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.

Editors: 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

Abstract

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.

Key Words: Biogas, Methane, Energy, Anaerobic digestion, Pollution control,

Agricultural wastes, Indonesia

Introduction

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 (2).

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 (7).
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
3. inlet
4. stirrer
5. gas meter
6. orsat apparatus
7. burner
8. water heater
9. water pump
10. outlet
11. partition

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 (15)

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 (1987)

References

1. Biro Pusat Statistik (1991). Indonesian Population According to 1990 Census (In Indonesian).
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3. Siagian, U. and S. Sasmojo (1993). The Potential of Biomass Energy Resources and Feasibility Study of the Implementation of Several Renewable Energy System in Indonesia (in Indonesian). Proceedings of ASEAN Non conventional and Renewable Energy Workshop , LIPI, Bandung, p: 28 52.
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6. Karossi, A.T.A., M. Poesponegoro, I. Suharto and E.I. Wiloso (1987). Biogasification of Cassava Solid Waste in Indonesia, a state of the art review. In Biogasification of Various Organic Residues in the ASEAN Region. ASEAN Committee on Science and Technology, Bandung, p: 1 8.
7. Wiloso, E.I., I. Suharto and R. Sarwono (1987). Biogas Production from Cassava Solid Waste in 176 L Digester at 30, 50, and 100 day Retention Times (in Indonesian). Buletin Limbah Pangan III(2): 261 270.
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11. Knoi, W., Most, M.M. & Waart, J. (1978). Biogas production by anaerobic digestion of fruit and vegetable waste, a preliminary study. J. Sci. Food Agric. 29: 822-30.
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13. Oi, S. Yamanaka, H. & Yamamoto, T. (1980). Methane fermentation of bagasses and some factors to improve the fermentation. J. Ferment. Technol. 58 (4): 367-72.
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15. Gunnerson, C.G. & Stuckey, D.C. (1986). Anerobic digestion: Principles and Practices for the Biogas System. World Bank Technical Paper No. 49, UNDP Project Management Report No. 5, Washington D.C.
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17. Biogasification of Various Organic Residues in the ASEAN Region. ASEAN Committee on Science and Technology, Bandung.
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