Study of LCA application in the energy systems focused on the Anaerobic
Digestion Gas (ADG)
Jeerayoos Tantiwiwat*, Helmut Yabar, Yoshiro Higano, Takeshi Mizunoya
University of Tsukuba, Graduate School of Life and Environmental Sciences, Japan; 1-1-1 Tennodai,
Tsukuba, Ibaraki, Japan 305-8572*jeerayoos_7@hotmail.com
Abstract
In this study we analyze a new type of renewable energy technology namely Anaerobic Digestion Gas (ADG) by using
Life Cycle Assessment as well as Life Cycle Costs in order to determine the feasibility of this technology. The study
proposes different scenarios and compares their performance in two stages: fuel source and power generation methods. The
study compares the performance between the utilization of ADG or other type of biomass source and between the utilizationof fuel via traditional thermal power generation method and via the fuel cell. In the case of the application of the ADG andfuel cell utilized systems the study uses data from the biomass utilization, especially in biomass waste such as livestock
manure and wastewater sludge, and also the fuel cell utilization in Japan. The evaluation is done in terms of global warming
potential, ozone depletion and acidification from a life cycle perspective. We will also analyze the financial cost in capitaland maintenance cost, then the feasibility to apply these types of energy systems.
Keywords: Renewable Energy, Life Cycle Assessment, Anaerobic Digestion Gas, Fuel Cell, Energy Technology
1. Introduction
At present, the environmental problems associated with human activities are gradually causing severe impact tomankind. Especially important is the huge dependence on fossil fuel as energy source. To address this challenge many
renewable energy sources have been developed. As one of the leading energy sources, the biomass energy usage is now
expanding all over the world. The biomass is the energy source from living organisms such as plants and can be used both
directly or converted into energy products such as bio-fuel. From the world aspect, the biomass energy usage has been
increased and also the related utilization technology has developed for the substitution of fossil fuels. Around 13.5% of worldenergy depends on renewable energy [1], of which the biomass energy utilization accounts for almost 80% and increasing
gradually worldwide. In case of EU countries, Germany’s biomass utilization accounts for 66% of all renewable energy usage
in the country. And according to a study in Sweden [2], the utilization of biomass is 32% of total energy demand in the
country, which is remarkably high. Thus, Sweden has shown the success in biomass utilization, which has set the example tomany countries to move toward the green energy utilization.
About the Biomass utilization in Japan [3,4,5], the Japanese government has established the Biomass Nippon
Strategy with the objective of increasing the biomass utilization in Japan by the year of 2020. This policy is very essential tofind the alternative solution for energy problem in both energy shortage due to the shutdown of nuclear power plants and also
the increase of carbon dioxide emissions due to the increase of the thermal power plants usage to cover the nuclear power
utilization and also to realize the “Recycle-Oriented Society”. As the goal of the strategy in 2010 [6] in terms of national
perspective, the increase of biomass utilization, focusing on the biomass waste, is aimed to improve to 80% nationwide. And
also the utilization of unused biomass is aimed to improve to 25% nationwide and also starting of the commercial use ofenergy crops. In the regional perspective, the pilot project of launching Biomass Town is aimed to be launched in 500 towns
all over Japan. In technological perspective, the biomass utilizing technology related projects are supported with funding andsubsidy from the government.
The biomass utilizing technologies used in present in Japan are mostly the composting for fertilizer from livestock
manure and wastewater sludge and the thermal recycle (incineration with energy recovery) from dry biomass sources. In
terms of composting technologies, the cost is cheap compared to other technologies and also easy to use. But the nutrient
yield for these types of fertilizer is still low and might not be able to be commercially used and there are probably better ways
to utilize these types of biomass waste instead of composting. About the thermal recycle, although this method is good interms of energy recovery, but the efficiency is still low and there is the problem in carbon dioxide emissions.
As the proposal for new technology, we introduce the Anaerobic Digestion Gas (ADG). ADG is the product of theanaerobic digestion process. Anaerobic digestion is a series of processes in which microorganisms break down biodegradable
material in the absence of oxygen. This method has been used for industrial or domestic purposes to manage waste and/or torelease energy and also been widely used as part of the wastewater treatment process. The ADG is considered as therenewable fuel because the process produces methane and carbon dioxide rich biogas suitable for energy production asshown in Figure 1. The feedstock sources are typically biodegradable waste such as human bodily waste, agricultural waste
or food processing waste, which can be found in our daily life and cause the environmental problems at present due to theirdifficulty of disposal and treatment. This is also benefitting in reduction of CH 4, one of the greenhouse gases, emitted to theatmosphere if the biodegradable waste decays on its own. Moreover, ADG can replace fossil fuels in energy conversion
devices and the solid residue, the nutrient-rich digestate, also can be used as fertilizer.

