沙漠研究 19-1, 9- 12 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Feasibility of Wild Grass Exploitation for Bio Fuel Production
Mitsuteru IRIE1, Ryoji OKAWARA2, Yukuo ABE1
Abstract: Cultivating fuel crops is planned in Papua New Guinea. In order to evaluate theproduction potential, available land which is covered by grass was found by satellite imageanalysis. Comparing between the input of the energy to the project and reduced amount of
CO2 emission, ethanol fermentation process consumes a lot of energy and makes negative
impact on CO2 emission totally. Power generation with the local grass is suggested asalternative energy for it.
Keywords: CO2 emission, Ethanol production, Grass land, Satellite image analysis

1. Introduction
Recent jump in crude oil price induces not only the focus on bio fuel, but also the food price rising.
Present situation is the beginning of shifting to the new generation of energy, so that there are a lot of casesthat the farmland for food crops are changed to that for energy crops because of easy obtainment. As aresult, it has been said that bio fuel production causes the incident of the early food crisis on someoccasions. However, strictly speaking, appropriate developments of bio fuel in marginal land such as
grassland, which has not been cultivated for food crops or dense forest, surely contribute to that issue
without the significant impact on local economics and environment.
Another discussion on bio fuel is energy input and CO2 emission balance for that production; harvest,transport, process and feedstock. Some critics argue that bio fuels will demand more energy than they
produceA). Transportation of resource and products, agricultural activities and ethanol production
processes consume a lot of fossil fuel in the conventional processes.
This study shows the feasibility of bio fuel project in the concrete site with the advanced exploitationof local resources. First, the available area in the study site was identified by the satellite image analysis,
then candidate crops are defined and ethanol production potential was evaluated. The reduction of CO2emission was compared with the input energy to the project. Finally, the solution for the negative cases in
the CO2 emission was suggested.
2. Study SiteThe study site is located in Papua New Guinea (PNG), one of South Pacific countries. The area ofPNG is 462,840 km² (1.25times than Japan). The population is 6180,000, thus population density is13person/km² (Japan 343/km²). This situation shows this country remaining undeveloped land foragriculture and high potential of new agricultural development. Current life style in PNG is Selfsufficiency. Because of the shortage of logistics, the farmers cannot access to the market and they only
cultivate the food of their consuming amount without excess production irrespective of enough land forcommercial agriculture under the adequate climate. These situations keep this country in low economicalgrowth. The study site was defined on East Sepik Province whose capital is Wewak. North bank of Sepik
River is a large vacant grass land.
3. Satellite Image Analysis for Finding Grassland and its Land Potential for Agriculture
Satellite image analysis is carried out focusing on the study site for finding the available grass land.
Unsupervised categorization is applied using the parameters of bands 1–6 of the LANDSAT image of 16
September 2002. Comparing the ground truth survey, categorizing to eight groups clearly indicates thegrassland (the black area in Fig. 2). There are flood plains along Sepik River. This area is considered tobe unavailable for agriculture. Excluding the flood plains, the total available grassland is about 2,000km2.
Shuttle Radar Topographic Mission (SRTM) data is downloaded and overlaid on the map. There is12Alliance for Research on North Africa, University of Tsukuba, Tennodai, Tsukuba, Ibaragi, Japan;
COSMO Oil company, Hamamatsucho, Sinagawa, Tokyo, Japan;

10Study siteWewak

Sepik RiverPapua New Guinea
Port Moresby
100km

10km

Sepik River

Fig. 2. Finding the grass land by the satellite image
analysis of unsupervised classification. Blackarea shows the grass land.

Fig. 1. Location of the study site.

a gentle slope from the north to the Sepik River, and the southern part of the land is almost completely flat.
The flat area would be waterlogged in the rainy season. On the other hand, the hilly areas in the northpart would contribute to the drainage of surface rainwater.
The topographic characteristics indicate that the drainage capacity of the soil in the southern part
might be a problem for agricultural activities. A soil survey was performed in the southern part and water
permeability was measured, which was 10-9 m/s. Drainage characteristics, evaluated by the pF (potential
free energy) test, were very low. The clay soil, containing large amounts of water, was not suitable forroot crops such as cassava, sweet potato and yam potato, which are typical candidate fuel crops in this area.
In areas with soils of this kind, sugarcane, rice and sago palm would be candidate crops for bio ethanol
production.
4. Simulation for Ethanol Production and Its CO2 balance
In this study, four kinds of crops are listed as candidates for fuel crops: sugarcane, cassava, rice andsago palm. These crops would be cultivated on land suitable for them. However, detailed soil
distribution data have not been obtained. It is assumed that each kind of crop is cultivated on one-fourthof the total area: 500 km2 each. Aramaki et al. (2008) calculated the ethanol production potential fromstatistical data for each crop. Table 1 shows the calculated ethanol production for each crop.
Aramaki et al. (2008) discussed life cycle assessment with regard to CO2 emission. Fig. 3 shows
project emission, which is the total emission from seeding to processing into ethanol. In the case ofsugarcane, the residue after squeezing the sugar juice can be exploited as fuel. Some former studies
showed that the energy extracted from the residue is adequate for the process of ethanol fermentation.
Thus, project emission is much lower than the baseline emission (shown as ‘Emission curtail’ in Fig.3).
On the other hand, cassava needs energy for saccharification and fermentation. As a result, project
Table 1. Ethanol production capacity of each crop.
Sugar caneminmaxDevelopment area (km2)
Row material yield unit
(Mg/ km2/365d)
Row material for 1m3 Ethanol(Mg/ m3)
Ethanol production(103 m3/365d)

