Methane Emission and Carbon Sequestration Potential from Municipal Solid Waste Landfill, India

Abstract

Quantities of waste generation are drastically increasing every day, and most of the waste is disposed of through open dumps and landfilling. Methane, carbon dioxide, and nitrous oxide are major greenhouse gases (GHGs) produced from landfill sites. However, the global-warming potential of methane is 21 times higher than that of carbon dioxide. Hence, there is immense concern for its utilization from landfill sites. In developing countries, the composition of municipal solid waste (MSW) has high amounts of biodegradable waste (50–60%). This leads to higher emissions of GHGs a per ton of MSW compared to the developed world. In this study, the attempt will be made to estimate the amount of carbon stored in MSW burial in landfills. Tests were conducted in two different locations at the Mavallipura landfill. MSW samples were collected for every meter interval (1–2 m, 2–3 m and so on) up to 6 m. The result shows that carbon stored in organic matter increases with depth from approximately 2.2% at 1.0 m depth to 4.8% at 6 m depth. Based on MSW’s carbon storage factor and data on MSW generation, global carbon sequestration from MSW burial in the Mavallipura landfill is estimated to be at least 10 million metric tons per year. In additional, the study aims to quantify methane-gas production from the ward levels and the Mavallipura landfill site in India.

1. Introduction

A harmonious and balanced relationship between humans and nature on the Earth is vital for the existence of life and sustainable development. As civilization advanced, humans directly or indirectly interfered with the natural environment for its comfort. Urbanization is a significant phenomenon that varies in social, economic, and environmental dimensions [1]. We have witnessed the dramatic shift in populations from rural to urban areas and the extensive expansion of the metropolitan regions [2]. At present, global climate change plays a vital role in environmental challenges facing society.

Consequently, more than 75% of global anthropogenic carbon-dioxide emissions have been produced from cities [2]. Meanwhile, large amounts of carbon have been identified in urban environments such as vegetation and soils and anthropogenic ones, including buildings and landfills [3]. Therefore, urban ecosystems’ carbon cycle has received considerable attention during recent years [4]. The research focused prirmarily on carbon storage in natural pools [5] and, rarely, on carbon stored in landfills (anthropogenic pools). Due to the drastic growth in population and improved living standards, solid waste has escalated across the world [6]. In developing countries, the rate of MSW generated per capita per year increased from 357.7–445.3 kg in the 1960s to 567–759.2 kg in the 2000s and for developing countries, from 40.2 to 284.7 kg in the 1980s to 109.5 to 525.6 kg in 2000s [6]. A landfill is the cheapest disposal method of solid waste; currently, landfilling is the most common way to store MSW in most countries [7]. In addition, few research studies [8,9] exist on investigating carbon storage in MSW landfills over large areas. These studies differ in how MSW landfill carbon dynamics are represented. A combination of urban expansion and minimal studies on MSW-landfill carbon dynamics has proven the need for more regional-to-global research to understand the importance of landfills in the carbon cycle.

In India, waste generation per capita increased from 0.44 kg/day in 2001 to 0.5 kg/day in 2011 due to lifestyles changing and a drastic rise in the procurement power of Indians. Increased population growth and waste generation per capita have resulted in a 50% increase in Indian cities’ waste generation. As per the Census 2011, India generates approximately 110,000 metric tons of solid waste daily. Various research conducted by NEERI and other experts has shown that the waste-generation rates are relatively high in cities with over 2 million inhabitants. A metropolis such as Bangalore, located in India’s southern part, generates about 3500 MT of waste per day [10]. Mumbai and Pune, located in India’s western region, generate about 7000 and 3000 MT waste per day [11,12]. Mumbai’s population increased from 8.2 million in 1981 to 12.3 million in 1991 (i.e., by 49%). The solid waste generated rose from 3.2 to 5.35 Gg per day during the same period, recording 67% growth. Chennai, a coastal city located in south India, witnessed a population growth of 21% from 1991 to 2001, while waste generation increased by 61% from 1996 to 2002. In Bangalore, the population increased by 53% from 1991 to 2012, while waste generation grew from 650 MTPD (metric tons per day) (in 2000) to 3500 MTPD (in 2015).

