1. Introduction
In most countries, rapid economic growth and urbanization cause shortage of energy and infrastructure and limit the available land and applicable methods for managing solid waste. In several developing countries, the increasing rate of urbanization has resulted in issues related to energy shortage and municipal solid waste (MSW) management [1]. Landfilling is one of the most convenient MSW management method that is widely used in both developed and developing countries [2]. Landfill gas (LFG) is a byproduct of landfilling MSW, naturally produced through the decomposition of organic matter in landfills [3]. As indicated in previous studies, LFG has been used as a renewable energy source for local power generation (via grid-connected energy systems) [4]. There are more than 1000 LFG plants worldwide, with the majority of them being in Europe and the United States of America (USA). At present, South Africa has four LFG plants, and the demand for LFG technology is increasing [5]. The Global Methane Initiative (GMI) offers technical assistance for the deployment of energy projects that use methane (CH4) gas worldwide, enabling partner nations develop and implement programs for the recovery and utilization of CH4 [6].
In this study, we examined the global perspective of LFG consumption and provide an overview of the CH4 generation and utilization technologies. We focused on the potential for LFG to produce energy and the possible social and economic effects of using CH4. In addition, we analyzed the geographical and economic growth implications on the characteristics and techno-economic feasibility of LFG generation projects.
2. Global Scenario of Landfill Technology for Waste Management and Energy Recovery
In accordance with a World Bank report, globally the average daily waste generation reached 0.74 kg per capita [7]. Economic development, in terms of the entity variables that have proportionally increased historically, has increased the global waste generation, with 2.01 billion tons of MSW being annually generated globally in 2018. Based on a projection (business as usual), this number is expected to increase to 3.4 billion tons MSW by 2050 [7].
As shown in Fig. 1, the average global landfill content consists of 37% of disposed waste, 33% dumped untreated waste, 19% of waste hat undergoes compositing and recycling, and 11% that undergoes partial thermal recovery, through modern mass burn incinerators. Upper-middle income countries carry out waste treatment and disposal in controlled landfill facilities. However, in countries that have low incomes, 93% of the waste is disposed via open dumping; while, in high-income countries, 2% of the waste is disposed via open dumping [7].
The World Bank data indicates that the global picture of LFG technology mostly spread after the industrial revolution. Approximately 45% of the total waste generated in the European Union (EU) is disposed in the landfill site. In China, landfilling is the most actively chosen technology, and approximately 89% of the country’s total solid waste is landfilled [8]. In England, 361 LFG utilization facilities were operational in 2015, over double the number of facilities that operated in 2001. In 2015, these plants produced 4106.4 GWh, using LFG technology. The LFG utilization technology continued to advance, primarily in wealthy countries. However, the introduction of the Clean Development Mechanism programs stimulated the development of LFG utilization technology in underdeveloped countries as well [9]. In South Korea, the waste sector contributes to 37.6% of the total CH4 emissions. In 2001, approximately 465,000 tons of the total annual CH4 emissions were from the waste sector [10].
Open dump, partially controlled, and sanitary landfills are the most common types of landfills [11]. An open dump landfill is a piece of land where MSW is dumped in the open, with the area having access to fresh air. Most developing nations have open dump landfills where the MSW is carelessly thrown into low-lying open regions. Based on the type of wastes, the locations of landfills and treatment facilities were discussed in detail in previous studies (e.g., toxic chemicals, biohazards, household, biomedical, and radioactive wastes, as well as construction, demolition, and renovation wastes) [12]. Notably, the essential parts of a landfill include its foundation, bottom liner, and barrier cover, collection systems for LFG and landfill leachate, gas flaring station, and soil layers on the top of the landfill area, which provide minerals and organic chemicals that can improve CH4 quality and quantity.
In general, LFG is removed from MSW dumps, using a blower/flare system and several wells [5, 13]. Depending on the gas’s intended use, this system routes the gathered gas to a central location, where it can be processed. The gas can be vented at this point or utilized advantageously in various LFG energy projects.
