Figure 1. Methane Emission Projections in India
India is one of the world's largest emitters of methane from landfill sites. In fact landfills are the second-fastest growing source for methane emissions in India after coal mining. There are nearly to 5,100 cities and towns in India, most of them having one or two landfills, which are a source of uncontrolled release of methane emissions. The quantification of methane from landfills is important to evaluate measures for reduction of greenhouse gas emissions. Presently, virtually none of the methane emitted from landfills in India is captured and utilized as a source of renewable energy. The main objective of the research was to estimate the methane emissions from selected urban landfills in India and to assess the energy recovery potential from these landfills. The assessment of energy potential was done using the first order decay model. The data for research analysis was gathered from US Environment Protection Agency Methane to Markets partnership program and the Central Pollution Control Board. The paper concludes that except one landfill, rest of the five landfills has the potential to recovery energy. There is a need to develop India specific landfill gas estimation model. The construction of regional landfills in place of scattered open dumps is required to properly manage the environmental impacts of landfill gas. In addition to reaping economic and health benefits, carbon credits can also be obtained.
India is one of the world's largest emitters of methane from landfills, currently producing around 16 Mt CO2 eq per year, and predicted to increase to almost 20 Mt CO2 eq per year by 2020. A study (Garg et al, 2003) using the Integrated Assessment Model for Developing Countries projects a much larger increase to 48 Mt CO2 eq by 2020 and 76 Mt CO2 eq by 2030 (Figure 1) (IEA, 2008).
Methane makes up around 29% of the total Indian GHG emissions, while the global average is 15%, primarily due to the large amount of agricultural methane emissions (Figure 2) (IEA, 2008).
However, emissions from waste (6%) are also proportionally higher than the global average (3%). The MSW generated in the major cities of India is normally disposed off in unsecured landfills where it gradually decomposes to produce methane and carbon dioxide both considered as potent GHGs. If LFG is not actively collected, it escapes into the atmosphere (CPCB, 2006).
Due to a high proportion of biodegradables, and the warm, wet climate, the rate of MSW decomposition in India is faster than in landfills in developed countries. The rates of methane flow can therefore be expected to peak shortly after a landfill is closed, and afterwards rapidly decrease (IEA, 2008).
Figure 1. Methane Emission Projections in India
Figure 2. GHG Emissions for the World and for India in the Year 2005
According to MoEF, 2010, India ranks 5th in aggregate greenhouse gas (GHG) emissions in the world, behind USA, China, European Union and Russia in 2007. The emissions of USA and China are almost 4 times that of India in 2007. The total GHG released from waste sector in 2007 was 57.73 million tons of CO2 equivalent, of which, 2.52 million tons was emitted as CH4. Figure 3 and Table 1 shows the absolute values of GHG emission from waste sector and also the emission distribution across its sub categories.
In India, waste is only systematically collected and disposed at waste disposal sites in cities, resulting in CH4 emission from anaerobic conditions. MSW in Indian cities is disposed in landfills by means of open dumping.
All of the waste disposal sites in the country are open dumps. These sites emit several gases including methane. Hence open disposal of waste is a prevalent practice in India. In Delhi, the Municipal Corporation of Delhi (MCD) with the help of the World Bank carried out feasibility studies at three landfill sites viz Okhla, Ghazipur and Bhalswa in 2008 (IEA, 2008). Feasibility studies were conducted at Okhla landfill site in Delhi (EPA, 2007), Deonar and Gorai Landfill sites in Mumbai. Pirana Landfill site in Ahmedabad (EPA, 2008), Uruli Devachi landfill site in Pune (EPA, 2008) and one site in Auto Nagar, Hyderabad. The results of these feasibility studies are encouraging except for Hyderabad site (EPA, 2007). The LFG utilization potential for selected landfills in India is summarized in Table 2.