This shows the drastic increase in the production of waste in Indian cities with regards to the population’s growth. Therefore, a thorough estimation of carbon stocks and dynamics in India’s landfills may significantly contribute to understanding urban areas’ role in the carbon cycle at regional to global scales.

A landfill has the potential to emit around 15–25 L/kg of gas per year over its operational period. This LFG can be used as a good fuel for power generation and the gas collected can be supplied to appropriate industries located in the vicinity for direct use in areas such as internal combustion engines, gas turbines, micro turbines, steam boilers, and other facilities [13]. The major cities in India are working hard to bridge the gap to achieve 100 per cent waste processing efficiency. However, still, there is work in progress and cities such as Gangtok, Bengaluru, Gurugram, Kumbakonam and North Delhi are in the process of improving their processing efficiency [14]. High population growth and waste generation per capita have resulted in a 50% increase in waste generation by Indian cities. A declining trend in the solid waste landfilled has been observed during the last six years, where landfilled waste decreased from 54% in 2015–2016 to 18.4% in 2020–2021. On the other hand, an increasing percentage of solid waste processed has been seen during the last five years, wherein the percentage of solid waste processed has increased from 19% in 2015–2016 to 49.96% in 2020–2021 (CPCB Delhi, [15]).

Methane is a primary constituent of GHGs with a Global Warming Potential of about 21 times that of carbon dioxide. Anaerobic decomposition of wastes due to microorganisms present in landfills leads to methane emissions, carbon-dioxide emissions, and gases such as H2S and NOx in lower amounts. Methane has a high thermal and calorific value which is comparable to that of a liter of kerosene. This high heating capacity of methane makes this gas an alarming threat. However, policies have been implemented around the world to minimize the emissions of methane from waste; Naveen et al. [16]. The negative impacts of LFG can be mediated by making use of eco-friendly technologies and adequate solid-waste management techniques. Sustainable means of waste management are reduced, reused, recycled, recovered and, finally, landfilled. Methane mitigation provides substantial benefits by reducing global warming and air pollution. Due to its short atmospheric lifetime, reductions in CH₄ emissions lead to visible climate impacts within a few short decades of policy implementation.

Modeling and estimation of landfill gas in waste landfills play a primary role in their design and the tapping of energy. In fact, quantitative assessment of the landfill gas emissions will help in evaluating India’s contribution to the global emission of GHGs. The behavior of MSW landfills can be evaluated over the years using various mathematical models available in the literature, to avoid disastrous effects. These models can predict the precise estimation of LFG emission and settlement rates over the years according to the rate of biodegradation and, thereby, help in the maintenance of landfill sites. Moreover, prediction of methane emissions can help in extracting information on global-warming potentials and designing adequate methane-control and accumulation systems for harnessing energy.

Presently, there is a lack of understanding of the global carbon cycle, and achieving a global carbon balance requires a terrestrial sink of 1–2Gt C yr-1 [13,14,15]. Several terrestrial carbon-storage models have been developed [16]. However, the global uptake of anthropogenic carbon by the terrestrial system has been mainly deduced by differences in the global carbon budget. In this study, the attempt will be made to estimate the amount of carbon stored in the MSW burial in the Mavallipura landfill site. The study aims to quantify methane-gas production from the ward levels and Mavallipura landfill site in India.

2. Site Description

The study area is situated in Bangalore north at latitude 13°50′ North, longitude 77°36′ East in Karnataka. The Mavallipura landfill site has processing units for the waste generated from Bangalore cities. The annual average rainfall is 978 mm. June to September is the primary rainy season and the secondary rainy season is from November to December. The landfill site is located 20 km away from Bangalore city. Since 2005, villagers have been used to the dumping of waste by the local authority in and around the 40.46 ha of land. The landfill site was operated by M/s Ramky Environmental Engineers; it can sustain 600 tons of waste per day. However, BBMP forcefully transmits approximately 1000 tons of waste per day from Bangalore cities. In 2007, villagers complained that the landfill site is unregulated and did not follow the waste-management rules. As per the villagers’ views, the company collects the unsegregated wastes and piles the untreated waste at the landfill site. Hence, the villagers demanded an instantaneous stop to landfill-site activities, as they were illegal and unscientifically managed. Finally, the landfill locations were closed [17]. The Mavallipura landfill site is about 40.48 ha located in Mavallipura village, of which approximately 35 acres is used for the landfill. The geographical representation of the Mavallipura landfill site is shown in Figure 1.

