Basic concept 1 © 2019 Koji Takakura 3.

Chapter 3 Composting technology – Basic concept

1 © 2019 Koji Takakura

3. Composting technology – Basic concept

3.1 History of composting

Humans have applied composting to plant culture, over a long history. However, composting in the ancient

times was only a result of natural composting of organic substances, or an attempt by humans based on the

rule of thumb as they observed the natural phenomena. It was Albert Howard who systematically organized

these experiences as a composting technology. Howard dedicated himself to a study on composting in the

Indore region of India between 1924 and 1934, and summarized the composting technology he has

developed under the title “Indore-style composting method.” The Indore-style composting method has been

appraised highly as the origin and the fundamental law of composting.

In Japan, composting started when the division of internal affairs of the Kanagawa Prefectural government

published in 1920 a booklet titled “Taihi no Susume (Everyone is Advised to Try Composting).” The

contents of the booklet are deemed appropriate even today, and raw garbage was gathering attention as a

source material of composting at the time already.

The booklet states as follows in one of its sections.

“Raw garbage generated in a large volume in cities is a good material for composting. These days, however,

people in cities are having trouble disposing of raw garbage, and have reluctantly landfilled these wastes. It

is truly regretful that the precious materials for composting are being buried in the ground. Thus, farming

families near cities are recommended to form an association for collecting raw garbage in cities and use it

for producing composts.”

Raw garbage composting has been an issue, in the past and in recent years alike.

3.2 Basic concept of composting

“Composting” is explained in many cases as “having organic components of wastes fermented by

microorganisms under an aerobic condition.” However, technologies that use life forms other than

microorganisms for composting, such as earthworm composting, have also disseminated widely. Taking

into consideration also the notable effects of composting, namely “improvement of physical properties

(ease of draining, air permeation, water retention as soil crumbs are formed), chemical properties (nutrient

supply and retention, buffer capacity to hazardous substances and pH) and biological properties (prevention

of diseases in soil, extraction of useful bacteria) of the soil,” the basic concept of composting may be

represented as follows.

“Composting is to convert organic substances into a soil improvement material that yields components for

helping plants grow and promotes soil crumb formation, through aerobic fermentation by microorganisms

and dietary effects brought about by life forms in the soil.”

Here, the working of microorganisms is represented as “fermentation,” for the reasons described below.



*1: The compost may be used after mixing with the soil and humus and going through aerobic

fermentation as the secondary processing, or fermented aerobically in the soil when applied

directly as a fertilizer without the secondary processing.

*2: Insects used include larvae of house flies (already in practical application) and larvae of soldier

flies.

Fig. 3-1: Raw garbage composting methods

3.2.1 Composting process involves “fermentation”

The decomposition process by microorganisms may be divided broadly into “fermentation” and “decaying,”

but how are they differentiated? Microorganisms discharge diverse substances as metabolites while

decomposing organic substances. For microorganisms, however, the process is nothing but a metabolic

activity using organic substances. On the other hand, humans distinguish the metabolites into “useful and

good ones” and “harmful and bad ones,” which have been named “fermentation” and “decaying”

respectively. What is more, the distinction is being made based on preference of each person.

Let us take “natto” as an example.

Natto is one of the fermented foods that

has traditionally been incorporated in

the dietary life of Japanese people.

However, many people feel that natto

has “decayed,” because of its peculiar

odor reminding of ammonia. Food

materials form threads in many cases

when decayed, and some people,

especially those from abroad, judges

that natto has “decayed” because of the

“odor” and the “forming of threads.”

Raw garbage

composting

Utilizing

microorganisms

Utilizing life forms

Aerobic fermentation

Anaerobic fermentation*1

Earthworm composting

Utilizing insect larvae*2

Looks good.

It’s fermenting!

It stinks and has

decayed.

Each person feels differently about an odor, and some think the

substance is fermenting while others think it is decaying.

