Bioresource Technology 90 (2003) 241–247

Pyrolysis of plant, animal and human waste: physical and

chemical characterization of the pyrolytic products
a,* b
Yoshiyuki Shinogi , Yutaka Kanri
a
National Institute for Rural Engineering, 2-1-6 Kannondai, Tsukuba, Ibaraki 305-8609, Japan,
b
MasterÕs Program in Biosystem Studies, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8677, Japan,
Received 15 April 2003; accepted 12 May 2003

Abstract
Pyrolysis (carbonization) has been proposed as one of several optional technologies for disposing and recycling waste products in
Japan. Plant wastes (sugarcane bagasse and rice husks), animal waste (cow biosolids) and human waste (treated municipal sludge)
were pyrolyzed at temperatures from 250–800 °C in closed containers. The carbonized materials were evaluated for specific physical
properties (yield, surface area, density) and specific chemical properties (total carbon, total nitrogen, pH, fixed carbon, ash content,
volatility) in order to compare differences in properties among the four waste products. The results indicated that (1) surface area,
total carbon, ash content and pH increased as the carbonization temperature increased, while carbonization yield decreased with
increasing temperature, (2) product density however was not affected by temperature and (3) correlation coefficients were deter-
mined among the physical and chemical properties and several significant correlations were observed. The data indicate that source
material had considerable influence on the physical and chemical properties of the carbonized products.
Ó 2003 Elsevier Ltd. All rights reserved.

Keywords: Carbon products; Carbonization recycling technology

1. Introduction other optional technologies to support these traditional

technologies. One waste product disposal strategy that
Recently in Japan and in many other countries, en- has received little attention in Japan, but is becoming
vironmental consciousness has been increasing and more common in the United States is the pyrolysis or
many strategies have been given for the reduction of carbonization of waste material, mostly from plants, for
environmental load produced by discarded waste prod- energy production. The off-gases that develop during
ucts. The concept of ‘‘zero emission’’ proposed by carbonization in an oxygen poor environment are used
Gunter Pauli (UNU) is the idea that has been proposed for their energy potential. The residue that remains is
to reduce environmental impact of waste products and rich in elemental carbon and may be used in various
utilize resources repeatedly and effectively. However, applications, such as a filter medium. Carbonization is
over the last several decades, the total amount of waste applicable in both developed and developing countries
products has been increasing and the sources have be- because it is easy to carry out and does not involve
come more and more diverse. To utilize resources ef- highly complex equipment.
fectively, therefore, it is important to develop various Carbonization is different from incineration in terms
kinds of recycling technologies. of supply of oxygen. Generally, wood is made of cellu-
In Japan, composting has not been widely accepted lose, hemicellulose and lignin which are comprised of
mainly due to lack of space. Incineration and landfills carbon, oxygen and hydrogen and when they are heated
will not be widely accepted due to dioxin exhaust and without or with a small supply of oxygen, carbon
lack of space, respectively. It is important to develop monoxide and hydrogen are produced and cellulose and
hemicellulose are volatilized at about 280 °C (Jyodai,
*
Corresponding author. Tel.: +81-298-38-7552; fax: +81-298-38-
1992). A product of the carbonization of wood, called
7553. wood charcoal, has been familiar in Japan from ancient
E-mail address: yshinogi@nkk.affrc.go.jp (Y. Shinogi). times. It has been used for many purposes, as a result of

0960-8524/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0960-8524(03)00147-0
242 Y. Shinogi, Y. Kanri / Bioresource Technology 90 (2003) 241–247

extensive research (Abe, 1988; Abe et al., 1998). For 1000

agriculture, wood charcoal has been used as a soil 900

amender to improve soil physical properties and as fil-
tering agent in fish aquaria. However, the intrinsic 800

mechanisms involved in its use as a soil amender have

Temperature (Furnace) (˚C)

700
yet to be clarified.
For carbon products other than wood charcoal, there 600

is some research on production of activated carbon from

500
waste products, including agricultural by-products
(Muroyama et al., 1996; Toles et al., 2000; Xia et al., 400

