Utilization of Regional Biomass Centered on Wastewater Treatment Plants
Masaaki Ozaki, Shuichi Ochi
Material and Geotechnical Engineering Research Group, Public Works Research InstituteMinamihara 1-6, Tsukuba city, Japan, 305-8516, ozaki@pwri.go.jp
Abstract: The purpose of this research is to utilize regional biomass at wastewater treatment plants.
Organic waste produced by the operation of infrastructure was considered to have big potential asregional biomass, so its the mass production was investigated. To permit the utilization of organic
materials such as trees and grass, the anaerobic co-digestion with bio-solid method and theslurry-compost of digestion sludge method were investigated. And finally, the maximum supply of
biogas was estimated and technology needed to use it as fuel of natural gas vehicles was discussed.
Keywords: steam-exploded wood, anaerobic co-digestion, slurry-compost, natural gas vehicle

Generated Sludge (1,000DSt)

1. Introduction
In Japan in FY 2003, approximately 36% of bio-solid was disposed of as landfill andapproximately 64% was used beneficially. In recent years, the rate of landfill has decreased andthat of beneficial use has steadily increased as indicated in Figure 1. Bio-solid was utilized mainly
on agriculture land. Recently incinerated ash and molten slag have been used as construction
materials: for cement production and as aggregate.
Energy utilization of bio-solid is classified mainly as two methods. One is biogas, whichis generated from anaerobic digestion and includes methane gas as its main constituent. The otheris solid fuel, which is made of bio-solid. Biogas is usually consumed in wastewater treatment
plant (WWTP), at digestion facilities, and in incinerators, but approximately 30% of that is left overand burned off.

2,500
Others
2,000

Fuel material
Agriculture land

1,500

Cement ingredient
1,000

Building material

500

Ocean dunping
Land reclamation

0
89 90 91 92 93 94 95 96 97 98 99 00 01 02 03
FY

Figure-1 Transition of generated bio-solid- 233 -

After the Kyoto Protocol came into effect in February 2005, the value of biogas has beentransformed from in-house consumption to positive utilization. Biogas is expected to be an energy
source that is characterized by carbon neutrality. And in this research, biogas is discussed mainly
from the viewpoint of regional biomass utilization.
2. Estimation of regional biomass production
Various initiatives have been taken in the field of biomass utilization, contributing to
reduced CO2 emission and becoming very important elements in measures to fight global warming.
Several problems face biomass utilization. Its collection and transportation is very costly,
because biomass is widely scattered in each region. And the facilities are small scale so they lackscale merit. Biomass is classified into waste biomass, unutilized biomass and resource vegetation.
It is assumed that waste biomass such as food waste and wood generated by construction will beutilized quickly, because this waste biomass has been collected at specific places.
A large amount of vegetation waste is generated by river dike maintenance and trimming
street-side trees. But it is difficult to say that vegetation waste is well utilized. For example,
vegetation waste generated in suburban areas is incinerated with municipal solid waste. And its
beneficial use for agriculture is restricted
Because the amount of vegetation waste from infrastructure operation is not included inorganic resources, it is not expected that the use of vegetation waste will increase in the near future.
If the amount of vegetation waste was precisely measured, utilization plans and methods would be
investigated by an assessment based on a feasibility study. And if the resource information wereopen to the public, private companies would have opportunities to conduct case studies.
The amounts of driftwood at approximately 200 dams in Japan were investigated during
2003 and 20051). As a result, the total volume of driftwood around dam reservoirs was estimated,
obtaining a rough value. This shows that to promote the utilization of driftwood as biomass
resources in the future, it will be necessary to continue the collection of these basic data, and to alsoestablish a driftwood utilization system by referring to advanced initiatives.
Table 1 indicates the types of public works that produce biomass. To study biomass
utilization, first, the amount and kinds of generated biomass will be precisely investigated. Next,
the total volume produced in Japan will be estimated. Lastly, information management systems
will be investigated.
Table-1 Kinds of biomass generated from national land manegementadministrative
infrastructure, land and transport
sectionroad
freeway, national highway, local highway
river
river, dam, erosion control, seashorecity
street, park, sewarage
airportrunwayharborwaterfront
railwayrailroad* biomass: grass, branches and leaves, drifwood, bio-solid- 234 -

