Estimation of Methane from Maseru City for Potential Electricity Generation

Urbanisation and industrialisation have increased municipal solid waste generation, contributing to environmental and health challenges. Inadequate waste management practices result in greenhouse gas emissions, particularly methane, exacerbating climate change [1].

Lesotho, like many developing nations, struggles with inefficient waste management systems. Open dumpsites such as Ha Ts’osane and Ha Nyenye serve as primary waste disposal sites, leading to uncontrolled methane emissions, spontaneous combustion, and contamination of water sources [2]. Approximately 78% of Maseru’s municipal solid waste is disposed of in unauthorised locations, highlighting the need for sustainable waste management solutions [3]. The lack of formal landfill infrastructure highlights the urgent need for sustainable waste management solutions. Figure 1 illustrates the open waste dump lifecycle characteristic of Lesotho [4].

Lesotho embarks upon its trajectory of industrialisation in pursuit of enhanced economic development, and there exists a concomitant escalation in the national demand for electrical power [5]. The relationship between economic expansion and electricity generation in Lesotho is deeply intertwined, as economic advancement propels a heightened demand for electrical power, whereas an adequate supply of electricity is essential for the perpetuation of growth [6].

The national electrification rate has attained a level of 41% across households, thereby necessitating an augmented commitment toward electrification initiatives aimed at accommodating the remaining 59% of households, predominantly situated in the country's rural locales. Currently, a mere 10% of rural households are connected to the electrical grid, in stark contrast to approximately 80% of urban households enjoying such connectivity [5].

The 2024 peak electricity demand for Lesotho is valued at 203 MW with the electricity consumption at 970 GWh. 532 GWh of the electricity consumption comes from local generation while 438 GWh is from imported electricity [7]. A comprehensive analysis was undertaken to assess the projected electricity demand for the nation of Lesotho from the years 2010 to 2030. The findings indicated that by the year 2030, Lesotho is anticipated to realise a national electrification rate of 54.2%, with urban households achieving a rate of 95% and rural households attaining a rate of 14%, reflecting significant increases from the baseline values of 19.4%, 54.1%, and 1.8%, respectively [5].

Furthermore, during the same temporal framework, the projections for the most probable scenario reveal the following outcomes: the peak demand is projected to escalate to 211 MW; the annual average energy consumption per household is expected to decline to 1,009 kWh/household from an initial 1,998 kWh/household; and the aggregate consumption is forecasted to rise to 1,128,284 MWh from 614,868 MWh [5]. This evidence underscores the ongoing necessity for the implementation of additional energy interventions such as landfill gas to energy to facilitate the attainment of energy self-sufficiency for the nation.

1.png

Despite its potential, Lesotho has not yet adopted LFGTE due to several key barriers, including high initial investment costs, limited technical expertise, regulatory gaps, and inadequate infrastructure for landfill gas collection and utilisation [10]. While LFGTE has been successfully implemented in other countries, little research has been conducted on its feasibility in Lesotho.

This study explores the feasibility of LFGTE at the proposed Ts’oeneng landfill in Maseru, addressing the reduction of greenhouse gas emissions and energy poverty which aligns with the National Climate Change Policy and National Strategic Development II for Lesotho [11]. The aim is to fill this gap by assessing the potential for electricity generation from methane emissions at the proposed Ts’oeneng landfill in Maseru. Using the LandGEM model, methane production will be estimated to determine its viability as an energy source. The findings will provide policymakers with data-driven insights to facilitate the adoption of LFGTE in Lesotho, addressing both waste management inefficiencies and energy shortages. By integrating waste-to-energy solutions into Lesotho’s energy strategy, this study highlights the importance of sustainable resource utilisation, environmental conservation, and economic development through renewable energy initiatives.

The potential for waste generation at the Ts’oeneng landfill was assessed utilising population projections derived from the Bureau of Statistics [13]. The estimation of methane emissions was conducted based on the potential waste generated by the city of Maseru and subsequently disposed of at the Ts’oeneng sanitary landfill for the temporal span of 2025-2045, as delineated in Table 1. The estimation of waste generation, derived from population projections, was executed employing Eq. (1) and Eq. (2). The total mass of methane produced from the dumpsite was determined following the LandGEM methodology, which incorporates Eq. (3). It is evident that the decomposition of organic waste within the dumpsites results in the production of methane, which is subsequently emitted into the atmosphere, thereby contributing to climate change; however, this methane possesses the potential for utilisation in energy generation [21].

The findings indicated that the volume of municipal solid waste escalates concomitantly with population growth as indicated in Table 1. The research forecasts that by the year 2026, methane emissions derived from MSW will amount to 1,119,275 m³, continuing to increase until 2045, reaching a peak of 17,257,175 m³, after which a gradual decline is anticipated. The estimations were conducted utilising the LandGEM model (version 3.02). The year 2045 is projected as the closure year for the landfill; therefore, even in the absence of incoming waste, methane production persists.

