Chapter 4 Basic theories of composting technology – Important items
4.

Basic theories of composting technology – Important items

Here, the mechanism of composting that utilizes activities of microorganisms is explained.
An environment that facilitates activities of microorganisms needs to be established for composting, andthis involves numerous items such as “oxygen,” “moisture content,” “temperature,” “pH,” “carbon-nitrogenratio (C/N),” “aeration volume,” “cutback frequency,” “form (size) of raw materials,” “void ratio,” “volume
weight (specific gravity),” and “fermentation process.”
The most important matters when composting is attempted are “to suppress generation of odors” and“produce the compost in the shortest period possible.” If we focused on realizing smooth fermentation forcomposting while preventing decaying, not all of the items mentioned above need to be managed equally.
We can concentrate our efforts on three points, namely “microorganisms,” “oxygen” and “moisture
content.”
Let me first explain mainly on the three points.
4.1

4.1.1

Microorganisms

The composting process is broadly divided into three stages

Judging based on the level of decomposition of organic substances and the fermentation heat generated, thecomposting process is usually divided into the “primary fermentation” and “secondary fermentation(maturing)” processes, as discussed above. On the other hand, the composting process may be broadly
divided into three stages, from a viewpoint of transition of microorganisms. The figure below illustrates aprocess of raw garbage composting. In the case of batch-type*1 composting, the stage shifts as time goes by
from the first stage to the second stage and then to the third stage as composting progresses, as if the
microorganisms are relaying the compost. In the case of continuous input-type*2 composting, the first to thethird stages progress at the same time at different places in the compost.
As shown in the figure, the components decomposed in each stage and the types of microorganisms that are
active are already known. If we assume that dominant species of microorganisms change in each stage, thetransition of the microorganisms may be facilitated, or smooth composting would be possible, by having alineup of microorganisms necessary for composting ready beforehand.
Since composting basically involves aerobic fermentation, aerobic microorganisms*3 and facultative
anaerobic microorganisms*4 are used. However, obligately anaerobic microorganisms*5 are also active inthe fibrous substance decomposition period of the second stage.

1© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items

Targeted raw garbage
Carbohydrates,
proteins, lipids

Fibrous substances(cellulose/
hemicellulose)

Filamentous
fungus/bacterium

Ray fungus/
actinomycete

LigninBasidiomycete

Fig. 4-1: Composting and transition of microorganisms*1

Batch-type: it is a method in which the series of composting processes is performed without
inputting additional raw garbage, for producing a compost product.

*2

Continuous input-type: it is a method in which raw garbage is continuously input (once a day
or once every other day, for example), and after inputting the raw garbage for the prescribedperiod, the compost to be made into a product is taken out and matured.

*3

Aerobic microorganisms: this type of microorganisms produces adenosine triphosphate (ATP;a form of biological energy) necessary for activities, using oxygen.

*4

Facultative anaerobic microorganisms: this type of microorganisms is usually active in ananaerobic metabolic pathway, but shifts to an aerobic metabolic pathway when there isoxygen, and produces ATP.

*5

Obligately anaerobic microorganisms: this type of microorganisms produces ATP in acondition that lacks oxygen. If there is oxygen, the microorganisms produce superoxide (aharmful substance) within and destroy themselves. Those possessing a detoxification enzyme
do not destroy themselves, but cannot multiply.

(1) First stage
Leftover foods and other substances that may be digested and absorbed easily (carbohydrates, proteins,
lipids) are decomposed in this stage. Perhaps it is easier for you to understand if you thought of the target ofdecomposition as something humans can digest and absorb. Bacteria and filamentous fungi (mold) are
active in this stage, raising the temperature of the compost. Rice and noodles lose their forms in about a day,but odors could generate easily if the moisture content is too high in this stage.

2© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
Typical microorganisms that may be used include lactic acid bacteria (yogurt) and yeast fungi (dry yeast),
but local fermented foods should be used to the extent possible. In Japan: natto (natto bacteria), malted rice(mold), a bed of salted rice bran used for pickling (yeast and lactic acid bacteria); in Nepal and Bhutan:
marcha (yeast bacterial, mold, lactic acid bacteria); in Indonesia: tempe (mold, yeast, bacteria), tape(filamentous fungi, yeast, bacteria, lactic acid bacteria), etc.
There is a reason for using microorganisms involved with fermented foods. Some organic farmers in Japan
make their own compost that has a unique formula and use microorganisms related to fermented foods inmany such cases. They seem to have felt some good effects on farm products, by providing the compost
they made.
Since microorganisms are very
active in the first stage, oxygen isconsumedrightaway andanaerobic

state

results,

an

where

In Indonesia…
Hey, I smell
tempe!!

diverse substances are discharged as
metabolites

in

the

decomposeorganic

process

In Japan…
Nice, it’s a nattosmell!

tosubstances.

