Journal of the Air & Waste Management Association
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Comparison study of landfill gas emissions from subtropical landfill with various phases: A case study in Wuhan, China Lie Yang, Zhulei Chen, Xiong Zhang, Yanyan Liu & Ying Xie To cite this article: Lie Yang, Zhulei Chen, Xiong Zhang, Yanyan Liu & Ying Xie (2015) Comparison study of landfill gas emissions from subtropical landfill with various phases: A case study in Wuhan, China, Journal of the Air & Waste Management Association, 65:8, 980-986, DOI: 10.1080/10962247.2015.1051605 To link to this article: http://dx.doi.org/10.1080/10962247.2015.1051605
Accepted author version posted online: 01 Jun 2015.
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Date: 04 November 2015, At: 00:44
TECHNICAL PAPER
Comparison study of landfill gas emissions from subtropical landfill with various phases: A case study in Wuhan, China Lie Yang,1,⁄ Zhulei Chen,2,⁄ Xiong Zhang,3 Yanyan Liu,1 and Ying Xie3 1
School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan, People’s Republic of China School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, People’s Republic of China 3 Wuhan Environmental Investment and Development Co. Ltd., Wuhan, People’s Republic of China ⁄ Please address correspondence to: Lie Yang, School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, People’s Republic of China; e-mail: [email protected]; or to Zhulei Chen, School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China; e-mail: [email protected]
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The compositions and annual variations of landfill gas (LFG) were studied at two large-scale sites of Chen-Jia-Chong Landfill. Seventy-six wells were built and used for the collection and measurement of LFG. The investigation revealed the similarities and differences of LFG components and variations at two sites with different phases. It was found that ambient temperature and rainfall exhibited strong correlations with LFG components at both sites. Methane (CH4) contents showed excellent correlations with CO2 at both sites. Notable correlations between hydrogen sulfide (H2S) and major components (CH4 and carbon dioxide [CO2]) were only observed in unstable methane phase. Especially, the CH4/CO2 volumetric ratio could act as an excellent indicator for anaerobic reaction stage by judging its phasic variations. The study is beneficial for the efficient operation of LFG collection system and could shed light on gas purification and utilization. Implications: The results in this paper could provide some beneficial information for landfill operators. Especially, the CH4/CO2 volumetric ratio could act as an excellent indicator for anaerobic reaction stage by judging its phasic variations. Moreover, the study could shed light on landfill gas purification and utilization.
Introduction Landfill is the most predominant method for municipal solid waste (MSW) disposal in most countries. However, a number of previous studies in the last two decades have indicated that landfill may impose a threat to the environment and human health due to the generation of landfill gas and leachate. Municipal solid waste (MSW) in landfills decomposes and produces methane (CH4) and carbon dioxide (CO2) gases, trace amount of toxic substances, and bad odor, which are the by-products of the decomposition (Shin et al., 2005). Landfill gas is ranked as the third highest source of global anthropogenic methane emissions, responsible for approximately 9–12% of those emissions in 2005 (Intergovernmental Panel on Climate Change [IPCC], 2007). In particular, the potential contribution of methane to the global warming is 21 times higher than that of carbon dioxide (Gewald et al., 2012). Carbon emission reduction has become a global issue with the increase of methane and carbon dioxide emissions. In recent years, there are generally four approaches for dealing with methane. Firstly, modified-soil covers are applied to promote methane oxidation (Einola et al., 2007; Chiemchaisri et al., 2011; Sadasivam and Reddy, 2014) and aeration is used to reduce
methane production (Ritzkowski and Stegmann, 2007; Raga and Cossu, 2013). Secondly, separate collection of organics before landfilling could efficiently reduce methane emission from landfills (Calabrò, 2009; Bernstad and Jansen, 2012). Thirdly, mechanical biological pretreatment was proven to reduce the gas generation potential and leachate strength of the residue (Bayard et al., 2008; Calabrò et al., 2011). In addition, landfill gas (LFG) is efficiently collected and used as bioenergy for electricity generation (Qin et al., 2001; Bove and Lunghi, 2006; Aguilar-Virgen et al., 2014). Overall, the application of LFG on power generation is more environmentally friendly and sustainable as a potential clean energy. Although varieties of models were applied to estimate the potential energy utilization from landfills (Mackie and Cooper, 2009; Gregg, 2010; Amini and Reinhart, 2011; Penteado et al., 2012), the acknowledgment of the MSW field degradation is indispensable, especially for large-scale landfills. The LFG collection system efficiency varies by the configuration of the system installed (e.g., type, active or passive, number of wells) and by operation management (depression intensity) (Calabrò, 2009). The performance of MSW anaerobic degradation has been investigated using the simulation experiments (MataAlvarez et al., 2000; Agdag and Sponza, 2005; Valencia
980 Journal of the Air & Waste Management Association, 65(8):980–986, 2015. Copyright © 2015 A&WMA. ISSN: 1096-2247 print DOI: 10.1080/10962247.2015.1051605 Submitted January 27, 2015; final version submitted May 6, 2015; accepted May 8, 2015.