3. Recycling technology for organic waste
To promote the utilization of organic waste such as trees, and grass and bio-solid, recycling
technology was developed considering the characteristics of both materials. From the results, it
was concluded that anaerobic co-digestion of steam-exploded wood and bio-solid is feasible andcan make a big contribution to biogas production. And the slurry-compost, method which
contributes to agriculture use of bio-solid, was developed to treat fermentation residue.
It was observed that crushed wood is useful as bio-solid dewatering agent. And it wasalso observed that steam exploded wood with a small amount of bio-solid is an adequate compostthat is usable as an, gardening material that can replace peat moss.
slurry-compost were considered by this research.

Anaerobic co-digestion and⹜ᢱᛩ౉Sampleinvestment

3.1 Anaerobic co-digestion
Wood material and dried grassalone are difficult to ferment and theyneed to be changed to a quality easily usedbymicroorganisms.
Thesteam-explosion method was investigated,
as indicated in Figure 2. This method
keeps samples at a high temperature andunder high steam pressure for a certain
time period then suddenly reduces thepressure. After that, the plant materials
are shattered and softened.
Methane fermentationwas

Steam drain
→㩷ឃ⫳᳇

Steam
⫳᳇ 䇭→

Pressure vessel
ട࿶ኈེ
䋳䋰㩷㪣

Silencer䉰䉟䊧䊮䉰䊷Steam-exploded
material῜⎈‛

Figure㧙2 Steam-explosion Device

done

using

steam-exploded

wood

and

bio-solid.

Steam-exploded broadleaf tree chips prepared under pressure of 2MPa for 15minutes, that wereconfirmed to be easy degradable by a preliminary examination, were used for the experiment. The
sequential experiment was done by inserting and removing samples once per day at 35 degrees for
50 days, while varying the ratio of the added plant waste to the bio-solid.
The methane gas productivity is important when the anaerobic co-digestion process isintroduced at an actual facility. But it is feared that the whole process might change into acidfermentation, because of overloading of the function of the existing digestion tank. In a laboratory,
the system does not change into acid fermentation but works well. Figure 3 shows the averagemethane gas recovered from steam-exploded wood and bio-solid under each condition after theexperiment process has stabilized. And Figure 4 shows the dissolution characteristic of TOC,
NH4-N and PO4-P in digestion sludge.

- 235 -

㪉㪇

㪈㪇

㪇
㪇 㪅㪉㪌

㪇㪅㪌

㪇㪅㪎㪌

㪈

㪈㪅 㪉㪌

ᷙวᲧ䇭䋨ᧁ⾰῜⎈‛㩷㪛㪪㩷䋯㩷ਅ᳓ᳪᵆ㩷㪫㪪䋩
Ratio
of organic waste addition to bio-solid(steam-exploded wood / bio-solid )㪈㪉 㪌㪇䋨㫄㪾䋯 㪣䋩

Dissolutionṁ⸃ᕈ㩷 㪫㪦 㪚 䋬㪥 㪟 㪋㪄㪥

Ratio䉧䉴
of digestion⊒↢୚₸gas㪊㪊(gas /䋨㫄
investment
material)䋯ᛩ౉㊂㩷㫄
䋩

㪊㪇

㪇

㪫㪦㪚
㪥㪟㪋㪄㪥
㪧㪦㪋㪄㪧

㪈㪌 㪇㪇

㪍㪇
㪌㪇

㪈㪇 㪇㪇

㪋㪇

㪎 㪌㪇

㪊㪇

㪌 㪇㪇

㪉㪇

㪉 㪌㪇

㪈㪇

㪧㪦 㪋㪄㪧䇭䋨㫄㪾 䋯 㪣䋩ో䇭䉧䇭䉴 gas䂔 Generated䊜䉺䊮䉧䉴䂓 Methane
gas

㪋㪇

㪇

㪇

㪇

㪇㪅㪌

㪈

㪈㪅㪌

Ratio of organic waste addition
to bio-solidᷙวᲧ䇭䋨ᧁ⾰῜⎈‛㩷㪛㪪㩷䋯㩷 ਅ᳓ᳪᵆ㩷㪫㪪䋩(steam-exploded wood / bio-solid )Figure㧙3 Recovery of methane gas        Figure㧙4 Dissolution characteristic of  from steam-exploded wood             TOC, NH4-N, PO4-P