Bangalore does not have scientific-treatment-method facilities for the solid waste generated by municipal and industries around Bangalore. This has led to the development of several illegal and unauthorized dumpsites in Bangalore. The trash produced by the bulk generators such as hotels, restaurants, Kalyana mandapas, markets, etc., is being directly collected and transported to treatment/disposal facilities. Figure 2 shows the location of these dumpsites along with wards and their boundary in Bangalore city.

Bangalore is the principal administrative, cultural, commercial and knowledge capital of the Indian state of Karnataka. It covers an area of 1258 km² and has a population of about 10 million. Presently, the Bruhat Bangalore Mahanagara Palike (BBMP), the agency vested with responsibility for the disposal of solid waste, is engaged in various activities to provide effective solid-waste-management (SWM) system for Bangalore city, incorporating a series of approaches such as the involvement of citizens, investment in infrastructure and technology, and monitoring the various systems that manage the time taken by the present mix of actions and techniques. For a more efficient and effective approach, Bangalore city has been divided into different administrative units. There are 294 Health wards within the Bruhat Bangalore Mahanagara Palike (BBMP). The BBMP has a city council which consists of 123 elected members, or councilors, each representing a ward. For administrative purposes, the city of Bangalore is divided into eight zones, namely: East (44 wards); West (44 wards); South (44 wards); Bommanahalli (16 wards); Mahadevapura (17 wards); R.R.Nagara (14 wards); Yelahanka (11 wards); and Dasarahalli (8 wards), which are further subdivided into a total of 198 wards administered by the BBMP, as shown in Figure 3. Average MSW generated data about all zones are collected from BBMP and estimated methane emission using the IPCC default method and mass balance method.

3. Theoretical Estimation Methods

3.1. Stoichiometric Mass-Balance Approach

The mass-balance approach is the most superficial level of emission estimation. Its use is generally discouraged because it gives a high estimate of emissions. This method does not include any factors and does not distinguish between various types of disposal sites. Theoretical emissions are calculated using stoichiometric equations as per Tchobanoglous et al. [18]. Comparisons for aerobic and anaerobic degradations considering complete degradation of waste are given by Equations (1) and (2).

C_2.98H_0.462O_1.02N0.099 + 2.659 O₂ → 2.98 CO₂ + 0.0825 H₂O + 0.099 NH₃

(1)

C_2.98H_0.462O_1.02N0.099 + 2.4287 H₂O → 1.1978 CH₄ + 1.2143 CO₂ + 0.099 NH₃

(2)

3.2. IPCC Default Methodology

According to this default method (IPCC method), the methane-generation capacity was calculated based on the decomposable degradable organic and does not include changes in carbon conversion to methane emissions with time (IPCC, 1996).

$${\mathrm{CH}}_4={\mathrm{MSW}}_{\mathrm{T}}\times { \mathrm{MSW}}_{\mathrm{F}}\times \mathrm{MCF} \times \mathrm{DOC} \times { \mathrm{DOC}}_{\mathrm{F}}\times \mathrm{F} \times \left(\frac{16}{12}-\mathrm{R}\right)\times \left(1-\mathrm{OX}\right)$$

(3)

where MSWT = total municipal solid waste generated, MSWF = fraction of MSW disposed of at the disposal sites (0.6), MCF = methane correction factor (0.6), DOC = degradable organic carbon (0.200), DOCF = fraction of DOC dissimilated (0.77), F = fraction of methane in LFG (0.5), R = recovery of LFG (0), and OX = oxidation factor (0).

