The Waste-to-Energy (WtE) Technology to Support Alternative Fuels for Agriculture in the Context of Effective Solid Waste Management in the Jabodetabek Area, Indonesia

Abstract

Jabodetabek has been termed Indonesia’s most populous urban area, and it is predicted to generate around 9.069 million tons/year by 2023. On the other hand, this area has promising agricultural prospects and requires a great deal of energy. Tractors, generators, and other agricultural equipment are necessary to increase productivity. Therefore, it can potentially convert waste into energy as an effective alternative fuel for agriculture. This study looked at ways to recover the waste to energy (WtE) with various technologies (incineration, gasification, pyrolysis, landfilling, and anaerobic digestion). The assessment indicators focus on the type of waste, energy production efficiency, energy produced, technological readiness, capacity, byproducts, costs, air pollution, water pollution, and soil pollution. Each WtE technology is assessed using a scale between 1 (worst) and 5 (best) on each performance indicator concerning related references. Based on the analysis, the anaerobic digester is the most attractive WtE technology to generate an alternative fuel for agriculture in the Jabodetabek area. This is an environmentally friendly and economical technology because the technology readiness level is relatively mature. Thus, this review will assist policymakers and implementing authorities in determining the potential of the right WtE technologies for effective alternative fuel generation for agriculture, particularly in the metropolitan region of Jabodetabek.

1. Introduction

The municipal solid waste (MSW) generation in Jabodetabek is 9.069 million tons in 2023 annually and continues to increase [1]. In the coming decades, developing nations in Asia and other parts of the world are anticipated to attain the same level as the MSW generation of affluent countries [2]. The improper management of municipal waste will result in various social and environmental issues, including air, soil, and water pollution, the spread of illness, and the release of greenhouse gases, primarily methane, that contribute to global warming. In the Jabodetabek metropolitan area, waste management is a very urgent problem. This region has the highest population density per square mile, so it produces a large amount of waste. The denser the population, the more municipal waste is generated. According to Mor and Ravindra [3], high-income countries generate more significant MSW than low- and middle-income countries. The non-organic nature of the MSW composition is the main driving factor for adopting from waste-to-energy (WtE) in high-income countries [4].

Currently, the main strategy implemented by the Jabodetabek government regarding waste management strategies is to reduce, recycle, and reuse waste. Most of the non-recyclable and/or non-reusable waste ends up in landfills. While landfill may be the most economical solution in the short term, its long-term impact on the environment and sustainability leads to complex problems. Over the past decade, countries worldwide have been looking for better ways to manage their MSW. According to Tun, et al. [5], MSW management in developing countries is worse than in developed countries because the management level depends on a country’s economic and social prosperity. In the Jabodetabek region, agriculture requires a great deal of energy and resources. Tractors, generators, and other agricultural equipment are required for the operation’s success. Instead, the ever-increasing prices of energy and conventional fuels and their detrimental impact on the environment attract the development of alternative fuel sources. Typically, diesel is used to power tractors and other agricultural vehicles, whereas electricity is utilized to power farm lighting and equipment. Thus, several scientists are pursuing the optimal method for harvesting alternative energy sources through appropriate WtE technologies [6,7,8].

Over time, it has become clear that alternative fuel for agriculture represents an increasing problem for nations worldwide. WtE technology and recycling have been proposed as potential solutions to the growing landfill problem. However, the success of these strategies remains debatable. Incineration, gasification, pyrolysis, landfilling, and anaerobic digestion are typical WtE technologies for alternative fuel for agriculture. All WtE technologies have specific requirements for preferred waste, which exhibit certain characteristics that meet the operational parameters for an efficient process. Compost (used as manure), char, and slag are all byproducts of anaerobic digestion that are useful in their own right (for construction materials) [4,9,10].

The review of suitable WtE technology for alternative fuel for agriculture in the Jabodetabek metropolitan area is an exciting study because it is a vital area that will attract stakeholders’ attention, including policymakers, investors, and scientists. This review presents a unique and novel contribution to solid waste management by applying WtE technology to support alternative fuels for agriculture. The energy output from waste processing can later be used as input power for each agricultural value chain. Therefore, WtE technology can assist in conducting more efficient and sustainable farming operations while reducing dependence on fossil energy sources. It also represents a positive step towards more sustainable waste management practices. In addition, this research might assist them in selecting the most eco-friendly technologies. This article thoroughly analyzes the present status and trends in WtE practice. This study highlights the potential of WtE technology for alternative fuel for agriculture to solve the waste problem in the metropolitan region of Jabodetabek. The current waste management situation in Jabodetabek was evaluated to attain this objective. Information was gathered from numerous sources to gain a complete understanding of the solid waste situation. WtE technologies include incineration, gasification, pyrolysis, landfilling, and anaerobic digestion. Their advantages and disadvantages will be evaluated in light of various technological performance measures.

2. Materials and Methods

2.1. Data Source Selection

Due to Indonesia’s status as a developing nation in Southeast Asia, its waste management infrastructure is inadequate. Similarly, WtE conversion is undergoing progress. Consequently, gathering the most recent information on waste management, particularly WtE conversion, is quite simple; nevertheless, most information is inaccessible. Therefore, research-related data are collected reasonably from scientific articles, news, government documents, and other accessible reports. Furthermore, these data are synthesized, analyzed, and evaluated regarding comprehensive urban waste management and WtE processes.

WtE technology has gained momentum in the last few decades and the approaches used have evolved significantly in the same period. The existing literature, therefore, includes considerable variation concerning focus and approach. To ensure consistency, the literature included in the review was selected based on the following overall criteria: (i) WtE technologies were reviewed in terms of their advantages and disadvantages; (ii) the potential of WtE technology is described to support alternative fuels for agriculture in the context of effective solid waste management in the Jabodetabek area; (iii) a selection of suitable WtE technology for the Jabodetabek area is calculated based on a simple weighting technique.