Cassava
Minmax

500
5120

500
6900

1563

12.7
202

3125

4.46272

175

350

Rice(Hokuriku193)

Sago palm

500

500

1000
(1 harvest a year)

4000

2.5

6.67

20030011

Reduced Emission (base-line emission)
Emission increment
Emission curtail
Factory
Products transportation
Material transportationAgricultural chemicals
Fertilizer
Nursery
MachineCultivationminmax

Sugar caneminmaxCassava

Fig. 3. Comparison between “Base-line emission” and “Project emission” for Sugarcane and Cassava.

emission exceeds baseline emission. Rice and sago palm show the same result. For these crops,
alternative energy resources covering the amount necessary for the process from raw material to ethanol
are required.
5. Grass as Energy Resource for Ethanol Production
The study site is covered with grass, locally called Kunai grass. Kunai grass is not exploited by thelocal people under the current situation but it is known to grow rapidly. This grass can be considered as
an available resource for energy production. In this study, part of the land would remain as grassland andthe harvested grass would be used for biomass power generation.
Power generation from Kunai grass is estimated by formula (1):
W=P * LHV * C(1)
W: Power production
P: Yield amount(kg), LHV: Lower heat value (J/kg)
C: Power generation efficiency coefficient (0.278 kWh/MJ)
P and LHV is estimated by the field survey shown as below
5.1. Grass yield
The weight of grass per unit area (2 m × 2 m) was determined. Sampling points are shown in Fig. 2.
At the first harvest on 4 June 2008, 2500Mg/ km2 was harvested on average. After the first harvest, thelocal people helped to measure the height of the grass every week because our laboratory is a long distancefrom the site. Fig.4 shows the average height of five grass plants. Two months after harvesting, theplants had already approached their maximum height. Plant density was not observed in this study, butleaf density would increase after the plants have reached their maximum height. As a rough estimate,harvesting could be done every 4 months, i.e. three times a year.
The second harvest was carried out on 26 October 2008. The amount harvested was 1130 Mg/ km2
on average. This was less than the first harvest. The first harvest included dead grass that had
accumulated over a long period. Therefore, yield at the second harvest, 1130Mg/ km2, represents the true
yield of grass.

120
100
80
60
40
point1point2

20

24-Sep10-Sep27-Aug13-Aug30-Jul

16-Jul

2-Jul

18-Jun04-JunHeight of the grass (cm)

12Fig. 4. Growth of Kunai Grass.

5.2. Lower heat value
At the first harvest, the grass was sampled to measure the heat value. The higher heating value ofcomplete dried grass was 16.8 MJ/kg. Considering the water content at the second harvest (53.3%), thelower heat value was 6.47 MJ/kg. From these numbers, the power production potential of the grassland is1210 MWh/km2.
5.3. Power generation potential of the grass land and master planning of crops and grass landThe energy demand for the production of 1 m3 bio ethanol is 9660 MJ heat and 300 kWh electricity.
This energy can be produced from 700 m2 of the grassland.
On the other hand, 1800-2500 m2 of sugarcane field, 1400-2800m2 of cassava field, 2500 m2 of rice
field and 1700m2 of Sago palm field can produce 1 m3 ethanol. Therefore, 22–28%, 20–33%, 22% and29% of the original grassland should be reserved for sugarcane, cassava, rice and Sago, respectively, andused to supply energy for fermentation. This means that the ethanol production from 500 km2 of the fourcrops would be 157–195, 140–235, 157 and 213 (m3/365d) respectively. In total, 667,000–800,000 m3
ethanol could be produced from the land per year. In order to replace the entire amount of gasoline
consumed in Japan with E3 (3% ethanol blended gasoline), 1,800,000 m3 of ethanol is required.
Therefore, this project site could produce around 40% of this requirement.
6. Conclusions
The available grass land area for the bio ethanol production was evaluated by the satellite image
analysis. It was about 2,000 m2. Based on the result of soil characteristics and topography, the fourcandidate crops were defined. The life cycle assessment for the crops shows the project emission is above
the base-line emission except the case of sugar cane. For alternating the fossil fuel consumption in thefermentation process, the biomass power generation is suggested. Part of the land should remain as grassland for power generation.
AnnotationA) http://www.nature.com/climate/2008/0801/full/climate.2007.71.html
References
Aramaki T., Saito K., Hanaki K., Irie M. (2008): Assessment methods for bio ethanol production project in developing country-Casestudy in Papua New Guinea. Proc. of 16th Symposium on Global Environmental Research, 31st Aug, Okayama (CD-ROM, InJapanese)