Table 1. Population projections waste increase per year

The outcomes derived from the LandGEM model as indicated in Figure 4 illustrate a progressive escalation in methane production, commencing from a comparatively modest quantity during the preliminary years. As the organic refuse within the landfill perpetuates its anaerobic decomposition, there is a marked increase in methane emissions, culminating in a zenith between the years 2043 and 2045. This apex coincides with the juncture at which the predominant portion of the organic constituents within the landfill has completed its decomposition, and methane production reaches its maximum capacity. Additionally, the graph delineates a reduction in methane emissions subsequent to this apex, as the supply of degradable organic matter wanes and the landfill nears its post-decomposition phase.

4.png

Figure 4. Estimate methane emission from Ts’oeneng landfill site in megagrams/year

LandGEM employs Eq. (3), and thus the parameters for the methane generation constant (K) and the methane generation potential (L₀) utilised in this analysis were the default values, given that this is a simulation and the T’soeneng sanitary landfill has yet to commence receiving waste from Maseru. Following the guidelines established by the United States Environmental Protection Agency, the default values assigned to K and L₀ are 0.5 per year and 170 m³ per ton, respectively [22].

3.1 Estimation of electrical energy generation potential

In this section, an evaluation of the methane energy potential derived from municipal solid waste (MSW) for the period spanning from 2025 to 2045 is presented. The quantification of methane production, as established through the LandGEM model, facilitated the assessment of the potential for electricity generation. The potential for methane energy (measured in MWh/year) derivable from the methane content is illustrated in Figure 5. The estimated electrical energy that can be harnessed from the methane content of the collected landfill gas is calculated and represented in Table 2. The estimation of the energy yield from the anticipated methane was conducted employing Eq. (4).

5.png

Figure 5. Methane energy potential

Table 2. Methane production and electrical energy potential

The electrical energy anticipated to be accessible, commencing in 2026 at the Ts’oeneng landfill, is projected to yield 2.9 MWh, escalating to 44.1 MWh by 2045, followed by a gradual decline thereafter. The initial output of 2.9 MWh in 2026 would diminish the volume of electricity imported into Lesotho and simultaneously enhance the diversification of the nation’s energy portfolio. According to the findings of Mpholo et al. [5], the energy demand within Lesotho is projected to reach 211 MW by 2030 [5], with an estimated 6% of this energy requirement potentially being satisfied through landfill gas-to-energy (LFGE) technology.

The electricity generation dynamics observed at the Ts’oeneng landfill as observed in Figure 5 are consistent with the conventional lifecycle of landfill gas energy production which is characterised by the initial phase (lag phase), active decomposition (methanogenic phase), peak production (optimal gas generation phase) and lastly the decline phase (post-closure phase) [8]. Initially, in the year 2026, it is anticipated that the electricity output will be approximately 2.8 MWh, which corresponds to the low-output phase, during which the decomposition of waste is still in its nascent stages and methane production remains minimal. As the volume of waste increases and microbial activity intensifies, it is projected that electricity generation will experience a consistent upward trajectory, culminating in an output of 44.1 MWh by the year 2045, indicating the apex of generation which will then be followed by a decline.

The peak implies that the landfill has achieved optimal gas generation, facilitated by the augmented input of waste, enhanced LFG capture techniques, and effective power conversion processes. After 2045, a gradual decline phase is anticipated as organic waste becomes depleted and methane output diminishes, which will result in a reduction in electricity generation. This pattern follows the typical trajectory of landfill energy production characterized by a slow increase, rapid expansion, peak, and subsequent decline, thereby underscoring the imperative for sustainable waste management practices and the potential integration of alternative energy sources.

The uncertainty could occur in multiple aspects of evaluation, making it valuable to examine the robustness of the obtained outcomes with sensitivity analysis evaluating key parameters on methane generation and energy output. Variations in the methane generation rate (k) showed that increasing k from 0.5 to 0.6 year^-1 accelerated peak methane production but shortened the gas generation phase, whereas lowering the k to 0.4 year^-1 delayed peak production while extending methane availability. Adjusting the methane potential (Lo) from 170m³/ton to 200m³/ton increased the total methane output boosting energy generation by approximately 15% over the landfill's lifetime. Additionally, a decrease in landfill gas collection efficiency (λ) from 75% to 60% reduced methane recovery by 20%, limiting the energy potential and increasing the emissions. These results highlight the significance of enhancing landfill management practices, gas capture infrastructure, and waste composition to maximize methane recovery and energy generation.