Utilization of Agricultural Wastes for Biogas Production in Indonesia
pp. 134-138 in Traditional Technology for Environmental Conservation and Sustainable Development in the Asian-Pacific Region
Proceedings of the UNESCO - University of Tsukuba International Seminar on Traditional Technology for Environmental Conservation and Sustainable Development in the Asian-Pacific Region, held in Tsukuba Science City, Japan, 11-14 December, 1995.
Kozo Ishizuka, D. Sc. ,
Shigeru Hisajima, D. Sc. ,
Darryl R.J. Macer, Ph.D.
Copyright 1996 Masters Program in Environmental Sciences, University of Tsukuba. Commercial rights are reserved, but this book may be reproduced for limited educational purposes. Published by the Master's Program in Environmental Science and
Master's Program in Biosystem Studies,
University of Tsukuba, 1996.
Edi Iswanto Wiloso
, Triadi Basuki, Syahrul Aiman
Research and Development Center for Applied Chemistry,
Indonesian Institute of Sciences, Kawasan Puspiptek,
Serpong 15314, INDONESIA
Indonesia has been facing the fuel energy problems in some parts of the country, especially
in rural areas. In order to reduce dependence on commercial energy, steps have been
taken to develop an alternative source, such as biogas. The main constraints for installing a digester, however, are the initial investment cost and the competition
over kerosene. In this paper, the application of an anaerobic process for biogas
production from cassava solid waste, water hyacinth, and manures are explained.
Biogas, Methane, Energy, Anaerobic digestion, Pollution control,
Agricultural wastes, Indonesia
Most of the Indonesian population live in rural areas. According to 1990 census,
they are about 69.07% of the total population (1). They are using non commercial
energy such as firewood and agricultural wastes as much as 40% of total national
energy consumption (2). Survey on rural energy done in 1990 revealed that about 88% of rural
families used firewood, and only 17% of them used charcoal and agricultural wastes
as an energy source for cooking (3). High consumption on firewood can lead to destruction of forest and the environment; therefore, the need to utilize more agricultural
wastes as an energy source is apparent. Recently, diversification on the use of
energy has increasingly become an important issue because the oil sources are depleting.
Up to now, commercial energy (oil and gas) is still an important export commodity and
a source of devisa income for Indonesia. However, it was estimated that in the early
of year of 2000, Indonesia will become a net oil importer if new oil sources are
not found and the domestic consumption on commercial energy is maintained at the same rate
Various kinds of agricultural wastes are generated in Indonesia. Some of these wastes,
listed in Table 1, are potential to be used as raw materials for biogas production.
The process (anaerobic digestion) converts organic materials into methane which
can be used as an energy source. Utilization of agricultural wastes for biogas production
can minimize the consumption of commercial energy source such as kerosene as well
as the consumption of firewood. In addition, the anaerobic digestion process reduces
the content of organic pollutant that can be hazardous to the environment. Three
examples of the application of this process, treatment of cassava solid waste which
is polluted river around tapioca starch industry, treatment of water hyacinth which
is problematic to Curug dam, and utilization of manures, are explained in this paper.
In the anaerobic digestion process, organic matter is digested in the absence of air.
The degradation of the large molecule, such as agricultural wastes, is carried out
in three stages. The first stage is known as liquefaction where complex organic
materials in solid forms are broken down by external enzymes into soluble forms. The
second stage is the acid formation where the bacteria produce volatile fatty acids
such as acetic, propionic and butyric acids. Carbon dioxide and hydrogen will also
be liberated in this stage. The third stage is the methane formation where the methanogenic
bacteria utilize products of the second stage and convert them into methane.
The Implementation of Biogas Technology in Indonesia
Some programs have been carried out by the government of Indonesia to promote the
use of biogas technology, such as installing a demonstration plant and training for
the public to operate the digester. However, biogas has not yet been popular in
rural areas. In 1984, the number of biogas digester installed in Indonesia was only 100 units
(5). Nine years later, this number increased to only 350 units (3). The reason
for the insignificant increase in the number of installed biogas digester was more
on the expensive capital cost to install the digester. In addition, kerosene has been
relatively inexpensive due to government subsidies on commercial energy.
There are many research activities in biogas technology carried out by research centers
and universities in Indonesia. The raw materials used for biogas production are
agricultural wastes, ranging from animal manures to a diverse selection of crop residues. Cassava solid waste, water hyacinth, and animal manure are among the agricultural
wastes that have been reported in more detail and will be explained in the following
sections. In general, the use of crop residues as the materials for biogas production is more difficult than that of manure. The reason is that hydrolysis of cellulosic
materials of crop residues is known to be a slow process and can be a major rate
limiting factor in the anaerobic digestion. In addition, the imbalance ratio of carbon to nitrogen of the raw materials can limit the rate of organic conversion into methane.
Biogas Production from Cassava Solid Wastes
In 1989, total harvested area of cassava cultivation was 1,243,000 hectares (4).
The roots of a cassava plant are edible and an important source of tapioca starch.
