Climate change is a pressing global issue that requires immediate action to protect the environment, human health, and future generations’ well-being. This phenomenon, caused by anthropogenic emissions, exacerbates the atmospheric greenhouse effect, raising the Earth’s surface temperature (Korre et al., 2009) . Carbon dioxide, among other gases, plays an important role, with developed countries prioritizing greenhouse gas (GHG) reduction through international agreements such as the Kyoto Protocol, Paris Agreement, and regional energy policies (European Commission, 2006) . Renewable energy, particularly hydropower, has attracted attention for its carbon emission implications. While hydropower generates clean electricity, its construction and operation can disrupt aquatic ecosystems, resulting in direct carbon emissions. Furthermore, GHG emissions continue throughout the hydropower system’s life cycle, known as indirect emissions. This dual impact motivates scholarly research into hydropower’s carbon emission dynamics (Chu et al., 2022) .

The carbon footprint and carbon credits have played a role in the establishment of a tradable permit system aimed at reducing GHG emissions through the pricing of pollution, utilizing mechanisms such as International Emission Trading, Clean Development Mechanisms, and Joint Implementation. In parallel, the Life Cycle Assessment serves to evaluate emissions and explore reduction strategies, providing a quantitative analysis of environmental aspects associated with a product or process. This assessment is crucial in assessing the environmental effectiveness of green chemicals, as it illuminates factors such as Global Warming Potential (GWP), energy consumption, eutrophication, and land use, thereby facilitating well-informed, environmentally conscious decision-making (Tufvesson et al., 2013) .

Ensuring environmental sustainability in electricity production entails a comprehensive assessment of all pertinent environmental impacts, with the carbon footprint serving as a pivotal metric to gauge GHG emissions and inform decision-making processes. Notably, upstream processes, particularly transportation, wield significant influence on the carbon footprint of energy production, underscoring the importance of holistic consideration of the entire life cycle of energy sources. Environmental sustainability evaluations should encompass multiple environmental impact indices to encompass the full spectrum of global atmospheric effects, prioritizing emissions reduction (Cristóbal et al., 2010) . An evaluation of the coal life cycle was conducted to quantify GHG emissions, revealing that the power generation phase notably influences environmental indicators. Comparative environmental assessments between power plants with and without CO₂ capture technology demonstrated a substantial decrease in GWP indicators post-integration, highlighting the positive impact of CO₂ capture technology in mitigating GHG emissions (Dincă et al., 2013) .

The IPCC’s Sixth Assessment Report highlights the substantial 3.9% contribution of the waste sector to global CO₂-eq emissions. Figure 1 illustrates that approximately 59 GtCO₂-eq emissions are attributed to various sectors: buildings (16%), transportation (15%), agriculture, forestry, and other land uses (AFOLU) (22%), industry (34%), etc. Within waste management, organic waste, encompassing food waste and sewage, stands out as a notable source of methane emissions (IPCC, 2007a; Bogner et al., 2007) .

In the domain of hydropower, the carbon footprint of large- and mid-scale projects in China ranges from 6.2 gCO₂-eq/kWh to 34.6 gCO₂-eq/kWh, with an average of 19.2 ± 6.8 gCO₂-eq/kWh (Li et al., 2017) . For typical hydropower stations in China, focusing on four specific stations ranging from 50 to 500 MW in capacity, emission rates are measured at 13.60 tCO₂-eq/GWh for 50 years and 8.13 tCO₂-eq/GWh for 100 years (Jiang et al., 2018) . The level of public awareness regarding the implementation of a Low-Carbon Economy (LCE) in China is significant. A majority of respondents in Zhengzhou have demonstrated a high awareness of the LCE and exhibit positive attitudes towards its adoption. Their proactive actions include rejecting plastic bags, recycling waste, conserving water and electricity, and purchasing environmentally friendly products, signaling a readiness to engage in pro-environmental behaviors (Chen & Taylor, 2011) . Effective waste management strategies play a critical role in curbing GHG emissions and fostering resource recovery. Overreliance on landfills is environmentally unsustainable and contributes to elevated GHG emissions. Thus, it is crucial to enhance public awareness and participation to ensure the success of improved waste management strategies in Jordan and similar nations (Aljaradin & Persson, 2012) .

Waste management in hydropower plants includes a wide range of activities, from the disposal of construction debris and operational waste to the treatment of organic matter and effluent. Each of these components contributes to the plant’s overall carbon footprint, although to varying extents. The carbon footprint of the waste sector in hydropower remains relatively under-researched, with few empirical data and systematic evaluations to inform policy and decision-making (IPCC, 2022; Wang et al., 2019) . The less apparent impacts of waste management decisions remain crucial, as they are inherently linked to our choices regarding waste and materials. Recycling and waste reduction efforts notably lead to reduced energy consumption and process emissions in industry (Jha et al., 2008) .

