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Article

Evaluation of a Small-Scale Anaerobic Digestion System for a Cattle Farm under an Integrated Agriculture System in Indonesia with Relation to the Status of Anaerobic Digestion System in Japan

by
Farida Hanum
1,2,*,
Masanori Nagahata
1,
Tjokorda Gde Tirta Nindhia
3,
Hirotsugu Kamahara
4,
Yoichi Atsuta
5 and
Hiroyuki Daimon
1,5,*
1
Department of Applied Chemistry and Life Science, Toyohashi University of Technology, Toyohashi 441-8580, Japan
2
Department of Chemical Engineering, Faculty of Engineering, Universitas Sumatera Utara, Medan 20155, Indonesia
3
Department of Mechanical Engineering, Faculty of Engineering, Universitas Udayana, Jalan Kampus Bukit Jimbaran, Kuta Selatan, Denpasar 80361, Indonesia
4
Global Engagement Center, Toyohashi University of Technology, Toyohashi 441-8580, Japan
5
Research Center for Agrotechnology and Biotechnology, Toyohashi University of Technology, Toyohashi 441-8580, Japan
*
Authors to whom correspondence should be addressed.
Sustainability 2023, 15(4), 3833; https://doi.org/10.3390/su15043833
Submission received: 13 January 2023 / Revised: 4 February 2023 / Accepted: 16 February 2023 / Published: 20 February 2023
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Abstract

:
The Integrated Agriculture System in Indonesia was established in 2009. By the end of 2018, 752 small-scale anaerobic digestion (AD) systems treating beef cattle manure were successfully installed. In this study, the system was studied comprehensively at the first attempt by considering the current operating conditions, the actual performance of the digester, and site-specific factors for biogas production. Compost and bio-urine were produced at approximately 0.13 t/day and 4.8 L/day, respectively. The digester produced an unstable biogas amount of 0.109 to 0.521 m3/day. However, digester in Japan produces biogas 980 m3/day. This observed difference was due to the difference in the inputs and technological peculiarities. The main purpose for installation of the AD system was also different. Producing compost and bio-urine were the aimed in Indonesia, while producing biogas and reducing sawdust usage were the target in Japan. Thus, this study suggested that monitoring and controlling the operational parameters of digester in Indonesia could increase the biogas production as a first step without installing any additional temperature controller or mixing equipment. This approach might also be useful for improving the quality of compost and bio-urine by providing stable treatment conditions.