1998; Ahmedna et al., 2000; Marshall et al., 2000; Ng

300
et al., 2002), but there is little research on pyrolyzed by-
products. Some research has been carried out in Japan 200

on carbonization products from chicken manure and

100
rice husk (Miyazaki Agricultural Research Center, 1996,
1997; Kumamoto Agricultural Research Station, 1999). 0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Carbonization products from plant and animal waste Time (hr)
material may be utilized as a substitute for wood char-
coal. Carbonization could be one of the hopeful options Fig. 1. Temperature control.
of disposing of waste products.
The objective of this work was to carbonize different Carbonization temperatures used were 250, 300, 400,
plant, animal and human source materials at different 500, 600 and 800 °C. The temperature was increased
temperatures and study the physical and chemical gradually at a rate of 2 °C/min until the specified maxi-
properties of the pyrolyzed products. Determination of mum temperature was reached. The temperature was
physical and chemical properties could guide researchers maintained for 2 h, after which the furnace was turned
in identifying specific end uses for the carbonized waste off and the retort chamber allow to cool down until
materials, such as a soil amender or as a low-cost ad- room temperature was reached. A temperature profile of
sorbent. the process is shown diagrammatically in Fig. 1.

2.3. Determination of physical and chemical properties

2. Methods
2.3.1. Yield
2.1. Source material
Weight of material was measured before and after
carbonization. Yield is given by the relationship:
Four source materials were used. Sugarcane bagasse
was obtained from Tokunoshima, Kagoshima, Japan. Yield ð%Þ ¼ ðWac =Wbc Þ
100
Rice husks were procured from our Institute. Activated
where Wac and Wbc are weights of material before and
and dewatered municipal sludge was removed from the
after carbonization, respectively.
sewage treatment facility located at Niihari Village, I-
baraki, Japan. Dewatered and stabilized cow biosolids
were obtained from National Institute for Livestock. All 2.3.2. Density
source materials were dried naturally and moisture Density was measured on carbonized particles of 2
contents of them were about 10% or less. mm or less. A specific weight of product was packed into
a graduated cylinder. The cylinder was tamped on the
2.2. Carbonization bench top and when the volume of material did not
decrease, the volume was recorded and density calcu-
The source materials were packed into 4 l steel vessels lated.
and sealed to exclude as much air as possible. The
weight was different from the source materials. Holes 2.3.3. Total carbon (T-C) and nitrogen (T-N)
were placed in the top of the vessels in order to vent off- T-C and T-N were measured with a nitrogen–carbon
gases from combustion of the source materials during analyzer (Shimazu Co. Ltd.).
heating.
A furnace (Koyo Lindberge Co. Ltd.) with retort was 2.3.4. Surface area
used for the carbonization. This furnace has a pro- For surface area analysis, all specimens were vacuum
grammable temperature controller that can be operated dried at 100 °C for 12 h. The BET surface area mea-
manually, and was used during the heating operation. surements were obtained from nitrogen adsorption iso-
 Y. Shinogi, Y. Kanri / Bioresource Technology 90 (2003) 241–247 243