These metabolites cause an odor,
butmicroorganisms

fermented

food

relatedgeneratetoonlyfamiliar odors, which are not likely
to be felt as offensive.

Fig. 4-2: A scent of fermented food might rise in thecomposting process if fermented food was used

(2) Second stage
Filaments of plants (cellulose is covered and protected by hemicellulose) are decomposed in this stage.
When the decomposition progresses to this point, the waste rarely generates an odor. Bacteria that work inthis stage may be collected from a forest, which are white-colored bacteria underneath decomposed fallen
leaves (humus).
It is easy to see that these bacteria are useful because they have already decomposed naturally fallen leaves
that contain plenty of fibers. Especially active are ray fungi, and mold and bacteria work together topromote decomposition of fibers.*6 We feel an earthy odor when we walk through a forest, which is
generated by ray fungi. Even though the name ray fungi does not sound familiar, now we know these fungi
may be found easily around us.
*6:

When the temperature of the compost rises to 65℃ or more in the first stage, fibers are
steamed and softened, and are now easy to decompose. Here, aerobic ray fungi decompose
hemicellulose, to expose the cellulose. A large amount of oxygen is consumed and ananaerobic state results, causing anaerobic fungi (bacteria) that decompose cellulose to become
active. In addition, mold that decomposes cellulose is also active.

3© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items(3) Third stage
Lignin contained in plants is decomposed in this stage. Lignin is a hard component of plants, and trees are
hard and stand firm because they contain a large amount of lignin. In other words, decomposition of lignin
takes a long time. The especially active bacteria here are basidiomycetes (mushrooms), which may becollected from a forest.
Mushrooms often grow on a tree. The tree has become brittle in such cases. This evidences that mushrooms
are decomposing lignin.

Photograph 4-1: Collecting ray fungi(white-colored bacteria)(filamentous and other bacteria may becollected at the same time)

Photograph 4-2: Collecting basidiomycetes(mushrooms)

Can non-edible mushrooms be also used?
Since the old times in satoyama, people have collected humus from the forest and used the compost forfarming by mixing the humus into the soil. The humus used for the purpose naturally contains mushrooms.
We often find mushrooms growing out from a field provided with humus and bark compost. We have alsocollected and eaten wild fruits (wild vine, akebi, wild strawberry, etc.) that are gifts of nature, andmushrooms often grow at the foot of these fruit trees.
Most of the wild mushrooms are not edible, but we can judge based on our experiences that mushrooms
may be used safely for decomposing organic substances, if not eaten as is.
If you feel reluctant about the use of non-edible mushrooms, there would be no problem in avoiding thedirect use of mushrooms. Even though the efficiency might be affected, the necessary microorganisms arecontained in humus also, as discussed above.

4© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items

4.1.2

Diverse microorganisms are involved in composting

As discussed above, one type of microorganism alone would not make composting complete. The dominant
species of microorganisms change with the progress (stages) of composting, from among bacteria,
filamentous fungi, ray fungi and basidiomycetes. In other words, transition of the dominant species of
microorganisms is made smooth by having the necessary microorganisms ready beforehand.
The concept is “to prepare microorganisms with a purpose, instead of expecting the necessary
microorganisms to grow spontaneously.”
It is also desirable to have as many types of microorganisms at hand, for each category of them. For
example, yogurt is usually purchased at a supermarket, and several types of yogurt products made bydifferent manufacturers should be obtained. Also, humus in a forest is for collecting ray fungi, but humus
contains diverse types of microorganisms, including filamentous fungi, lactic acid bacteria, yeast bacteria
and basidiomycetes.
You are strongly recommended to collect humus from a forest.

4.1.3

Indigenous bacteria are excellent for composting

Since microorganisms necessary for composting may be collected around us, no special microorganism
needs to be used. This also reflects the way of thinking of organic farmers of Japan. Microorganisms arealways involved when plants are grown in the soil of a farmland. Compost naturally contains a large
amount of microorganisms, and if these are microorganisms found in the region, the compost would blend
well with the soil and help the plants greatly to grow. Such microorganisms are referred to as “indigenous
bacteria.”
Since the idea of “indigenous bacteria” derives from experiences and practices of organic farmers, theauthor believes they should be used in composting also. Another good point is that these microorganisms
may be obtained easily at a low cost anytime, anywhere, because no special microorganism is used.

4.1.4

When fermented food is not available

Some might not want to purchase fermented foods for composting, or it might be difficult to obtainfermented food in some countries and regions. There are three ways to deal with such situations.