1. Introduction

The production amount of beef cattle in Indonesia increased by 2.39% per year on average from 2017 to 2021 [1]. In 2021, the beef cattle population was estimated at approximately 18.1 million heads [2]. In general, domestic beef cattle production could only satisfy approximately 50% of the demand in Indonesia. To fulfil the demand for meat, the government has been importing beef cattle, mainly from Australia [3]. Therefore, an increase in cattle production would positively impact economic growth in Indonesia. However, it would also generate a large amount of manure that would be discharged into the environment. Traditionally, manure is disposed of in landfills or applied to agricultural land without any treatment [4,5]. These disposal methods cause environmental problems such as complaints of unpleasant odours from nearby neighbours, harmful microbial growth, and soil and water pollution [6]. Anaerobic digestion (AD) is considered an advantageous process to treat livestock manure. It can not only reduce environmental problems but also provide biogas for local energy needs [7]. In addition, the digestate can be utilized as a compost and liquid fertilizer. AD is the process by which microorganisms degrade biodegradable matter under anaerobic conditions to produce biogas. Biogas composition is characterized in terms of methane (CH4), carbon dioxide (CO2), hydrogen sulfide (H2S), ammonia (NH3), and impurities such as water vapour and other gases [8].
AD systems treating livestock manure in Indonesia were installed in the 1980s as a project funded by the Food and Agricultural Organization to explore and utilize biogas as an alternative source of renewable energy [9]. Many similar AD programs have been implemented by international and national organizations collaborating with the government of Indonesia. One of these programs is the Integrated Agriculture System (SIMANTRI; abbreviation of “Sistem Pertanian Terintegrasi” in Indonesian) established by the government of Bali Province. The SIMANTRI program was designed to achieve a zero-waste approach by producing food, feed, fertilizer, and fuel (4F). The integrated agricultural activities are comprised of increasing food production from cattle and producing livestock feed from agricultural residue, organic fertilizers from digestate, and biogas as fuel. Increasing the production of biogas for use as fuel is not a major purpose of the SIMANTRI program. The main focus of the program is to produce organic fertilizers to reduce the excessive use of chemical fertilizers for crops. The utilization of chemical fertilizers in the long term increases environmental pollution and degrades soil quality [10]. Such use has contributed to reduced soil organic matter content and increased soil acidification. In addition, chemical fertilizers may affect heavy metal accumulation in soil and plant systems [11]. For this reason, organic fertilizers produced from digestate in the treatment of beef cattle manure under the SIMANTRI program could help overcome the environmental problems associated with soil damage caused by chemical fertilizers and beef cattle manure disposal.
Some reports have covered small-scale AD system implementation under the SIMANTRI program in Bali Province from different perspectives [12,13,14,15,16,17,18]. The reports sought to investigate the influence of the program on the utilization of local feed resources [12] and to evaluate the effectiveness of the program on increasing farmers’ income [13,14,15,16]. Most of these reports discussed the economic benefits associated with installing the systems. However, studying the current operational conditions associated with biogas production from these systems and improving its efficiency are not well documented and should be studied in depth.
There are several renewable energy development projects supported by the Japanese government, various organizations, and companies in Indonesia. Under these projects, AD systems have been installed. However, most of these systems are constructed on a large scale with high initial costs, which is not suitable for farmers who live in developing countries such as Indonesia. Recently, our research team developed a relatively small-scale and simple AD system that was installed in a small-scale Japanese pig farm at low initial cost [19]. In the future, a similar system is planned to be installed in Indonesia due to its low cost and simple operation. The small-scale and simple AD system implemented in Japan would be a good example for Indonesia and other developing countries. Therefore, construction of a similar system in Indonesia due to its low cost and simple operation would be an important goal for the near future. Several previous studies of the SIMANTRI program calculated the potential of biogas production from cattle manure [17], and evaluated the digester design [18]. However, no study has been carried out to investigate the operational conditions of the system under the program. Therefore, the current work aimed to comprehensively study the AD system under the SIMANTRI program for the first time by identifying the current operating conditions, the actual performance of the digester, and site-specific factors. In addition, this present work was conducted on the AD systems in Japan to study the possible strategies for improving biogas production and enhancing the AD efficiency under the SIMANTRI program. The comparison between the two countries also clarifies the positioning and performance of the AD system in Indonesia. Therefore, the current operating conditions and the performance of AD systems in Indonesia must be understood clearly to support future research on installing AD systems adopted from the system in Japan. Several technical factors were also proposed to enhance the biogas production amount by addressing how to improve efficiency from a technological perspective in Indonesia.

2. Materials and Methods

The raw materials of the present study were obtained from two places: a beef cattle farm in Kemenuh village, Gianyar Regency, Bali Province, Indonesia, and a dairy cattle farm in Toyohashi, Aichi, Japan.

2.1. The Small-Scale Anaerobic Digestion System Treating Beef Cattle Manure under the SIMANTRI Program

A low-cost and small-scale anaerobic digester is used at the beef cattle farm under the SIMANTRI program. A Chinese fixed dome digester model was selected due to its low cost, low maintenance requirement, and long lifetime (more than 20 years). The AD system consists of a dome-shaped digester with a biogas holder on the top of the digester, inlet, and displacement tanks. The existing design, capacity, and structure of the digester in Indonesia were obtained by interviews with the farmers. An interview with SIMANTRI program staff from the Department of Food Crops, Horticulture, and Plantation of Bali Province was also conducted to understand the operating procedures of the AD system under the SIMANTRI program. The experimental data were collected directly from the field site.

Data Collection

The physicochemical characteristics of raw cattle manure such as moisture content, pH, TS, and VS were measured according to American Public Health Association (APHA) Standard Methods for the Examination of Water and Wastewater [20]. The hydraulic retention time (HRT) was calculated based on the daily feedstock input.
The biogas production amount was measured daily by using a compact multirange residential diaphragm gas meter (BK-G1.6, Elster Instromet, Steinfurt, Germany). The pH value of digestate discharged from the digester was measured twice a day (morning and afternoon before introducing the substrate) by using a Senz pH meter (Trans Instruments, Singapore). The measurements were carried out at the farm from 13 June to 17 July 2018, for a total of 32 days. The ambient temperature during this period was measured twice a day (morning and night) by using a thermometer. All statistical analyses were completed using Microsoft Excel 2016. Some basic physicochemical characteristics of the raw cattle manure used in this experiment are shown in Table 1.

2.2. The Small-Scale Commercial Anaerobic Digestion System Treating Dairy Cattle Manure in Toyohashi City, Aichi, Japan

The AD system in Toyohashi City was developed and constructed by the authors with farmers and companies. The material flow, biogas production amount, and electricity generated from the AD system were investigated and obtained by interviews with the farmers.