Numerous industrialized nations, including England, China, Uruguay, Mexico, and the USA, harvest the gases produced from landfills [3]. According to the Landfill Methane Outreach Program (LMOP) by the United States Environmental Protection Agency (US EPA), the CH4 generation potential (L0) denotes the CH4 (m3) available for the site-specific variables per ton of waste. The composition of the waste, and to some extent, that of the organic matter fraction of the waste are the determining factors of the CH4 generation rate (k). Notably, the L0 value can be determined based on the carbon content of the waste, stoichiometric conversion factor, and biodegradable carbon fraction. The typical values for L0 range from 125 m3/t to 310 m3/t. The US EPA uses a default L0 value of 170 m3/t. According to an analysis carried out in a previous study [14], the production of LFG begins a few months after the MSW is disposed and typically lasts for 10 years or longer, depending on the composition of the waste and the amount and distribution of moisture in the MSW. In several nations, full-size sanitary landfills yearly produce LFG between 5 L/kg and 40 L/kg. The MSW generated in major Indian cities is rich in organic matter and has the potential to produce 15–25 L/kg of gas annually, during the course of its life (most LFG projects operate up to 30 years) [13]. The gas collected from smaller landfills can be supplied to nearby enterprises for direct use in internal combustion engines, gas turbines, micro turbines, steam boilers, and other facilities. Furthermore, the gas collected from large landfills can be advantageously used as a clean fuel for power generation [15].
The LFGcost-Web LFG Energy Cost Model [16] portrays the overall economic analysis used to compare the costs of treatment of waste (waste conversion) and the levelized cost of electricity, or cost of fuel to determine the suitable layout configurations for all ranges of LFG plants. The data on the capital, operational, and maintenance costs were collected from literature survey and estimated by considering the costs of existing technological facilities in Ethiopia and through energy and mass balances as well.
3. LFG Production and Characteristics
In general, LFG is a naturally occurring gas that is produced from the breakdown of organic matter in landfills. CO2, CH4 (the main component of natural gas), and trace amounts of organic chemicals make up the majority of LFG [17]. The CO2 contained in LFG should be sequestrated [18], and landfill leachate needs to be carefully treated [19]. The conversion of landfilled waste substances into LFG occurs via waste decomposition and degradation. The time duration and stage of CH4 generation amount generally have many intrinsic and environmental determinant variables. Those determinant variables are, temperature, moisture level, waste composition, and a variety of substrates for microbial degradation are some of the variables that have an impact on this process. The LFG synthesis process involves several chemical events, including hydrolysis, acidogenesis, methanogenesis, and maturation [20, 21].
The overall LFG maturation cycle has five basic phases (shown Fig. S1), as follows:
Aerobic decomposition: Aerobic decomposition involves bacteria that digest garbage in the presence of oxygen. O2 is used to form CO2, as heat is created. The active duration of the process can be anywhere between a few months and a year, depending on the circumstances. Organic waste is broken down into its lengthy molecular chains of complex carbohydrates, proteins, and lipids by aerobic bacteria, which can only exist in the presence of oxygen. CO2 is the main byproduct of this process. Phase 1 continues until there is no more oxygen left.
Acidogenic: Anaerobic conditions are established during this stage, resulting in the formation of organic acids, CO2, H2O, and hydrogen (H2). The anaerobic conditions cause a low rate of energy release. The pH of the leachate can go below 5, as a result of acid production. The anaerobic bacteria transform substances produced by aerobic bacteria into acetic, lactic, and formic acids, as well as alcohol products, such as methanol and ethanol, without the need for oxygen. As the acids react with the moisture in the landfill and nitrogen (N) is consumed, CO2 and H2 are formed.
Acetogenesis: At this stage, acids and alcohols are converted to acetic acids, and CO2 and H2 are also formed. The acid and leachate contents cause a noticeable rise in the chemical oxygen demand (COD). The organic acids produced in phase II are broken down by anaerobic bacteria into acetate, another organic acid. By consuming the CO2 and acetate, this process transforms the garbage into a more neutral environment, wherein the bacteria that produce CH4 can flourish.
Methanogenesis: CH4 and CO2 are produced as byproducts of the acetogenesis phase, and H2 is consumed. The available substrates have an impact on the CH4 content. The production rates and composition of LFG remain largely consistent. Notably, LFG typically comprises of 50–55% CH4 by volume, 45–50% CO2, and 2–5% other gases, such as sulfides. In phase IV, LFG is generated steadily for 20 years (on average).