The search was conducted on the Google Scholar platform with the default parameters because it provides the most robust, current, comprehensive, and widely used search engine information for interdisciplinary analysis and peer-reviewed literature. The time range is set to any time and the output is sorted by relevance. This study also considered expert advice to determine the source of the databases to be used. A glossary of key topic terms was developed, as shown in Table 1. Boolean operators are used to collect relevant literature during the procedure. “AND” and/or “OR” operators are used for databases and search engines to limit down and retrieve relevant results.

2.2. Review Approach

This work implements a systematic literature review to capture all relevant research targeting WtE technologies in support of alternative fuels for agriculture. A five-step guideline was developed to help researchers improve systematic reviews (Figure 1). This includes: planning, searching, selection, extraction, and execution [11]. First, the planning stage describes the main objectives targeted at the literature review. Second, the search stage is carried out to determine quality information sources relevant to the topics discussed. The relevant keywords to the topic must be defined in this stage. Third, the selection stage contains the filtering process of the information sources collected. At this stage, each paper’s title, abstract, and keywords are scanned and identified for possible relevance to the purpose of the literature review. Fourth, the extraction stage contains a quality appraisal process that evaluates the application of WtE technology in supporting alternative fuels for agriculture. At this stage, papers are fully read and accurately analyzed, concentrating on their purpose, description, and methodology. Finally, the execution stage contains the synthesis of studies. This combines information from several relevant sources to form a new conclusion or judgment about a particular topic. Synthesis can be performed by identifying similarities, differences, or relationships between ideas in the sources analyzed. The synthesis process involves analysis, comparison, and critical evaluation of the information found in relevant sources [12].

In order to gain a greater understanding of the current state of research on the potential of WtE technologies to support alternative fuels for agriculture, the published literature in the field was evaluated and characterized critically, resulting in an informative list of references. This strategy consists of two primary steps: document review and critical evaluation of relevant research. Then, a form was created to document and characterize the specifics of WtE technology supporting alternative fuels for agriculture within the context of effective solid waste management. The form of documentation begins with categories pertaining to the general characteristics of articles in terms of authorship, article title, publication year, document type, first author’s affiliation, and areas of interest.

The titles and abstracts of all retrieved documents were evaluated for inclusion in the final classification. When the information provided in the title and abstract was insufficient, a full-text review was also performed. Only articles discussing WtE technology for efficient solid waste management were considered for this review.

2.3. WtE Technology Weighting

The determination of suitable WtE technology to produce alternative fuels for agriculture in the Jabodetabek area is calculated based on the weighted total score of each performance indicator. This simple weighting technique refers to the standardized protocol by Perrot and Subiantoro [13] with scale and weight percentage modifications. Firstly, we input a score while comparing each performance indicator between WtE technologies based on the systematic literature review results. To avoid subjectivity, this assessment refers to the literature related to the performance of each WtE technology [4,13,14,15,16,17,18,19,20,21]. Secondly, each input score ($S_j$) is multiplied by the predefined weight ($W_j$) for each performance indicator, and the weighted total score (${WTS}_i$) is considered as the final value used for selecting the appropriate WtE technology. This calculation is expressed in Equation (1), where $i$ represents the attributes of various WtE technology alternatives and $j$ represents the attributes of the performance indicators list ($j=1, 2, 3, \dots , n$). The greater the weighted total score, the more likely the technology is to be implemented in the Jabodetabek area.

(1)${WTS}_i={\sum }_{j=1}^n{W}_j{S}_j$

The scoring is carried out to give a relative value to each performance of each WtE technology so that it is possible to carry out comparisons or further analysis. We ensure that the score assigned is objective so that we can produce relevant and accountable results. Each WtE technology will be assessed using a scale between 1 (worst) and 5 (best) on each indicator. For instance, the anaerobic digester is the preferred method for reducing air pollution, followed by incineration, pyrolysis, gasification, and landfilling. In terms of air pollution, the anaerobic digester receives a score of 5, incineration a score of 4, pyrolysis a score of 3, gasification a score of 2, and landfilling a score of 1.

In addition, this study determines the composition of a higher predefined weight (15%) for environmental performance indicators (air, water, and soil pollution, and byproducts), while 10% of the predefined weight is given to performance indicators of produced energy and cost, and 5% of the predefined weight is given to performance indicators of waste type, energy production efficiency, technology readiness, and capacity. It needs to be emphasized that the determination of the predefined weight composition refers to the results conducted by Nanda, et al. [22]. They report that the highest priority in determining the location of WtE technologies is environmental factors, followed by social and safety factors, and economic factors. The daily generation of MSW has risen steadily, resulting in environmental deterioration and contamination. This trend is attributed to the swift growth of the global population, urbanization, increased material consumption, growing product complexity, and the proliferation of various substances. Therefore, environmental aspects have the most significant weight to ensure that the WtE technology runs in an environmentally friendly manner at a reasonable price (Table 2).

3. Results and Discussion

3.1. Various WtE Options

WtE technology to support alternative fuels for agriculture in Indonesia is a subject of constant debate and speculation as a potential waste diversion method from existing landfills. Metal and glass, which are non-combustible and recyclable, can be repurposed. Certain portions of combustible trash, such as paper, cardboard, and plastic, can also be recycled or utilized as WtE material. According to Mukherjee, et al. [4], two forms of processing, thermal and non-thermal, comprise the evolving WtE technology. Dry waste with a low moisture level is better suited to thermal treatment. Non-thermal treatment techniques such as landfilling, anaerobic digestion, and composting are suitable for trash with a high water content.

3.1.1. Thermal Processing

• Incineration

The standard technology for recovering energy from waste is incineration. Incineration is an exothermic process involving total oxidation that generates flue gases, ash, and heat. The procedure is burning waste in a furnace and utilizing the heat to generate electricity. Overall, 70% and 90% reductions in waste mass and volume can be achieved through incineration [23]; at the same time, heat and/or electricity can also be generated. The US EPA has declared that waste incineration is now a clean energy option since pollution levels are low enough [24]. Carbon dioxide produced by incineration waste is contributed by plastic and synthetic fiber scrap in incinerated municipal waste [25]. In developing countries, incineration is the most reliable and cost-effective way to turn waste into energy when used for mass combustion without pre-treatment. Incineration usually happens at different stages, depending on the operating conditions and the type of waste being burned.