(1) Humus in a forest
Humus in a forest contains diverse types of microorganisms, and if they are collected, they may replace
microorganisms in fermented foods. However, as discussed above, organic farmers have made uniquecompost by skillfully using fermented foods. If possible, fermented foods should be used.

5© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items(2) Lactic acid bacteria and yeast bacteria floating in the air
Have you ever heard of “monkey booze”? It is a sake-like liquid made when wild fruits (akebi, wild vine,
wild strawberry, etc.) left by a monkey in a tree cache or a hollow in a rock are naturally fermented. It
indicates that sake-like liquid may be obtained when wild fruits are fermented, although it is uncertain
whether monkeys really store wild fruits for the purpose. Yeast bacteria in the air that are attached on the
fruit skin are involved, which is the same principle with a wine that is made by crushing grapes along withthe skin.
Next, have you heard of “asazuke” picked vegetables? Salted leaves of Chinese cabbage and othervegetables are pickled overnight. The sour taste derives from lactic acid. In other words, lactic acid bacteria
in the air that had attached on the leaves are involved.
Have you also heard of “flower yeast”? It is a type of yeast bacteria used for making Japanese sake and ismade by separating the yeast bacteria from flower nectar. Yeast bacteria in the air have attached on thenectar, along with lactic acid bacteria.

4.1.5

Making seed compost by cultivating microorganisms

Raw garbage is a delicious bait for microorganisms, and diverse microorganisms try to use the bait at once.
In other words, a competition is going on among the microorganisms. Composting is a fermentation
process, and it is essential to adjust the environment so that activities of microorganisms useful for humans
would be dominant.
For the purpose, a large number of microorganisms fit for fermentation are prepared and mixed with raw
garbage. The produced compost contains plenty of cultivated microorganisms, which may be reused as seed
compost. The concept of reusing the seed compost is referred to as returned compost, which is discussed indetail in another Chapter. If the concept of returned compost was adopted, the cultivation of
microorganisms would be necessary only in the initial stage when composting is started.
The methods to cultivate microorganisms are discussed in detail in the section for practical application,
after conveying the basic theories of composting. A method that may be applied easily without a hindrance
at a site of composting, instead of a method for pure culture prepared in a test lab, etc., has been adopted.

6© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
4.2

OxygenComposting is basically aerobic fermentation, in which oxygen is supplied as appropriate through agitation
and aeration, and microorganisms decompose organic substances while promoting the aerobic state.
Composting is possible also through anaerobic fermentation without using oxygen, but the resulting
compost is used in either of the following ways: after the secondary processing in which the compost ismixed with soil and humus and aerobic fermentation is performed; or applied as a fertilizer directly into thesoil without going through the secondary processing, and fermented in an aerobic condition in the soil.
Aerobic fermentation offers diverse advantages.

4.2.1

Risk of odor generation may be reduced

The figure below illustrates in a simplified way the difference between aerobic (a condition with oxygen)
and anaerobic (a condition without oxygen) composting.
Composting is possible both in aerobic and anaerobic states. However, there is a potential risk of decaying
with the anaerobic composting. Especially with easily decomposed organic matters, such as raw garbage
that decays easily, an odor would rise right away if oxygen supply was not controlled skillfully. It is
customary to express composting as “causing the waste to decay.” This means that if raw garbage was piled
and left as is, it starts decaying right away and is composted while emitting an odor.

Difference between aerobic and anaerobic conditions
Organic waste

Aerobic

Anaerobic

Fermentation

Fermentation

Decaying

CompostFig. 4-3: Difference between aerobic and anaerobic conditions

7© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
The figure below illustrates the decomposition of organic substances under aerobic and anaerobic
conditions, in a simplified way with a focus on odors. The organic substances assumed is raw garbage thateasily emits odors.
Aerobic

Anaerobic
Trimethylamine
Methyl mercaptan

Odor of rotten egg,fish or cabbage

Raw garbage

HydrogensulfideOdor of sweat,sochs or arm pit
Ammonium oxidizing bacteria

Butyric acid
Valeric acid
Propionic acid

Odorless

Fig. 4-4: Difference in odor emissions between aerobic and anaerobic conditions

Ammonia (NH3), which is an odorous substance, is generated in both aerobic and anaerobic composting.
However, in the case of aerobic composting, ammonia-oxidizing bacteria promotes nitrification ofammonia (NH4+ → NO3-) right away, so only a slight ammonium odor is felt. Ammonia oxidizing
bacteria are found everywhere, especially in farmlands. On the contrary, ammonium accumulates in thecase of anaerobic composting, raising the concentration and causing an irritating odor. Moreover, diverse
other odorous substances are generated. An odor in a shoe or a sock, which is familiar to us, is caused byvaleric acid. Think of it this way, and you would get the point: “the air does not flow through shoes easily,and shoes are in an aerobic condition and are therefore odorous.”