Figure 3. GHG emission from waste sector in thousand tons
Table 1. GHG emissions from waste sector (thousand tons)
Table 2. LFG Utilization Potential for Selected Landfills in India
Landfill Gas (LFG) is generated by the decomposition of municipal solid waste (MSW) in landfills. The anaerobic decomposition of MSW in landfills causes generation of LFG. The composition of LFG is generally about 50% methane (CH4) and 50% other gases, including carbon dioxide (CO2) and trace amounts of other compounds. LFG generated from landfills can be captured by gas collection and control systems. The collected LFG can be used as fuel in energy recovery facilities, such as internal combustion engines, gas turbines, microturbines, steam boilers, or other facilities that use the gas for electricity generation thereby reducing GHG emissions. However before installation of such systems it is important to predict the methane generation from the landfill site. The information needed to estimate the LFG generation and recovery from a landfill includes
The main objective of any LFG Model is to evaluate the feasibility and potential benefits of collecting and using the LFG for energy recovery or other uses. The LFG model provides estimates of potential LFG recovery rates by multiplying LFG generation by the estimated LFG recovery efficiency known as collection efficiency.
Most of the LFG models are based on first-order exponential decay function that assumes LFG generation to be at its peak following a time lag representing the period prior to methane generation. Generally the model assumes a one-year time lag between disposal of waste and LFG generation. For each unit of waste, after one year the model assumes that LFG generation decreases exponentially as the biodegradable fraction of the waste is decomposed. The mathematical equation is given below:
Equation 1 - First Order Decay Model
Q = ∑0n (1/ %vol)kMLoe-k(t-t lag)
Where:
Q total quantity of landfill gas generated (Normal cubic meters)
n - total number of years modeled
t - time in years since the waste was deposited
tlag - estimated lag time between deposition of waste and generation of methane
%vol - estimated volumetric percentage of methane in landfill gas
L0 - estimated volume of methane generated per tonne of solid waste
k - estimated rate of decay of organic waste
M - mass of waste in place at year t (tones)
The year of maximum LFG generation normally occurs in the closure year or the year following closure. Methane generation is estimated using two parameters: (i) L0, the methane generation potential of the waste, and (ii) k, the methane generation rate constant. LFG generation is assumed to be at its peak upon closure of the landfill or final disposal of the waste at the landfill site. The methane generation rate constant, k, determines the rate of generation of methane from waste in the landfill. The k value describes the rate at which waste placed in a landfill in a given year decays and produces methane gas. The higher the value of k, the faster total methane generation at a landfill increases and then declines over time. The value of k is a function of the following factors: (i) waste moisture content, (ii) availability of nutrients, (iii) pH, and (iv) temperature.
The value for the potential methane generation capacity of waste (L0) depends only on the type of waste present in the landfill. Higher the cellulose contents of the waste, the higher the value of L0. In practice, the theoretical L0 value may not be reached in dry climates where lack of moisture in the landfill reduces the action of methane-generating bacteria. The L0 value describes the total amount of methane gas produced by a tonne of waste.
According to US EPA, collection efficiencies at landfills typically range from 60% to 85%, with an average of 75%. The values assigned as input variables for LFG projections are given in Table 3.
Table 3. LFG Model Input Variables
In this research, the authors have investigated the LFG to energy potential from six landfill sites in India. There are close to 5,100 cities and towns in India, most of them having at least one (mostly two) such landfill sites, which are a source of uncontrolled release of methane emissions. The MSW (Management and Handling) Rules, 2000 stipulates that LFG control system should be installed including a gas collection system at the landfill sites. The rule also specifies that the concentration of methane gas emissions at landfill site shall not exceed 25% of the Lower Explosive Limit (LEL) which is equivalent to 650 mg/m³. Further the LFG from the site shall be utilized for either direct thermal applications or power generation as per the practicability (MoEF, 2000).
The type and number of landfill sites selected for evaluating the LFG energy potential was based on the population figures of different cities. These cities were having a population greater than 2 millions. According to CPCB, 2008, the waste generation in these cities ranged between 0.22-0.62 kg/capita/day. The compostable fraction varied between 40-60%, Recyclables 11-22%, C/N ratio 21-39, higher calorific value (on dry weight basis) 800 – 2632 Kcal/Kg and moisture content 21-63%.
For the sake of gathering the needed data related to landfill opening and closure year, and waste design capacity, the researchers use the data of Municipal authorities provided to US EPA's international methane to markets partnership programme and some of the data was gathered from the Central Pollution Control Board (CPCB) (Table 4).
Table 4. Key Input Variables for the LFG Model
The following subsections provide an analysis of the results obtained for the six landfill sites in India.