Fig. 3-2: Each person feels differently about odor



The “odor” generated from metabolic activities of microorganisms relates delicately with fermentation and

decaying in the composting process, and is related deeply with the types of microorganisms used in

composting, as explained later.

Let us now take a look at composting. Compost is a product made through metabolic activities of

microorganisms, and brings about common benefits for humans, such as helping plants grow. When viewed

this way, it seems more appropriate to think of composting as a “fermentation” process, rather than just

“decomposition.” The term “fermentation” is used hereinafter for representing the composting process, but

the term “decomposition” is also used from time to time. However, please keep in mind that the term

“decomposition” also refers to “fermentation.”

3.3 Basic process flow of composting

The basic process flow of composting may be divided into three steps, namely “pre-treatment,”

“fermentation” and “preparation as a compost product.”

3.3.1 Pre-treatment process

(1) Removing foreign matters

Raw garbage is usually discharged, collected and transported in mixture with other types of wastes. As such,

the mixing ratio of foreign matters is high, and mechanical or manual foreign matter removal process is

necessary as a pre-treatment. However, the removal ratio would be limited naturally if foreign matters were

removed from a mixture of wastes, leading to incomplete removal of foreign matters and decline in the

quality of compost products.

Photograph 3-1: Removing foreign matters

mechanically and manually

Photograph 3-2: Only metals are removed in

magnetic sorting

Looking at the situation from an opposite angle, a method was adopted in some cases that only raw garbage

that may be composted was sorted and collected from the mixture of wastes. This led to production of

compost with extremely small mixing ratio of foreign matters that were evaluated highly. In any case, it is

inefficient to extract the targeted waste from mixture of wastes. Therefore, it is essential to establish a

system in which “raw garbage is sorted and stored” at the source of wastes and “only the raw garbage is

collected using exclusive vehicles” for transportation.



Photograph 3-3: Only raw garbage is picked

up from mixture of wastes

Photograph 3-4: Raw garbage is sorted at the

source of wastes and collected by an

exclusive vehicle

(2) Limitation of mechanical foreign matters removal

A large volume of raw garbage is generated in urban areas, where a large-scale composting plant is built for

composting the raw garbage, in many cases. It is desirable if the raw garbage was sorted and collected, but

in reality, this is extremely difficult and mechanical sorting of waste mixture is adopted in many cases.

However, there is a limitation in the accuracy of sorting, and the accuracy affects the quality of compost

produced.

Here, let us look at the foreign matter removal process assuming that a large-scale composting plant

operated by the conventionally adopted method is built next to a landfill disposal site, for simulating the

process flow of composting.

Processing capacity assumed: 1,000 ton/day of mixed waste

Sorting method: bag tearing process manual sorting trommel sieving machine (sieve

mesh of 70 mm) specific gravity separating apparatus (for removing

sand, glass and metals) (a magnetic sorting apparatus is used in some

cases) vibration sieving machine (sieve mesh of 7 mm)

Fermentation method: indoor aeration standing fermentation method

Shipment mode: packaged in plastic bags

[1] Reception of mixed waste

A part of or the whole of the mixed wastes carried into the landfill disposal site is to be composted, and is

carried into the composting material storage yard (indoor or outdoor) and stored for a while. The raw

garbage is decomposed while decaying, and generates odor and wastewater. If the waste was stored for a

long time, decaying and decomposition of the raw garbage progresses, lowering the ratio of raw garbage in

the mixed waste that is to be processed in the next step for foreign matter removal. One might erroneously

imagine that filthy and odorous plastic bags are being handled.



Photograph 3-5: Temporary storage of mixed

waste (outdoor)

Photograph 3-6: Temporary storage of mixed

waste (indoor)

[2] Removal of foreign matters

Plastics might get finely broken if mixed using a heavy machine or by an influence of ultraviolet rays.

Plastic bags containing mixed waste go through a bag tearing process, have foreign matters removed and

recyclable wastes collected on a manual sorting line, and processed by a huge trommel sieving machine

(with a sieve mesh of 70 mm, for example) for removing large foreign matters.