4.2.2 The composting period may be curtailed
Let us look at the decomposition of glucose that may be used easily as a metabolite by microorganisms.
Biochemical reaction formulas are used because microorganisms are involved.
In aerobic condition:

C6H12O6 + O2 + H2O → 6CO2 + 12H2O + 38ATP

In anaerobic condition:

C6H12O6 → 2C2H5OH + 2CO2 + 2ATP

Adenosine triphosphate (ATP) has generated. Think of ATP simply as “energy of life forms.” All life forms,
including humans, need to generate ATP in the body for their activities.

8© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
The amount of ATP generated is surprisingly different between the aerobic and anaerobic conditions. Using
the same glucose, 19 times as much ATP is generated in the aerobic condition compared to the anaerobic
condition. Since ATP relates to activities of microorganisms, they become more active by promoting the
aerobic condition, thereby curtailing the period needed for composting.

4.2.3

Hygienic compost may be produced

In a composting process, a high-temperature period should always be secured for 48 hours or more at 65℃
or higher, or for seven consecutive days or more at 60℃ or higher. Diverse types of organic wastes arecomposted, and unsanitary microorganisms and seeds of weeds might get mixed. By securing thehigh-temperature period, these may be killed or deactivated. Especially at composting centers, a large
amount of organic wastes is accepted, and it is impossible to control all the organic wastes. As such,measures need to be implemented that take unsanitary microorganisms and seeds of weeds into
consideration. The table below shows the relationship between the temperature and the germination ratio of
weed seeds and extinction of unsanitary bacteria.
If composting was attempted using a household composting container, no heat accumulation effect may be
expected because the amount of compost is small, and the temperature does not rise so much. Based on our
experience, the temperature rises only to about 50℃. However, management of organic wastes is possible
when composting is performed at home. As such, no high-temperature period at 60℃ or higher needs to be
secured.

Table 4-1: Temperature kept for weed seeds and germination ratio
Planted and kept at
temperatures below
50℃

Planted and kept for
two days at 60℃

Control (unprocessed)

Germination ratio (%)

Germination ratio (%)

Germination ratio (%)

Crabgrass

96

0

7

Barnyard grass

72

0

87

Umbrella sedge

56

0

30

Lamb’s-quarter

26

0

16

Persicaria lapathifolia

8

0

53

Purslane

85

0

91

Amaranthus blitum

68

0

70

Yukinogusa plant

7

0

51

Fatoua villosa

26

0

19

Species9© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
Table 4-2: Temperature and duration of time needed for extinction of pathogenic bacteria and parasites
Species

Conditions for extinction
Temperature (℃)

Duration of time (min)55 to 60

30

56

60

60

15

55

15 to 2060

15 to 20

Dysentery bacillus

55

60

Staphylococcus

50

10Streptococcus

54

10

Cestode (tapeworm)

55 to 60

5

Necator americanus

45

50

Eggs of roundworms

60

15 to 20

Pathogenic bacteria
Typhoid bacillus
Salmonella
Bacillus coli

Parasites

A simplified graph is also shown for conveying a clearer image of the relationship between the temperatureand the duration of time needed for extinction of pathogenic bacteria, prepared based on the materials
reported by the World Bank in 1980. The graphclearly shows that unsanitary microorganisms
become extinct in a short period of time if thetemperature was raised. This does not meanthat unsanitary microorganisms proliferate in acompost when the temperature is low, but suchmicroorganisms remain in the compost without
being extinct.
As can be seen, a high-temperature period
needs to be secured in order to produce ahygienic compost. For raising the temperature,
the activity of microorganisms needs to be
increased, or the amount of generation of ATP
needs to be increased. ATP is converted to heat
when consumed as energy in a body, and theFig. 4-5: Relationship between temperature andduration of time needed for extinction ofpathogenic bacteria

temperature rises as the heat accumulates.

10© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items

4.2.4

Composting period may be curtailed further as temperature rises

How do microorganisms, especial those effective forcomposting, decompose raw garbage and otherorganic wastes? You might imagine microorganisms
eagerly munching on organic wastes, but it is notcorrect. Amoebas and paramecium, which areprotozoans, sometimes envelops an organic substanceand digest and absorb it in the body. On the other hand,bacteria do not have a mouth and do not digest andabsorb food material in the body.
The truth is, bacteria discharge an enzyme they

Photograph 4-3: Temperature management
during compostingproduced in the body to outside, and the enzyme reacts
with organic substances and makes them lower in molecules. Then, bacteria absorb the lower-moleculeorganic substances into the body. In a human body, the enzyme is discharged in the small intestine fordecomposing an organic substance into an amino acid or other low-molecular substances, which are thenabsorbed. It might be easier for you to understand the mechanism if you thought that bacteria are doing thesame thing outside of their body.
EnzymeAbsorption

The truth is:

EnzymeAbsorption

Absorption

EnzymeEnzymeBacteria “munching on organic
substances” is only an illusion and isincorrect

Each bacterium discharges an enzyme, fordecomposing and absorbing organic
substancesFig. 4-6: Bacteria dissolve organic substances using enzyme

Next, let me explain the relationship between the temperatures under which the enzyme is active and thedecomposition speed. To chemical reactions, the Arrhenius’s Law applies that states the reaction speed
doubles when the temperature rises by 10℃. With an enzyme reaction, which is among biochemical
reactions, the reaction speed is also accelerated when the temperature rises. With composting, the11© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
decomposition speed of organic substances is said to accelerate by 1.5 to 1.8 times when the temperaturerises by 10℃.
An enzyme is a catalytic protein generated in a cell of a life form. Some people are concerned that proteins
undergo thermal denaturation when exposed to a high temperature, and loses the catalytic action(deactivated). It is true that some enzymes become slower in reactions or become deactivated under thetemperatures higher than 40℃, but the heat resistance varies depending on the type of enzyme.

4.2.5

Higher temperatures could eliminate drainage

Planning of a drainage facility sometimes starts in the design phase of a compost center, because
wastewater is generated, especially when raw garbage composting is attempted. However, wastewater is
not generated from a compost if satisfactory fermentation progressed. In other words, compost centers
basically need no drainage facility. Raw garbage contains more than 80% of water, which does not drip
while the garbage is fresh. However, as time goes by, cell membranes and cell walls are decomposed by
microorganisms and the water that was contained in the cells seeps out. Furthermore, water is formed byhydrogen, which is a constituent element of carbohydrates, lipids, proteins and other components of raw
garbage, as microorganisms use the hydrogen. The generated water sometimes flows out as wastewater,when excessive in the amount. Decaying of raw garbage is a phenomenon in which it falls into ananaerobic state, due to the excessive moisture that results as the water in cells seeps out and the water isformed therein.
The moisture content of raw garbage is 80% or greater, and a large amount of water is brought in as watercontained in cells or attached on the waste when composting is performed, and water is generated further
from reactions of microorganisms. However, the water evaporates when satisfactory fermentation
progresses and the temperature rises. When performing continuous-type composting in which raw garbage
is input every day into the seed compost or fermenting compost, the amount of input raw garbage should be
adjusted so that an appropriate moisture content (40 to 60%) may be attained while maintaining a balanceamong the amount of evaporated water, the amount of water brought in with the raw garbage, and theamount of water generated through decomposition by microorganisms. When batch-type composting is also
performed, the amount of input raw garbage should be adjusted so as to attain an appropriate moisture
content of the mixture. The temperature rises as time goes by with both methods, and water deficiency
results because a lot of water is evaporated. Thus, water needs to be added. In either of the methods,
wastewater is not generated as long as satisfactory fermentation is underway.
If wastewater is generated, it indicates that the moisture content is too high. If the situation was left as is, ananaerobic state results and odors, including that of ammonia, become worse. In addition, the composting
period would be extended. It is necessary to implement measures, such as adding dry auxiliary materials,
for adjusting the moisture content. Also, wastewater causes nutrient elements (nitrogen, phosphate,potassium and others) that should remain in the compost to flow out.

12

© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items(1) A large amount of water is contained in cells and water is generated when microorganisms
consume organic substances[1] Water contained in cells
Water not only attaches on the surface of raw garbage but is also contained in cells. The water contained incells seeps out when microorganisms
break through the cell walls and cell
Enzymemembranes. To help you understand thepoint clearly, it is like “a hole being
pierced through a plastic bag containing
water.”

Cell walls andmembranes
are broken[2] Water generating from a reaction
I have explained, indicating the reaction
formula,

that

when

consumeglucosemicroorganisms
formetabolism,

Fig. 4-7: Cells contain a large amount of water thatseeps out when the cell wall is broken

adenosine triphosphate (ATP) that serves
as energy for life forms is generated. The reaction formula is shown below again, and you are asked to takea look at it carefully.