Maturation: At this phase, the gas production decreases due to substrate depletion.
Table 1 provides an overview of each LFG component’s impact on the environment and human health.
4. LFG Design, Operation, and Characteristic Parameters
A blower/flare (or vacuum) system and a series of wells can be used to recover the LFG from MSW dumps [13]. Depending on the gas’s intended use, this system routes the gathered gas to a central location, where it can be processed. From here, the gas can either be flared or utilized profitably in an LFG energy production plant. The production of LFG often begins a few months after waste disposal and lasts for 10 years, or even longer, depending on the composition and characteristics of the waste and the availability and dispersion of moisture. Full-size sanitary landfills typically produce LFG of 5–40 L/kg.
Several nations base their estimates of LFG emissions primarily on the first-order decomposition of organic matter in MSW [25]. LandGEM, which is a spreadsheet tool [26], has been used to determine the total amount of CH4, CO2, and other miscellaneous organic compounds produced through landfill waste decomposition. First order decay equation is the most useful equation for estimating LFG generation [27]. To measure the emissions from the breakdown of landfilled waste in MSW landfills, the scholars used a first-order decomposition rate equation in the LandGEM model. The software offers a comparatively straightforward method for calculating the LFG emissions, as reported by various LFG initiatives around the world.
where Mi = waste accepted in the ith year (megagram, Mg), QCH4, annual methane generation (m3/year), i = 1 – year time increment, n = (year of the calculation) – (initial year of waste acceptance), j = 1 – year time increment, k = methan generation rate per year, Lo = potential methane generation capacity (m3/Mg), tij = jth section waste, Mi, accepted in ith year.
The input data for LandGEM spreadsheet [26] can be correlated directly with the specific geographical conditions of the landfill region. LandGEM assumes that methane production peaks quickly after the first disposal of waste (after a brief delay while anaerobic conditions are created in the landfill). The model also predicts that when organic material decomposes, the rate of landfill methane generation will drop exponentially (first-order decay).
The estimated CH4 content was 40–60%. The first-order decomposition rate equation applied in the LandGEM model could be used to calculate the emissions; however, the results may not be accurate if the content was lower or higher than 40–60%. The production of CO2 was highly determined or affected by the concentration of CH4 generation.
Eq. (2) was used to determine the production of CO2 (QCO2) from the production of CH4 (QCH4) and the proportion of CH4 in the atmosphere (PCH4) [27]:
where QTotal is the total production of LFG.
Compared to natural gas, LFG is cheaper and contains nearly 50% of the calorific value (16,78–20,495 kJ/m3) of natural gas (35,406 kJ/m3) [28]. Thus, if we extract large amounts of LFG, the electricity production using turbine or internal combustion engines would be safe and efficient. Furthermore, we can improve the LFG heating value by decreasing the contents of O2, N2, and CO2 in the LFG [29].
For LFG generation estimation, we employed the LandGEM spreadsheet software. This model can estimate LFG accurately and determine the amounts of CH4 and CO2 generation, with respect to opening and closure year of the landfill site. According to the LandGEM software specification, the generation rate of CH4 during annual MSW disposal can be used to calculate or estimate the annual amount of CH4. The CH4 generation rate, k, is a country and site-specific value used to determine the CH4 generation potential of MSW on specific landfill area. Thus, a higher k value indicates a high volume of CH4 per kg of MSW [30]. Note that the L0 and k values are strongly dependent on the landfill type (Table S1).
The capacity of CH4 generation of the waste also depends on the characteristics of the MSW (Table S2). Site specific parameters (e.g., inert-decomposable and semi-decomposable) are generally used to characterize the MSW and its potential for CH4 generation [2]. Each waste body has its own value of CH4 generation potential. Food and yard waste are considered decomposable.
The LFG rate-of-generation value has different variables, which determine its level of potential. For example, decomposable MSW have higher CH4 generation potential than inert and semi decomposable solid waste in the landfill. The waste stream, temperature, annual precipitation (moisture), and pH value of the soil in the landfill are considered to be the general determining factors of the generation rate of LFG [2].