3. Results and Discussion

3.1. Structure and Operation of Digesters under the SIMANTRI Program in Indonesia

The detailed structure and dimensions of the fixed dome system are schematically shown in Figure 1. The digester was constructed underground at a depth of 3 m below the ground surface to protect it from physical damage, such as cracking due to sunshine, to provide a more stable internal temperature, and to save space on the ground. The digester is a cylindrical vertical container with a capacity of approximately 15 m3, diameter of 2.5 m, and height of 3 m. The inlet tank was constructed with a square shape, while the displacement tank and sludge-drying bed are rectangular in shape and of different size.
A temperature controller is not equipped in the digester. Since the digester was constructed underground, the soil temperature can be assumed to represent the digester temperature. Because of tropical conditions in Indonesia, the difference between soil and ambient temperatures is not significant during day or night. The average ambient temperatures during the study at morning, noon, and night were 28, 30, and 27 °C, respectively (Figure 2). Therefore, the digester temperature followed the trend of ambient temperature. Generally, the average temperature throughout the year also does not change significantly. For these reasons, it can be expected that there will be no significant changes in temperature inside the digester at all times. The digester operates without a pump or internal mixing equipment to reduce the installation and operational costs. The inlet point of the digester is placed higher than the outlet point; this design was adopted not only to mix the slurry inside the digester during the feeding period but also to enable easy gravity displacement for discharging slurry through the displacement tank. In the absence of internal mixing equipment, the slurry in the digester is mixed via hydraulic variation during feeding, and slurry movement is due to biogas production. The produced biogas is stored in the biogas holder. The biogas pressure increases with an increasing volume of biogas produced. The biogas pressure pushes some of the slurry from the digester into the displacement and inlet tanks. The slurry discharged from the displacement tank into the sludge-drying bed is called digestate. The sludge-drying bed is used not only for collecting the digestate but also for solid–liquid separation. When the biogas valve is opened for gas utilization, the pressure drops, and a proportional amount of slurry immediately flows back from the displacement and inlet tanks into the digester, resulting in intermittent natural mixing. The biogas is used twice a day in the morning and afternoon before introducing the feedstock into the digester because of reduced pressure inside the digester. The change in slurry level in the digester depends on the amounts of input substrate and gas production.

3.2. Material Flow of an Anaerobic Digestion System under the SIMANTRI Program

The material flow of the AD system treating beef cattle manure is shown in Figure 3. The input amount of feedstock is 0.66 t/day of beef cattle manure and the urine mixed with wash water is at a ratio of 1:1. The digester is fed twice a day in the morning (9:00 AM) and afternoon (5:00 PM). The digester operates with an HRT of approximately 23 days based on the daily amount of input substrate. The biogas produced is passed through the desulfurizer, which uses iron oxide to eliminate hydrogen sulfide. The precipitate of Fe2S3 and water were produced on its surface [21,22]. Such precipitate reduces the efficacy of desulfurization process which can be avoided by flashing the desulfurizer with water every three months. After the desulfurization process, the biogas is stored in a 1 m3 gas bag. Digestate is collected from the sludge-drying bed manually by using a pitchfork or shovel twice a day and separated using a static screen filter with a mesh size of 1 mm. Approximately 60 litres of digestate liquid is mixed with 0.5 kg of organic supplements composed of bone meal flour (pulverized bones of slaughtered cattle), rice husk charcoal, and chicken eggshell powder (from the local chicken breed), supplied free of cost by the Department of Food Crops, Horticulture and Plantation of Bali Province. The supplements are needed to provide a good nutrient content and adjust the pH to produce liquid fertilizer [23].
The digestate liquid is stored in a closed plastic container (100 litres) for a week to enhance the homogeneity of the solid–liquid mixture. A closed container was selected to prevent offensive odours from being released into the atmosphere. Then, the digestate liquid is filtered to separate the supplement residue. The residue is mixed with the digestate solids to make compost. The liquid is aerated for approximately 4 h by using a small-stepped cascade aerator to reduce the amounts of biodegradable organic compounds and other dissolved gases. The aerator comprises a series of steps in which the liquid plunges from one step to another. A pump is used to transport the liquid from the storage tank to the upstream channel. After aeration, the liquid is kept in the closed plastic container for up to 2 days at ambient temperature to remove the supplement residue remaining in the liquid by gravity separation. The liquid fertilizer, called bio-urine, is produced with a total amount of 4.8 L/day on average. It is applied for foliar feeding and soil amendment. However, it has an unpleasant smell that might be caused by the poor biodegradability of organic compounds during the short-term aeration process. Zhang et al. [24] reported that the aeration period for digestate liquid should be within 6–7 h. For this reason, consumers refuse to purchase the bio-urine. Therefore, it is only utilized by farmers in the group under the SIMANTRI program to grow their crops free of charge. The utilization of digestate liquid as fertilizer is currently a common practice. In this regard, Reuland et al. [25] stated that the digestate liquid provided better conditions for plant growth than unseparated digestate. In addition, Ntinas et al. [26] demonstrated the efficient application of digestate liquid from livestock manure as a fertilizer for the hydroponic cultivation of baby lettuce grown in a greenhouse using a floating system. Similarly, Levin et al. [27] confirmed that the liquid fraction from cow manure exhibited better fertilization performance for cucumber due to the fast release of nutrients (i.e., nitrogen) to the plants. The digestate liquid produced from AD can be a promising fertilizer for plant growth, and trails for increasing the quality of the digestate liquid must be evaluated. So, it can be suggested that a longer aeration period within 6–7 h is necessary to increase its quality.
The present study also continued to utilize the digestate solid for composting. In this regard, the digestate solid is placed in five open ponds and dried with sunlight during the first week. Next, it is moved into a composting house with a size of 9 m2, and a compost pile is made using a shovel. The pile is turned manually in the third and fourth weeks of composting by using a pitchfork or shovel for aeration purposes. Composting is completed within 5 weeks. The obtained compost is mixed thoroughly before packaging. The total amount of compost produced is approximately 0.13 t/day. The compost is sold to fruit and vegetable farmers at a price of approximately 0.07 USD per kilogram of compost. Even though the pH and moisture content of compost are not controlled, consumers are satisfied with the quality of the compost due to the increase in plant productivity.