3.3. Landfill-Gas-Emissions Model (LandGEM)

LandGEM model was developed by the Control Technology Center (CTC) of the United States Environmental Protection Agency (USEPA). LandGEM is a simple tool for assessment of rate for landfill gas, methane, carbon dioxide. Default parameters can be incorporated in LandGEM when no site-specific data are available [19]. LandGEM is based on the first-order decomposition rate equation to estimate annual emissions over time in a specific landfill. The formula used in LandGEM (version 3.02) is presented in Equation (4).

$$Q_{C{H}_4}={\displaystyle \sum }_{i=1}^n{\displaystyle \sum }_{j=0.1}^{1}k{L}_o\left( \frac{M_i}{10}\right)e^{-k{t}_{ij}}$$

(4)

where $Q_{C{H}_4}$ = annual methane generation in the year of the calculation (m³/year); i = 1-year time increment; n = (year of the calculation) − (initial year of waste acceptance); j = 0.1-year time increment; k = methane generation rate (year-1); L_o = potential methane generation capacity (m³/Mg); M_i = mass of waste accepted in the ith year (Mg); t_ij = age of the jth section of waste mass M_i accepted in the ith year (decimal years, e.g., 3.2 years).

3.4. Total Organic Carbon (TOC) Analyzer

Photocatalytic oxidation estimates TOC in the presence of UV light and oxygen. Titanium dioxide catalyzes the oxidation of organic compounds in an aqueous medium. This reaction yields carbon dioxide, water, acid, base, or salt of any organically bound elements. The liberated carbon dioxide is detected by non-dispersive infra-red (NDIR) detector. TOC is measured by injecting a portion, ten or hundred microliters, of the sample into a heated TOC (to 680 °C in an oxygen-rich environment inside) combustion tube packed with an oxidation catalyst. Water is vaporized and total carbon, organic carbon, and inorganic carbon is converted to carbon dioxide. The carrier-gas flow stream carries this CO₂ from the combustion tube to a non-dispersive infrared gas (NDIR) analyzer; finally, carbon dioxide (CO₂) is measured. Based on the standard solutions, the calibration curve is prepared, and TC concentration is obtained and expressed in percentage. For estimation of the TOC, schematic diagram is shown in Figure 4.

4. Estimation of Carbon Stored in Mavallipura Landfill

4.1. Waste Generated Pertaining to All Zones

Bangalore generates around 3500 tons of municipal solid waste, with per-capita generation of 0.4 kg/day of domestic waste. We provide an overview of zone-wise data of February 2013 on MSW per day at Bangalore city, as shown in Figure 5. Zone-wise analysis indicates the variability in waste generated in each zone, shown in Figure 6. A quantum of waste generation in three zones (East, West, and South) is high compared to others. In addition, the much lower waste generation in Yelahanka could be attributed to low economic activities.

Average MSW generated data from all zones were collected from BBMP and estimated methane emission using the IPCC default method and stoichiometric mass-balance method were discussed. Total ward-wise waste generated is 100,792.10 MT per day. The calculation of methane emitted from zones during February 2013 in Bangalore was established on the amount of waste disposal and use of three independent methodologies, namely, the Intergovernmental Panel on Climate Change (IPCC), experimental and the Stoichiometric method, which showed a massive difference in the total amount of estimated emissions.

Table 1. Statistical analysis of methane emissions from solid waste generated per month across the zone.

Zones Greater Bangalore Municipality BBMP	Total SW/Month (Tons)	Mean SW Generated (Tons/Day)	Std Deviation	Ward Wise SW Generated (Tons/Day)	CH4 Emissions (Tons/Day)
					IPCC	Stoichiometric
East (44 wards)	25,317.36	904.19	33.66	20.55	32.55	320.99
West (44 wards)	24,385.64	870.92	48.90	19.79	31.35	309.18
South (44 wards)	20,142.81	719.39	41.13	16.35	25.90	255.38
Bommanahalli (16 wards)	9075.55	324.13	52.56	20.26	11.67	115.07
Mahadevapura (17 wards)	11,238.56	401.38	29.75	23.61	14.45	142.49
R.R.Nagara (14 wards)	4351.71	155.42	18.36	11.10	5.60	55.17
Yelahanka (11 wards)	2594.03	92.64	12.66	8.42	3.34	32.89
Dasarahalli (8 wards)	3686.43	131.66	9.69	16.46	4.74	46.74
Total	100,792.10	3599.72	246.71	136.54	129.59	1277.90

indicated that stoichiometric estimation of emissions from waste is much higher than value determined by the Intergovernmental Panel on Climate Change. Meanwhile, mismanagement of waste, either due to lack of adequate workforce or a vital functional element in waste management, creates serious health and environmental implications.