C6H12O6 + 6O2 + 6H2O → 6CO2 + 12H2O + 38ATP
While there are six units of H2O on the left side of the reaction formula, there are 12 of them on the rightside. This indicates that when microorganisms consume oxygen and water for metabolizing glucose, the
12 H atoms in the glucose molecule react with three units of O2 and generate six units of H2O.
Similar reactions take place with the H atoms contained in carbohydrates, lipids and proteins that are themain components of raw garbage. In other words, water is generated when microorganisms decompose
organic substances using oxygen. If an excessive amount of raw garbage was mixed without considering
for the fermentation state of the compost, the progress of satisfactory fermentation is prevented due to theexcessive moisture content and the temperature would
not rise. In such cases, the water contained in thecompost is not emitted as steam and the amount ofwater increases further as the water contained in cells
and water from the reaction are added, and the excesswater seeps out from the bottom surface of thecompost as wastewater. The wastewater contains
nitrogen, phosphate and potassium that should serve as
the fertilizing components of the compost. It is such a“mottainai” situation.

13

Photograph 4-4: Wastewater seeps out whenthe moisture content of the compost isexcessive© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items(2) It is better not to dehydrate raw garbage
Since water accounts for 80% or more of raw garbage, the amount of input raw garbage is restricted for
adjusting the moisture content to 40 to 60% that is fit for composting. If raw garbage was dehydrated, its
amount to be input may be increased and efficient composting might be possible. However, there are also
demerits of dehydration. The readers are recommended to consider whether to incorporate a dehydration
process after fully understanding the demerits.

[1] Installation of a dehydration system
Needless to say, a dehydration system needs to be installed for raw garbage, and the initial costs, runningcosts and maintenance and management processes need to be studied.

[2] Installation of a drainage treatment system
Drainage from dehydrated raw garbage contains nutrient factors such as nitrogen, phosphate and potassiumthat were contained in the raw garbage. If the drainage flows into a river or other waters, the BOD rises andorganic pollution results. For dealing with the situation, installation of a drainage treatment facility (itsinitial costs, running costs, maintenance and management) needs to be studied.

[3] Suppression capacity against pathogens in soil
One of the effects expected of compost is that an outbreak of diseases of farm products may be suppressed.
A test was performed for producing high-quality compost by recycling food materials. In the test, thedifference in the effect to suppress the growth of pathogens in soil (mainly filamentous fungi) was
appraised for different production methods of compost. In the test, it was revealed that the capacity tosuppress pathogens in soil was lower in dehydrated leftover vegetables compared to not-dehydrated ones.
4.3

Points of caution in aerobic fermentation

There are points of caution to note when supplying oxygen for aerobic fermentation.

4.3.1

Appropriate amount of air should be supplied

Especially in the first stage of composting in which easily decomposed organic substances such as raw
garbage is decomposed, microorganisms consume a large amount of oxygen, and causes a partiallyanaerobic state to result. If extensive aeration was performed for resolving the condition, heat would be
dissipated along with the air and the rise in the temperature of the compost would be prevented. The same
applies when the garbage is agitated too many times for sending in the air. The scale of aeration and thetime (continuous or intermittent) need to be controlled for raising and maintaining the temperature (to 65℃
or higher).
The photographs below show the difference in cross-section observed at a time of piling and fermentation,
when aeration was performed and not performed, using cases with cattle manure as an example.

14© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items

Approx. 30 cm

Photograph 4-5: Piling and fermentation(without forced aeration/ without agitation)

Photograph 4-6: Piling and fermentation(with forced aeration/ without agitation)

The whitish color shows the portions where aerobic ray fungi have grown, indicating that composting has
progressed. The photograph to the left shows that when neither forced aeration nor agitation was performedon the piled waste, the ray fungi have proliferated in a portion at about 30 cm from the surface. This
indicates that by merely piling the waste, the air penetrates only to about 30 cm from the surface. On thecontrary, ray fungi have proliferated on the entire surface when forced aeration was performed as shown in
the photograph to the right. The progress of composting completely differs depending on whether the air is
supplied or not.
However, a problem arises even when forced aeration was done, if the waste was not agitated. No ray
fungus is seen to have grown near the walls on both sides. This is because the walls block the air fromcirculating. Since the air flows into an area with low pressure loss, an air passageway is always formed.
Forced aeration alone cannot make homogeneous compost.
There are two methods for supplying oxygen, namely agitation and forced aeration. Even though the air is
supplied efficiently by forced aeration, thorough agitation is necessary for homogeneous composting.
Agitation is performed once every day or every other day in many cases, even when the air is supplied byagitation alone, in consideration of the burdens of agitation work.