3.3. The pH and Biogas Production of a Digester under the SIMANTRI Program

There is a lack of research on small-scale AD systems, and most of the current studies do not provide sufficient data on the operational conditions and actual performance of digesters. In addition, the majority of the studies have been conducted at the lab scale. Thus, the comparison of biogas production from small-scale AD systems is currently a challenge.
In Indonesia, all small-scale AD systems under the SIMANTRI program are operated with similar procedures and operation conditions. Only the size of the digester is different, depending on the number of cattle. Although this study is the first and only attempt to directly measure the biogas production amount from a digester under the SIMANTRI program, the average daily biogas production amount should show similar behaviour in all digesters under the same program. The pH and daily biogas production amount from the digester are given in Figure 4.
To evaluate the biogas production amount, the biogas amounts produced from the anaerobic digesters treating cattle manure in the previous study and this study were compiled (Table 2). Garfi et al. [28] and Ferrer et al. [8] estimated that the biogas production amount was approximately 0.12 and 0.47 m3/m3digester day, respectively. Lansing et al. [29] reported a biogas production amount of 0.32 m3/m3digester day in a plug flow tubular digester operated in continuous flow mode at 25–27 °C. For the 15 m3-capacity of digester used in this study, the biogas production amount should be approximately 1800 to 7050 L/day. In addition, Adeoti et al. [30] estimated the biogas production potential from cattle manure as approximately 78 L/head/day. Based on this estimation, biogas could be produced at approximately 3198 L/day. Despite several major differences in the digester operating conditions and manure characteristics between these studies, the biogas production amount observed in this study was very low and fluctuated for a long time. This result could be attributed to the short HRT and uncontrolled operating parameters of the digester, such as the organic loading rate, temperature, and pH value. In the present work, the pH value changed significantly from 6.2 to 8.7. The highest biogas production was achieved at pH 8.3, and the lowest was obtained when the pH increased above 8.5. The biogas fluctuations might be reduced by maintaining pH at the optimum level (7.5–8). Previous studies also reported that a high pH value of 8.5–8.8 can lead to an increase in the free ammonia concentration, which may inhibit methanogenic activity and reduce biogas production [31,32]. Since pH was uncontrolled in the digester, variations in pH caused an imbalance in the AD process, resulting in an unstable biogas production amount. Another factor affecting biogas production is organic loading rate, which was calculated to be 2.2 g VS/L/day based on the measured input amount of substrate. Unfortunately, it was not controlled relative to the actual loading rate into the digester every time. Pasang et al. [33] reported that an organic loading rate of up to 5–6 gVS/L/day resulted in the highest biogas production from cattle manure in a lab-scale continuous study. The low temperatures of the digester (26–32 °C) also could have affected the very low and fluctuating biogas production amount. Even though the climate conditions in Indonesia are suitable for digester operation (above 20 °C) [34,35,36], the temperature is still lower than the optimum temperature for the digestion process.
The biogas produced is used as supplementary cooking fuel by two households near the farm. Recently, to expand the utilization of biogas, a biogas generator with a capacity of 1 kWh was developed to generate electricity for lighting surrounding the farm [21,37]. To increase the biogas production amount, monitoring and controlling the operating conditions of the digester are required in the future. Such efforts are necessary not only to ensure digestion efficiency but also to prevent digester failure. The procedures include maintaining the optimal conditions related to pH and organic loading rate, analyzing the mass balance of carbon and nitrogen, and measuring methane yield and ammonia concentration. Such attempts could be important as a first step without any additional temperature control or mixing equipment. This approach might also be useful for improving the quality of bio-urine and compost due to the stable treatment conditions. Biogas production can also be increased by adding organic-rich waste, such as food waste, as a co-substrate or additive to digesters treating cattle manure. Moreover, anaerobic co-digestion of cattle manure and food waste is an alternative strategy to improve the economic viability of AD systems due to higher biogas production. In 2021, the food waste generated in Indonesia was estimated at approximately 20.9 million tons [38], which is the highest of food waste generation in Southeast Asia countries. It is mostly landfilled without any treatment. The high amount of food waste at landfill sites has also led to several problems, such as foul odours and toxic leachate affecting surrounding areas [33]. Thus, the co-digestion of cattle manure and food waste might be the most feasible breakthrough method for handling both biomass resource problems in Indonesia.