Table 2. Methane emission from solid waste generated per day across the zone.

No. of Days	Total MSW Generated in Tons per Day (198 Wards)	CH4 Emissions (Tons/Day)
		Default Methodology, IPCC	Stoichiometric Mass Balance Approach
1	3321.23	119.56	1179.04
2	3578.44	128.82	1270.35
3	3544.48	127.60	1258.29
4	3730.72	134.31	1324.41
5	3674.68	132.29	1304.51
6	3604.77	129.77	1279.69
7	3684.87	132.66	1308.13
8	3639.01	131.00	1291.85
9	3643.06	131.15	1293.29
10	3571.99	128.59	1268.06
11	3708.40	133.50	1316.48
12	3610.59	129.98	1281.76
13	3597.66	129.52	1277.17
14	3666.78	132.00	1301.71
15	3694.97	133.02	1311.72
16	3584.03	129.03	1272.33
17	3445.72	124.05	1223.23
18	3719.34	133.90	1320.36
19	3718.83	133.88	1320.19
20	3612.93	130.07	1282.59
21	3720.65	133.94	1320.83
22	3607.94	129.89	1280.82
23	3650.82	131.43	1296.04
24	3471.45	124.97	1232.37
25	3493.83	125.78	1240.31
26	3540.13	127.44	1256.75
27	3478.88	125.24	1235.00
28	3475.91	125.13	1233.95
Total	100,792.10	3628.52	35,781.20

indicates that the Intergovernmental Panel on Climate Change estimation of emissions from waste is much higher than the stoichiometric determined value. A reduction in waste generation is possible through reduced waste generation, segregation at source level, reuse, and recovery of waste. Generally, for organic waste (60–70%), composting and anaerobic digestion are treatment options, whereas inorganic waste (20–25%) is used for recycling. The remaining waste that cannot be recycled is ultimately dumped in landfill sites. However, source segregation with treatment at ward levels (local levels) plays a significant role in minimizing the organic fractions in dump site.

4.2. In-Situ Waste Sample Collection

Estimation of the carbon stored in the buried organic matter in the Mavallipura landfill site was carried out. Using a hand auger, the solid-waste samples were collected at two different locations in the Mavallipura landfill, as shown in Figure 5. Auger drilling operation using a 150 mm diameter was carried out in a landfill site. The purpose of the auger drilling operation was to characterize the municipal solid waste visually, and retrieve bulk samples of debris from different depths and varying degrees of degradation and age.

The changes in the composition of MSW should form essential criteria for any waste-management system. Hence, the data available on the MSW compositions from different boreholes, A and B, was collected and analyzed. MSW composition mainly depends on several factors such as cultural traditions, food habits, and socio-economic and climatic conditions. It also varies from place to place. Studies were carried out in the Mavallipura landfill site with a 100 kg MSW sample. The collected MSW sample was sorted physically into various ingredients, such as paper, fiber, metals, soils, glass, and miscellaneous waste on a sorting platform. The individual components were separated and weighed. From Figure 6, the observed municipal solid waste comprises 8-to-10%-yard waste (garden waste), 20 to 21.9% of paper and cardboard waste in the landfill, indicating recycling activities of paper and cardboard at the source itself. The total of 35 to 39% of plastic might be due to urbanization and the increased use of plastic carry bags, 9 to 9.7% was miscellaneous wastes (including textile, rubber, leather, and other) and 16 to 16.8% metals and glass products, which are effectively recycled by segregation at sources itself.

