Potential reduction of greenhouse gas emissions from waste banks and 3R waste treatment facilities in Bandung City

The Indonesian government has established a 30% reduction by 2030 target for reducing GHG emissions, through the 3R (Reduce, Reuse, Recycle) approach. In the City of Bandung, various institutions are involved in waste handling and reduction. The objectives of this study were to determine the GHG emissions, resulting from household waste disposal at Sarimukti Landfill, without (scenario 1) and with (scenario 2) the utilisation of Waste Banks, 3R Waste Treatment Facility (TPS 3R), and an incinerator in a TPS 3R, at Ciwastra Market, as well as to estimate the GHG emissions, once Bandung City successfully achieves its waste reduction and waste management target in 2025, as stated in the Bandung Mayor Regulation No. 1426 of 2018, leveraging all existing facilities with the landfilling (scenario 3) and incineration (scenario 4) method. The calculations made were aligned with the Intergovernmental Panel on Climate Change (IPCC) 2019 Guidelines Tier 1. The findings of this study revealed that, in the first scenario, the GHG emissions amount to 185,271.934 tons of CO2eq. In the second scenario, the emissions amount to 150,423.096 tons of CO2eq. Consequently, the reduction in GHG emissions achieved is 34,848.847 tons CO2eq. In the third scenario, the emissions are 64,373.560 tons of CO2eq, while in the fourth scenario, GHG emissions are 70,001.973 tons of CO2eq. These findings highlight the substantial GHG emission reductions achievable through the implementation of waste management strategies. By adopting these approaches, it is possible to mitigate the environmental impact of waste disposal and contribute to the reduction of GHG emissions, well in tandem with the climate change mitigation goals.


Introduction
Climate change is primarily caused by greenhouse gas (GHG) emissions, including methane, carbon dioxide, and nitrous oxide [1].GHG emissions from fossil fuels and land use have been increasing since the 19th century, reaching their highest levels in 2019.The Paris Agreement in 2015 set the ambition to limit global temperature rise to 1.5 o Celsius and well below 2 o Celsius above pre-industrial levels.However, based on emission trends, planned infrastructure, and current national policy commitments, the targets set in the Paris Agreement are challenging to achieve [2].
At the United Nations Climate Change Conference (COP26) in 2021, the Government of Indonesia increased its commitment by revising the Nationally Determined Contribution (NDC) document for Indonesia to reduce GHG emissions from 2020 to 2030 by 29% (unconditional) to 41% (conditional), compared to the business-as-usual scenario in 2030 [3].The waste management sector contributes to approximately less than 5% [4] up to 11% of global GHG emissions [2].Therefore, the Indonesian government has set targets for reducing GHG emissions by increasing the level of waste reuse through 1263 (2023) 012021 IOP Publishing doi:10.1088/1755-1315/1263/1/012021 2 composting and the 3R (Reduce, Reuse, Recycle) approach, aiming for a 22% reduction in 2020 and 30% reduction in 2030 [3].
Bandung City is the capital of West Java Province and the fourth largest city in Indonesia.Similar with many other cities in developing countries, waste management in Bandung relies on a conventional collection and disposal system [5].Bandung City has a large population, exceeding 2 million people [6].Consequently, the potential GHG emissions generated will be influenced by the population size and consumption levels [7], particularly by increasing waste generation.
In addition to conventional practices, since 2018, Bandung City has implemented a special waste management programme, known as KangPisMan (Kurangi, Pisah, Manfaatkan), adapted from the 3R concept.To support KangPisMan, the Bandung City Government has set the target of "1 Kelurahan 1 Bank Sampah" (1 Subdistrict 1 Waste Bank).In Bandung City, Waste Banks not only accept inorganic waste for recycling, but also provide training to the local community on how to manage their organic waste, through composting and biopores [8].In Bandung Regency, one main Waste Bank has successfully reduced the potential GHG emissions by 0.0007% [8].Bandung City itself has 151 subdistricts.With the target of "1 Kelurahan 1 Bank Sampah," there could be a minimum of 151 Waste Banks in Bandung City that can contribute to reducing the waste burden in the landfill.Therefore, Waste Banks in Bandung City have significant potentials to reduce GHG emissions from household waste management.In addition to Waste Banks, since 2020, Bandung City has introduced another alternative through the 3R Waste Treatment Facility (TPS 3R).The TPS 3R in Bandung City serves as a waste sorting facility, before disposal in the TPA, as well as a place for processing organic waste through maggot BSF treatment, composting, and biodigester utilisation.Moreover, the TPS 3R at Ciwastra Market includes waste treatment, using an incinerator.
The aims of this study encompassed assessing the GHG emissions resulting from household waste disposal at Sarimukti Landfill, under certain scenarios: one involving the integration of Waste Banks, TPS 3R, and an incinerator at Ciwastra Market within the TPS 3R, and the other without the implementation of these waste management measures.Additionally, the study sought to estimate the GHG emissions that would be achieved, once Bandung City successfully attains its waste reduction and waste management targets, as outlined in Bandung Mayor Regulation No. 1426 of 2018 for the year 2025, with the utilisation of existing facilities, employing both landfilling and incineration techniques.