A method that cuts (tears) the bags with a blade is usually adopted for the bag tearing process, but there is

also a method that places the plastic bags on a belt conveyor and has the bags come in contact with a

heating wire, for having them dissolved with heat. Either way, bags that were not completely torn are

removed by the sieve.

Photograph 3-7: Bag tearing and manual

sorting line

Photograph 3-8: Collecting recyclable wastes



Photograph 3-9: Old wastes in the red frame

and new wastes in the yellow frame

Photograph 3-10: Huge trommel sieving

machine

[3] Fermentation of raw garbage

After removing foreign matters, the raw garbage is carried indoor for conducting standing fermentation

while adjusting the moisture content, controlling the temperature, and performing aeration. The

fermentation product contains a large amount of foreign matters. Especially to note is that a plastic bag

piece that measures 70 mm or more would pass through the sieve mesh of 70 mm, if pressed with force.

Photograph 3-11: Indoor standing

fermentation

Photograph 3-12: Fermentation product

contains many foreign matters

[4] Removal of foreign matters

After fermenting for the set duration of time, the fermentation product is thrown into a vibration sieving

machine (with a sieve mesh of 7 mm, for example) for removing small foreign matters. Organic matters

such as raw garbage have turned into dark brown to black color, on which white foreign matters such as

plastics stand out.



Photograph 3-13: Fermentation product

becomes brownish to blackish in color

Photograph 3-14: Vibration sieving machine

removes small foreign matters

[5] Storage of compost

After sieving, the compost waits to be shipped in a storage yard. The compost produced inevitably contains

foreign matters (mainly plastics) that have passed through the 7-mm sieve mesh.

Photograph 3-15: Compost product waits to

be shipped in a storage yard

Photograph 3-16: Whitish particles are

foreign matters that passed through the 7-mm

sieve, mainly plastics

[6] Preparing the compost for shipment

The compost product is either “pulverized,” “pelletized” or “packaged in a bag” for shipment, to suit the

customers’ needs.



Photograph 3-17: Compost is sometimes

“pelletized” to suit the customers’ needs

Photograph 3-18: Packaged compost is being

shipped

Plastics become finely broken down as time goes by, and inevitably pass through the sieve mesh and get

mixed into the compost product. Wind sorting could be performed prior to fermentation, but plastics that

cannot be wind-sorted remain, depending on the moisture content, material form, etc. If wind sorting was

performed after fermentation, the compost is also blown away with the wind, causing the product loss to

increase.

It is difficult to completely remove foreign matters from the mixed wastes, especially plastics, regardless of

whether manual or mechanical sorting was performed. It is important to promote sorting at the place of

origin of wastes, in order to produce compost with a small mixing ratio of foreign matters.

3.3.2 Fermentation process

The fermentation process is the most important process that determines the product quality, and is usually

divided into the primary fermentation and secondary fermentation (maturing) steps.

Primary fermentation: easily decomposed organic substances are mainly decomposed rapidly,

generating a large amount of fermentation heat that raises the temperature.

Secondary fermentation (maturing): decomposition and decaying of easily decomposed organic

substances progress and the process stabilizes.

Basically, the air is supplied as appropriate to realize aerobic fermentation, and water is also added if

deficient, for adjusting the moisture content. At this time point, seed compost (made by culturing

microorganisms) and auxiliary materials (rice hull, sawdust, etc.) are added for leading to satisfactory

fermentation under the desirable conditions, which may be realized by adding appropriate microorganisms,

promoting ventilation through the raw materials, adjusting the moisture content and pH, etc.

It would be costly if new seed compost was prepared each time to be added. Since the compost after

completion of the secondary fermentation also contains a large amount of high-quality fermentation

microorganisms, a part of it is used as the seed compost for reducing the costs. Such seed compost is

referred to as returned compost. Also, opportunities are sought for obtaining the auxiliary materials at a low

cost, for example, by obtaining those generated as wastes in the neighborhood.