Solid-waste samples were collected at two different locations in the Mavallipura landfill. Samples were collected for every half meter interval (0–0.5 m, 0.5–1 m, and so on) until a depth of 6 m. The solid-waste sample’s first half meter was discarded as it contained the soil cover mixed with the upper layer of waste. Samples were collected in plastic bags, sealed, and labeled, then brought back to the laboratory, and all the samples’ moisture content was determined. The rest of the samples were spread out for air drying in the room, as shown in Figure 7. They were further dried at 65 °C in an oven, and then the various components were manually separated and weighed. The soil component was separated using sieves of different sizes into three fractions, namely, <2.36 mm but >1.18 mm, <1.18 mm but >600 µm, and <600 µm. The smallest bit (<600 µm) was used to determine the TOC analyzer’s carbon content.

4.3. In-Situ Testing: Temperature Test

The temperature of the MSW material was recorded as soon as the waste was brought to the surface and an attempt made to evaluate the age of the MSW material; newspaper, magazines, or other documents can provide general information on the age of the MSW in the landfill at the location of the bore. As Figure 8 shows, the temperature tended to increase with depth, due to the heterogeneity of the material. The highest temperatures for landfills were generally reported at mid-waste elevations with temperatures decreasing near the top. The temperatures near the top underwent variations like seasonal temperature fluctuations, whereas the temperatures at greater depths generally follow stable trends. The initial decomposition of wastes in a landfill occurs under aerobic conditions. Anaerobic conditions prevail upon the depletion of oxygen at the bottom of the landfill. However, the trend shows some variations due to the heterogeneity of the waste.

4.4. In-Situ Testing: Moisture Content Test

At each depth, the moisture content of the MSW material was estimated using dry gravimetric moisture content: the ratio of the mass of water in a waste sample to the mass of solids in the waste sample, expressed as a percentage. During the moisture-content determinations, the temperature was maintained at 60 °C to avoid combustion of volatile materials. As Figure 9 shows, the moisture content tended to increase with depth. The moisture content increased with depth due to degradation. The increase in moisture content may also contribute to the increase in moisture-content-withholding capacity of MSW due to the disintegration of particles after degradation.

4.5. In-Situ Testing: Unit Weight Test

In the Mavallipura landfill, the in-situ method of measuring the unit weight by replacing the waste with calibrated gravel was used. The weight of waste removed from a 0.5–1.0 m length of the borehole was measured and the volume of the material was evaluated by backfilling the 0.5–1.0 m interval with gravel of known unit weight. The unit weight of MSW is expressed as a kN/m³. Figure 10 shows the unit-weight profile with depths ranging from a low unit weight of 3.8 kN/m³ near the surface and the highest value of approximately 8.4 kN/m³ at a depth of 6 m. The unit weight tended to increase with depth.

4.6. In-Situ Testing: pH Test

The acidity or alkalinity of an MSW sample can be expressed on the pH scale. The unit of the scale is called pH value. This scale runs from 0 to 14 pH values. The neutral point in this scale is at pH 7.0. All values above pH 7.0 represent alkalinity and all values below 7.0 denote acidity. The degree of alkalinity increases as values go above pH 7.0 and the degree of acidity increases as the pH decreases below 8.0. Figure 11 shows a pH variation of 8.3 to 8.9. pH is controlled principally by a series of chemical reactions. The important reaction is the degradation of organic materials to produce carbon dioxide and a small amount of ammonia. These dissolve in the leachate to form ammonium ions and carbonic acid. The carbonic acid dissociates with ease to produce hydrogen cations and bicarbonate anions, which influence the level of pH of the system. Additionally, pH is also influenced by the partial pressure of the generated carbon-dioxide gas which is contact with the leachate.

4.7. TOC Test

The typical height of solid-waste dumping is 6 m above ground level and the deposit consisted of uncompacted waste. By using a total organic carbon (TOC) analyzer, total organic carbon expressed as a percentage was evaluated with respect to depth. As Figure 12 shows, the carbon stored in organic matter increases with depth from approximately 2% at 1.0 m depth to 23% at 6 m depth. Similarly, the total carbon content of MSW in other countries has been reported to be in the same range, with 15.74 to 29.67% being identified for Taiwan [20]. These ranges are more representative of a heterogeneous material obtained from MSW in-situ testing.