The required area for the landfill site and its depth, together with the level of bed in the lower end layer of the surface, were calculated according to Eq. (3).
where Wcollected average is the average annual collected waste in the year of calculation, and V is the weight of the waste after compaction, with the typical value being 800 kg/m3.
The required thickness of the cover and mixture soil for the desired biological decomposition was assumed to be 20% of the desired average 20-m depth of the desired solid-waste landfill site. As indicated by a previous study [31], the overall size of the landfill site was estimated using the volume of the waste after compaction, while considering 20% additional volume on the layer and mixing soil, as shown in Eq. (4):
The area of the landfill site was estimated using the total landfill volume and its depth was also calculated, using Eq. (5):
After carrying out the geometrical analysis of the desired landfill site, we estimated the LandGEM model parameters, based on the waste amount and area.
5. CH4 Generation Potential
To estimate the CH4 generation potential at different CH4 generation capacities and rates, we selected the following parameters and year of optimum landfill operation. For the analysis, we assumed that the annual MSW disposed in the landfill area was 100,000 tons. Furthermore, we assumed that the total landfill-site operating duration was 30 years, based on the standard range from the US EPA and LMOP. The analysis was carried out using a first order decay equation and the LandGEM spreadsheet tool [26]. Notably, three scenarios, Conditions I, II, and III, were considered. The three scenarios are explained as follows.
Condition I: According to the EPA, standard values for CH4 generation rate (k) and L0 for the case of Controlled Air Act (CAA) conventional value have a huge potential of CH4 generation. According to the LMOP, the geographical area and MSW that have conventional values of k (0.05/year) and L0 (170 m3/Mg) have better potential of generating CH4, compared to arid and wet conditions. The projects in this condition have an efficient economy of scale, due to mass CH4 gas generation potential for power generation due to large amount methane generation through efficient and matured decomposition cycle. In this condition, the soil and environmental condition (moisture, soil characteristics and heat) provides efficient generation of CH4.
As shown in Fig. S2, the CH4 generation potential of MSW in the CAA conditions indicates and increase until the closing year of operation, with a sharp decline in the closing year. The estimated duration for the CH4 gas generation potential was considered to be 30 years. In general, the k value depends on the soil characteristics and moisture (average annual rainfall level) and organic contents of the MSW [32]. Fig. S3 portrays the CH4 generation from the total LFG generation in the closing year of the landfill site, as per the CAA conditions. For the closing year, the optimum ranges was based on the data acquired from ([22]). The overall amount of produced LFG relies on the type of waste, environment of the site, and effectiveness of the LFG collection system. Moreover, there are important sources that can determine the uncertainties in the LFG generation, which are often related to the data on the waste properties and site conditions.
Condition II: In this condition, the L0 value is similar to Condition I conventional CAA value and k values is lower than CAA conventional condition which determines the amount of CH4 obtained. Climatic factors, like as rainfall, have a significant impact on the production and properties of landfill leachate. The leachate produced in arid climates contain higher levels of contaminants than that produced in humid settings [22]. Based on the LMOP, in terms of the area-specific parameters for arid areas, we used the k value of 0.02/year and L0 value of 170 m3/Mg. The total LFG generation was directly proportional to the CH4 gas amount obtained from the total collected LFG, as shown in Fig. S4. Note that the primary sources of leachate depend on biological processes and are impacted by the waste, rather than runoff and precipitation (type, amount, moisture, and degree of compaction). As shown in Fig. S5, the amount of CH4 utilization increased until the maximum capacity (in the closing year of the landfill area). Furthermore, the CH4 production increased at higher k values (as long as the landfill was still accepting new waste) and decreased swiftly once the landfill closed. The amount of moisture in the waste, availability of nutrients for the bacteria that produce CH4, pH, and temperature affected the k value. As shown in Fig. S5, after closing the landfill site, the total amount of CH4 obtained from the landfill decreased rapidly.
