Sutikno, Unila Lampung

Potency of agro-industrial waste biomass for second generation of bio-ethanol production

as petroleum substitution

byIr. Sutikno, M.Sc., Ph.D,

The University of Lampung, Bandar Lampung. 35145

Sutikno, Unila Lampung

Potency of agro-industrial waste biomass for second generation of bio-ethanol production

as petroleum substitution (presented at Sustainable Biofuel Development Researach Workshop,

February 4-5, 2009, in Sultan Hotel Jakarta)

Ir. Sutikno, M.Sc., Ph.D, The University of Lampung, Bandar Lampung. 35145

Introduction

Indonesian fossil fuel reserves decrease steadily. In 1974, Indonesia had fossil fuel

reserves of 15.000 metric barrel (MB) and decreased to 5.123 MB in 2000 and to 4.301

MB in 2005 (OPEC, 2005). This was due to exploitation of the fossil fuel for many years

and limitation of geology exploration and survey to find out new fossil fuel reserves.

Without new fuel reserve addition, Indonesian fossil fuel reserve can only be explored

until the year of 2035 (Dartanto, 2005).

Meanwhile, Indonesian petroleum consumptions increase significantly. The

consumption increase is mostly due to Indonesia population and economic growth

(Dartanto, 2005). The petroleum consumption increased from 996.400 barrel daily in 2000

to 1.143.700 barrel daily in the year of 2004 (OPEC, 2005). At the same time, Indonesian

petroleum production decreased from 1.272.500 barrel daily in 2000 to 1.094.000 barrel

daily in the year of 2004 (Danarto,2005). Thus, in 2004 Indonesia had to import 49.300

barrel petroleum daily to fulfill Indonesian petroleum demands.

To overcome fossil fuel reserve depletion and petroleum consumption increase,

Indonesian government makes several efforts. One of the government efforts was the

establishment of energy policies which were declared in Inpres number 1 in the year of

2006, Inpres number 2 in the year of 2006, and Pepres number 5 in the year of 2006

(Hayun, 2008). The Inpres and Pepres instructed to develop and utilize fuel alternatives

for reducing Indonesian dependence on fossil fuel. One of the fuel alternatives is bio-fuel

such as bioethanol, biobutanol and biodiesel which utilize biomass as raw materials. The

use of biofuel as petroleum-based fuel substitution can improve sustainability and reduce

greenhouse gas emissions (Brown et al., 1998; Carere et al., 2008).

Agro-Industrial Waste Biomass

Agro-industrial waste biomass is byproduct of industries which use agricultural

products as raw materials. For example, bagasse, palm oil empty bunch (tandan kosong

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kelapa sawit), and rice straw are byproducts of sugar industries, palm oil industries, and

paddy plantation, respectively. The agro-industrial byproducts are commonly cell walls

which contain lignin, cellulose, and hemicellulose (Gomez et al., 2008). Quintero-

Ramirez (2008) stated that cellulose consist of high molecular weight polymers of glucose

that are held rigidly together as bundles of fibers to provide material strength;

Hemicellulose consists of shorter polymers of various sugars that glue the cellulose

bundles together, and lignin providing rigidity to the structure consists of a tri-dimensional

polymer of propyl-phenol that is imbedded in and bound to the hemicellulose (Figure 1).

Cellulose, hemi cellulose, and lignin contents of bagasse, oil palm empty bunch, and rice

straw are not the same and stated at Table 1.

Figure 1. Polymer structure of lignocellulosic biomassSource : Quintero-Ramirez , 2008.

Table 1. Cellulose, hemi cellulose, and lignin contents of agro-industrial waste biomass in Indonesia

NoKinds of Biomass

Component Content (%) of Biomass Reference

Cellulose Hemi Cellulose Lignin1 Rice straw 37.71 21.99 16.62 Dewi, 20022 Bagasse 52.70 20.00 24.20 Sansuri et al., 2007

3Oil palm empty bunch

45.80 26.00 - Isroi, 2008

Agro-industrial waste biomass in Indonesia is abundance and inexpensive and it can

fulfill Indonesian transportation fuel demands if it is converted to bioethanol via

fermentation. Indonesian paddy production in the year of 2007 was 57.160.000 ton dry

milling paddy (Media, 2008). Every ton paddy provides 5 ton rice straw as byproduct

(Agustina, 2007 in IPB, 2008). This means that in 2007, total rice straw produced was 5 x

57.160.000 ton = 285.800.000 ton. Rice straw contains 37,71% cellulose, 21,99% hemi

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cellulose, and 24,20% lignin (Dewi, 2002). Based on formula found by Badger (2002),

total bioethanol produced from the straw is 45.753.728 kilo litters (kL). This amount of

bioethanol has been able to fulfill the Indonesian petroleum consumption which is only

16.418.000 kL in the year of 2004 (Wahid, 2008). With the same approach, total

bioethanol which can be generated from oil palm empty bunch and bagasse is 7.872.359

kL and 2.000.000 kL, respectively (Table 2).