A major fraction (72% - 79%) of solid waste generated in Indian households is organic (Ramachandra et al., 2012) . The authors considered methane and carbon dioxide emissions from waste samples to calculate annual solid waste emissions. With 2044 tonnes of organic waste generated daily citywide, methane and carbon dioxide emissions are 19.13 and 242.83 kilograms per day, respectively. Multiplying methane emissions by 21 yields a carbon footprint of 644.61 kilograms per day of CO₂ equivalent. Assuming untreated waste reaches disposal sites, less populated city wards emit less, contrasting densely populated wards. Core city wards, denser in population, exhibit higher carbon footprint potential (Ramachandra et al., 2014) . Waste management decisions have a notable effect on GHG, and it is estimated that recycling alone could potentially save 1% to 6% of national GHG. However, it’s important to acknowledge that these figures are rough estimates and may not be suitable for precise planning purposes. The passage identifies several critical areas for future research, including landfill methane capture rates, the impact of paper reduction and recycling on forest carbon sequestration, and the possibility of carbon sequestration in landfills (Ackerman, 2000) . In the characterization of selected municipal solid waste including organic matter content, biochemical constituents, and leaching behavior, the research identifies lignin-like compounds as a key factor negatively impacting biodegradability. These fractions were then analyzed for organic matter content, leaching behavior, biochemical constituents, Biochemical Oxygen Demand (BOD), and Bio-Methane Potential (BMP) (Bayard et al., 2018) .

Although the Lao People’s Democratic Republic (Lao PDR) makes a relatively modest contribution to global GHG emissions, the country is facing the impacts of climate change as other parts of the world. This includes increased occurrences of storms, flooding, prolonged droughts, and intensified urban heat. These hazards pose a threat to socio-economic progress and hinder the nation’s efforts to achieve Sustainable Development Goals. The breakdown of the national GHG emissions profile, based on data from the year 2000, reveals emissions from multiple sectors: energy, industrial processes, agriculture, land use change and forestry (LUCF), and waste. Notably, LUCF stands out as the largest contributor, comprising 83% of the total emissions, followed by Agriculture at 15%, and Energy at 2%. The primary climate risks identified for Laos encompass floods, epidemics, storms, and droughts, detailed in Table 1 (MoNRE, 2019) .

The Nam Theun 2 hydropower plant (NT2), located in Lao PDR as depicted in Figure 2 , stands as a significant infrastructure asset, leveraging water power to generate electricity. Oversight of environmental and social initiatives at NT2 falls under the purview of external entities, including technical advisors from lending agencies, the Laotian Government via the Panel of Experts and Independent Monitoring Agencies, independent consultants, and multilateral development institutions (Nam Theun 2, 2023; NTPC, 2004) . The plant adheres to stringent waste management protocols, ensuring compliance with ISO 14001 standards, particularly in e-waste management, alongside adopting best practices to address challenges and solutions specific to Lao PDR (Keovongsa et al., 2023) . As a pivotal player in regional energy provision, NT2 fulfills a vital role in meeting energy demands. Nonetheless, the operation of such a facility may draw environmental scrutiny, particularly regarding the calculation and verification of its carbon footprint for regulatory adherence and organizational transparency (Villar et al., 2014) .

In NT2, an assessment was conducted to evaluate the organic carbon stock within the 450 km² reservoir area, encompassing various cover types such as forests, agricultural soils, swamps, and others. The total organic carbon stock was estimated to be 5.1 ± 0.7 MtC, with 2.2 MtC attributed to aboveground biomass,

litter, and deadwood, and 2.9 MtC to belowground biomass and soil organic carbon. It’s noteworthy that the organic carbon stock within the NT2 reservoir area was found to be lower compared to other tropical reservoirs in South America or Africa (Descloux et al., 2011) .

This research study aims to analyze the carbon footprint in the sector of the hydropower plant during its operational phase. Specifically, the focus will be on evaluating carbon emissions associated with management practices, including the disposal of construction waste, organic waste, and other by-products generated during the plant’s operation.

This research study conducts a comprehensive case study to gain insights into the environmental impact of waste management in hydropower plants. It also aims to identify potential strategies for reducing the carbon footprint in the waste sector, drawing from the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories Volume 5 Waste (Buendia et al., 2019b) , Volume 2 Energy (Buendia et al., 2019a) and Requirements for Specification with guidance at the organization level for quantification and reporting of GHG emissions and removals (ISO, 2018) . The main contributions of this paper are summarized as follows:

This paper is organized as follows. Section 2 discusses the methodology used in this study. In Section 3, the study results are presented. Finally, conclusions and remarks are given in Section 4.

In order to analyze the carbon footprint generated in the waste sector of the NT2 during its operational phase, the study referenced the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, which includes Volume 5 Waste (Buendia et al., 2019b) and IPCC Volume 2 Energy (Buendia et al., 2019a) . The methodological guidance for the estimation of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) emissions is illustrated in Figure 3 .

This study addresses methodological concerns, including uncertainty assessment in the choice of method, emission factors, activity data, completeness, and

developing a consistent time. These issues are associated with the classification within Volume 5 Waste (Buendia et al., 2019b) and Volume 2 Energy (Buendia et al., 2019a) . The carbon footprint equation and calculation in the waste sector of the NT2 are based on the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC, 2019c) .