3.4. Material Flow of a Small-Scale Commercial Anaerobic Digestion System Treating Dairy Cattle Manure in Toyohashi City, Aichi, Japan

The status of a small-scale commercial AD system in Japan must be described to study the similarities and differences relative to cattle manure management in Indonesia. This is important for understanding the motivational perspectives for installing the system in both countries. Thus, the material flow of a small-scale commercial AD system in Japan must be described in detail. The material flow of the system is shown in Figure 5. Generally, in Japan, dairy cattle manure is mixed with sawdust for composting due to the ability of sawdust to adjust the moisture content of dairy cattle waste (70–80%) [39,40,41]. The usage of sawdust increases with an increase in the number of cattle heads. Since woody biomass is commonly used for power generation in Japan, the amount of sawdust produced is decreasing. Therefore, the price of sawdust is increasing every year. There are 180 cattle heads at this dairy cattle farm, and the number will increase in the coming years. Therefore, another method for manure management is needed. Moreover, reducing the amount of compost produced might be important due to limited land availability for compost application. In addition, reducing the odour problem from dairy cattle farms is needed. A low-cost and small-scale commercial AD system was developed at the dairy cattle farm as an alternative method for solving such problems. The system was installed in March 2020.
The system consists of a raw material storage tank, a digester, wet and dry desulfurizers, a gas storage bag, a power generator, a converter, and a power conditioning system. The digester is made of reinforced concrete coated with galvalume steel and has a 480 m3 capacity. The slurry in the digester is circulated using a pump. Some of the slurry is withdrawn from the bottom into the upper side of the digester. In addition, two agitators are used in the digester for mixing the slurry. The movement of feedstock in digesters is an important consideration, as it facilitates the distribution of micro-organisms and heat in the digester, resulting in higher biogas production [42,43]. The input amount of feedstock is approximately 16 t/day cattle manure, which is mixed with approximately 2 t/day wash water discharged from the cattle house. The digester is fed every hour. The HRT of the digester is approximately 26 days based on the daily input of substrate. The biogas produced is passed through the wet and dry desulfurizers and stored in a 90 m3 gas storage bag. The biogas production amount from approximately 180 cattle heads was measured to be approximately 980 m3/day, with a methane concentration of 60%. The biogas is converted to electricity by a power generator with a capacity of 50 kW. The exhaust heat from power generation is used to produce hot water to maintain the temperature of the digester at 39 °C. Then, the converter and power conditioning system are used for stabilizing and injecting the electricity into the power grid. The electricity produced is 34,104 kWh/month on average and is sold to a private electric company.
In addition to producing biogas as a renewable energy source, the system also generates digestate as a by-product. The digestate is treated with solid–liquid separation using a filter press. The digestate liquid is mixed with cationic polymer flocculants at a rate of approximately 20 kg/day in the flocculation tank. It is separated by using a screw press. The liquid fraction is treated in a wastewater treatment system with a 20 m3 capacity before being discharged to the river, and the solid fraction is utilized for compost. The digestate solid is mixed with sawdust at approximately 2 t/day in a composting house with a size of 800 m2. The compost amount produced is approximately 4 t/day. Composting is accomplished within 4 weeks under controlled conditions, such as moisture content and temperature. Although the compost is produced under controlled conditions, the quality is still not suitable according to Japanese farmers’ requirements. Since farmers need high-quality compost, only limited compost can be sold to the market in Japan. Therefore, most of the compost produced was distributed free of charge to farmers near the cattle farm.