therms at 77 K using a Micromeritics Gemini 2375 ture. Wood loses 30–40% and 20% of its mass at 200 and
Surface Area Analyzer (Micromeritics, Norcross, GA). 400 °C respectively, but only 20% of its mass between
Surface areas (SBET ) were determined from adsorption 400 and 800 °C, after that, the mass remains constant.
isotherms using the BET equation, as part of the Star- Reduction in yield is the smallest from cow biosolids,
Driver v.2.03 software package associated with the while it is the largest from bagasse. The bagasse yield
Gemini 2375 surface area analyzer. profile is almost the same as that of wood charcoal over
the entire temperature range (Abe, 1988).
2.3.5. pH According to Yoshida (1999), mass loss during car-
All specimens were soaked with a specific volume of bonization depends on the source material. Carboniza-
distilled water and boiled for 5 min and allowed to cool tion, especially at high temperatures, not only reduces
down naturally to room temperature and the pH of the mass significantly, but also eliminates the original odor
solute was observed. of the source material. Therefore, the waste products
can be more easily handled.
Fig. 3 shows the relationship between product density
2.3.6. Moisture, ash content, volatility and fixed carbon and carbonization temperature. It has been known that
content wood charcoal density decreases with an increase in
Percentage of water, ash, volatility and fixed carbon temperature between 200 and 400 °C, after which the
were determined by standard published procedures (in density increases. In other words, there is a minimum
Japanese standard for coal and coke). value around 400 °C (Sumiyaki Association, 1991). In
this study, the same tendency was shown. However, this
change is not significant compared with material differ-
3. Result and discussion ence. Product density from activated sludge is the largest
at about 0.7 g/cm3 , while that from bagasse is the
3.1. Physical properties smallest at about 0.1 g/cm3 . Density of carbonized
products is dependent on the density of the source ma-
Changes in yield with carbonization temperature for terial. The density of wood charcoal by comparison is
the four source materials are shown in Fig. 2. Yield is 0.42 (400 °C, oak), 0.14 (400 °C, pine) g/cm3 , respec-
reduced for all materials with increased temperature. A tively. There is about a sevenfold difference in density
large decrease in yield occurs between 200 and 400 °C among the source materials in this study.
for all by-products. This decrease is likely due to the Fig. 4 shows the relationship between surface area
destruction of cellulose and hemicellulose that has been and carbonization temperature. Surface area was most
observed for wood charcoal. Cellulose drastically re- well developed in sugarcane bagasse at carbonization
duces weight around 180–250 °C, while lignin reduces temperatures above 500 °C. There was some surface
weight almost linearly with temperature (Sumiyaki As- area development in carbonized cow biosolids as well,
sociation, 1991). Yields decrease slowly between 400 and especially at carbonization temperatures above 500 °C.
800 °C. This pattern is similar to those obtained for Rice husks and activated sludge developed very little
wood as a source material in the production of charcoal. surface area. Surface areas were generally below 100 m2 /
It is thought that same process occurs for these carbon g. Surface area for bagasse at 800 °C was 83 m2 /g, while
products. It has been shown that for wood charcoal, that of wood charcoal and activated carbons are re-
yields decrease with increase in carbonization tempera- ported to be about 400 and 1000 m2 /g, respectively (Abe,

Fig. 2. Generation percentage and temperature. Fig. 3. Density and temperature.

244 Y. Shinogi, Y. Kanri / Bioresource Technology 90 (2003) 241–247

Fig. 4. Surface area and temperature.

Fig. 5. pH and temperature.

1988). Wood charcoal is reported porous and carbon

products from other source materials are expected to be nutrients for plants. After this temperature range, the
the same. Surface area gives an indication of the extent pH attained remains almost constant, probably because
of porosity as highly porous structures, especially mi- the ash content remains relatively constant (see Fig. 9).
croporous structures, have high surface area. Surface The pH values at 800 °C range from activated sludge
area is one of the important parameters to evaluate at pH 8.5 to cow biosolids at a pH of 10.6. The pH of
absorption, especially for organic molecules. Carbon the carbonization products can be used as an important
products are highly porous media and have large po- parameter to evaluate surface condition of the material.
rosity. The pH is one of the indicators that show surface con-
In order to achieve high surface area, pyrolysis ditions and enables one to guess surface electric charge
products as described in this study must be activated properties. However, in order for pH to indicate surface
with one of several types of activation methods (Mar- conditions, the ash must be removed with acid. The
shall et al., 2000). Given a particular activation method, presence of ash on the product surface can decrease
large surface areas can be produced and these carbons surface area by plugging pores with residue and render
are normally utilized as a gas phase adsorbent (Xia et al., the surface more alkaline than it actually is.
1998). Although the pH of the original source materials
There are some studies on surface area index of car- differ from each other, with some being acid and others
bon products with temperature. Some reported that alkali (Fig. 5), the carbonization process has great in-
surface area index increases with temperature (Xia et al., fluence on the pH regardless of the source of material.
1998), while some reported that there is a maximum Carbonization at temperature of 600 °C and above
value with temperature (Abe, 1994). There are almost renders all the products alkaline (pH > 7:0). Abe et al.
the same tendencies for pore volume. According to io- (1998) reported that the destruction of cellulose and
dine absorption tests, total pore volume and absorption hemicellulose around 250–300 °C produces organic ac-
potential for bagasse is larger than that of activated ids and phenolic substances that lower the pH of the
sludge and there is an almost linear increase in tem- product. At these temperatures, a ‘‘dew-like’’ condition
perature. Pore volume of bagasse and rice husk is larger is created and water is absorbed by the pyrolysis prod-
than those of wood charcoals (Sumiyaki Association, ucts, thereby becoming acid around 300 °C, after which
1991). alkali salts begin to separate from the organic matrix
As it is mentioned, surface area index is one of the and increase the pH of the product. After all the alkali
effective parameters to evaluate absorption. However, it salts are ‘‘leached’’ from the pyrolytic structure, the pH
is required to make clear the mechanism of absorption, becomes constant at a temperature around 600 °C. This
be it van der Waals or ionic mechanisms. synopsis agrees fairly well with the result of our study.
It is reported that the buffer capacity of the carbon-
3.2. Chemical properties ization product to regulate soil pH is not so strong
(Shinogi et al., unpublished observations). Buffer ca-
Fig. 5 shows that there is a change in product pH that pacity is another important property which must be
occurs between 300 and 500 °C, which is attributed to a taken into consideration when carbon products are used
separation of the organic (carbon) and inorganic com- as soil amenders to improve soil chemical properties.
ponents (alkali metal salts) (see Fig. 9). This inorganic It is reported that wood charcoal produced at a high
component, called ash, is the source of non-organic pyrolysis temperature is alkaline and it can consume
 Y. Shinogi, Y. Kanri / Bioresource Technology 90 (2003) 241–247 245