(1) Concept of returned compost

Composting is done after mixing the seed compost into organic wastes, but not all of the mixture is shipped

as a compost product. Since the seed compost is added for promoting satisfactory composting of organic

wastes, it is collected and used repeatedly. Since the product of secondary fermentation is returned to the

primary fermentation process, it is referred to as returned compost.

Since organic wastes that have been input are composted as they are decomposed by microorganisms, the

decomposition ratio of organic substances in the waste may be clarified for each type of organic wastes.

Therefore, the composting ratio (amount of compost produced/amount of organic wastes input × 100) may

be estimated.

Example 1: Calculation of the amount of compost that may be produced from 1 ton of raw

garbage

Conditions: moisture content of the raw garbage: 80%; decomposition ratio of the raw

garbage: 75%; moisture content of the compost product: 50%

1 ton × (1 - 0.8) × (1 - 0.75) / 0.6 = 0.1 tons (Composting ratio: 10%)

0.1 tons of compost product is derived from the mixture of seed compost and raw garbage compost.

Fig. 3-3: Concept of returned compost

1 ton of raw garbage is

input into seed compost Mixture of seed compost

and raw garbage compost

Shipped as a compost

product: 0.1 tons

Since a part of the seed compost may

be lost, auxiliary materials are added

for increasing the volume

Re-used as returned compost



The table below shows examples of decomposition ratio of composting raw materials. Using the figures as

a reference, an approximate amount of compost that may be taken out as a compost product may be

calculated.

Table 3-1: Decomposition ratio of compost raw materials (examples)

Raw materials Raw

garbage

Sludge in a

septic tank

Cattle

manure

Poultry

manure

Porcine

manure

Rice

hull Sawdust

Rice

straw

Decomposition

ratio (%) 75 30 40 35 35 10 5 30

3.3.3 Product preparation process

This is the process for preparing the fermented compost as a commercial product. The compost is sieved

for removing foreign matters, for finishing it as a product. Then, processes such as sieving for collecting

particles of the specified sizes, granulation, and packaging are performed for making the product

convenient for storage prior to shipment, stockpiling, transport, and use.

Not all the compost sieved for removing foreign matters is made into products, but instead, the seed

compost that was added for promoting satisfactory fermentation is collected as returned compost.

A big chunk of materials removed by sieving is returned as a raw material, as it could function as the

returned compost also. However, if materials that remained on the sieve were used as the returned compost,

foreign matters are also returned at the same time. As such, foreign matters on the sieve become

concentrated as time goes by. For this reason, materials that are judged to contain a large amount of foreign

matters are discarded.

The diagram below illustrates the basic processes of composting discussed so far.

Fig. 3-4: Basic processes of composting

Returned compost

Organic waste Pre-treatment Fermentation Preparation as

products

Removal of foreign

matters

Compost product

Discarded materials

that are unfit for

composting



References:

Koji Takakura: Kaigai Gijutu Kyoryoku wo Tsuujita Takakura-shiki Konposuto no Gijutsu Iten ni

Kansuru Kenkyu (A Study on Technical Transfer for Takakura Composting Method through Overseas

Technological Cooperation), doctoral thesis, Graduate School of Life Science and Systems Engineering,

Kyushu Institute of Technology, May 2016

Institute for Global Environmental Strategies: Nama Gomi Konposutotte Sugoi! (Raw Garbage

Composting is Great!), 2013

Institute for Global Environmental Strategies: Composting for Waste Reduction; INFORMATION KIT,

2010

Minami-Boso City Government: III. Taihi no Seizo Hoho (III. Compost Production Method)

Kanagawa Prefectural Government: Taihi no Susume, Taisho Jidai no Taihi no Tsukurikata (Everyone is

Advised to Try Composting – Production Method of Compost during the Taisho Era)

Basic concept 1 © 2019 Koji Takakura 3.

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