4.8. Volume of Mavallipura Landfill

The total volume of municipal solid waste in the Mavallipura landfill was determined by measuring the landfill area and average depth. A GPS tracker (Garmin) with an altitude display was used to measure the dumpsite’s perimeter. The perimeter of the dumpsite is 867 m, and it encloses an area of 59,828 m² (Figure 13a). Based on the contour map, the landfill’s average vertical depth is 17 m—a typical Mavallipura landfill site sketch (Figure 13b). The uncompacted-waste dump area at the top level is about 875 m²; the volume was estimated for each respective depth until 6 m, and the carbon stored in each layer was determined. The mass of the MSW in landfills above the ground level was calculated based on the density and volume of each respective layer. Carbon stored in the uncompacted waste was calculated based on the carbon content obtained from the TOC analyzer and the mass of MSW stored in the landfill with these respective layers. The carbon stored in the uncompacted waste is as shown in

Table 3. Carbon stored in solid-waste dump above ground level.

Above GL Depth, m	In-Situ Density, kN/m3	Mass of MSW Stored in Landfill, Metric Tons	Carbon Content Obtained from TOC Analyzer, %	Carbon Stored in Landfill, Metric Tons
1	4.02	1157	2	23.14
2	4.5	1245	5	62.25
3	5.8	1552	7.5	116.4
4	7.0	2168	12	260.16
5	7.45	2327	16	372.32
6	8.0	2562	23	589.26
Total estimated MSW carbon stored above the ground level				1423.53

.

Due to the physical nature of the solid waste present in the landfill, it is tough to conduct the boring and sampling below the ground level. Hence, the total volume was calculated based on the contour map. The total volume of the landfill below ground level was 52,714 m³, assuming that the bulk unit weight is 8 kN/m³, and the carbon content 23%. The total mass of MSW stored is 42,171 metric tons, and the total carbon stored in the MSW is 9699 metric tons below the Mavallipura landfill, as estimated. Finally, the sum of the net amount of standing stock carbon deposited above and below dump is 11,122.53 metric tons.

4.9. Global Carbon Sequestration from Mavallipura Landfill

Carbon sequestration from the MSW buried in the Mavallipura landfill on a global scale was estimated using Equation (5).

Cseqi = Gi × LFfri × CSFm

(5)

Gi is the mass of MSW generated in the Mavallipura landfill, which is 600 metric tons per day; LFfri is the fraction of waste generated in Bangalore buried in landfills; CSFm is the carbon stored factor is 0.302 based on the EPA’s guidelines.

Global carbon sequestration due to MSW burial in the Mavallipura landfill is estimated to be 10 × 106 tons per year. Only stored carbon associated with paper, plastic, wood, and yard, etc., was considered.

Barlaz [21] reported the global carbon sequestration of MSW burial in a US landfill as estimated to be 118.7 × 106 per year. Bogner [22] determined the carbon sequestration of MSW burial in a US landfill to be 31.6 × 106 tons per year.

Carbon sequestration is one of the significant factors that should be considered when comparing the environmental benefits and liabilities associated with MSW landfills in specific and MSW management strategies in general. Other factors include gaseous emissions from MSW decomposition and the equipment used for MSW landfill operation, energy consumed during MSW landfill construction and maintenance, and methane’s potential recovery for energy. Hence, appropriate treatment options are necessary to treat the municipal solid waste’s organic fractions to reduce greenhouse-gas emissions. Decentralized treatment options of converting to energy or composting would provide a better solution by converting the waste to wealth.

5. Methane Production from Mavallipura Landfill

5.1. IPCC Default Method

The methodology was adapted from IPCC [23]. Methane emission for Bangalore waste was estimated as

Methane emission = 1227.5 × 0.80 × 0.6 × 0.200 × 0.77 × 0.5 × 16/12 = 63 Gg/yr

The obtained methane emission was used to calculate energy and power generation using a density of methane at standard conditions, which was taken as 0.7167 kg/m³, and the calorific value (lowest) as 9000 kcal/m³. Energy production for one year adopting, a gas collection of 80%, is 2375 TJ, and the corresponding power generated was calculated as 75 MW.