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et al., 2009). There is still a great gap for compositions and collection efficiency between simulation experiments and field studies. This paper aims to investigate the characteristics and annual variations of LFG components (CH4, CO2, H2, H2S, and O2) at two sites with various landfill ages. Meanwhile, climate parameters (ambient temperature and rainfall) are studied to figure out the effects on LFG generation. The emphasis is placed on the similarities and differences between two sites in different phases of anaerobic degradation.
Table 1. The details of the two study areas
Material and Methods
installed in each well for monitoring the gas composition (CH4, CO2, H2, H2S, and O2). The data were transmitted to the control system and stored in the database. The depression of each well was constant. The biogas was collected and pumped into the extraction and purification system. Climate data (ambient temperature and rainfall) were also collected for analyzing their influences on LFG generation. Ambient temperature was measured every day. The rainfall data for each month were obtained from Wuhan Meteorological Bureau, Wuhan, China. Data of ambient temperature and rainfall in 2010 are shown in Figure 2a.
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Site description Chen-Jia-Chong Landfill (30°43′37.03″N, 114°32′35.09″E) is located in Wuhan City of central China. The landfill was opened in 2007 for municipal solid waste (MSW) dumping, acting as one of the biggest sanitary landfill with a high-density polyethylene (HDPE) cap in central China. During the landfilling process, HDPE membrane (1.5 mm) was used as the intermediate cover. Once each landfill cell was finished, the intermediate cover was laid to avoid odor and effects of flies. The average amount of waste disposed at this landfill reaches about 2400 t/day. The landfill is divided into six areas, two of which (A-1 and A-2) were chosen as the study area because of the effective landfill gas collection (Figure 1). The organic matter content of fresh waste ranged from 31% to 47%, and the average moisture content reached 53%. A landfill gas-fired power plant has been in operation based on the biogas from sites A-1 and A-2 since May 2009. The landfill age of site A-1 (from April 2007 to July 2008) was 1.5–3.5 yr and that of site A-2 (from August 2008 to September 2009) was 1–2 yr during the study period of 2010. The details of two sites are presented in Table 1.
Site
Period
A-1
April 2007–July 2008 August 2008– September 2009
A-2
Amount (million ton)
Area Number of (ha) Wells
1.04
6.05
30
1.62
8.65
46
Statistical analysis A number of gas components emitted as LFG were measured, and the emission characteristics of different sites were examined through statistics analysis. Correlation analysis using SPSS (Statistical Product and Service Solutions) 19.0 software (IBM, Armonk, NY, USA) was conducted to analyze the relationship between the gas components (CH4, CO2, H2, H2S, and O2) and the climate parameters (ambient temperature and rainfall). Meanwhile, relationships among gas components were also analyzed. The differences presented were conformed by t test at 95% and 99% confidence levels.
Data collection and pattern There were 30 and 46 wells built for LFG collection at sites A-1 and A-2, respectively. Sensors (biogas sensors; smartGAS, supplied by York Instument Corp., Beijing, China) were
Results and Discussion Comparison of LFG component distribution Shortly after MSW is landfilled, the organic components undergo biochemical reactions. The principal biochemical reaction in landfills is anaerobic degradation, which occurs in three main stages (hydrolysis, acetogenesis, and methanogenesis) that could be divided and extended further to several phases, as shown in Figure 2b (Themelis and Ulloa, 2007; Heyer et al., 2013). In general, LFG concentrations of the same landfill cell were highly variable as a result of the heterogeneity of solid waste in the investigated landfill sites (Chai et al., 2011). The LFG composition (CH4, CO2, H2, and H2S) of two sites with different ages were compared and analyzed in this section.
Variation of CH4 and CO2 contents
Figure 1. Study areas and LFG collection system in Chen-Jia-Chong Landfill.