4.3.2

Moisture content

The optimum range of moisture content for composting is generally between 40 and 60%. If a large amountof water penetrated into voids of the raw materials, the aerobic condition turns immediately into ananaerobic condition. In the case of sludge made from raw materials having small particle diameters, aerobic
fermentation might not be possible unless the moisture content is adjusted to 50% or less. The airpermeability is improved when rice hull, sawdust, rice straw or other large organic substances were added
as auxiliary materials, and satisfactory aerobic fermentation may be maintained with the same sludge evenwhen the moisture content exceeded 60%. In the photograph, a case with rice straw being mixed into thecow manure as an auxiliary material is shown. Since cow manure contains a lot of water and is densely

15© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
constituted with a small void ratio, rice straw was
mixed for securing an appropriate void ratio in
addition to adjusting the moisture content. The mixture
maintainedtheaerobic

fermentation

andmicroorganisms remained active, and as a result thetemperature rose highly.
By the way, the dissolved oxygen in water is about 8
ppm (0.008%) (at 25℃), in contrast to the oxygen
concentration of 21% in the air. As can be seen, theamount of oxygen decreases dramatically when the air

Photograph 4-7: Rice straw was added to cow
manure, for adjusting moisture content andsecuring void ratiothat fills the void is replaced by water. Excessive
moisture content brings about an anaerobic state, causing odors to rise.
(Note: the unit used for the dissolved oxygen is mg/l, but ppm was used here as is customarily used, forfacilitating comparison with the oxygen density in the air.)When the moisture content falls below 30%, activities of microorganisms are hindered in the dry condition
and fermentation would not progress.

The optimum range of moisture content forcomposting is 40 to 60%
Anaerobic state

In a dormant
state

Decaying

Excessive
moisturecontent

Drying

Activities slow down
(Raw garbage is notdecomposed)

Odor

Odor

Fig. 4-8: Optimum range of moisture content for composting16© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
When compost is stored, a dry state with the moisture content of 30% or less is maintained because
activities of microorganisms need to be suppressed. Some microorganisms might be damaged when the dry
state was kept over a long period, but many of them transform into a form that can endure dryness, and fall
into a dormant state. You might understand the point better if you imagined a dry yeast used in breadmaking and a koji-mold used when making miso paste.

4.3.3

Checking the moisture content for smooth composting

The author has focused so far on the three most important matters for smooth composting. The matter of
the top priority in composting is to suppress odors caused by decaying. Otherwise, composting centers that
attempt volume reduction and recycling of wastes would be regarded as troublesome facilities in thecommunity. Then, what is needed for preventing decaying?
The necessary microorganisms are prepared beforehand so that the microorganisms necessary in each stage
would emerge and become dominant, for each step of composting. However, the expected effect might not
be obtained if unable to realize the environmental conditions fit for the purpose. Even if forced aeration andagitation were performed and the necessary void ratio was secured, oxygen supply might be impaired
significantly if the moisture content was excessive.
In other words, the most crucial point is to accurately check and control the moisture content so as toprevent the moisture content from becoming excessive, for avoiding decaying and promoting satisfactoryfermentation. Daily moisture content checking is very important, and it helps not only to suppress decaying
as discussed above but also to raise the temperature and curtail the composting period.

(1) Method of moisture content checking
There are various methods of fermentation adopted at compost centers, such as piled-up-type andwindrow-type. The degree of unevenness of moisture content enlarges as composting comes to be
performed at a greater scale. Therefore, the moisture content needs to be checked in a prompt and easy way
at sites, and it would suffice by roughly confirming whether “the moisture content is within the appropriate
range (40 to 60%).”A method employed at many sites is by “gripping the compost by a hand.”i

Low moisture content (less than 40%): when the compost is gripped and then the hand is
opened, no cake is formed.

ii

Excessive moisture content (more than 60%): when the compost is gripped in a hand, water
seeps out from between the fingers.

iii

Appropriate moisture content (40 to 60%): when the compost is gripped in a hand, no water
seeps out from between the fingers and a cake is formed when the hand is opened. (However,a cake might not be formed easily with some types and forms of raw materials, even when the
moisture content is appropriate. In such a case, the moisture content is judged as appropriate
if the palm feels moist with water.)
17© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items