Fig.1: Component of ADG
For the utilization of ADG [7], we will focus on the fuel cell which directly converts the hydrogen source throughchemical reaction to generate the electricity power. With most of the emissions are water (H 2O) and zero carbon dioxide
emission, this technology can help reduce the global warming potential gases in both terms of carbon dioxide and alsomethane and utilize them as the power energy. The fuel cell type that we will study applying ADG as one of the fuelreforming methods is Molten Carbonate Fuel Cell (MCFC). There are three advantages for using this type of fuel cell. First,
by utilize the high operation temperature of MCFC which is enough to causes gas reformation, it is able to feed the reformed
gas into the system directly after removal of the contaminant (scrubbed). Second, the high concentration of CO2 in ADG isused to dilute the anode gas, and able for recirculation in the system. Finally, we are also able to utilize the high temperature
waste heat from the system instead of the traditional heat source. For example, we can transfer the waste heat to the hot-water
heat exchanger to control the temperature inside the anaerobic digester.
However, while these alternatives have the image of being environmental friendly, if we measure their footprint
from a life cycle perspective they might be still causing great impact on the environment. In this study, we analyze a new
type of renewable energy technology namely Anaerobic Digestion Gas (ADG) by using Life Cycle Assessment as well asLife Cycle Costs in order to determine the feasibility of this technology.
As the result, we can pinpoint the main problems and be able to reduce the impact and also improve the efficiencyof the energy system. Finally the feasibility study can lead to promote the utilization and distribution of energy systems
utilizing fuel cell and ADG to help realize a sustainable and environmental-friendly energy system.
2. Method
The study proposes different scenarios and compares their performance in two stages: fuel source and power generation
methods. The study compares the performance between the utilization of ADG or other type of biomass source and between
the utilization of fuel via traditional thermal power generation method and via the fuel cell. In the case of the application of
the ADG and fuel cell utilized systems the study uses data from the biomass utilization, especially in biomass waste such as
livestock manure and wastewater sludge, and also the fuel cell utilization in Japan.
The evaluation is done in terms of global warming potential, ozone depletion and acidification, other environmental
factors and also material and energy consumption from a life cycle perspective. We will also analyze the financial cost in
capital and maintenance cost, then the feasibility to apply these types of energy systems. The calculation process will be done
via the software for calculating in terms of Life Cycle Assessment.
2.1 Case StudyAs the case study, we’ve used the biomass utilization from Hita City [8], located in Oita prefecture, Japan. The
biomass utilization data are as described in Table 1;

Biomass Type
Biomass Waste
Livestock Manure
Wood Waste
Construction Waste
Food Waste
Draff (Beer Kasu)
Sewage Sludge
Human Waste Sludge
Rural Community Sewerage
Waste Edible Oil
Unused Biomass

Table 1: Biomass Utilization in Hita City
StorageUtilized
Wet Wt.
Wet Wt.
Utilization
Conversion & Treatment Method
Ratio (%)
（t/year）（t/year）
386,667
298,06277.08
243,931
196,376
81
Composting
29,509
Bark Compost
94,93533,61196
Bedding Material
28,122
Chip
1,416
1,416
100
Chip
8,208
ー
0
Incineration
5,983
5,983
100
Feedstuff
2,811
2,811
100
Cement Material
28,825234
0.8
Composting
558
300(kl)0Incinerationー
32,395
11,252
34.73

Forest Remainder

21,143ー0

Rice Straw
Rice Husk

8,616
2,636

8,616
2,636

100
100

Bedding Material
Carbonize, Bedding Material

Based on the data analysis, the utilization of biomass is divided into 2 types; biomass waste and unused biomass. In
biomass waste, the livestock manure and wood waste occupied almost 63% and 25% of biomass waste utilized respectively
as shown in Figure 2. In unused biomass, forest remainder and rice straw occupied most of the unused biomass at 65% and
27% respectively as shown in Figure 3.