The methane gas production increased in proportion to the ratio of added steam-exploded
wood to the bio-solid. On the other hand, a large quantity of soluble TOC and PO4-P tend toremain in digestion sludge, but soluble NH4-N decreased considerably when the steam-exploded
material increased. It is observed that the system has high potential for practical use, if soluble
TOC and PO4-P in digestion sludge can be decreased effectively.
3.2 Slurry-compost2)
When slurry organic material such as bio-solid is utilized on agricultural land, the watercontent of the material is usually decreased by de-watering and compost is made from de-wateredsludge. Slurry-compost is a technology developed to be applied to all kinds of slurry organic
material. Excess sludge and digestion sludge are utilized in this research on the beneficial use offermentation residue.
Slurry-sludge could be stabilized without de-watering if a large quantity of dissolved
oxygen was provided. The purpose of aerobic digestion is not only the reduction of sludge but
also its stabilization. ³Slurry-compost´ would be considered to be an improved aerobic digestion
technology, if oxygen could be provided from a liquid surface by giving it high oxygen content.
The sludge stabilization process can be assessed based on its CO2 production
accompanying the decomposition of its organic material. The transition of generated CO2 isindicated in Figure 5 and Figure 6, where excess sludge (thickened sludge: MLVSS = 26 g/L) anddigestion sludge respectively (MLVSS = 6.8 g/L) were raw materials. The liquid phase(slurry-sludge) was 0.8 L and the gaseous phase (oxygen) was 2.1 L in this experiment. And theoxygen was filled up at pressure of 2 atmospheres and maintained over 30% by filling up again.

- 236 -

㪊㪌㷄

㪌㪇㷄

㪍㪇㷄

㪎㪇㷄

㪏㪇
㪍㪇
㪋㪇
㪉㪇
㪇
㪇

㪌

㪈㪇

㪈㪌

㪉㪇 ᣣ
(days)

㪉㪇㷄㪈㪇㪇㫄㪾㪚㪆㪾㪤㪣㪭㪪㪪㪄ᶖൻᳪᵆ
mgC/gMLVSS- Digestion sludge㫄㪾㪚㪆㪾㪤㪣㪭㪪㪪㪄૛೾ᳪᵆ
mgC/gMLVSS- Excess sludge

㪉㪇㷄
㪈㪇㪇

㪊㪌㷄

㪌㪇㷄

㪍㪇㷄

㪌

㪈㪇

㪈㪌

㪎㪇㷄

㪏㪇
㪍㪇
㪋㪇
㪉㪇
㪇
㪇

(days)㪉㪇 ᣣ

Figure㧙5 Transition of generated CO2    Figure㧙6 Transition of generated CO2
in excess sludge               in digestion sludge

The amount of generated CO2 differed according to temperature conditions or the kinds ofsludge used as raw material, but it was restrained after two weeks in each case. In particular, it
was observed that the digestion sludge was decomposed quickly under the normal temperature.
Because the digestion sludge was decomposed biologically under an anaerobic atmosphere, it was
assumed that another microorganism population (aerobic microorganism) treated the sludge
biologically under an aerobic atmosphere.
A small-scale facility could be constructed for the slurry-compost method, and it would beeasy to operate. So it is assumed that it would be beneficial in coping with small-scale demandand seasonal fluctuation of production.
4. Maximum supply of biogas3)
The sludge digestion process has been introduced at approximately 350 WWTPs in Japan,
and about 280 million m3 biogas has been generated per year. Power facilities, such as gas engines
or fuel cells, have been installed at some WWTPs. Recently the number has been increased but it
is still limited. About 180 million m3 biogas has been utilized as fuel, including digestion tankheating and as additional fuel for incinerators. But the remaining biogas (about 100 million m3)
has been burned off as excess biogas.
Table 2 indicates the quantity of biogas usable as fuel that is supplied to all WWTPs in
Japan, including cases where hypothetical conditions are set. The hypothetical conditions were
calculated for a case where the quantity of solid material input was over 3.0%, the ratio of digestion
tank utilization was 85% and the digestion period was 20 days, and the digestion tank was heated at
35 degrees by biogas, because there are many WWTPs with surplus capacity to satisfy these factors.
In addition, the biogas of all bio-solid was also calculated.
The remaining biogas will be about 250 million m3 at efficient treatment and about 300
million m3 for digestion of all bio-solid respectively. The reduction of CO2 will approach 200
thousands tons if the existent remaining biogas is totally utilized. This quantity is equivalent tothat adsorbed by about 60 thousands hectare of natural forest.