Condition III: In this scenario, we assumed inventory wet condition had a L0 value of 96 m3/Mg and k value of 0.7/year. The dissimilated organic fraction and degradable organic carbon (DOC) were transformed into LFG constantly (beginning in 2030) as indicated in Fig. S6. The total amount of CH4 gas generated in the inventory wet condition decreased sharply when the landfill site reached closing year of the landfill, as shown in Fig. S7. Notably, the power generated using this condition was less sustainable, in terms of the utilization of CH4 gas, at the end of the landfill site in the closing year, with no CH4 generation potential, compared to that in the CAA arid and conventional conditions.
In Conditions I, II, and III, we observed variable CH4 generation potentials and capacities for the same landfill area. As shown in Fig. 2, the CAA conventional condition provides more CH4 gas than that obtained in the CAA arid and inventory wet conditions. From this comparison, we can deduce that the CH4 gas generation potentials and rates at different conditions varies significantly; thus, LFG projects need to consider the characteristic parameters of LFG sites and the chemical properties of MSWs. According to the US EPA, the recommended value for L0 is 56.6–198.2 m3/Mg. The value for the L0 largely depends on the type and characteristics of garbage present in the landfill, with the exception of arid areas, wherein a lack of moisture may limit the CH4 generation.
6. LFG Power Generation and Environmental Benefits
LFG is used as a power generation energy source, especially in large-scale power plants, for economic gain. The LFG with a CH4 content of approximately 40–65% in volume can be employed to produce electricity, using internal combustion engines (1–3 MW), turbines (greater than 5 MW), micro-turbines (30–250 kW), and fuel cells. However, the gas must be flared if its CH4 content drops below 35–40 vol% [33, 34].
Several factors, such as technical and economic characteristics, as well as environmental impacts, may influence the type of energy technology applied at landfill sites [35]. Due to their numerous advantages and high electrical efficiency, internal combustion engines are widely utilized to produce energy from LFG. Table 2 compares the benefits and drawbacks of several commonly used LFG energy systems.
6.1. LFG Power Generation Potential
The economics in the selection of electricity-generation LFG technologies mostly rely on external factors, such as the available tax credits (e.g., renewable revenue streams and certificates on renewable energy technologies) and the price at which electricity can be sold [22]. The power purchase agreement is a convenient way of receiving more revenue, with renewable portfolio standards. Several systems, including internal combustion engines (ICEs), turbines, micro turbines, and gradual oxidizers (GOs), have been used to generate energy from LFG [40]. The Brayton cycle is the underlying mechanism of the operation of gas and micro turbines [41]. It was computed the gross power generation potential in a particular year after predicting the yearly LFG generation [13] using Eq. (6):
where GPGPT is the gross power generation potential, is the system collection system (the average value is 85%), is LFG energy content (calorific value, typically 500 BTU/ft3), and is the heat rate of equipment. Then, by directly considering the parasitic load, we determined the net potential of power generation. We assumed that the auxiliary equipment energy loss was 6% for steam/gas turbine and 2% for reciprocating combustion engine [13].
The LFGcost-Web [16] was employed to estimate the average generation cost of the LFG, compared to other sources, such as steam, hydro, diesel, geothermal, combined cycle, and turbine generation. The average electricity-generation cost of LFG from MSW was calculated as USD 0.0604/kWh, which is higher than that of hydro power (USD 0.0018/kWh) and steam power (USD 0.0415/kWh) generation, but lower than that of geothermal (USD 0.0637/kWh), combined cycle power (USD 0.0763/kWh), diesel (USD 0.1773/kWh), and gas turbine (USD 0.1966/kWh) generation [42].
To produce electricity or convert the form of energy, the required capital cost is the basic constrain when selecting the fuel technology [43]. We compared the cost of electricity production from different technologies in Table 3; the LFG generation (CH4 is more advantageous than combined power cycle with oil and fuel cells with economy of scale as well). International Methane Pledge (IMP) suggests national to use methane gas for power generation due to its advantage when we use in large amount.
LFG yields lower CO2 emissions (0.27 × 10−9 kg/kWh) than others energy sources, such as fuel oil (0.85 kg/kWh), gas (0.85 kg/kWh), and coal (1.18 kg/kWh). Furthermore, LFG has lower CO2 emission, compared to other primary fuels in the global energy systems [44]. ICEs are commonly used electricity-generation auxiliary components for LFG projects. They have high efficiency and low cost, when installed directly in the gas output of the LFG layout [22]. In the USA, more than two third (>66%) of landfills generate electricity using this technology. ICEs are highly efficient than gas turbine and can convert LFG (50% CH4) to electricity effectively.