The variations of CH4 and CO2 at site A-1 and site A-2 are presented in Figure 2c. The CH4 contents ranged from 45.48% to 62.91% and from 14.54% to 65.59% for site A-1 and site A-2, respectively. Both methane contents from A-1 and A-2
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Figure 2. (a) Temperature data and rainfall data during the year 2010. (b) Gas quality during the “life time” of a landfill (Heyer et al., 2013). (c) Annual variations of CH4, CO2, and CH4/CO2 from both sites. (d) Annual variations of H2S, H2, and O2 from both sites.
were in accordance with the data of Figure 2b and kept increasing. Moreover, it is observed that CH4 content of A-2 showed a higher growing rate of 3.51 times than that of A-1 for 36.69% during 2010. As for carbon dioxide, the contents of CO2 ranged from 21.74% to 31.60% and from 22.29% to 31.62% for site A-1 and site A-2, respectively. Both CO2 contents of A-1 and A-2 showed slightly increasing trends. CO2 content of A-1 displayed a more stable curve with smaller fluctuation values (26.03 ± 4.29%). There may be several potential causes that may explain the differences between A-1 and A-2 for CH4 and CO2 variations. A lot of variations in the LFG emission are observed due to hydrogeology of the site and the methods of landfilling (i.e., open dumping or sanitary landfill) (Frid et al., 2010; Kumar et al., 2004). Chen et al. (2008) found that CH4 and CO2 emission rates depended on soil pH, moisture content, pressure, total organic carbon, type and age of the burial waste, type and depth of soil cover, and methane oxidation. In addition, it is reported that 2–3-yr-old landfill had the highest methane and carbon dioxide emission rates, whereas 5-yr-old landfill was the least (Hegde et al., 2003). As for Chen-Jia-Chong Landfill, hydrogeology, pressure, waste composition, and landfilling
method were nearly the same for sites A-1 and A-2. HDPE cover was employed as the temporary and final caps, whereas methane oxidation was only effective in conventional soil covers (Einola et al., 2007; Park et al., 2010; Capaccioni et al., 2011; Chiemchaisri et al., 2011). Accordingly, soil characteristics were unlikely to be the key impact factors. Hence, landfill age could explain the phenomenon above and the differences may be attributed to the different stages of anaerobic reactions. Differences of oxygen concentrations may also explain the above phenomenon. CH4/CO2 of A-2 was found to be lower than that of A-1 from January to June (Figure 2c). MSW in A-2 with higher oxygen concentrations may be attributed to the shorter landfill age. Powell et al. (2006) found that air injection could cause a decrease of CH4/CO2. In other words, lower oxygen concentrations are favorable for higher CH4/CO2. In addition, no similarity of variations was observed between rainfall and CH4/CO2, which should be attributed to the isolation function of HDPE membrane covers (Zhang et al., 2013). In conclusion, site A-1 could be inferred in a stable methane phase and site A-2 was in an unstable methane phase (Figure 2b) approximately. In addition, the CH4/CO2 ratio showed different sensitivities at A-1 and A-2. As reported by
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Capaccioni et al. (2011), the total emission rate appeared well correlated with the CH4/CO2 volumetric ratio. Precisely, the CH4/CO2 volumetric ratio increases up to typical values for a mature LFG (Capaccioni et al., 2011). In this study, CH4/CO2 at A-1 kept a stable value of about 2.00, whereas that at A-2 increased up to nearly 2.00 and then got into a stable state, as shown in Figure 2c. The phenomenon observed in Figure 2c showed great accordance with related literatures. Accordingly, the CH4/CO2 volumetric ratio could act as an excellent indicator for the characteristics of LFG generation.
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Variation of H2S, H2, and O2 contents The variations of H2S, H2, and O2 at site A-1 and site A-2 are illustrated in Figure 2d. The concentrations of H2S ranged from 47.08 to 120.01 ppm and from 81.22 to 215.27 ppm for sites A-1 and A-2, respectively. It was observed that H2S of A-2 presented lower concentrations than that of A-1 from January to June, but higher concentrations from July to December. Overall, H2S of A-2 presented an increasing trend, whereas that of A-1 showed a decreasing trend. In general, H2S concentration is remarkably higher than all the other sulfur compounds and therefore chosen as one of the typical LFG components for investigation (Kim et al., 2005, 2006; Kim, 2006). H2S is produced by sulfate-reducing microorganisms, with a sulfate ion acting as a terminal acceptor and the reaction proceeds at neutral or slightly alkaline pH (Farquhar and Rovers, 1973). As shown in Figure 2d, H2S concentration at A-2 presented an increasing trend with low O2 concentrations, on account of H2S generation in the anaerobic stage reasonably. Moreover, landfill age of MSW could also affect H2S generation. Kim (2006) compared emissions of reduced sulfur compounds from young and old landfill facilities. The results showed that H2S generation had an evident correlation with the landfill age. For H2 concentration, H2 concentrations from both of site A-1 and site A-2 showed decreasing trends. It is obvious that H2 concentration of A-2 was significantly higher than that of A-1 during the whole year. H2 is a typical product of the hydrolytic process in acid phase, as shown in Figure 2b, and forms CH4 and H2O with the addition of CO2 (Farquhar and Rovers, 1973), that is, H2 is produced during the nonmethanogenic stage but consumed during the methanogenic stage. This could explain the downtrend of H2 in the study period for A-1 and A-2. The differences of H2 concentration between A-1 and A-2 could be resulted from the landfill ages and the stages of anaerobic reaction. In addition, O2 of A-2 presented higher concentrations than that of A-1 from January to June, but lower concentrations from July to December. As shown in Figure 2b, O2 would be gradually consumed over time; therefore, the O2 concentrations presented a decreasing trend in both sites. Higher concentrations of O2 at site A-2 from January to June could be attributed to shorter landfill age, whereas lower concentrations at site A-2 from July to December may be explained by fractional air leakage at site A-1, which was caused by the sealing property. Chen et al. (2011) found that the sealing property of the HDPE layer would affect the test results at a landfill of Ningbo, China. Usually, the
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HDPE leakage aggravated with time, and site A-1 had longer landfill age. Hence, It is necessary to keep the maintenance of HDPE to guarantee the sealing property in the long run.