- 237 -

Table-2 Quantity of biogas supply at total WWTPs
condition of bio-solid
qauntity of remaining quantity of refined
reduction of CO2
treatment at WWTP
biogas (1,000m3)
biogas (1,000m3)(t)present remaining biogas
107,200
53,600199,400
125,600
467,500
efficient treatment
251,300
155,400
578,200
digestion of all bio-solid
310,800* using the data in FY2002 for condition of biogas production

5. Biogas vehicles3)
New beneficial uses of biogas have been introduced and biogas is utilized outside WWTP
after considerable refining. Refined biogas is provided to a plant manufacturing City Gas in
Kanazawa city4). And in Kobe City, a plant has been equipped to supply refined biogas to natural
gas vehicles (city busses, trucks, etc,) .
Biogas has usually been utilized at large-scale WWTPs, but it tends to be burned off at
small-scale WWTPs because of limited users and utilization methods. Biogas is considered to be aresource equal to natural gas when it is refined. It would be possible to drive natural gas vehicles
by fuelling them with refined biogas, so we call such a vehicle a ³biogas vehicle´.
Attempts to power cars by biogas are not a new idea. The ³pressurized gas supply
project´ was carried out in 1942 in Kyoto City during the Second World War. More than 100
Biogas vehicles were driven at the same time, but the project was given up at 1950 because thequantity of biogas available fell as its content in sewerage declined.
Table 3 indicates the quantity of biogas supplied at each WWTP under the same assumed
conditions as in Table 2. About 10 standard cars can be operated as biogas vehicles at WWTP thatretain about 100 thousands m3 of biogas per year. And it is estimated that 60 and 310 normal cars
could be operated at WWTP that retain biogas at rates of about 500 and 2,500 thousands m3 peryear respectively. At large-scale WWTP, more than 4,500 tons of CO2 emissions could be
reduced.
There are several technologies, such as the membrane system, that refine biogas, reducing
CO2 after sulfide separation. It was assumed that adsorption reduction, which uses treatedwastewater at WWTP, would be a useful method. Biogas includes a very small quantity of silicatecompound that originates from shampoo, and this material must be reduced.
On the other hand, the law requires that natural gas vehicle fuel must have an odor. A
fixed quantity of propane gas will be added to fuel for Biogas vehicles to add an odor and perform
calorie coordination. And Biogas vehicle fuel must also be compressed to 20MPa for house use
and small-scale filling up facilities, and to 25MPa for business use. Business use pressure permits
high speed filling and could be applied at gas stations, but an employee responsible for its use must
always be on duty at such facilities.