The steam and gas turbines applied for municipality LFG electricity production use compressed gas and heat; the gas expands in the turbine then, rotates the generator, to produce electricity. Similar to reciprocating engines, gas turbines have a lifetime of 25 years and steam turbines have a lifetime of 50 years [45]. For large LFG-to-energy plants, with capacities more than 1 MW, turbines are often employed. Micro turbines are ideal for small applications and operate at low combustion temperatures and compression ratios [41]. Micro turbines have an electric yield of about 30%, with an operational availability of up to 95% and the ability to use LFG with the CH4 concentration exceeding 35%; nonetheless, they require expensive and substantial maintenance services every eight years for continuous operation [42].
Gradual oxidizers (GOs) are recently developed appliances that function at lower temperatures. They have 95% operational availability, 29% electric energy production, and can function with LFG containing CH4 at concentrations as low as 1.5%. Notably, GOs need substantial and expensive servicing every 9 years, for continuous operation [45, 46]. Without a doubt, GOs seem to be the only practical replacements for LFGs (i.e., LFG with low CH4 concentration that cannot be used with traditional technologies). With the application of controlled heat pump, it is possible to achieve a higher efficiency, using the exhaust heat to heat water, and the low-pressure steam from the engine cooling system heat exchanger can also be used to produce electricity [47].
ICEs may be viable for LFG-to-electricity generation, due to its low capital cost compared to gas turbine and boiler. This technology comprises of a consolidated advantage, with minimum economical risks [39]. Gas turbines is the most commonly used technology in LFG-to-energy projects, after ICEs, with lower performance and higher loss than ICE, based on the same thermodynamic cycles. Moreover, ICEs are easy to transport and have a flexible design [28]. Based on the overall cost and efficiency correlation for the targeted application of LFG, ICEs are efficient at converting LFG into electricity [48], attaining electrical efficiency of 30–40%. Note that cogeneration, also known as combined heat and power (CHP) applications, in which the waste heat from the engine cooling system is recovered to produce hot water, or from the exhaust to produce low-pressure steam, offers a higher efficiency.
6.2. Cost of Power Generation from LFG
The price of producing electricity from CH4 gas depends on several variables, e.g., whether a gas recovery system is present or not, the size of the waste, and the conversion technology used. In addition to the equipment costs, soft expenditures and grid connectivity charges are frequently included in the project cost components [32]. In addition to these expenses, the collection system and generation equipment also have operation and maintenance costs.
The price of producing 1-kWh electricity can vary from as little as USD 3.4 to as much as USD 10. Where a collection infrastructure is in place, energy production is typically significantly more cost-effective. Do reduce the cost of systems that convert CH4 to energy, it is important to include government incentives, as such incentives can directly affect LFG utilization and thus, global and regional GHG emissions. According to the amount of CH4 gas collected in each year, there is economy of scale (under conventional CAA condition there is incremental generation of methane gas until the closing year of the landfill), and additional reciprocating engines are required each year on the existed connecting units assembled (additional ICs, gas turbines, and boilers installed in the initial years of energy generation) for energy generation [49]. The electricity generation from LFG gas can increase each year, due to population growth and the resulting increase in waste generation. Therefore, the total annual cost for each income-level of the population and the amount of CH4 gas from the collected MSW will vary significantly.
6.3. Environmental Benefits of LFG Power Generation
With an atmospheric life of only approximately 12 years, CH4 is a powerful GHG (more than 25 times stronger than carbon dioxide over a 100-year span). Thus, one of the best strategies to limit human influence on global climate change is to reduce the CH4 emissions from MSW landfills. Also, as CH4 is produced in all landfills, there is higher potential in reducing the CH4 emissions by flaring or collecting the LFG for energy production.