Study area
This study was conducted in Bandung City.The research involved surveys at the Regional Waste Disposal Site in West Java, specifically Sarimukti Landfill, as well as several central Waste Bank warehouses and the TPS 3R in Bandung City.

Data collection
Primary data collection was conducted through field observations and interviews at the West Java Provincial Environmental Agency, the Technical Unit for Waste Management in Bandung City, the Bandung City Environmental Agency, the Central Waste Bank in Bandung City, and TPS 3R in Bandung City.The purpose of these activities was to understand the existing conditions and the waste management practices implemented, as well as to determine the waste generation and composition in Bandung City.Secondary data, in the form of literature studies on GHG inventory guidelines for the waste and energy sectors, as well as waste reduction targets, was also collected.

Scenarios
The collected data was processed, according to the guidelines provided by the Intergovernmental Panel on Climate Change (IPCC) 2006 [9] and the refined IPCC 2019 Tier 1 guidelines.The IPCC method was employed to calculate GHG emissions, in order to determine the emissions from four scenarios.Scenario 1 GHG emissions from household waste in 2022 were estimated, under the assumption of no waste reduction.Scenario 2 GHG emissions in 2022 were estimated, under the existing conditions, taking into account the reduction efforts by the municipal waste management institutions in Bandung City, including TPS 3R, Waste Banks, and the TPS 3R at Ciwastra Market.Scenario 3 Estimated GHG emissions in 2025 were assumed, based on the Household Waste Reduction as stated in Bandung Mayor Regulation No. 1426 of 2018.The waste generation was assumed to be 667,092 tons/year, with a waste reduction target of 34.34% and a waste management target of 65.66%.All inorganic waste was assumed to enter the Waste Bank, all organic waste was processed through composting, and the remaining residual waste was disposed of in the Waste Bank.Scenario 4 Similar to Scenario 3, this scenario assumed the residual waste to be treated through incineration.

Estimation of GHG emissions
The formulas used to calculate GHG emissions for each waste management activity differed.The formula for calculating GHG emissions disposed of in the landfill was based on the landfilling formula.The formula for the TPS 3R activities involved biological processing through composting.The formula for the TPS 3R at Ciwastra Market activities employed incineration.As for the Waste Bank, the formulas combined landfilling in the landfill and incineration.Once the emissions had been calculated, the results were subsequently converted into CO2 equivalents, using the latest standard values of Global Warming Potential (AR5).

Landfilling method
In calculating GHG emissions from landfilling, data on waste generation and composition obtained from primary data was utilised, while emission factors employed default values provided by IPCC.The landfilling system in the landfill was operated as an open dumping system, with a height of 50 m.CH4 emissions were calculated, using the following formula: Where, CH4 emissions were CH4 emitted in year T (Gg), T was the inventory year, X was the type of waste, R was Recovered CH4 at SWDS in year T (Gg), and OX was the waste oxidation factor in year T (fraction).
To find out the amount of CH4 generated, a calculation was needed to measure the methane potential that will be calculated by the equation: Where, CH4 generatedx,T was CH4 formed in year T as a result of the decomposition of organic components stored in waste (DDOC), DDOCm was the mass of DOC (decomposable organic carbon component) stored in waste at TPA (Gg), F was a fraction of CH4 generated in landfill, and DDOCm was obtained from the following equation: Where, DDOCm was the mass of decomposable DOC deposited (Gg), W was the mass of waste deposited (Gg), DOC was the fraction of degradable organic carbon in years of waste deposition (Gg C/Gg waste), DOCf was the fraction of DOC that can be decomposed (fraction), and MCF was CH4 correction factor for aerobic decomposition in the year of deposition (fraction).
To find out the DOC value, the following formula was used: where, DOC was a fraction of degradable organic carbon in bulk waste (Gg C/Gg waste), DOCi was a fraction of degradable organic carbon in waste type, and Wi was the fraction of waste type by waste category.
The CO2 emission [10] was calculated using the following equation: where, F was a fraction of CH4 generated in the landfill, OX was the oxidation factor, 44 was the molecular weight of CO2 (kg/kg-mol), and 16 was the molecular weight of CH4 (kg/kg-mol).