Because the makeup of waste and its characteristics vary, it is necessary to research both aspects before developing an incinerator. Sometimes additional fuel is used along with the waste during incineration. For effective incineration operation, the average calorific value of the waste must be greater than 1900 kcal/kg [26]. Therefore, incineration is suitable for flammable non-biodegradable waste with a low moisture content. Due to the latent heat of vaporization, when the waste’s water content rises, its calorific value will begin to drop. Therefore, trash is sometimes pretreated (thermal, mechanical, chemical, and biological) to eliminate excess moisture and harmful substances such as chlorine and mercury. The incinerator can generate 544 kWh of energy and 180 kg of solid residue per ton of municipal waste incinerated [19]. Consonni and Viganò [15] argued that the energy recoverable from 1 ton of waste depends heavily on (i) the characteristics of the waste and (ii) the characteristics of the WtE installation, particularly its size.

• Gasification

In the gasification process, organic molecules are heated to temperatures greater than 650 °C to be converted into synthetic gas (syngas) and solid byproducts (char). The primary gasification product is syngas, which can be burned to generate power. Different gasification systems, such as fixed bed, fluidized bed, and retained gasification, can be characterized by reactor type and flow. Syngas can also be used to make chemicals and liquid fuels from scratch. Although gasification is well-established in the coal sector, syngas has only lately been investigated as a possible means of producing energy from municipal waste. According to the results of the experiments, the CO₂ emissions from the gasification process are lower than those from an incinerator of the same capacity [27]. Several countries in Asia have applied gasification technology widely, followed by Europe, Africa, and the United States.

• Pyrolysis

Pyrolysis is an advanced thermal treatment method that operates in 400–800 °C without oxygen. This technique produces pyrolysis gas, oil, and charcoal, the yield and quality of which depends on the heating rate, process temperature, and duration of residence. Both WtE by pyrolysis and gasification can treat any municipal waste, and both have the potential to be highly efficient. Plastic, tires, electronic equipment, electrical waste, wood waste, etc., are suitable raw material waste for effective pyrolysis. When comparing the environmental impact and potential energy generation, MSW pyrolysis and gasification technologies are superior to incineration technologies. Unlike incineration, which requires extensive exhaust gas cleaning, pyrolysis and gasification technologies can reduce the waste volume by up to 95% with far less effort [19]. According to Baggio, et al. [28], using a gas turbine, pyrolysis may turn waste into energy with a net conversion efficiency of 28–30%.

Various regions of worldwide have utilized pyrolysis. The only MSW pyrolysis plant in Europe has been operating since 1986 in Burgau, Germany. WasteGen UK Ltd. was the technology supplier for the Burgau plant [23]. The facility processes approximately 38,000 Mg annually of municipal solid waste and sewage sludge. Multiple plants based on Mitsui Recycling 21 technology were constructed in Japan at the start of the twenty-first century to pyrolyze municipal solid waste. The process temperature and heating rate determine the pyrolysis gas, oil, and char yields. Typically, the gaseous fraction increases with increasing temperature. In comparison, greater oil yields can be obtained with a reduced temperature and a rapid heating rate.

3.1.2. Non-Thermal Processing

• Landfilling

Landfilling is managing or destroying waste by disposing and piling waste in a recessed location, compacting it, and then filling it with soil. It can also be defined as the controlled disposal of land trash to reduce environmental impacts. Even though unclean landfilling is a more straightforward and cost-effective method for disposing of vast volumes of waste, it poses a major environmental risk. Recent research has revealed that landfilling has the most significant environmental impact compared to alternative waste management choices [29,30,31]. In addition, this effect will result in negative health effects, land deterioration, and groundwater contamination. Certain wealthy nations have begun to prevent landfilling by stringent legislation, waste reduction, and recycling.

• Anaerobic digester

An anaerobic digester is another way urban waste can make energy. It is a process in which bacteria work without oxygen to break down things that can be broken down (anaerobic). Methane and carbon dioxide make up biogas, a renewable energy source. The process parameters and the composition of the biogas, which is usually 50–75% CH₄, 25–50% CO₂, and 1–15% other gases (e.g., water vapor, NH₃, H₂S, etc.), can affect the quality of the biogas. Biogas is typically used to convert decomposing waste into energy. Through a series of steps, the anaerobic digester will decompose the organic waste and convert it into methane. The first step is called “hydrolysis,” and it occurs when complex organic compounds like carbohydrates, proteins, and fats in waste are broken down into dissolved organic substances like sugars, amino acids, and fatty acids. Also, during fermentation, organic molecules break down into acetic acid, H₂, and CO₂. The last step is methanogenesis, which is when methane is made. Methane is a source of energy used to make electricity and other things.

Anaerobic digester technology offers economic benefits and is environmentally sustainable [32]. This technology can produce 2–4 times as much methane per ton of waste in 3 weeks as a landfill can in 6–7 years. With a conversion efficiency of 35%, 1 m³ of biogas generated by the anaerobic digestion process may provide 2.04 kWh of energy. Based on a 60% organic matter and 40% moisture composition, 1 ton of waste can release about 150 kg of methane [33]. However, the primary issue with anaerobic digesters is the duration of microbial responses (usually 20–40 days).

3.2. WtE Technology Characteristics

3.2.1. Strengths and Weaknesses

The primary objective of any waste management system is to control sanitary and environmental impacts. A good waste management system also permits energy generation from waste, followed by efficient residue disposal. The ideal choice of waste treatment technology should consider the region’s financial requirements, energy-generating capabilities, trash reduction potentials, and environmental requirements. Therefore, selecting the finest available waste treatment technology that meets all the necessary criteria for improved waste management is vital. Each technology has advantages and disadvantages in converting waste into energy (Table 3).