- 238 -

Table-3 Quantity of biogas supply at each WWTP
WWTP

qauntity of remaining quantity of refined
number of driving biogas vehicles
biogas (1,000m3)
biogas (1,000m3)
normal car 2t packer large bus
large-scale
2,500
1,250
310
250
50
middle-scale
500
250
60
50
10
small-scale
100
50
10
10
2
* driving length per year and per fuel unit, normal car: 60,000km/year and 15km/m3
2t packer: 20,000km/year and 4km/m3, large bus: 50,000km/year and 2km/m3³Natural gas´ supplied by gas companies have been designed as standard fuel for natural
gas vehicles. Each refined biogas must be inspected to confirm that it has the same quality as³natural gas´. If biogas refining systems are standardized, Biogas vehicles will be introduced
easily.
6. Conclusion
Measures to increase biogas production were investigated by this research. These werethe utilization of steam-exploded wood with bio-solid, efficiently using digestion tanks, and bydigesting all bio-solid. For example, a high temperature - high concentration digestion system
works satisfactory in Osaka city6). In the future, Economical anaerobic digestion systems thatprovide a steady high sludge decomposition rate must be done.
It will become increasingly important to develop technologies for utilizing biogas: biogas
vehicle systems for example. In order to utilize regional biomass centered on WWTP, thefollowing issues must be tackled. Utilizing biomass must not only benefit WWTP, but also
regional areas. And it must also be possible to use the fermentation residue.
Reference:
1) Masato TAKAHASHI, Katsuhito MIYAKE, Takanori MAKI, Shuichi OCHI, Masaaki OZAKI, The Amountof Driftwood Flowing into Dam Reservoirs and Examples of its use as Woody Biomass, Civil Engineering
Journal, 48-7, 48-53, 2006 (in Japanese)
2) Tadashi SHOJI, Shuichi OCHI, Masaaki OZAKI, Production and Use of Slurry-compost of Sewage
Sludge, Civil Engineering Journal, 48-6, 40-45, 2006 (in Japanese)3) Takanori MAKI, Masaaki OZAKI, Vehicles Using Digestion Gas as Fuel, Civil Engineering Journal,
47-2, 34-39, 2005 (in Japanese)
4) Sakae HIDUKI, City gas supply using a sewerage system, Reclamation and Utilization, vol.28, no.110,
17-20, 2005 (in Japanese)5) Yoshinori KAWATA, Tsuyoshi TAKIMURA, Hideaki ONISHI, ³Bio-natural gas´ made of digestion gas
and its utilization as fuel for natural gas vehicles, Proceedings of 42nd conference for sewerage research‫ޔ‬
55-57‫ޔ‬2005 (in Japanese)
6) Kiyonori TAIMATSU, Improvement of anaerobic digestion and digestion gas utilization, Reclamationand Utilization, vol.28, no.110, 44-50, 2005 (in Japanese)- 239 -









Biogas Solid fuel

Energy utilization

Incinerated ash
 Molten slag

Agriculture land
 Construction material

Beneficial use of bio-solids

Introduction

Masaaki Ozaki
Public Works Research InstituteUtilization of Regional BiomassCentered on Wastewater
Treatment Plants

89

90 91

92

93

94 95

96
FY

97 98

99

00

Approximately 64% of bio-solids was used beneficially.

0

500

1,000

1,500

2,000

2,500

01 02

03

Land reclamation

Ocean dunping

Building material

Cement ingredient

Agriculture land

Fuel material

OthersTransition of generated bio-solid

Maximum supply of biogas
 Biogas vehiclesAnaerobic co-digestion
 Slurry-compost

Introduction
 Estimation of regional biomass production
 Recycling technologies for organic wasteContents

Generated Sludge (1,000DSt)- 240 -

- 241 -Compost, construction material
 Biogas, solid fuel



Waste
biomass

Green biomass

Regional biomass

Unutilizedbiomass

Resource
vegetation

In-house consumption
 Positive utilization

Utilize the products efficiently

Regional biomass

Vegetation
waste

Gather regional biomass at WWTP
 Step up the production of recycle

Utilization of regional biomass
centered on WWTP

Food waste
Wood generated by construction

Waste biomassInventory system of green biomass

The amount and kinds of generated
biomass will be precisely investigated.
 Total volume produced in Japan will be
estimated.
 Information management systems will
be investigated.

Green biomass utilization

River dike maintenance Trimming street-side trees

Unutilized biomass
 Resource vegetation
 Vegetation waste

Estimation of regional biomass
production

- 242 Technologies for recycling

Alternative material of peat moss
(Thick layer basic materials spaying)
Pilot works for practical use about
the developing and existing usefultechnologies

Data base for biomass

Driftwood into dam reservoirs

Develop the system which provides
and manages the data base of
biomass from each public work.