Incineration method
In calculating the GHG emissions from solid waste incineration, it was necessary to estimate the GHG emissions from both the waste and energy sectors.The emissions from the waste sector were determined by the combustion of waste, resulting in CH4 emissions, CO2 emissions, and N2O emissions.On the other hand, the emissions from the energy sector were derived from the CO2 emissions resulting from the use of fuel to operate the incinerator.The activity data was obtained from available primary data, and emission factors, such as dmi, CFi, FCFi, and OX were applied using the default IPCC values for a semi-continuous fluidised bed incinerator.The fuel used was pertalite with a standard density of 715 kg/m 3 and the lubricating oil used has a density of 870 kg/m 3 .
CH4 emissions were calculated, using the following formula: where, CH4 Emissions was CH4 emissions in inventory year (Gg/yr), IWi was the amount of type solid waste incinerated or openly burned (Gg/year), EFi was CH4 emission factor (kgCH4/Gg waste), 10 -6 was the conversion factor from kilograms to gigagrams, and i was category or type of waste that is incinerated/openly burned.
CO2 emissions were calculated, using the following formula: where, CO2 Emissions was CO2 emissions in inventory year (Gg/year), MSW was the total amount of municipal solid waste as wet weight incinerated or open burned (Gg/year), WFj was a fraction of waste type/material of component j in the MSW (as wet weight incinerated or open-burned), dmj was dry matter content in component j of the MSW incinerated or open-burned (fraction), CFj was carbon fraction in the dry matter (ie carbon content) of component j, FCFj was a fraction of fossil carbon in the total carbon of component j, OFj was oxidation factor (fraction), 44/12 was the conversion factor from C to CO2, and j was component of the MSW incinerated/open-burned such as paper/cardboard, textiles, food waste, wood, garden (yard) and park waste, disposable nappies, rubber and leather, plastics, metal, glass, other inert waste, with ∑    = 1.
N2O emissions were calculated, using the following formula: where, N2O Emissions was N2O emissions in inventory year (Gg/yr), IWi was amount of type i solid waste incinerated or openly burned (Gg/year), EFi was N2O emission factor (kg N2O/Gg waste), and i was category or type of waste that is incinerated/openly burned, determined as follows: where, DA was activity data (Tj), FE was the emission factor, Fbbm was fuel consumption in a year (kilo liter), NCV was Net Calorie Value or the net calorific value of fuel, 10 -6 was the conversion factor from kilograms to gigagrams, and ρ was the density of the fuel used.

The biological treatment method
The applied biological treatment method was composting at TPS 3R.CH4 Emissions where, CH4 Emissions was total CH4 emissions in inventory year (Gg CH4), Mi was mass of organic waste treated by biological treatment type i (Gg), EF was emission factor for treatment i (g CH4/kg waste treated), i was composting or anaerobic digestion, and R was the amount of CH4 recovered in inventory year (Gg CH4).

N2O Emissions
where, N 2 O Emissions was N 2 O Emissions in inventory year (Gg N 2 O), Mi was mass of organic waste treated by biological treatment type i (Gg), EF was emission factor for treatment i (g N2O/kg waste treated), and i was composting or anaerobic digestion.