3.5. Anaerobic Digestion Management and Policy in Indonesia and Japan

AD management and policy in Japan and Indonesia should be compared to improve the AD system in Indonesia and to encourage mutual learning between these two nations. The system investigated in this study is an AD system with different size in the two countries. The description of each system is shown in Table 3.
In Indonesia, the farmers are responsible for operating the digester and performing other farming activities based on the guidelines and policy created by the government. The SIMANTRI program adopts the direct policy approach. In addition to funding, strategic planning is implemented to support the integrated farming activities. The government also provides staff from the Department of Food Crops, Horticulture, and Plantation of Bali Province to improve their knowledge and skills. With proper digester handling, biogas production could be improved. As renewable energy, biogas can be sold under a feed-in tariff (FIT) program. A FIT program for electricity has been operating in Indonesia since 2009 [44]. In 2012, the Indonesian government added biogas to its FIT list. However, the practical realization of this program faces many challenges, such as the complex structure of governance, lack of community knowledge about renewable energy, and complicated payment rules [45]. Moreover, the program is only available for medium and large power plants (more than 10 MW power). Because of the small amount of biogas produced from the studied digester, it cannot be sold under the program. In fact, most digesters are installed on small-scale farms in Indonesia with a capacity of 3–15 m3. To promote the future deployment of renewable energy in Indonesia, the government should extend the list of capacities that may qualify for FIT program (e.g., above 1 MW).
In contrast, in Japan, the system adopts a direct policy approach under the regulations and standards concerning water pollution control [46,47]. In addition, the Ministry of Economy, Trade, and Industry launched a FIT program for renewable energy in 2012. The program is an indirect policy that does not oblige farmers to participate. However, the program enables farmers to sell the electricity generated to a private electric company to gain extra revenue. The selling price based on the FIT program is 0.28 USD per kWh [48].
Generally, AD systems have been applied only on a large scale in Japan due to high initial costs. Therefore, low-cost and relatively small-scale AD systems (180–900 m3 capacity) have been developed, which are among the pioneering systems in Japan to be economically successfully installed in many places. By the end of 2018, there were six AD systems. Four systems were installed at medium-sized pig farms (Aichi, Shizuoka, and Mie Prefectures), one system was installed at a Japanese agriculture site (Aomori Prefecture) treating Chinese yam residue, and one system was installed at a relatively small-scale dairy cattle farm (Aichi Prefecture) that was investigated in this present study. To reduce the initial cost of installation, most operations were performed manually, equipment was simplified, imported equipment was introduced, and some existing wastewater treatment and composting facilities were used for treating the digestate liquid and solids. The initial cost for installing a relatively small-scale AD system (300 m3 of capacity) to treat dairy cattle manure was approximately 695,155 USD, including power generation and wastewater treatment facilities. The system was estimated to represent more than a one-third reduction in price compared to another AD system in Japan. To compare the costs and sustainability of AD systems in Indonesia and Japan, the initial costs based on the input amount into the digester in Japan (50,400 USD/m3-input) are five times higher than those in Indonesia (10,300 USD/m3-input). The system in Indonesia operates at a low cost because no electricity or pump is needed. In Japan, the running cost was estimated at approximately 764 USD/month. A salary was not included in the estimation because the digesters are operated by the farmers in both countries.
The digestate solids are treated to produce compost in both countries. Despite uncontrolled quality during production, the compost can be sold commercially in Indonesia. In Japan, the compost is not for sale. Even though it is produced under controlled conditions, it still fails to meet the compost quality requirements of farmers. The purposes of installing AD systems also differ in the two countries. In Indonesia, producing compost and bio-urine and reducing odour problems are the main purposes. In Japan, installation of the system is aimed to reduce the amount of sawdust usage (200–300 t/month), produce less compost, and minimize odour problems. In addition, the AD process provides economically valuable products in the form of biogas. In Japan, biogas for electricity generation is the primary product of digesters because of its high selling price based on the FIT program. The biogas production in Indonesia is observed to be very low (0.32 m3/day) compared to Japan (980 m3/day). The different operating conditions can be attributed to the large differences in biogas production. The biogas production in Indonesia should be enhanced in the future to create a sustainable society. Biogas production also offers cost savings from the reduced need to purchase cooking fuel and electricity from the public grid. Therefore, the farmers operating digesters should receive adequate technical training on digester operation under the optimal conditions without additional instrumentation.