5.2. LandGEM Model

The Mavallipura landfill’s methane emission was calculated based on the landfilled-waste data for the period 2007 to 2013. The estimated amount of generated methane is the landfill site (1,022,000 mg/year), annual acceptance rate, and concentration of total non-methane organic compounds (4000 ppmv as hexane) and the years of waste acceptance. Figure 14 illustrates the drift of methane gas emissions in different years of Mavallipura-landfill site projects. Results revealed that the amount of annual waste generation in the Mavallipura landfill is in the range of 110,000 tons to 220,000 tons from the opening of the landfill to the closure of the landfill.

Over time, the landfill scenario has been changing. With a drastic increase in waste generation rates, scarcity of land availability, and GHGs issues, there is a unique need to modify the existing landfill design aiming at the energy and power generation from waste with the requirement of less area. The calculations of methane emitted from the landfill during 2007–2013, at the Mavallipura landfill, were established based on the amount of waste disposal and use of two independent methodologies, namely, Intergovernmental Panel on Climate Change (IPCC) and LandGEM, showing a minor difference in the total amount of estimated emissions.

Deforestation and human activities that emit large volumes of carbon dioxide are to blame for climate change. However, a lot of people are unaware that solid waste is a component of the climate-change feedback loop. Greenhouse-gas (GHG) emissions are the primary cause of climate change. Solid waste and some of these emissions are directly related. GHG emissions are caused by the production, distribution, and consumption of goods as well as the formation of waste, which have an impact on the climate of the planet [24].

6. Recommendation and Protection Measures

A wide range of mature, environmentally effective waste-management strategies can minimize GHG emissions from this sector and provide public health, environmental protection, and sustainable-development co-benefits [25]. These technologies can directly reduce GHG emissions (landfill gas recovery, improved landfill practices, engineered wastewater management) or avoid significant GHG generation (controlled composting of organic waste, modern incineration, and expanded sanitation coverage) (high evidence, high agreement). Waste minimization, recycling, and reuse have a growing potential to indirectly reduce GHG emissions through raw-material conservation, energy and resource efficiency, and fossil-fuel avoidance (medium evidence, high agreement) [26,27,28,29].

Waste-management decisions are often undertaken locally without the quantification of GHG mitigation, underestimating the waste sector’s role in decreasing global GHG emissions (medium evidence, high agreement). Flexible strategies and financial incentives can expand waste-management options to achieve GHG mitigation goals. In integrated waste management, local technology decisions depend on many competing variables, including waste quantity and characteristics; cost and financing issues; infrastructure requirements, including land area, collection, and transport considerations; and regulatory constraints. LCA provides decision support tools (strong evidence, high agreement) [30].

7. Conclusions

This study indicated that the stoichiometric method estimation of methane emissions from waste is much higher than the Intergovernmental Panel on Climate Change determined values. A reduction in waste generation is possible through reduced waste generation, segregation at source level, and the reuse and recovery of waste.

This study’s objective illustrated the carbon storage factor for MSW and data on MSW generation; the global carbon sequestration from MSW burial in the Mavallipura landfill is estimated to be at least 10 × 106 tons per year. Based on the landfill site’s characterization, it can be said that the Mavallipura landfill site is still in a process of degradation.

Over time, the Mavallipura-landfill scenario has been changing. With a drastic increase in waste-generation rates, scarcity of land availability, and GHGs issues, there is a unique need to modify the existing landfill design aiming at the energy and power generation from waste with the requirement of less area. The calculations of methane emitted from the landfill during 2007–2013 at the Mavallipura landfill were established based on the amount of waste disposed and use of two independent methodologies, namely, Intergovernmental Panel on Climate Change (IPCC) and LandGEM, which showed a minor difference in the total amount of estimated emissions. The maximum methane production rate occurred in the year 2007–2013.