The projected LFG generation and recovery for Okhla landfill site is given in Figure 4. As it is evident from the graph, the peaking value of LFG was in the year 2008. If the gas recovery is started in the year 2011 assuming a collection efficiency of 60% approximately 2,700 m3/hr of LFG can be recovered.
The projected LFG generation and recovery for Hyderabad landfill site is given in Figure 5. As it is evident from the graph, the peaking value of LFG was in the year 2005. If the gas recovery is started in the year 2011 assuming a collection efficiency of 60% approximately 58 m3/hr of LFG can be recovered.
The projected LFG generation and recovery for Pirana landfill site is given in Figure 6. As it is evident from the graph, the peaking value of LFG was in the year 2008. If the gas recovery is started in the year 2011 assuming a collection efficiency of 60% approximately 1,700 m3/hr of LFG can be recovered.
The projected LFG generation and recovery for Deonar landfill site is given in Figure 7. As it is evident from the graph, the peaking value of LFG will be in the year 2010. If the gas recovery is started in the year 2011 assuming a collection efficiency of 60% approximately 6,000 m3/hr of LFG can be recovered.
The projected LFG generation and recovery for Uruli Devachi landfill site is given in Figure 8. As it is evident from the graph, the peaking value of LFG was in the year 2008. If the gas recovery is started in the year 2011 assuming a collection efficiency of 60% approximately 1,300 m3/hr of LFG can be recovered.
The projected LFG generation and recovery for Gorai landfill site is given in Figure 9. As is evident from the graph, the peaking value of LFG was in the year 2006. If the gas recovery is started in the year 2011 assuming a collection efficiency of 60% approximately 2,500 m3/hr of LFG can be recovered.
The results show that the maximum potential for LFG recovery is from Deonar landfill site in Mumbai and the lowest being at the Hyderabad landfill site. Further, there are certain limitations in the estimation of methane emissions as the above estimations are based on secondary data. For practical values under Indian conditions, detailed studies are required to arrive at suitable factors and default values. Although a comparison has been made for six landfills sites but they may not be considered as representative sites.
Figure 4. The Projected LFG Generation And Recovery For Okhla Landfill Site
Figure 5. The Projected LFG Generation and Recovery for Hyderabad Landfill Site
Figure 6. The Projected LFG Generation And Recovery For Pirana Landfill Site
Figure 7. The projected LFG generation and recovery for Deonar landfill site
Figure 8. The projected LFG generation and recovery for Uruli Devachi landfill site
Figure 9. The projected LFG generation and recovery for Gorai landfill site
In India, not a single landfill site has been developed for LFG recovery and utilization. The application of LFG Model at different landfill sites in India demonstrates the model's potential to analyze the feasibility of methane recovery potential. The results show that methane emissions as estimated by the LFG model are strongly influenced by the waste disposal rate. This type of model validation is needed to develop a more accurate model so that estimated yield can effectively determine the viability of LFG to energy projects. The Model parameters are highly dependent on prevailing site conditions and LFG capture efficiency.
The success of an LFG recovery project is dependent on an accurate and timely estimation of the produced LFG, as an overestimation could lead to its failure. The estimation depends on the accuracy of the selected model, the quality of available data and the selection of the correct coefficients. The researchers propose further study using a different LFG model. It is recommended that data from more landfill site be used in the LFG model before implementation of LFG to energy projects at national level. Further, the results of the LFG model can be validated experimentally by conducting a pump test on these landfill sites. The objectives of conducting the pump test would be to measure the vacuum (pressure) and flow relationships while actively extracting LFG from the landfill, measure sustainable methane levels of the extracted LFG and utilize the results of the pump test to refine the projections of LFG recovery. The results of the pump tests carried out by the Municipalities with the assistance from US EPA and the World Bank at Delhi (Okhla), Hyderabad (Auto Nagar), Mumbai (Deonar), Ahmedabad (Pirana), Pune (Uruli Devachi) and Mumbai (Gorai) have also shown similar results.
This research can be replicable to hundreds of landfill sites in India in order to recovery a valuable source of renewable energy which is otherwise getting wasted.
This research was supported by the Ministry of Environment and Forests (MoEF), Government of India. We would like to sincerely thank the staff of MoEF for their constant support and co-operation.