Recycling and utilizing biomass frompublic works

administrative
infrastructure, land and transport
sectionroad
freeway, national highway, local highway
river
river, dam, erosion control, seashorecity
street, park, sewarage
airportrunwayharborwaterfront
railwayrailroad* biomass: grass, branches and leaves, drifwood, bio-solid

Kinds of biomass generated fromnational land management

Burning up at the field

Spreading over the grass

Bio-solids
SludgeGreenbiomass
Plant
waste

(Slurry（Compost
compost)）Fermentation
Fermentation

Co-digestion
Fermentation

Fertilizer

Alcohol
Organic acid

Methane gas

Recycling technology for organic
waste

Chipping branches

Trimming street-trees (e.g. Tottori river and road office)

MowingRiver dike maintenance (e.g. Edogawa river office)Infrastructure operation at river androad offices

- 243 -Green biomass is shattered and softenedKeep at a high temperature and under highsteam pressure for a certain period Then suddenly reduces the pressure

Steam explosion methodGreen biomass (Wood, dries grass) Bio-solid

Material

Steam-exploded broadleaf tree chips prepared underpressure of 2MPa for 15 minuets.

Wood chips before and after thesteam explosion treatment

(1) Anaerobic co-digestion

Recycling technology for organic waste

Steam
蒸気 →

Steam-exploded
material
爆砕物

Silencer
サイレンサー

Steam drain→ 排蒸気

Inserting and removing samples once per day at 35
degrees for 50 days, while varying the ratio of theadded plant waste to the bio-solid.

Sequential methane fermentation
experimentPressure vessel
加圧容器
３０ L

試料投入
Sampleinvestment

Steam-explosion device

Ratioガス
of digestiongas
発生倍率(gas / investment
material)
3
3

0

10

20

30

0.25

0.5

0.75

1

1.25

(steam-exploded wood / bio-solid )organic
to 水
bio-solid
混Ratio
合 比 of（木質 爆waste
砕 物 addition
DS ／ 下汚 泥 TS）

0

全 ガ ス□ Generated
gas
メタンガス
■ Methane
gas





All kinds of slurry organic material“an improved aerobic digestion”

Considered to beThe reduction of sludge and its stabilization
 Oxygen could be provided from a liquidsurface by giving it high oxygen content“Slurry-compost”

Material(2) Slurry-compost

Recycling technology for organic waste

Methane gas production increased in proportion to
the ratio of added steam-exploded wood to the biosolid.

（m ／投入量 m ）

40

0

20

40

60

80

0

20℃
100

（mg／ L）
0

0

10

20

500
250

30

750

50

60

40

0.5
1
1.5
混 合Ratio
比 （of木organic
質 爆 砕waste
物 Daddition
S ／ 下to水bio-solid
汚 泥 TS）(steam-exploded wood / bio-solid )

0

TOC
NH4-N
PO4-P

1000

1250

1500

10

50℃

15

60℃

日
20 (days)

70℃

0

20

40

60

80

0

20℃
100

5

35℃

10

50℃

Digestion Sludge

15

60℃

Because the digestion sludge was decomposed biologically under an anaerobic
atmosphere, it was assumed that aerobic microorganism treated the sludge.

Digestion sludge was decomposed quickly under the normal temperature.

5

35℃

Excess Sludge

Transition of generated CO2

A large quantity of soluble TOC and PO4-P tend to remain indigestion sludge, but soluble NH4-N decreased considerably
when the steam-exploded material increased.

Dissolution
溶 解 性 T O C ， N H 4- N

Dissolution characteristics of TOC,
NH4-N, PO4-P
PO 4- P （ m g／ L）

Recovery of methane gas fromsteam-exploded wood

mgC/gMLVSS-消化汚泥
mgC/gMLVSS- Digestion sludge- 244 mgC/gMLVSS-余剰汚泥
mgC/gMLVSS- Excess sludge

(day
20 日

70℃

- 245 -

焼却炉補助燃料
Incinerator
44%
fuel 44%

Beneficial
Use 37%

有効利用量
37%

Bio-gas was generated 280 million m3 per year in Japan.
And approximately 30% is left over and burned off

Tank heating34%

嫌気性消化への熱供給利用量
34%

Left over
未利用量
29%29%

Airその他
Others 6%
con6%
Dry
場内冷暖房
fuel3% 3%
汚泥乾燥
6%
6%
Power
generation
41%

ガス発電
41%

Recently the number has been increased
but it is still limited.