Adopting a new WtE technology is contingent on its technical and economic viability, a thorough understanding of the process steps, chemical and physical parameters, and operational, maintenance, and capital costs. The logistics design, determination of collection areas, and capacity proposals are crucial steps in the conceptual development of a WtE project. Modeling and simulation are also vital for optimizing each process so the WtE conversion can operate effectively and efficiently. By analyzing parameters like collection locations, collection patterns, waste collection costs, equipment, labor, transfer station locations, processing facilities and landfills, waste stream delivery, and the recycling ratio to WtE alternatives, significant cost savings and optimization of WtE process steps can be achieved.

3.2.2. Technology Suitability by Waste Type

MSW, an alternative fuel for agriculture, is generally a complex mixture of several materials with different physical and chemical characteristics and sizes. These ingredients typically have a different water content and calorific value. For alternative fuel for agriculture, MSW is a mixed and segregated waste stream of organic and inorganic compositions. Particular wastes, such as paper and plastics, are segregated at sources and recycling centers. Other waste components, such as glass and metal, are not included as they are unsuitable for energy recovery. Each type of waste has different characteristics that directly affect the application of WtE technology.

Table 4 presents the potential application of WtE technology for alternative fuel for agriculture by type of waste. Some technologies require certain pre-processing, such as drying and sizing, to achieve effective operation. Based on the analysis, mixed waste that is not segregated can potentially be applied to WtE technologies, such as incineration, gasification, pyrolysis, and anaerobic digesters. As for segregated waste, components categorized as combustible materials (plantation waste, plastics, paper, and textiles) can apply incineration, gasification, and pyrolysis. Meanwhile, waste components that are categorized as non-combustible materials (food waste) can apply an anaerobic digester. Landfilling technology is suitable for all types of waste, but this technology cannot convert waste into energy. Landfilling needs to be combined with a bioreactor to capture methane from waste.

3.2.3. General Performance Indicators of WtE Technologies

Performance indicators for each WtE technology vary greatly. WtE can have a significant positive impact, depending on the efficiency of the process for converting waste into an energy source. Through the use of advanced technology, WtE has the potential to effectively reduce the impact of pollution and dioxin emissions, which in turn can provide better protection of the environment and human health. Most WtE projects aim to optimize the utilization of urban waste by reducing the volume of waste in landfills, reducing greenhouse gas (GHG) emissions, increasing resource use efficiency, recycling energy, and creating employment opportunities.

However, there are several requirements and considerations in selecting the appropriate WtE technology, such as input waste type, energy production efficiency, produced energy, technology readiness, annual capacity, byproducts, capital cost, global warming potential, air, water, and soil pollution, as explained in Table 5. This description can be used as a reference for input scores to avoid subjectivity. The indicators for various WtE technologies can be described as follows: (1) based on the input waste type, landfilling and anaerobic digesters can only process specific types of waste compared to incineration, gasification, and pyrolysis; (2) based on energy production efficiency, gasification has a high efficiency compared to the others; (3) based on produced energy, gasification can produce the highest amount of energy compared to the others; (4) based on technology readiness, landfilling has the highest level of maturity compared to the others; (5) based on capacity, landfilling has the highest storage capacity compared to the others; (6) based on byproducts, the anaerobic digester produces biosludge as compost which is useful for plants or soil; (7) based on capital costs, landfilling has a lower capital cost compared to the others; (8) based on global warming potential, landfilling has the worst impact on global warming; (9) based on air pollution, incineration has the highest level of air pollution; (10) based on water pollution, landfilling has the highest level of water pollution; finally, (11) based on soil pollution, anaerobic digesters have the lowest level of soil pollution compared to the others.

MSW is responsible for 3–4% of worldwide greenhouse gas (GHG) emissions and is the environment’s third-greatest anthropogenic methane gas source [46]. This can impact the global problem of climate change, which requires concerted efforts from all nations to mitigate it. The use of GHG-lowering technologies is crucial. While the CO₂ emissions from each WtE technology are different, they all contribute to the overall problem of climate change. Compared to other technologies (incineration, gasification, pyrolysis, and anaerobic digesters), landfilling has the highest global warming potential, as shown by the literature assessment (746 kg ≈ CO₂ per MWh electricity generation unit) (Table 5). The WtE technology with the lowest global warming potential is the anaerobic digester (222 kg ≈ CO₂ per MWh power generation unit). The lower the global warming potential, the more environmentally friendly the WtE technology.

In terms of cost, each type of WtE technology is different and is influenced by various factors, such as geographic location, installation size, type of waste, technology used, government incentives, raw materials and the availability of skilled labor. In general, costs in WtE technology include initial investment costs such as land acquisition, equipment procurement, raw material requirements, and indirect costs include planning costs, contract support, and technical and financial services during the development stage. All of these costs are categorized as capital costs. Based on Table 5, the lowest capital cost is landfilling and the highest capital cost is incineration and pyrolysis. The capital cost of landfilling is relatively low compared to other waste processing technologies because the waste treatment process in landfilling is relatively simple and does not require expensive special equipment. Meanwhile, incineration and pyrolysis have high capital costs because they require expensive special and complex equipment that requires a lot of energy to produce high temperatures.

3.3. Energy Input in Agricultural Production

Dramatic increases in yield per hectare can be achieved by using energy inputs to power various agricultural machinery equipment (Figure 2). This is because the power that humans can give is very limited. The average adult can only continuously produce about 75 W of energy (0.75 kWh for a 10-h workday) [47]. To go beyond the subsistence level, additional sources of energy are needed. Agriculture requires energy for crop production, as well as agricultural processing for additional value. Agriculture extensively uses human, animal, and mechanical energy for crop production. Agriculture’s energy requirements are classified as direct and indirect [48]. Direct energy is necessary to execute numerous crop production activities, including land preparation, irrigation, threshing, harvesting, and transportation of agricultural supplies and goods. In contrast, indirect energy is consumed in manufacturing, packaging, and transporting fertilizers, insecticides, and agricultural equipment. On the farm, indirect energy is not used directly. Fertilizers, seeds, machinery production, and pesticides are primary indirect energy sources [49].