Current waste management practices in Bandung
The waste management practices in Bandung City are organised into several distinct systems, spanning from waste generation, to its ultimate disposal at the Sarimukti landfill (Figure 1).The process commences with the collection of household waste from individual residences to Waste Processing Facilities (TPS).If the neighborhood has TPS 3R, the waste will be collected to TPS 3R.This collection is carried out by the community, in accordance with the policies set forth by their respective neighborhood units (RW), and typically involves waste carts operated by designated personnel.Subsequently, the transportation of waste from TPS to TPA falls under the purview of the municipal government.At the TPS, waste is temporarily stored, before being dispatched to the landfill.Conversely, waste delivered to the TPS 3R undergoes specific treatment to mitigate the volume of waste entering the landfill.Household waste in TPS 3R is segregated into three categories, as part of the Kangpisman programme's public awareness initiatives: organic waste, inorganic waste, and residuals.These TPS 3R employ diverse techniques to process organic waste, such as composting, maggot BSF (Black Soldier Fly) utilisation, and biodigester processing.Inorganic waste is typically collected by waste cart operators for sale to waste banks.Residual waste is subsequently disposed of at the Sarimukti landfill.The Ciwastra region employs an incinerator, in addition to the maggot BSF and composting processes.The incinerator at the TPS 3R at Ciwastra Market is classified as semi-continuous with a fluidised bed configuration, effectively managing an average of 12,309.54kg/day of waste.
Consolidating the waste management initiatives, the Sarimukti landfill serves as the primary regional disposal site for West Java, catering to waste from four distinct areas: Bandung City, Cimahi City, Bandung Regency, and West Bandung Regency.The landfill is subdivided into four zones, with only zones 3 and 4 currently operational.Operational since 2005, the Sarimukti landfill is slated for use until 2025, after which it will be revitalised and succeeded by the Legok Nangka landfill.

Scenario 1
The estimation assumes GHG emissions from household waste in the year 2022, utilising the total waste generation data for Bandung City obtained from Indonesia's Solid Waste Information System (SIPSN), amounting to 581,876 Gg/year.As seen in Table 1, under Scenario 1, which considers the absence of waste reduction measures and employs the waste disposal scheme in the landfill, the total emissions reach 185,271.934tons of CO2eq.
It is noteworthy that, Scenario 1 exhibits the highest GHG emissions, primarily attributed to the absence of waste reduction efforts, resulting in a substantial volume of waste being disposed of.Furthermore, the waste composition in Bandung City is characterised by a significant proportion of organic waste.Organic waste presents a CH4 emission factor ranging from 0.07 to 0.11 kg CH4/dry weight or 0.42 to 0.47 kg CH4 per wet weight, based on specific waste data pertaining to Indonesia [11].Moreover, owing to its easily degradable organic matter, organic waste contributes significantly to the overall emissions, due to its high content of degradable organic carbon (DOC), thereby influencing the greenhouse gas emissions profile [12].

Scenario 2
Based on the calculations, the GHG emissions for Scenario 2, which represents the existing waste management conditions in Bandung City, amount to 150,423.096tons of CO2eq (Table 2).Among all the waste management activities, the highest GHG emissions are attributed to waste disposal in the landfill, totaling 147,775.028tons of CO2eq from the total waste input to the landfill, which is 464,111 Gg/year.This can be attributed to the significant waste generation still being directed to the landfill.Furthermore, GHG emissions from incineration activities at the TPS 3R at Ciwastra Market are also considerable, resulting in 2,328.061tons of CO2eq from a waste quantity of 4,492 Gg/year.Composting activities at the TPS 3R, with a waste quantity of 1.82 Gg/year, generate emissions of 319.592 tons of CO2eq.The GHG emissions can be calculated for each waste management activity by dividing the total GHG emissions by the weight of the waste.Landfilling results in emissions of 318.404 tons of CO 2 eq/year, composting yields 175.6 tons of CO 2 eq/year, and incineration produces 518.360 tons of CO2 eq/year.Composting exhibits the lowest GHG emissions.Aerobic composting can produce a small amount of CH4 due to the anaerobic conditions caused by specific heights, during the composting process.In addition to generating low GHG emissions, composting also addresses the issue of limited landfill space, as it can reduce waste volume by 50% to 70% [13].On the other hand, incineration activities result in the highest emissions.However, if incineration can be utilised as an energy source, it can have significant environmental benefits.Incineration can generate electricity up to 774 kWh per ton of municipal solid waste [14].
The waste collection activities carried out by the Waste Bank in Bandung City do not generate GHG emissions; in fact, they can prevent the occurrence of GHG emissions.This is because, the waste collected by these institutions is sold or recycled by consumers, thereby avoiding disposal in landfills or the need for incineration activities.The Waste Bank has successfully saved 1.996266 Gg/year of inorganic waste, preventing the release of 1,524.801tons of CO2eq from landfilling activities and 2,644.776tons of CO2eq from incineration activities.Additionally, the Waste Bank activities in Bandung City also provide economic and environmental benefits.