Utilization of biogas

Digestion process has been introduced
at approximately 350 WWTP.
 Power facilities, such as gas engines or
fuel cells, have been installed at some
WWTP.

Maximum supply of biogas

0 km

150

3. In addition, the biogas of all bio-solid was calculated.

Hypothetical conditions:
1. The quantity of solid material input was over 3.0%.
2. The ratio of digestion tank was 85% and the digestion period was 20 days,
and the digestion tank was heated at 35 degrees by biogas.

condition of bio-solid
qauntity of remaining quantity of refined
reduction of CO2
treatment at WWTP
biogas (1,000m3)
biogas (1,000m3)(t)present remaining biogas
107,200
53,600199,400
efficient treatment
251,300
125,600
467,500
digestion of all bio-solid
310,800
155,400
578,200* using the data in FY2002 for condition of biogas production

Quantity of biogas supply
at total WWTP

1,000,000～

Generated bio-gas(m3/year)

Distribution of digestion facilities

- 246 -Biogas is utilized outside, such as City gas,
WWTP after considerable refining.

“Biogas vehicles”

Refined biogas = natural gas

Natural gas vehicles

New beneficial use of biogas

Spring 2008 open3
 2,000m /day
 40 buses (50km/day)

Full-scale plant(PWRI, Kobe City, KOBELCO ECO-SOLUTIONS CO.)Refined biogas = 98% methane gas Kobe city bus opened the business from2nd October, 2006

Kobe biogas

Kobe biogas

Biogas vehicles

City gas has been designed as standard
fuel for natural gas vehicles.
 Each refined biogas must be inspected toconform that it has the same quality as“natural gas”.
 If biogas refining systems are standardized,
biogas vehicles will be introduced easily.
Standardization of biogas

Small-scale:
About 10 standard cars could be operated as “Biogas vehicles” at WWTP thatretain about 100 thousands m3 of biogas per year.

Large-scale:
The “pressurized gas supply project” was carried out during 1942-1950.
More than 100 biogas vehicles were driven at the same time.

qauntity of remaining quantity of refined
number of driving biogas vehicles
biogas (1,000m3)
biogas (1,000m3)
normal car 2t packer large bus
large-scale
2,500
1,250
310
250
50
middle-scale
500
250
60
50
10
small-scale
100
50
10
10
2
* driving length per year and per fuel unit, normal car: 60,000km/year and 15km/m3
2t packer: 20,000km/year and 4km/m3, large bus: 50,000km/year and 2km/m3

WWTP

Number of driving biogas vehicles
at each WWTP







Left small tank: adsorption type
Right big tank: usual typeGas storage tank by adsorption(e.g. Tsuruoka city)

Change vegetation waste into green biomass



Biogas vehicles system

Technologies for utilizing biogas

Economical co-digestion system Utilization of fermentation residue

Recycling technology for green biomass

Data base of regional biomassGasmolecule

Compression zone

Summary

Adsorption media

Adsorption zone

Biogas adsorption system

発電

水素化

Generation
発電

Regional utilization

Household

家庭・地域へ遠隔輸送利用Transportation

Vehicles
自動車

横置き（大型）
Adsorption
tank (large-scale)

吸着貯蔵

縦置き（コンパクト型）
Adsorption
tank (smallscale)

吸着貯蔵

ガススティションGas
station

City都市ガス
gas

Naturalgas vehicles
天然ガス自動車

0

500

1,000

1,500

2,000

2,500

89

90

91

92

93

94

95

FY

96

97

98

99

00

01

02

03

Slag
Ash
CarbonDried
CompostDewatered
SlurryTransition of generated bio-solid

廃熱は、メタン発酵槽の加Fermentation
tank heating
温に用いるガス精製機器棟
Biogasrefining plant

Methane
メタン発酵槽
fermentation
tank

各種のバイオマス
Regional
biomass

Biogas utilization project

Generated Sludge(1,000DSt)- 247 -