Lampung province in southern Sumatra is one of the area where cassava processing
plant to produce tapioca starch are concentrated. In 1984, it was estimated that cassava solid
waste generated from tapioca industries in this province was approximately 536 tonnes
per year. From this amount, about 21% of cassava solid waste is processed to produced feed, food and citric acid; while the rest was discarded into the environment
(6). The rivers around the industry, therefore, become grossly polluted. To overcome
this problem, studies on the use of cassava solid waste for biogas production was
carried out at Research Center for Applied Chemistry Indonesian Institute of Sciences
Table 1: Production of agricultural wastes in 1989 (4)
Type of waste Production (ton/year)
Rice straw 44,723,000
Sugarcane bagasse 8,561,606
Cassava residue (root shell and stalk) 6,714,000
Cattle manures (cow and buffalo cattle) 126,200,900
Table 2: Biogas production form cassava solid waste (7)
Retention time Organic loading Biogas production Methane content
(day) rate (g/L.d) rate (L/L.d) (%)
30 1.915 0.74 51
50 1.176 0.65 54
100 0.588 0.42 56
Note: reactor working volume 176 L; feed conc. 5 % (w/v); temperature 35oC; pH 6.50 7.17
The digester of 176 liter working capacity used in this experiment was constructed
from a metal plate. The gas holder placed on the top of the digester floated as
biogas was generated. The digester was equipped with a water heater and a circulation
pump to maintain the process at 35oC. Monitoring was carried out for the amount of biogas produced, methane content,
and pH values during digestion process. The amount of gas produced was measured
by gas meter and the presence of methane in the biogas was detected by orsat apparatus.
A schematic diagram of the digester is given in Figure 1. Cassava solid waste used as
the main substrate consisted of carbohydrate (83.57%), protein (1.92%), and fat (0.26%)
(8). Cow dung was used as the inoculum to start the digestion process. The C N P
ratio of the substrate, 100 : 2.68 : 0.60, was adjusted by the addition of Urea and
TSP fertilizers as nitrogen and phosphorous sources respectively. Lime was used
to neutralize the pH of the feed before it was loaded. Substrate concentration was
5% (w/v). The results of the experiment are summarized in Table 2.
1. hot water
2. temperature control
5. gas meter
6. orsat apparatus
8. water heater
9. water pump
Figure 1: The schematic diagram of the digester
Biogas Production from Water Hyacinth
Water hyacinth (Eichhornia crassipes
) is one of the aquatic weeds found abundantly in some areas of Indonesia. It has
a very high growth rate, and in huge amount this aquatic weed can create problems
such as blocking waterways and irrigation. At Curug dam, Purwakarta, West Java,
the production of water hyacinth was estimated to be 4.9 ton/day in 1977. Studies on the use
of water hyacinth into biogas was done by Institute for Ecology, Padjadjaran University
in Bandung (9).
The digester was built from ferro cement with total volume of 1 m3, and a 0.5 1 m3 gas holder was placed on top of the digester. Cattle manure was used as the inoculum
at the beginning of the process. Before being fed into the digester, water hyacinth
was treated by washing with water to remove dirt and then it was cut into pieces.
Water content of the fresh water hyacinth was 89.5% and the ratio of carbon to nitrogen
was 27. The biogas produced from the process was 620 L/kg dry water hyacinth with
methane content of 52%. This amount was obtained when only part of leaves and stalk
used for digestion. If the whole part of the plant (including shoot) was fed into
the digester, biogas production dropped to 331.4 L/kg dry weight. This gas was used
to boil water. It was found that biogas consumed to boil two liters of water was
83 liters and the time needed was 35 minutes.
Biogas Production from Manure
A survey done in 1989 revealed that total cattle in Indonesia was 13,298,300 with
fresh dung production of about 126,200,900 tonnes per year (4). Only cow and buffalo
were considered in the survey, while other livestock dung was not covered due to
the problem of collecting manures. To elucidate the potential use of manures as the raw
material for biogas production, an experiment was carried out at the Faculty of Animal
Husbandry, Bogor Agricultural University (10).
The digester was made of concrete wall with working volume of 3.5 m3. The gas holder, placed on top of the digester, was made of a metal plate provided
with a stirrer. The digester was fed every day with 20 kg of fresh manure and diluted
with water at the ratio of 1 to 1. The temperatures inside the digester ranged from 22.0 to 28.5 oC. A total number of 5 7 head mature pigs or 2 mature cattle are needed for the digester
to produce biogas of 1400 liters daily. This amount of gas appeared to be enough
for the fuel energy needed by a family of 6 persons. The biogas produced has been
used for various activity as summarized in Table 3.
Table 3: Utilization of biogas for cooking (10)
Activity Biogas consumed (liter) Time consumed (min.)
Boil 15 L of water 364 50
Cook 8 kg of cassava 959 90
Cook 1 kg of rice 557 45
Table 4: Methane content in biogas from several agricultural wastes
Substrate Methane content References
apple bagasse 50 57% 11
water hyacinth 52 76% 9
potato 51.5% 12
sugarcane bagasse 60 80% 13
orange peel 50 55% 14
cassava solid waste 51 56% 7
Table 5: Biogas production from agricultural wastes
Process substrate Retention Temp. Biogas production
time (day) (oC) (L/L.d)
Batch elephant grass 27 0.35
Continue elephant grass 40 27 0.85
swine manure 30 31 1.00
grass 60 35 0.79
cassava solid waste 50 35 0.65***
manure/night soil* 60 25 0.1 0.2
cattle manure** 50 27 0.2 0.3
*) Chinese model digester
**) Indian model digester
***) Wiloso et al
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