Fig. 6. Total carbon.

Fig. 7. T-N (total nitrogen).
þ
protons (H ) from the soil, which enables the charcoal
to improve soil acidity (Abe, 1988).
Total carbon (T-C) is one of the parameters that
may be used to evaluate the extent of carbonization.
Fig. 6 shows the effect of carbonization temperature on
T-C content of the different source materials. Total
carbon content increased the most for bagasse, from
43% in the non-carbonized samples to 75% at 800 °C.
The other three materials saw only a slight change in
T-C. The increase in T-C observed for bagasse is
similar to that observed for wood charcoal (develop-
ment of wood charcoal and wood acid liquid). In
biomass with little ash content, such as bagasse (see
Fig. 9), the T-C should increase with carbonization
temperature, since there is an enrichment of elemental
carbon as the other elements, such as nitrogen, are
largely removed with the off-gases during the carbon- Fig. 8. Fixed carbon and temperature.
ization reaction. The lack of change in T-C with in-
creased carbonization temperature for rice husks, cow
biosolids, and activated sludge is probably due to the
high ash content of these products, particularly at Fig. 8 shows the change in fixed carbon content with
higher pyrolysis temperatures (see Fig. 9). changes in pyrolysis temperature result from the engi-
Fig. 7 shows the carbonization temperature effect on neering analysis (fixed carbon ratio). The percent fixed
total nitrogen (T-N) content. T-N content is highest in carbon is the largest for bagasse throughout the tem-
the biosolids and sludge and lowest in the plant mate- perature range but smaller than that reported for wood
rial, rice husks and sugarcane bagasse. T-N decreases charcoal at 380 °C (Yoshida et al., 2000). Generally, the
with increased pyrolysis temperature for activated fixed carbon ratio increases with increased carboniza-
sludge and cow biosolids, while there is no significant tion temperature for all products. For bagasse, there
change from bagasse and rice husk. The decrease in T-N was a peak at 600 °C, after which the fixed carbon
in the high nitrogen-containing samples is likely due to content declined. Therefore, these by-products are not
the removal of nitrogen during formation of the off- suitable for fuel material.
gases. Off-gases are composed in part of NOx and NH3 Fig. 9 shows relationship between ash content and
and their removal would cause a decrease in the percent carbonization temperature. Generally, ash content for
of this element. biosolids, sludge and rice husks is larger than for wood
Total nitrogen (T-N) is one parameter that is used in charcoal and it increases with increased carbonization
evaluating the potential of a material to be used as a soil temperature. Ash content is greatest in cow biosolids
amender. In terms of T-N content, especially from with a maximum of 65% at 800 °C, while that of bagasse
sludge, it is better to carbonize the sludge at a relatively is the smallest throughout the temperature range. In-
low temperature (200–400 °C) than at higher tempera- creased ash content is the result of the reduction in
tures in order to utilize the T-N content of the sample content of the other elements during pyrolysis. Elements
for plant nutrition purposes. such as nitrogen, carbon, hydrogen, oxygen and sulfur
246 Y. Shinogi, Y. Kanri / Bioresource Technology 90 (2003) 241–247