Fig.2: Biomass Waste Composition (in Wet Wt.)

Fig.3: Unused Biomass Composition (in Wet Wt.)

In terms of utilization, 64% of utilized biomass is composted. And most of wood waste is utilized as bark compost,
bedding material and turned into wood chip. But the food waste and waste edible oil are still not utilized as they areincinerated as shown in Figure 4.

Fig.4: Biomass Utilization Ratio (in Wet Wt.)
As shown in Table 2, Hita city government sets the goal of biomass utilization and also tries to introduce manyutilization technologies;

Table 2: Biomass Utilization Target
Wet Wt.
（t/year）

Biomass Waste

Storage
Wet Wt.
（t/year）
386,667

Livestock Manure

243,931

18,250225,681

Utilization
Ratio (%)
>95
7.5
92.5

Wood Waste

94,93594,935100

Construction Waste
Food Waste
Draff (Beer Kasu)
Sewage Sludge
Human Waste Sludge
Rural Community Sewerage
Waste Edible Oil
Unused Biomass
Forest Remainder
Rice Straw
Rice Husk

1,416
8,208
5,983
2,811

1,416
8,208
5,983
2,811
27,1932,190300(kl)

100
100
100
100
92.6
7.4
100
>40
>40
100
100

Biomass Type

29,383300(kl)32,395
21,143
8,616
2,636

Utilized

8,616
2,636

Conversion & Treatment Method
Bio-gasification (Pig Manure)
Composting
Bedding Material, Chip (For Paper
Product), Composting, Fuel
Fuel
Bio-gasification
Feedstuff
Cement Material
Composting
Bio-gasification
BDF
Fuel
Bedding Material, Fertilizer
Bedding Material

Among the technologies expected to be introduced, Hita City has already used the bio-gasification utilizing
livestock manure, food waste and sludge to produce methane in biogas plant within City’s Biomass Recycling Center. The
detail of the methane fermentation plant is described as shown in Figure 5 and the detail of average electricity generation andself-sufficiency generated from gas engine utilizing produced biogas [9] are described as shown in table 3.

Fig.5: Detail of Methane Fermentation Plant, Hita City Recycling Center
Table 3: Average Electricity Generation and Self-Sufficiency
Category
2007
2008
2009
Amount of Electricity generated (kwh)
1,682,991
1,812,058
1,785,188

2010
1,926,189

Amount of Electricity sold (kwh)
Sum of Electricity sold (Yen)
Sale of Tradable Green Certificates (kwh)362,616
4,171,541
924,347

115,308
981,5100

184,632
1,562,222
0284,532
3,284,757
957,072

Thus, we’d like to use the data of Hita city methane fermentation plant and power generation plant as the base forthe research of introducing the new technology using fuel cell to utilize ADG or biogas to generate electricity power.

3. Conclusions
The results of this study are expected to be as below;
1) In terms of environmental factors, the new proposed energy system, fuel cell utilizing ADG, is expected to haveremarkably low emissions due to methane utilized as hydrogen source with zero emission, carbon dioxide
circulated and utilized in MCFC system and other pollutants removed before being fed into the reforming system.
Thus, this system is expected to greatly contribute to emission reduction.
2) Since the fuel cell system can utilize ADG to generate electricity power and waste heat from the system also can be
efficiently utilized, this system is highly evaluated in an energy aspect.
3) On the other hand, the material consumption, especially in heavy metals and rare metals, might be in high amount,which will affect in both terms of pollutant emissions and cost of fuel cell.
4) The financial cost is expected to be higher compared to other technologies but also expected to be worthy for longterm investment.
About the feasibility, this new system is expected to show high feasibility to be used in many regions which haveenough biomass resources to be converted into ADG and can be the targets of the introduction of the fuel cell system in orderto replace traditional power generation system. However, there might be difficulties in introducing the fuel cell system due tothe high initial cost. Thus, this system distribution and utilization might be limited only in developed countries, which haveenough infra-structures to support this new system.

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