Energy input in agriculture consists of various energy sources used in agricultural production processes. Energy consumption in the agricultural sector depends on the number of agriculturists, the quantity of arable land, and the level of mechanization [51]. Energy input in the agricultural value chain is shown in Figure 2. Generally, the main chain in farm production includes pre-harvest, harvest, post-harvest, and distribution, with various activities such as land preparation, harvesting, drying, transportation, etc. All of these activities require energy which can be sourced from electricity, mechanical power, fuel, and thermal. These energy inputs require limited resources, so it is vital to consider their use wisely and efficiently. In addition, using renewable energy and more efficient technologies can help reduce the environmental impact of agricultural production. Table 6 shows the inputs used in agricultural production activities and their energy equivalents.

The literature study results show that the amount of energy is equivalent to farm power machinery and fertilizing, i.e., 62.70 and 99.40 MJ ha⁻¹. A relatively small amount of energy is found in activities such as drying (0.84 MJ kg⁻¹), transportation (1.16 MJ ha⁻¹), and irrigation (1.02 MJ m⁻³). According to Pimentel and Pimentel [57], the irrigation energy requirement for rice production in the United States is 8949MJ ha⁻¹ (18% of total energy demand). Electric motors mainly use electrical energy to run irrigation pumps. Agricultural productivity can be increased through mechanization and switching from energy use from non-renewable sources to renewable sources to achieve self-sufficient and sustainable agricultural production systems. The use of larger tractors and tillage management techniques and the increased use of fertilizers will result in significant increases in energy efficiency.

3.4. WtE Technology to Support Alternative Fuels for Agriculture in Jabodetabek

3.4.1. Waste Management

Jabodetabek is a vital area with a population of around 31 million people in 2020 [58]. Its territory includes six municipalities with a total land area of 6757.8 km². Jabodetabek is predicted to produce around 9.069 million tons/year of MSW by 2023 [1]. MSW management in Jabodetabek relies on an outdated scheme known as the conventional collect–transport–dispose (Figure 3). This scheme will accelerate the overfilling of landfills. Government agencies such as the Environmental Service under the Ministry of Environment and Forestry are the primary stakeholders responsible for managing waste. Urban waste management facilities in Jabodetabek include trucks, temporary shelters, waste banks, and landfills.

In addition to formal waste management, there is extensive informal recycling in Jabodetabek, which includes scavengers, intermediaries, grinders, and recyclers. Scavengers collect valuable waste at the source and then sell it to intermediaries. The middleman performs further sorting and cleaning and then sells the processed waste to the grinder. This grinder is the party that carries out further waste processing until the preparation stage to convert waste into raw materials, such as grinding plastic waste or pressing bottles. The dealer or grinder then sells the waste to a recycling facility.

The unplanned growth in many cities caused by rapid urbanization has resulted in infrastructure challenges that undermine the capacity of the central government to increase the level of municipal solid waste management services. The management of MSW in Jabodetabek is faced with various complex problems, such as the sustainable growth of slum areas, lack of public infrastructure, inadequate budgets, corruption, ineffective education, and public distrust of the government. In addition, the lack of awareness, education, and waste sorting facilities are the main obstacles to waste management in the Jabodetabek metropolitan area.

3.4.2. Current Status of WtE Technology

WtE, or energy from waste in Indonesia, is a hotly discussed topic and a possible means of diverting waste from existing landfills. Although various thermal and non-thermal WtE technologies are available to generate energy in Indonesia, there are still considerable obstacles to adopting WtE policies due to the high cost of constructing new facilities, financial hazards, and minimal economic benefits. Landfills will gradually fill up near significant cities and reach their maximum capacity. One example of a well-known waste disposal site (TPS) in the Jabodetabek area is the Bantargebang, Bekasi region. Currently, the landfill height in Bantargebang has reached 50 m on an area of 104 ha, with waste per day of around 7400 tons. Thus, this TPS is anticipated to achieve its maximum capacity in 2022. This TPS is being made more durable by developing an integrated waste management facility, compacting solid waste, and increasing the space.

The implementation of WtE technology in Bantargebang has been implemented with limited capacity. This technology works based on the incineration method located centrally at the Bantargebang landfill and has generated 783.63 MWh of electricity by 2020. This thermal power plant uses supercritical steam fueled by waste or methane gas. However, the electricity capacity is still relatively low compared to the projected potential of waste into electricity in Jabodetabek of 820.90 GWh in 2020, based on calculations by the intergovernmental panel on climate change by Ismangoen, et al. [1]. Waste processing and utilization in these various areas are expected to be one of the solutions to the volume of waste accumulated in Bantargebang. According to the preceding description, Jabodetabek’s WtE status utilizing WtE technology is in its infancy. As a result of the abundance of waste raw materials in the Jabodetabek region, the development of WtE technology will soon become quite common throughout the region. Most WtE initiatives attempt to demonstrate full-scale usage of municipal trash through reduced waste streams at disposal sites, greenhouse gas (GHG) reduction, resource efficiency, energy recovery, and job development.

3.4.3. Potential of Suitable WtE Technology

In practice, the Jabodetabek regional government has two main concerns regarding waste management strategies: environmentally friendly and economical. Thus, it is crucial to consider the correct criteria when making comparisons. Air, water, and soil pollution are the primary economic and environmental considerations. The raw input score to determine the appropriate WtE technologies is shown in Table 7. This input score is given carefully based on the results of a systematic literature review. Based on the numerical analysis, the WtE technologies with the highest to lowest weighted total scores are anaerobic digesters (4.10), gasification (3.40), pyrolysis (3.25), incineration (2.75), and landfilling (1.95) (Table 8). Therefore, anaerobic digester technology is the most attractive solution for the Jabodetabek area in general. According to Ismangoen, et al. [1], the waste composition generated in the Jabodetabek metropolitan area shows that food waste has the highest proportion (53%) compared to other components such as paper, wood, plastic, etc. Therefore, the anaerobic digester is a suitable WtE technology. In addition, it is an environmentally friendly and economical solution because its technological readiness is relatively mature.