Table 2 Bioethanol potency generated from agro-industrial waste biomass via microbial fermentation in Indonesia

No Agro-industrial Waste Biomass

Total (ton/year)Potensial Ethanol produced (kL) *

Reference

1Rice Straw (data 2006)

285,800,000 a) 45,753,728 b)*$a) Media, 2008b) Badger, 2007

2 Bagasse (data 2002) 39,539,944 c) 7,872,359 d)* c) Anonim, 2005 d) Badger, 2007

3Oil palm empty bunch (data 2006)

20,750,000 2,000,000 Isroi, 2008

*) Calculated based on formula found by Badger, 2007.$) Enough for fulfilling premium demand yearly which was only 16.418.000 kL in the year of 2004

(Wahid, 2008)

Second Generation Bioethanol Production

Unlike the first generation bioethanol which is produced from starchy materials

such as corn in the USA (USDA, 2007) (Figure 2) or sugary materials such as sugar cane

in Brazil (Badger, 2002), the second generation bioethanol is generated from

lignocelluloses (Carere et al., 2008, Gomez et al., 2008, Jagger, 2009). There are four

steps to produce second generation bioethanol, i.e. (1) pretreatment of agro-industrial

waste biomass, (2) hydrolysis of cellulose and hemicelluloses, (3) fermentation of glucose

into bioethanol, and (4) bioethanol recovery (Figure 3).

To generate second generation bioethanol, lignocelluloses are collected and then

pretreated physically, chemically, biologically or combination among the three

approaches. Objectives of the pretreatment are to decrease cellulose crystallinity, increase

lignocellulosic surface area, remove hemicellulose, and break lignin seal (Quintero-

Ramirez, 2008) so that cellulose and hemicellulose hydrolysis into simple sugars can run

maximally. The simple sugars are then fermented by microbes such as Saccharomycess

cerevisiae into ethanol solution (Chanda et al., 1995). After recovery and purification,

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bioethanol fulfilling technical specification of transportation fuel is ready to substitute

petroleum for transportation.

Figure 2. Steps of first generation bioethanol production from corn

Source : McCoy, 1998.

Figure 3. Steps of second generation bioethanol production from agricultural waste biomass

Source : Knauf and Moniruzzaman, 2004.

Up to now, the production cost of second generation bioethanol is still high; A Key

to unlocking low cost the second generation bioethanol is a pretreatment step which

provides significant effects on the other steps (Figure 4). The pretreatment generally refers

to the disruption of the naturally resistant carbohydrate-lignin shield that limits the

accessibility of enzymes to cellulose and hemicellulose (Yan and Wyman, 2008).

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Figure 4. A simplified process flow diagram for biological conversion of cellulosic biomass to ethanol illustrating potential effects of pretreatment on other operation

Source : Yang and Wyman, 2008.

However, the choice of pretreatment technology is not trivial and must take into account

sugar-release patterns and solid concentrations for each pretreatment in conjunction with

their compatibility with the overall process, feedstock, enzymes, and organisms to be

applied. Therefore, researches to find out the best pretreatment for certain agro-

industrial waste biomass in Indonesia should be carried out intensively and Indonesian

New & Renewable Energy Society (METI) should coordinate and communicate among

Indonesian researchers in order to realize production in commercial scale of the

second generation bioethanol in Indonesia in efficient and effective ways. It is hoped

that Indonesia which has huge and cheap waste biomasses can catch up other country

progress such as Brazil which has build several pilot plants of the second generation

bioethanol from sugar cane bagasse in the year of 2009 (Jagger, 2009).

Conclusion

Productions of the second generation bioethanol from agro-industrial waste

biomass are essential in order to overcome our excessive dependence on petroleum

for liquid fuels and also to address the build-up of greenhouse gases that cause global

climate change. Biological conversion offers a potential for radical technical advances

through application of the powerful tools of modern biotechnology to realize truly low

costs. However, pretreatment step is the key cost element in the biological conversion

of agro-industrial waste biomass to bioethanol or other products, such as biobutanol,

that still require low cost sugars to be cost competitive. In addition, pretreatment step can

have invasive impacts on the performance and cost of virtually all other operation steps.

Thus, pretreatment steps must be advanced and carefully integrated with the rest of

the process to realize the full potential of cellulosic ethanol or other biologically

derived products. Although a wide range of pretreatment approaches have been

conducted over the years, only a few achieve the high yields of sugars from biomass with

low enough costs to be considered attractive, and all of them rely on chemical addition.

Unfortunately, relatively little funding has targeted advancing either the technologies or

their understanding, impeding significant breakthroughs that reduce cost and more

confident commercial applications. It is now time for far more aggressive and intensive

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to carry out fundamental and applied researches on the pretreatment step and its

integration with the rest of the second generation bioethanol process.

Sutikno, Unila Lampung

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