In general, the LFG from MSW landfill is collected using a connection of blowers and series of walls in general vacuum systems. The gas collected through this system and accumulated in the central unit point undergoes treatment according to the final target of LFG utilization. In most cases, LFG projects use this gas for direct flaring, for electricity or non-electricity generating units [50]. The environmental benefits of LFG can be calculated separately for the projects that consider and do not consider electricity generation, as follows:
CH4 collected and destroyed: The total amount of CH4 collected each year (m3/Year), which is either burned by flaring or used in the LFG energy project, can be calculated using Eq. (7):
Direct CH4 reduction: The total amount of CH4 collected each year, measured in million metric tons of carbon dioxide equivalents per year, (MMTCO2E/Year), is either burned by flaring or used in the LFG energy project and can be calculated using Eq. (8):
where, is methane gas global warming potential which is directly reduced with the volume utilized and this direct methane reduction have an indirect methane reduction advantage by energy substitution through the energy system (fossil fuel or biomass).
CH4 utilized: This is the amount of CH4 that the LFG energy project or other end goals use in one million metric tons per year, (MMTCO2E/Year), which can be calculated using Eq. (9):
where GWP of CH4 in utilized methane is global warming potential through direct emission in the open landfill area to the environment. CH4 utilized for energy or other end target is calculated through actual gas utilized in the project and its amount of direct relieved effect on the environment.
Depending on the efficiency and design of the system, during its operational lifetime, an LFG energy project will likely capture between 60% and 90% of the CH4 produced by a landfill. As the gas is burned to produce electricity or heat, the CH4 collected will be converted to water and carbon dioxide [24]. Furthermore, non-renewable resources (such as coal, oil, and natural gas) can produce the same amount of energy as that produced from LFG. Gradual LFG use and collection at landfills can enhance regional air quality which can allow the global targeted protocols and agreements to maintain the global temperature.
Low amounts of NMOCs in LFG are eliminated or transformed during burning, thus, lowering the potential health hazards associated with LFG. If fossil-fuel combustion at utility power plants is avoided, there will be less pollution; thus, the emissions of SO2 (a major contributor to acid rain), particulate matter (a respiratory health concern), nitrogen oxides (which can contribute to local ozone and smog formation), and trace hazardous air pollutants, which are released into the air from the power plants, can be reduced.
7. Summary and Outlook
In general, LFG is a result of the breaking down of organic waste in landfills. LFG consists of a minor quantity of non-CH4 chemical molecules, 50% CO2, and 50% CH4 (the main component of natural gas). CH4, which is a powerful GHG, traps the heat in the atmosphere for up to 28–36 times longer than CO2. The implication of CH4 generation potential is dependent on soil characteristics, moisture, decomposable portion of MSW in the landfill, temperature, and CH4 generation potential and capacity in arid, conventional, and wet areas. In CAA, conventional landfill (Condition I) operation generates massive amounts of CH4 gas, compared to Conditions II and III in arid and wet conditions, with variable k (CH4 generating potential) and L0 (CH4 generation capacity) of each geographical condition.
The LFG market share is expected to reach approximately USD 3178.3 million, projected to register a compound annual growth rate of 8.1% from 2022 to 2030. With the concomitant loss of production, significant unanticipated expenses, and, in some circumstances, loss of life, the occurrence of catastrophic operational failures resulting from garbage slides, long-lasting fires, and flooding conditions could be less likely with the use of this strategy. Notably, LFG generation has a higher operating and maintenance cost than other feedstock types. Because of the high capital and operational expenses associated with LFG generation, we can anticipate a decline in the market’s demand for LFG throughout the projected period.
The future landfill might be a better instrumented structure that updates the operator on its performance and status in real-time monitoring and optimization features. This strategy may assist in lowering the likelihood of significant failures, loss of productivity, and fatalities. Furthermore, LFG can be used as a low-carbon and environment-friendly substitute for traditional fossil fuels. Upon combustion, LFG creates bioenergy, which is a clean fuel for energy production. In the future, the generation of bioenergy from biomass and LFG will most likely increase with the energy demand, which expand the market. Therefore, governments and decision makers must encourage the use of CH4 emissions from landfills for power generation because it is a renewable source of energy and can reduce the emissions of GHGs.
PDF Links
PubReader
Full text via DOI
Download Citation 
Supplement
Print 