The equation of CO₂ emission from the road transportation is (Waldron et al., 2006; IPCC, 2019a) :

${\text{CO}}_2\text{emission}={\displaystyle {\sum }_{\text{a}}\left[{\text{Fuel}}_{\text{a}}\ast {\text{EF}}_{\text{a}}\right]}$(1)

where

The equation of Tier 1 emission of CH₄ and N₂O is:

${\text{CH}}_4\text{and}{\text{N}}_2\text{O}\text{emissions}={\displaystyle {\sum }_{\text{a}}\left[{\text{Fuel}}_{\text{a}}\ast {\text{EF}}_{\text{a}}\right]}$(2)

where

The equation of CH₄ emission from solid waste disposal is (Towprayoon et al., 2019a; IPCC, 2007b) :

${\text{CH}}_4\text{emission}=\left[{\displaystyle {\sum }_{\text{x}}{\text{CH}}_4{\text{generated}}_{\text{x},\text{T}}}-{\text{R}}_{\text{T}}\right]\ast \left(1-{\text{OX}}_{\text{T}}\right)$(3)

where

The equation of CH₄ emission from the biological treatment is (Pipatti et al., 2006) :

${\text{CH}}_4\text{emission}={\displaystyle {\sum }_{\text{i}}\left({\text{M}}_{\text{i}}\ast {\text{EF}}_{\text{i}}\right)\ast {10}^{-3}}-\text{R}$(4)

where

The equation of N₂O emission from the biological treatment is:

${\text{N}}_2\text{O}\text{emission}={\displaystyle {\sum }_{\text{i}}\left({\text{M}}_{\text{i}}\ast {\text{EF}}_{\text{i}}\right)\ast {10}^{-3}}$(5)

where

The equation of CO₂ emission based on the total amount of waste combusted is (Towprayoon et al., 2019b) :

${\text{CO}}_2\text{emission}={\displaystyle {\sum }_{\text{i}}\left({\text{SW}}_{\text{i}}\ast {\text{dm}}_{\text{i}}\ast {\text{CF}}_{\text{i}}\ast {\text{FCF}}_{\text{i}}\ast {\text{OF}}_{\text{i}}\right)}\ast 44/12$(6)

where

The equation of CH₄ emission based on the total amount of waste combusted is:

${\text{CH}}_4\text{emission}={\displaystyle {\sum }_{\text{i}}\left({\text{IW}}_{\text{i}}\ast {\text{EF}}_{\text{i}}\right)\ast {10}^{-6}}$(7)

where

The equation of N₂O emission based on the waste input to the incinerators is:

${\text{N}}_2\text{O}\text{emission}={\displaystyle {\sum }_{\text{i}}\left({\text{IW}}_{\text{i}}\times {\text{EF}}_{\text{i}}\right)\ast {10}^{-6}}$(8)

where

The equation of CH₄ emission from the domestic wastewater is (Bartram et al., 2006; IPCC, 2019b) :

${\text{CH}}_4\text{emission}=\left({\text{TOW}}_{\text{j}}-{\text{S}}_{\text{j}}\right)\ast {\text{EF}}_{\text{j}}-{\text{R}}_{\text{j}}$(9)

where

The equation of N₂O emission from the wastewater effluent is:

${\text{N}}_2\text{O}\text{emission}={\text{N}}_{\text{Effluent}}\ast {\text{EF}}_{\text{Effluent}}\ast 44/28$(10)

where

Once the emission sources have been identified, activity data collected, and emission factors determined, GHG emissions can be calculated using the identified quantification approach (IPCC, 2019c) :

${\text{CO}}_{\text{2-}}\text{eq}=\text{Annual Activity Intensity of Emission Source}\ast \text{EF}\ast \text{GWP}$(11)

where

The waste sector of NT2 was assessed for its carbon footprint, revealing emissions totaling 4109.11 tCO₂ equivalent. The Carbon Footprint Intensity was calculated at 17.83 tCO₂ equivalent per ton of waste, with contributions from various sources including waste incineration, solid waste disposal, waste transportation, and domestic wastewater. These findings emphasize the necessity of mitigating emissions from waste management to maximize the environmental benefits of renewable energy production at the hydropower plant. Key mitigation measures include transitioning to alternative transportation methods, reducing waste generation, implementing waste reduction at the source, and promoting recycling initiatives.

Conducting a comprehensive lifecycle analysis of waste management practices is essential for gaining a holistic understanding of the carbon footprint and developing effective strategies to minimize environmental impact. However, this presents challenges such as resource allocation and the need for expertise. Addressing these challenges is crucial for devising strategies that effectively reduce environmental impact.

Integrating sustainable waste management practices into hydropower plant operations poses additional challenges, including stakeholder engagement and ensuring social acceptability. Despite these challenges, it is imperative to incorporate sustainable waste management practices into hydropower plant operations to align with global efforts to mitigate climate change and transition towards a more sustainable energy production paradigm.

We extend our gratitude to the management and staff of the Environment Department at NT2 for their invaluable assistance in providing the necessary information for this study.