Fig. 9. Ash percentage. Fig. 10. Volatility and temperature.

are volatilized during heating to varying degrees while 70

Bagasse
the inorganic salts that comprise the ash are not vola- 60

Ash Percentage(%)
Rice Husk
tilized. Therefore, ash content increases. Ash is normally 50 Activated Sludge
considered beneficial to plant nutrition, so the ash 40 Cow Sludge
content of biosolids and sludge could make these car-
30
bonized products beneficial as a soil amender.
20
Fig. 10 shows the relationship between percent vola-
tility and carbonization temperature. Volatility declined 10

rapidly between room temperature and 600 °C and re- 0

0 20 40 60 80 100 120
mained relatively constant between 600 and 800 °C. The
Generation Percentage(%)
percent volatility was generally larger than that of wood
charcoal (Yoshida et al., 2000). The curves for percent Fig. 11. Relationship generation and ash percentage.
yield (Fig. 1) and percent volatility as a function of
carbonization temperature were similar. This can be 3.3. Correlations among physical and chemical properties
explained by the fact that as carbonization proceeds, the
off-gases generated reduce mass of the remaining residue Table 1 shows correlation coefficients (R) among the
and also reduce volatility of the sample. physical and chemical properties measured in this study.
According to Yoshida (1999), there is smaller carbon There were relatively high correlations between surface
content, but larger oxygen and hydrogen content from area and T-C (R ¼ 0:67) and fixed carbon (R ¼ 0:64).
the carbon products manufacturing at 380 °C from There were high values (R ¼ 0:88) between yield and
various plant waste products, when compared to wood fixed carbon. Density was highly correlated with total
charcoal. Generally, plant waste products have small nitrogen (R ¼ 0:82), total carbon (R ¼ 0:75) and ash
fixed carbon content, but larger ash and volatility values content (R ¼ 0:79). T-C showed high correlations with
than wood, and therefore they are not as suitable for ash (R ¼ 0:85) and fixed carbon (R ¼ 0:88). The pH
fuel as wood (Fig. 11). correlated well with volatility (R ¼ 0:76).

Table 1
Correlation coefficient
Surface Yield Density (g/ T-N T-C pH Moisture Ash Volatility Fixed
area (m2 /g) (%) cm3 ) (%) (%) (%) (%) (%) carbon (%)
Surface area 1 )0.61 )0.37 )0.26 0.67 0.29 0.72 )0.32 )0.27 0.64
Yield 1 0.17 0.11 )0.64 )0.34 )0.62 0.19 0.70 )0.88
Density 1 0.82 )0.75 0.32 )0.46 0.79 )0.34 )0.56
T-N 1 )0.56 0.36 )0.41 0.62 )0.25 )0.44
T-C 1 )0.2 0.85 )0.85 0.05 0.88
pH 1 0.06 0.52 )0.76 0.08
Moisture 1 )0.62 )0.07 0.63
Ash 1 )0.48 )0.64
Volatility 1 )0.35
 Y. Shinogi, Y. Kanri / Bioresource Technology 90 (2003) 241–247 247

4. Conclusions sults indicate that carbonization products may be used

as soil amenders or adsorbents. In other words, valuable
From the results obtained for T-N content, it can be potential uses are proposed for these products as op-
expected that when carbonized products are used as soil posed to the loss of these uses if the source materials are
amenders to supply nutritional value to plants, it is composted, incinerated or landfilled.
better to carbonize at relatively low temperatures to
retain the high T-N content in by-products such as cow
biosolids and activated sludge. However, for the nitro- Acknowledgements
gen to be available for plants, it is necessary to deter-
mine water solubility of the nitrogen. In other words, it The authors wish to thank Wayne E. Marshall for
should be required to determine a solubility profile at technical advise and useful comments during the prepa-
different pH values. ration of the draft.
Carbonization products are generally considered to
be porous materials that can improve soil physical
properties such as soil texture, permeability and water
holding capacity. For example, carbonization products References
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