The use of this anaerobic digester has also been backed by the Indonesian government, which wants to increase the use of renewable energy. Indonesia’s Ministry of Energy and Mineral Resources has set an ambitious target to develop biogas into biomethane and compressed biomethane gas (CBG), reaching up to 1230 MMbtu per day in 2023 [59]. This action aligns with the government’s efforts to promote the use of renewable energy, particularly in the bioenergy sector. The government’s biogas development program encompasses various aspects, including household biogas, communal biogas, and industrial biogas, as well as the production of biomethane and CBG. The main challenge in implementing WtE is the social aspect, in the form of a lack of public knowledge about the role of waste management. Public resistance, such as from scavengers, to the application of the technology can influence local government decisions and hinder the project. These barriers usually stem from the lack of involvement of local authorities with all relevant stakeholders. Therefore, for this option to be implemented successfully in Jabodetabek, it is vital to ensure the effectiveness of the existing waste management strategy towards the 3Rs (reuse, reduce, and recycle).

3.4.4. Anaerobic Digester as Alternative Fuel Source

The Jabodetabek area has promising agricultural prospects. Fertile soil and a supportive climate make it an ideal location for productive farming activities, particularly in the Bogor area [60]. However, the Jabodetabek area also faces significant challenges regarding waste management. The substantial amount of waste generated by the community and industries is a serious concern. Nevertheless, there is considerable potential in transforming these challenges into opportunities. The abundant waste can be converted into a valuable source of energy. Through WtE conversion, the Jabodetabek area has the opportunity to support sustainable agriculture. The energy generated from waste can be utilized to operate various agricultural tools and machinery. As a result, the operational costs of agriculture can be significantly reduced. Furthermore, this contributes to a decrease in dependence on fossil energy sources. By combining the high potential of agriculture with the utilization of energy from waste, the Jabodetabek area can achieve more efficient, economical, and sustainable agriculture while also delivering positive environmental benefits.

The results of our analysis confirm that the anaerobic digester has promising prospects as an alternative fuel source for agricultural production in the context of effective solid waste management in the Jabodetabek area. Abundant organic waste such as livestock, crops, waste water, food waste, and other organic waste can be a source of input for the anaerobic digester (Figure 4). The methane gas produced in biogas can be implemented to generate electricity and power for farm machinery. In general, the electricity generated can be utilized for each agricultural value chain, such as irrigation, sorting, crops protection, grading, drying, storage, and milling. The energy generated can be distributed to various farm machinery such as land preparation, threshing, harvesting, and cutting. Pumps for irrigation and other equipment such as diesel engines can be run with gas-powered engines sourced from biogas.

Biogas is a suitable WtE technology for most regions in developing nations, such as Jabodetabek, because the waste composition contains a greater proportion of organic matter and a relatively high proportion of water [61]. Many factors, such as the type of manure, reactor design, pH, temperature, and available waste, strongly influence biogas production. In addition, biogas production is also highly dependent on the ratio of total solids to waste raw materials. For example, the optimum temperature, pH, and humidity for biogas production are 35–40 °C, 6.5–8.5, and 70–85%, respectively. Unsuitable environmental conditions will inhibit the growth of bacteria, resulting in a smaller amount of gas. In addition, the size and type of digester also affect biogas production. Several kinds of digesters that are commonly used include digesters in the form of tanks, domes, or open ponds. The selection of the type and size of the digester must be adjusted to the raw materials used and the desired biogas production needs.

3.5. WtE Technology in Southeast Asian Countries

Waste is the most evident environmental problem in many Southeast Asian countries’ urban regions [62]. The area has also experienced rapid urban growth since the late 1980s. Population growth, changes in consumption patterns, economic development, income fluctuations, urbanization, and industrialization have resulted in an increase in waste generation and a diversification of waste types. Indonesia is Southeast Asia’s largest waste producer with a total annual waste generation in 2012 of 22,500 million tons per year [5]. With accelerating urbanization, economic growth, and changing lifestyles, the urban population in Southeast Asia is projected to increase to almost 400 million by 2030. The progress of WtE technology in Southeast Asian countries can be seen in Table 9.

Indonesia, Thailand, Singapore, and Myanmar are countries that have operated and commercialized WtE technology. Meanwhile, Malaysia, the Philippines, Brunei, Vietnam, Laos, and Cambodia are still in the process of realization, and Timor-Leste is still in the stage of academic study. Indonesia has implemented gasification to convert waste into energy. Gasification for municipal solid waste faces several challenges in its global adoption. This is related to technical complexity [35,76]. Municipal waste is complex and diverse in composition, containing organic materials, plastics, paper, metals, etc. Waste must be prepared and pre-processed before it can be used as fuel for gasification. Efficient and consistent waste separation and processing can be a difficult technical challenge to overcome.

In general, the WtE technology types most and least applied in Southeast Asia are incineration, gasification, and biogas. The largest WtE technology capacity is 7500 tons day⁻¹ in Indonesia and Vietnam. Based on the analysis, incineration produces the highest electrical energy compared to gasification and biogas. Most Southeast Asian countries are still in the early stages of technological development. However, due to the region’s promotion of renewable energy supplies, particularly in Indonesia, Malaysia, Thailand, and Singapore, the development of WtE technology can be seen broadly across the region in the near future. If managed correctly, the benefits of WtE technology include reduced carbon emissions, minimal soil contamination, chemically stable combustion byproducts, and sustainable electricity production.