4. Conclusions

This study evaluated the current status of an AD system in Indonesia under the SIMANTRI program by identifying the current operating conditions, the actual performance of the digester, and site-specific factors. In addition, this study compared AD systems between Indonesia and Japan to find possible strategies for improving the biogas production amount and enhancing the SIMANTRI program. The big differences observed for biogas produced between Indonesia and Japan were due to the difference in the inputs and technological peculiarities. The purposes of installing AD systems in Indonesia and Japan are also different. In Indonesia, producing compost, bio-urine, and reducing odour problems are the main purposes. However, in Japan, system installation aims to reduce the amount of sawdust usage, produce less compost, and minimize odour problems. Even though the purposes and economic conditions of Indonesia and Japan are different, AD systems were selected in both countries to solve environmental issues such as odour problems and soil and water pollution caused by the improper treatment of cattle manure.
Recently, in Indonesia, biogas production has been expanded to power lighting surrounding the farm. To increase biogas production in the future, monitoring and controlling the operational parameters of the digester could be important as a first step without the installation of any additional temperature controllers or mixing equipment. This approach might also be useful for improving the quality of bio-urine and compost due to the stable treatment conditions. Further investigations should be conducted in this field with long-term monitoring to optimize the operating conditions of the AD process for enhancing biogas production. Biogas production can also be increased by adding organic-rich waste, such as food waste, as a co-substrate or additive to digesters treating cattle manure. Co-digestion might be the most feasible breakthrough method for handling both biomass problems. Moreover, this approach shows great promise as a low-cost method to enhance biogas yield without any additional instrumentation. Finally, investigating ways to improve the method for reducing bio-urine odour problems is an important challenge in Indonesia.

