certain community to carry out the process of waste generated by that community.
c. Urban → when composting is carried out with waste generated in residential, commercial and industrial sectors.
d. Agricultural → when composting is carried out in the agricultural productive sector; or when the waste comes exclusively from that sector. Some authors call it agrocomposting.
e. Agro-industrial → when composting is carried out in the agro-industrial sector; or when the waste comes exclusively from that sector.

Infographic of the classification of Composting Systems
Classification of Composting Systems according to different characteristics under which this bioprocess is carried out.

5. According to the Orientation

It refers to the spatial orientation of the mass of waste that is being composted and/or the flow that it carries.

a. Horizontal → when the waste mass or the process itself has horizontal orientation and/or flow.
b. Vertical → when the waste mass or the process itself has vertical orientation and/or flow.
c. Inclined → when the waste mass or the process itself has an inclined orientation and/or flow.
d. Mixed → when the waste mass or the process itself has a combination of two or more of the above orientations.

6. According to the Filling

It refers to the time limit or number of times that waste is incorporated into the composting process.

a. Just one time → when the waste is incorporated only at the beginning of the process.
b. Continuous → when the incorporation is unlimited in time, that is, input waste can be placed in the same composting process indefinitely at different times. In general, in this type of system there is a continuous output of compost, an unlimited compost harvest is carried out as long as the input of waste is also unlimited.
c. Limited → when the incorporation (Entry) of waste is carried out at different times, but they have a capacity limit to complete a maximum quantity depending on the dimensions of the system.

7. According to the autonomy

It refers to the degree of autonomy or manuality during one or more phases of the process. Likewise, it refers to autonomy in decision-making to carry out work during the process.

a. Manual → when the whole process is carried out entirely with the hands or with tools where the motor force comes directly from the physical work of a human being or an animal.
b. Mechanical → when the entire process or most of it is executed by mechanical forces where the force comes from a machine.
c. Mixed → when during the composting process there is a balanced combination between a manual and a mechanical process.
d. Automatic → when the entire process or most of it is activated and executed by mechanical forces where the force comes from a machine or devices supported by a previous programming and subject to measurement of variables from the composting process itself.
e. Semi-automatic → when during the composting process there is a significant automatic part, and the rest of the parts of the process are manual, mechanical or both.

8. According to the Biology

It refers to the type of organism in charge of the transformation of the waste.

a. Microbiological → when biotransformation, from the beginning to the end of the process, is carried out by aerobic microorganisms (fungi and bacteria).
b. Vermicomposting → when the biotransformation, from the beginning to the end of the process, is carried out by earthworms.
c. Larvicomposting → when biotransformation, from the beginning to the end of the process, is carried out by insect larvae.
d. Combined → when the composting process is carried out by a combination of two or more of the aforementioned ways, either at the beginning or at the end of composting.

9. According to the temperature

It refers to the increase in temperature and maximum temperature reached during the composting process.

a. Mesophilic → when the temperature of the waste mass during the composting process does not reach or exceed 40°C. Other authors call mesophilic composting as passive composting or cold composting.
b. Thermophilic → when the temperature of the waste mass during the composting process exceeds 40°C, and the maximum temperature can be above 60°C. Other authors call thermophilic composting as active composting or hot composting.

10. According to the Size

It refers to the maximum amount of waste that is generated and can be composted at a given time within the same composting unit, be the unit a defined space, a structure or a device.

Although this section refers to the amount of organic waste generated either by a person, by a single family or by a community, the classification according to size can also be applied to agricultural, livestock, commercial or agro-industrial composting systems.

Perhaps, the classification by size of a composting system is the most ambiguous part of this classification, and can accept multiple interpretations and generate several doubts.

a. Small → when the amount of waste is small enough with a minimum such that it can be composted; or when the amount of waste is the amount of organic waste that an average person or family can generate daily, and this amount can be composted in the same composting unit. Example, 0.1 kg to 2 kg per day.
b. Medium → when the amount of waste exceeds the amount of organic waste generated daily by an average family, and said waste can be composted in units that include several families. Example, greater than 2 kg and less than 50 kg per day.
c. Large → when the amount of waste exceeds the amount of organic waste generated daily by several families and already belongs to one or more communities. Example, greater than 50 kg and less than 1,000 kg per day
d. Industrial → when the amount of waste generated and composted is greater than 1,000 kg per day.

Graphical representation of the size of composting systems
Classification of composting systems according to their size, in number of kilograms of organic solid waste generated and/or composted daily.

Composting machines size according to the market classification of composting machinery in the home, commercial and industrial sectors.

Machines of:
0 to 50 kg/day
51 to 100 kg/day
101 to 300 kg/day
301 to 500 kg/day
501 to 1,000 kg/day
greater than 1,000 kg/day

Composting system size based on the best indicator of organic waste generated and composted over time:

Sizekg/daykg/weekt/montht/year
Small< 2< 15< 15< 1
Medium>2 to <50>15 to <500>0.1 to <6>1 to <12
Big>50 to <1,000>500 to <5,000>6 to <50>12 to <200
Industrial>1,000>5,000>50>200

kg: Kilogram
t: Ton

11. According to other terms

It refers to the appointment of composting systems based on some particular conditions.

a. Composting in situ → when composting is carried out in the same place where the waste originates, such as a home, a job, a farm, an agribusiness, an educational center, a restaurant, a shopping center, etc.
ex situ, when composting takes place outside the unit where the waste originates.
b. Collective composting → when composting is carried out by several people who belong to the different units that generate the composted waste.
c. Commercial composting → when the compost is marketed as a product for sale.
d. Monocomposting → when composting only one type of organic waste. In this case, municipal waste such as food waste is considered a single type of waste.
e. Co-composting → when two or more different types of waste are composted. Some authors subdivide them into:
i. Binary → when only two types of organic waste are composted; for example, chicken manure and pruning remains.
ii. Tertiary → when three types of organic waste are composted; for example, chicken manure, pruning debris and sawdust.
iii. Combined → when multiple types of waste are composted at the same time.
f. Precomposting → when organic waste, at the beginning of the process, undergoes a partial transformation by microorganisms. Subsequently, these pre-composted waste can have different uses; for example, food from other organisms such as earthworms or insect larvae.

Final thoughts

This classification of composting systems can have multiple uses. It can be used to analyze the rapid evolution that composting is having in Costa Rica or any other country, study its present situation and see new trends.

Additionally, this may help in formal and informal education. Also, it may have scope and be a support for the formulation of norms, rules, laws, regulations, guidelines and decision-making.

The classification proposed here is not a fixed and immovable classification, but is presented as a baseline that can receive changes and suggestions. It will be moved by the new challenges in the management of organic waste and by the ingenuity of the innovators and curious to put into practice challenging composting systems.

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