3.6. Critical Analysis

Successful WtE conversion technology implementation necessitates a solid waste management system to improve the collection and treatment of individual waste types. For a WtE project to be successful, several governmental agencies, such as state utilities as power takers, municipalities for waste supply, and land locations for processing, must work together closely. Increasing carbon emission output fees is another policy option for sustaining stringent environmental emission requirements. WtE project proposals and reports should use life cycle analysis (LCA) as a comprehensive performance evaluation tool for identifying significant drivers and environmental elements.

Capital and regulating air emissions such as dioxins, furans, NOx, SOx, CO, CO₂, acid, and other greenhouse gases are the most significant obstacles to bringing WtE technology to market. Ash, slag, charcoal, and tar are solid waste materials that must be managed safely. Synthetic gas purification must also meet all mandatory safety requirements before being used in power plants. The socioeconomic acceptability of the WtE technology concept by local communities and investors is an essential factor to examine alongside the technological obstacles when assessing the technology’s viability. One or more WtE methods will be integrated into future WtE technologies to increase the energy output [4]. In this case, we could use a mix of thermal and non-thermal technology to convert useful energy from waste. This technology is considered more effective in the Jabodetabek area or other areas. It will be a cost-effective system that promotes recycling, reduces emissions, and addresses the problem of sustainable urban waste disposal.

4. Conclusions

The Jabodetabek metropolitan area may benefit from WtE technology for energy recovery, and this study thoroughly assesses that possibility. Municipal solid waste can be considered one of the greatest potential renewable energy sources to reduce, reuse, and recycle waste. Waste conversion to energy can be regarded as an economically viable and environmentally beneficial alternative energy source. This study explores alternative WtE technologies, including incineration, gasification, pyrolysis, landfilling, and anaerobic digester for possible future implementation in Jabodetabek. The performance indicators assessed are the type of waste, efficiency, the energy produced, technological readiness, capacity, byproducts, costs, air pollution, water pollution, and soil pollution. Environmental and cost aspects have the most significant weight to ensure that WtE runs in an environmentally friendly manner at a reasonable price. Based on the numerical analysis, the WtE technologies with the highest to lowest of weighted total scores are anaerobic digester (4.10), gasification (3.40), pyrolysis (3.25), incineration (2.75), and landfilling (1.95). Therefore, anaerobic digester technology is the most attractive solution for the Jabodetabek area in general. This is an environmentally friendly and economical solution because the technological readiness level is relatively mature. The application of this anaerobic digester has also been supported by the Indonesian government which is committed to increasing the application of renewable energy. Therefore, efforts from all stakeholders, especially the government, are needed to support the implementation of the anaerobic digester as one of the steps to convert waste into energy. And thus, waste management in Jabodetabek will run effectively and efficiently.

Author Contributions

Conceptualization, H.I. and A.S.; methodology, M.A.N. and H.I.; software, M.A.N.; validation, I.W.B.; formal analysis, M.A.N.; investigation, M.A.N.; resources, A.K.W. and A.S.; data curation, H.I.; writing—original draft preparation, M.A.N. and L.O.N.; writing—review and editing, W.S. and L.O.N.; visualization, M.A.N.; supervision, L.O.N., I.W.B. and K.B.S.; project administration, A.K.W. and A.S.; funding acquisition, K.B.S., L.O.N., and I.W.B. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All the data supporting the results are included in the article.

Acknowledgments

The authors are grateful to the Universitas Padjadjaran, Indonesia for the article processing charge (APC).

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Figure 1. The review approach of the systematic literature review (modified from Sadiq, et al. [11]).

Figure 2. Energy input in the agricultural value chain (modified from Energypedia [50]).

Figure 3. Conventional schemes in urban waste management.

Figure 4. Biogas as an alternative fuel for agricultural production.

Table 1

List of keywords used for literature search.

Search String
(“Waste-to-energy (WtE) Technology”)
(“Strengths and Weaknesses” AND “WtE technology”)
(“Solid Waste Management” OR “Waste Management” AND “Jabodetabek”)
(“Alternative Fuels” AND “Agriculture”)
(“Alternative Energy Source” AND “Agriculture”)

Note: Each of the sources contains different search strings to enhance the search outcomes.

Table 2

Composition of the predefined weight on each WtE technology performance indicator.

Performance Indicators	Weight (%)
Waste type	5
Energy production efficiency	5
Produced energy	10
Technology readiness	5
Capacity	5
Byproducts	15
Cost	10
Air pollution	15
Water pollution	15
Soil pollution	15
Total	100

Table 3

Advantages and disadvantages of various WtE technologies.

WtE Technology	Strengths	Weaknesses	Source
Incineration	✓ Reduce the volume of waste by up to 90%	✓ Requires a pre-drying unit if the waste has a high moisture content ✓ Requires technology for air pollution control	[4,14,34]
Gasification	✓ Can prevent the formation of dioxins, furans, and NOx ✓ Can produce the inert and vitrified ash ✓ Can produce high-quality syngas and cleaner energy	✓ Requires a series of pre-drying and cleaning of syngas ✓ Requires consistent, similar waste (such as wood chips, tire waste, paper and cardboard, and plastics) ✓ Requires waste pre-processing such as pelletization and torrefaction ✓ Contains tar which can clog downstream pipes and equipment	[15,35,36]
Pyrolysis	✓ Has a low production cost and is flexible for large-scale commercialization ✓ Increases the efficiency because it has natural catalysts such as charcoal, zeolite, and dolomite	✓ Requires physical separation of non-combustible materials (metal and glass) first ✓ Requires additional costs for the need for synthetic catalysts such as nickel and ruthenium ✓ Produces charcoal which can be contaminated with heavy metals and organic pollutants	[16,37]
Landfilling	✓ Can produce methane gas to be used as an energy source ✓ Has a more economical operating cost than burning waste	✓ Requires a large amount of isolated land ✓ Requires higher landfilling costs ✓ Produces more potent greenhouse gases than carbon dioxide from decomposing waste ✓ Contaminates groundwater from hazardous leachate in landfills	[17,38,39,40,41]
Anaerobic Digester	✓ Generates biogas which can be used for cooking, heating fuel and electricity directly ✓ Produces compost that can be used for fertilizer in agriculture or as a soil amendment	✓ Has challenges related to low biodegradability ✓ Has high maintenance and operating costs ✓ Requires heating in cold climates in the digester ✓ Reduces the waste volume by about 50%	[18,42,43,44]

Table 4

Potential application of WtE technology by type of waste to produce alternative fuels for agriculture.