No cake is formed:
low moisture
content of less than40%

Take thecompost on a
hand

Grip firmly

Water seeps out :excessive moisture
content of morethan 60%

Open thepalm

Water is not seeping and acake is formed: appropriate
moisture content between
40 to 60%
Fig. 4-9: Simple method to check moisture content(2) Points of caution in moisture content checking[1] Moisture content measurement by heating
The method adopted at analysis centers, in which compost is heated to 105 to 110℃ to have the containedwater entirely evaporated, enables accurate measurement of the moisture content. However, the information
sought at composting sites from moisture content checking is whether oxygen may be supplied smoothly.
In other words, the amount of water attached on the compost surface and the amount of water thatpenetrated into voids need to be clarified. If raw materials of the compost did not absorb water easily or if
the moisture content checking was done immediately after adding water, the moisture content might
become excessive because a large amount of water penetrates into voids while the compost surface remains
wet.
Let us look at moisture content adjustment for compost that mainly relies on rice hull, as an example. (Themoisture content data of the rice hull and rice bran are those measured after heating the compost.)
30 kg of rice hull is mixed with 10 kg of rice bran, and X kg of water is added to make the moisture content
approximately 50%. Assuming that the moisture content of the rice hull is 9% and that of rice hull is 12%,the necessary amount of water to be added X kg may be obtained by the following equation.
(30 × 0.09 + 10 × 0.12 + X)/(30 + 10 + X) × 100 = 50

18

X = 32.2© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
If the amount of water obtained by the calculation, or 32.2 kg of water was added, water flows out from the
mixture. Next, let us consider a case that uses sawdust instead of rice hull. The test was performed atexactly the same conditions, but no water dripped out from the mixture. What could be the reason for thedifference? It is found in the low water absorption ratio of rice hull. While the water absorption ratio of
sawdust is about 250%, that of rice hull is only about 74%. Think of the amount of water to be added
obtained by the calculation as a reference value, and in actual practice, it is necessary to add water while
checking the moisture content carefully by gripping the mixture in a hand.
Although microorganisms cause the water contained in cells and the water derived from reaction of the raw
garbage to seep out gradually, the temperature would rise promptly if the moisture content was adjusted
appropriately in an initial stage, and the water would evaporate and an appropriate range of the moisture
content would be maintained. Sometimes water is added to make up for excessive water evaporation.

[2] Compost moisture meter
A compost moisture meter measures the water on the surface of the compost and the water that has
penetrated into voids, in a form of an electric resistance value, and converts the result into the moisture
content. Different moisture content values might be obtained in some cases even when the moisture content
was the same, because the value could differ depending on the concentration of ionized substances in thewater. As such, a caution is needed when using a new raw material for composting.

References: Koji Takakura: Kaigai Gijutsu Kyoryoku wo Tsuujita Takakura-shiki Konposuto no Gijutsu Itenni Kansuru Kenkyu (A Study on Technical Transfer for Takakura Composting Method throughOverseas Technological Cooperation), doctoral thesis, Graduate School of Life Science andSystems Engineering, Kyushu Institute of Technology, May 2016
 Editorial supervision by Shunrokuro Fujiwara, edited by Rural Culture Association Japan: Katei
de Tsukuru Namagomi Taihi (Home-made Raw Garbage Compost), Rural Culture Association ofJapan, 1999
 Toshihide Matsuzaki: Tsuchi to Taihi to Yukibutsu (Soil, Compost and Organic Matters),
Ie-no-Hikari Association, 1992
 Deborah L. Martin and Grace Gershuny, editorial supervision by Shingo Iwata, translated byMidori Sahara: Katei de Dekiru Taihi-zukuri Hyakka (The Book of Composting), Ie-no-Hikari
Association, 2004
 Shinjiro Kanazawa: Konposuto Fujuku Katei ni Okeru Yukibutsu no Henka Narabini Sono Hyoka(Changes in Organic Substances in Composting Process, and Evaluation Thereof), Suishitsu
Odaku Kenkyu (Journal of Researches on Water Pollution) Vol. 9, No.5, 1986

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© 2019 Koji TakakuraChapter 4 Basic theories of composting technology – Important items
 Shunrokuro Fujiwara: Taihi no Tsukuri-kata, Tsukai-kata (How to Make and Use Compost),
Rural Culture Association of Japan, 2003
 Institutefor

GlobalEnvironmental

Strategies:

Composting

for

Waste

Reduction;

INFORMATION KIT, 2010
 Minami-Boso City Government: III. Taihi no Seizo Hoho (III. Compost Production Method) Japan Soil Association: Ko Hinshitsu Hiryou Ninshou Seido Suisin Jigyou Hokokusho (Report on
the Project for Promoting High-quality Fertilizer Certification System) (Shokuin Risaikuru Taihino Hinshitsu Kojo to Fuka Kachi Kojo) (Quality Enhancement and Added Value Enhancement
for Compost Made by Recycling Food Materials), March 2016
 Japan Soil Association: Hinshitsu no Yoi Shokuhin Risaikuru Taihi Seizo no Tebiki (Gaiyo)(Guide Book for Producing High-Quality Compost by Recycling Food Materials (Summary)),
March 2015
 Michinori Nishio: Dojo Biseibutsu no Kiso Chishiki (Basic Knowledge on Microorganisms inSoil), Rural Culture Association of Japan20© 2019 Koji Takakura