Scenario 3
Based on the calculations, the estimated GHG emissions in Scenario 3, in line with the government targets for Bandung City in 2025, amount to 64,373.560tons of CO2eq.In this scenario, it is assumed that, all inorganic waste enters the Waste Bank, thereby preventing the generation of GHG emissions.
As for the disposal of waste in landfills, it is assumed that, all of it consists of residual waste, resulting in a smaller quantity.With this target in place, it is expected that, Bandung City can efficiently reduce waste, by decreasing both the amount of waste generated in landfills and GHG emissions.As seen in Table 3, in Scenario 3, there is a decrease in GHG emissions, compared to the existing conditions in Scenario 2. This is attributed to the improved waste management efficiency, where all organic waste from food and leaves in Bandung City is directed towards composting.Improving the efficiency of food waste separation can increase clean carbon emissions [15].Furthermore, this target promotes recycling initiatives, which directly leads to a reduction in GHG emissions by reducing waste accumulation.Indirectly, it helps in reducing GHG emissions by decreasing the use of raw materials extracted from nature and reducing energy consumption from fossil fuels in the production of new goods [16].Secondary production requires less energy, water, and chemicals compared to primary production, resulting in cost savings [17].Additionally, there is less waste production, leading to avoided costs for manufacturers.Moreover, implementing the 3R (Reduce, Reuse, Recycle) approach can not only reduce waste at the source (households) but also generate social, economic, and environmental added value [18].

Scenario 4
Based on the calculations, the estimated GHG emissions in Scenario 4 (Table 4), in line with the government targets for Bandung City in 2025, amount to 70,001.973tons of CO2eq.The emissions in this scenario are higher, compared to Scenario 3, because the residual waste is treated through incineration.However, if the incineration process is utilised for renewable energy generation based on waste, it can help reduce GHG emissions [19].If the energy system relies more on renewable energy sources, the electricity generated can contribute to significant GHG reductions.

Conclusion
There are three highlights in this study, as follows: In the first scenario, it is assumed that all waste is directly disposed of at the Sarimukti Landfill, without any waste reduction measures, resulting in GHG emissions of 185,271.934tons of CO2 eq/year; In the second scenario, which represents the existing conditions, including reduced waste accumulation at the Sarimukti Landfill, incineration activities at the 3R Waste Treatment Facility in Ciwastra Market, composting activities at the 3R Waste Treatment Facility, and waste collection activities by Waste Banks, the GHG emissions amount to 150,423.096tons of CO2eq.The achieved reduction in GHG emissions is 34,848.847tons of CO2eq.Conversely, scenarios three and four are based on the potential waste generation in 2025, as stipulated in Bandung Mayor Regulation No. 1426 of 2018, assuming the waste composition consists solely of residual waste.In scenario three, GHG emissions are assumed to result solely from waste disposal at the landfill and composting activities, resulting in emissions of 64,373.560tons of CO2eq.In scenario four, GHG emissions are assumed to result solely from incineration and composting activities, resulting in emissions of 70,001.973tons of CO2eq; The implementation of Waste Banks in Bandung City plays a significant role in preventing GHG emissions, as the waste collected by these banks is not subjected to landfilling or incineration.By considering the contribution of Waste Banks, it is estimated that 1,524.801tons of CO2eq of GHG emissions are avoided through landfilling, while 2,644.776tons of CO2eq of GHG emissions are avoided through incineration.The waste collection activities conducted by Waste Banks effectively curtail GHG emissions, as the collected waste is sold for recycling purposes by consumers.

Figure 1 .
Figure 1.Current waste management practices in Bandung.

Figure 2
illustrates the comparison between four scenarios.This comparison emphasises the significant potential for reducing emissions by implementing waste management strategies, with the utilisation of Waste Banks, 3R Waste Treatment Facility (TPS 3R), and an incinerator in a TPS 3R at Ciwastra Market in Scenario 2, Scenario 3, and Scenario 4. Embracing these approaches offers the opportunity to alleviate the environmental consequences of waste disposal and make a valuable contribution to achieving climate change mitigation objectives.