Waste Type	The Potential of Suitable WtE Technology to Produce Alternative Fuels for Agriculture
	Incineration	Gasification	Pyrolysis	Landfilling	Anaerobic Digester
Mixed waste	√	√	√	-	√
Segregated waste
a. Food waste	√	√	√	-	√
b. Plantation waste	√	√	√	-	√
c. Plastic waste	√	√	√	-	-
d. Paper waste	√	√	√	-	-
e. Textile waste	√	√	√	-	-

Note: symbol of ‘√’ and ‘-’ demonstrate WtE technology has the potential to be applied and vice versa, respectively.

Table 5

The general performance indicators of various WtE technologies.

Indicators	Notes	WtE Technology
		Incineration	Gasification	Pyrolysis	Landfilling	Anaerobic Digester
Input waste type	Waste type	All	All	All	Specific	Specific
Energy production efficiency	%	21.0	35.0	20.5	none	10.4
Produced energy	GJ	5,806,909	9,665,899	5,661,455	none	1,015,671
Technology readiness	Maturity level	Very mature	Moderately mature	Less mature	Extremely mature	Mature
Capacity	Tons per year	150,000	250,000	250,000	2,737,500	100,000
Byproducts	Type	Residue ash	Syngas	Pyrolysis gas	Leachate	Biosludge
Capital cost	US$/tons	400–700	250–850	400–700	10–30	50–350
Global warming potential	kg CO2	424	412	412	746	222
Air pollution	NOx level	Extremely high	High	Moderately high	Very high	Low
Water pollution	Water pollution level	Very high	High	Moderately high	Extremely high	Low
Soil pollution	Soil pollution level	Very high	High	Moderately high	Extremely high	Low
Reference		[5,13,19,20,45]	[5,13,19,20,45]	[5,13,19,20,45]	[5,13,20,21,22,45]	[5,13,19,20,45]

Table 6

The energy equivalents of agricultural production inputs.

Input	Unit	Energy Equivalent (MJ Unit−1)	References
Human labor	h	1.96	[52]
Machinery	h	62.70	[53]
Fuel
a. Gasoline	L	41.75	[47]
b. Diesel	L	56.31	[47]
Chemical fertilizer
a. Nitrogen	ha	66.13	[54]
b. Phosphate	ha	12.44	[54]
c. Potassium	ha	11.15	[54]
d. Sulphur	ha	1.12	[54]
e. Zinc	ha	8.40	[54]
Planting	ha	6.64	[49]
Irrigation	m3	1.02	[55]
Electricity	kWh	3.6	[56]
Drying	kg	0.84	[47]
Transportation	kg	1.16	[47]

Table 7

The raw input score to determine the appropriate WtE technologies.

Performance Indicators	Raw Input Score on Various WtE Technologies
	Incineration	Gasification	Pyrolysis	Landfilling	Anaerobic Digester
Waste type	5	5	5	1	3
Energy production efficiency	4	5	3	1	2
Produced energy	4	5	3	1	2
Technology readiness	4	2	1	5	3
Capacity	3	4	4	5	2
Byproducts	4	3	2	1	5
Cost	2	3	2	5	4
Air pollution	1	3	4	2	5
Water pollution	2	3	4	1	5
Soil pollution	2	3	4	1	5
Total	31	36	32	23	36

Table 8

The weighted total score for selecting the appropriate WtE technology for Jabodetabek.

Performance Indicators	The Weighted Total Score on Various WtE Technologies
	Incineration	Gasification	Pyrolysis	Landfilling	Anaerobic Digester
Waste type	0.25	0.25	0.25	0.05	0.15
Energy production efficiency	0.20	0.25	0.15	0.05	0.10
Produced energy	0.40	0.50	0.30	0.10	0.20
Technology readiness	0.20	0.10	0.05	0.25	0.15
Capacity	0.15	0.20	0.20	0.25	0.10
Byproduct	0.60	0.45	0.30	0.15	0.75
Cost	0.20	0.30	0.20	0.50	0.40
Air pollution	0.15	0.45	0.60	0.30	0.75
Water pollution	0.30	0.45	0.60	0.15	0.75
Soil pollution	0.30	0.45	0.60	0.15	0.75
Total	2.75	3.40	3.25	1.95	4.10

Table 9

The progress of WtE Technology in Southeast Asian countries.

Country	WtE Plant Name or Installation Site	Status	WtE Technology Type	Capacity (Tons Day−1)	Generated Electricity (MW Day−1)	References
Indonesia	Bantargebang	ao	Gasification	7500	15.6	[22,63]
Malaysia	Taman Beringin	wr	Incineration	1200	18.8	[2,5,64]
Thailand	Nonthaburi	ao	Gasification	1000	2.8	[65,66]
Singapore	TuasOne	ao	Incineration	3600	120	[67,68]
Filipina	Davao City	sp	Incineration	600	0.204	[69]
Brunei	Sungai Paku	wr	Incineration	800–1000	nr	[70]
Vietnam	Hanoi	wr	Incineration	7500	75	[71]
Laos	Nam Son	wr	Incineration	4000	75	[72]
Cambodia	Phnom Penh	wr	Incineration	3000	50	[73]
Myanmar	Yangon	ao	Incineration	60	0.76	[74]
Timor-Leste	Dili	su	Biogas	203	10	[75]

Note: ao: already in operation, wr: will be realized, su: still under study, and nr: not yet reported.

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