Author Contributions

Conceptualization, F.H. and M.N.; methodology, Y.A. and H.D.; investigation, F.H., M.N., T.G.T.N. and H.K; writing—original draft preparation, F.H., Y.A., H.K. and H.D.; review and editing, F.H., Y.A. and H.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by: 1. The Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research Grant Number 21H03662 and partially supported by “Knowledge Hub Aichi”, Priority Research Project (4th term) from Aichi Prefectural Government. 2. The Indonesian Endowment Fund for Education, Ministry of Finance, and from the Directorate General of Higher Education, Ministry of Research, Technology and Higher Education in The Republic of Indonesia (FY 2017–2021).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Figure 1. Schematic diagram of a small-scale fixed dome system treating beef cattle manure under the SIMANTRI program.
Figure 1. Schematic diagram of a small-scale fixed dome system treating beef cattle manure under the SIMANTRI program.
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Figure 2. Ambient temperature at morning, noon, and night over the experimental period.
Figure 2. Ambient temperature at morning, noon, and night over the experimental period.
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Figure 3. Material flow of a small-scale anaerobic digestion system treating beef cattle manure under the SIMANTRI program.
Figure 3. Material flow of a small-scale anaerobic digestion system treating beef cattle manure under the SIMANTRI program.
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Figure 4. pH and biogas production amount of a small-scale anaerobic digester treating beef cattle manure under the SIMANTRI program.
Figure 4. pH and biogas production amount of a small-scale anaerobic digester treating beef cattle manure under the SIMANTRI program.
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Figure 5. Material flow of a developed small-scale commercial anaerobic digestion system treating dairy cattle manure in Toyohashi City, Aichi, Japan.
Figure 5. Material flow of a developed small-scale commercial anaerobic digestion system treating dairy cattle manure in Toyohashi City, Aichi, Japan.
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Table
Table 1. Physicochemical characteristics of cattle manure obtained from a farm in Kemenuh Village, Indonesia.
Table 1. Physicochemical characteristics of cattle manure obtained from a farm in Kemenuh Village, Indonesia.
ParameterUnitValue
Total solidsg/L186 ± 0.78
Volatile solidsg/L52 ± 0.43
pH-7.27 ± 0.7
Moisture content%81.60 ± 0.16
The results are expressed as the means of triplicate measurements with standard deviations.
Table
Table 2. Biogas production amounts from anaerobic digesters treating cattle manure.
Table 2. Biogas production amounts from anaerobic digesters treating cattle manure.
StudyAdeoti et al. [28]Garfi et al. [26]Lansing et al. [27]Ferrer et al. [8]This Study
Digester designNRPlug flow tubularPlug flow tubularPlug flow tubularFixed dome
Size of digester (m3)NR10852.415
Temperature (°C)NR2225–2720–2526–32
pHNR7.636.24–6.588.586.23–8.75
Hydraulic retention time (day)NR90396023
Daily feeding (m3/day)NRNR2.2NR0.66
Biogas production amount with different units78 L/head/day
(Simulation)		0.12 m3/m3-digester/day
(Investigation)		0.32 m3/m3-digester/day
(Investigation)		0.47 m3/m3-digester/day
(Investigation)		109–521 L/day
(Investigation)
Total amount of cattle manure generated (kg/day) 328
Size of digester (m3) 15 *15 *15 *15
Number of cattle (head)41 * 41
Estimated biogas production with uniform units (L/day)3198180048007050315
(Average)
NR: not reported. *: assumed to be the same value as in this study.
Table
Table 3. Comparison of representative small-scale anaerobic digestion systems treating cattle manure between Indonesia and Japan.
Table 3. Comparison of representative small-scale anaerobic digestion systems treating cattle manure between Indonesia and Japan.
CountryIndonesiaJapan
Province/cityBaliAichi/Toyohashi
Type of animal (head)Beef cattle (41)Dairy cattle (180)
Amount of manure and wash water (t/day)0.33 and 0.3316 and 2
Policy approachDirectIndirect
Related program4FFIT
Capacity of anaerobic digestion reactor (m3)15300
HRT (days)2316
Temperature (°C)Ambient (26 to 32)39
Anaerobic digester operationWithout pump, heating and
mixing system		With pump, heating, and mixing system
Digestate solids usageCompostCompost
Digestate liquid treatment methodProduce bio-urine
(liquid fertilizer)		Treat into wastewater treatment
Biogas production (m3/day)0.32980
Initial cost of anaerobic digestion
System (USD in August 2022)		6370 *695,155 **
Initial cost based on input amount (USD/m3-input)10,30050,400
Operator of anaerobic digestion systemFarmerFarmer
Number of small-scale anaerobic
digestion system in surrounding areas		752 plants (Dec 2018) ***1 plant (July 2020) ****
Purpose of anaerobic digestion project
  • Produce compost
  • Produce bio-urine
  • Reduce the odour problem
  • Reduce the amount of sawdust usage
  • Reduce the amount of compost produced
  • Reduce the odour problem
Biogas usage
  • Cooking fuel
  • Power generation
(on-site use)
  • Power generation
(off-site use)
Utilization of produced biogas
  • Use as alternative energy
  • Sell renewable energy to private electric company
4F: food, feed, fertilizer, and fuel production under the SIMANTRI program; FIT: feed-in tariff, 0.28 USD/kWh (August 2022); * including cattle house and organic fertilizer production facilities; ** including power generator and wastewater treatment facility; *** each anaerobic digestion system has different digester conditions and size; **** 5 more anaerobic digestion systems with different types of substrates and digester sizes.
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Hanum, F.; Nagahata, M.; Nindhia, T.G.T.; Kamahara, H.; Atsuta, Y.; Daimon, H. Evaluation of a Small-Scale Anaerobic Digestion System for a Cattle Farm under an Integrated Agriculture System in Indonesia with Relation to the Status of Anaerobic Digestion System in Japan. Sustainability 2023, 15, 3833. https://doi.org/10.3390/su15043833

AMA Style

Hanum F, Nagahata M, Nindhia TGT, Kamahara H, Atsuta Y, Daimon H. Evaluation of a Small-Scale Anaerobic Digestion System for a Cattle Farm under an Integrated Agriculture System in Indonesia with Relation to the Status of Anaerobic Digestion System in Japan. Sustainability. 2023; 15(4):3833. https://doi.org/10.3390/su15043833

Chicago/Turabian Style

Hanum, Farida, Masanori Nagahata, Tjokorda Gde Tirta Nindhia, Hirotsugu Kamahara, Yoichi Atsuta, and Hiroyuki Daimon. 2023. "Evaluation of a Small-Scale Anaerobic Digestion System for a Cattle Farm under an Integrated Agriculture System in Indonesia with Relation to the Status of Anaerobic Digestion System in Japan" Sustainability 15, no. 4: 3833. https://doi.org/10.3390/su15043833

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