Relationships among LFG components and the external factors As a simple means to investigate the factors affecting LFG emissions, we conducted a correlation analysis of LFG components with the measurement of other parameters (including climate conditions) concurrently. The results of this analysis made for the A-1 and A-2 sites are shown in Table 2, respectively. Both similarities and differences were observed between the two sites. It indicated that the climate parameters (ambient temperature and rainfall) exhibited strong correlations (all of P values were over 0.05) with LFG components at both site A-1 and site A-2. There have been several literatures about climate effects on LFG emissions (Tecle et al., 2009; Uyanik et al., 2012). The influences of atmospheric pressure on landfill methane emissions at landfills with soil covers have been investigated, and notable effects were pointed out by some researchers (Czepiel et al., 2003; Nwachukwu and Anonye, 2013). For 36 hr following a rainfall event, both CH4 and N2O emissions were significantly correlated with moisture content of the cover soil at the two landfill sites without HDPE membrane cover (Zhang et al., 2013). However, the correlations between LFG components and climate parameters were poor in this study, which should be attributed to the isolation function of HDPE membrane covers. It is critical because HDPE can reduce heat loss and injection of water and oxygen into landfills. Chen et al. (2011) found that after welding the HDPE geomembranes together to form a whole airtight layer upon a larger area of landfill, the gas flow in the general pipe increased 25% comparing with the design where the HDPE geomembranes were not welded together, which means that the gas extraction ability improved. Moreover, CH4 contents showed excellent correlations with CO2 at both sites (r = 0.952 and 0.727). The similar phenomenon was also observed in other landfills (Uyanik et al., 2012). The reaction in the anaerobic decomposition releases a very small amount of heat and the product gas mainly contains about 54% methane and 46% carbon dioxide (Themelis and Ulloa, 2007), which could reasonably explain the strong correlations observed above. The significant correlations between oxygen and major components (CH4 and CO2) at both sites are obvious during anaerobic reaction. Landfilled organic waste generates landfill gas (LFG) when it degrades in anaerobic environment (Niskanen et al., 2013). Nevertheless, there were still several differences for composition variations between the two sites. Firstly, H2S and H2 variations showed positive correlations at site A-1, but negative correlations at site A-2. Hydrogen was consumed during the methanogenic stage (Themelis and Ulloa, 2007) and showed a downtrend at both sites (Figure 2d). H2S was produced in the methanogenic stage and reached a peak at a time, then the concentration would get into a slow downward trend (Kim, 2006). Kim (2006) found that the mean value of H2S from a young landfill was 139.07 ppm, whereas its counterparts in an
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Yang et al. / Journal of the Air & Waste Management Association 65 (2015) 980–986 Table 2. Correlation matrix between different parameters at site A-1
Parameter Site A-1 CH4 CO2 H 2S
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H2 O2 CH4/CO2 AT Rainfall Site A-2 CH4 CO2 H 2S H2 O2 CH4/CO2 AT Rainfall
CH4 r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N
CO2
H2S
H2
O2
1 12 0.952** 0.000 12 0.125 0.699 12 −0.315 0.319 12 −0.922** 0.000 12 −0.180 0.575 12 −0.297 0.348 12 −0.351 0.264 12
1 12 −0.030 0.925 12 −0.459 0.134 12 −0.935** 0.000 12 −0.472 0.122 12 −0.127 0.693 12 −0.307 0.332 12
1 12 0.798** 0.002 12 0.133 0.679 12 0.570 0.053 12 −0.327 0.228 12 −0.129 0.690 12
1 12 0.512 0.089 12 0.444 0.149 12 −0.395 0.204 12 −0.003 0.993 12
1 12 0.359 0.252 12 −0.084 0.795 12 0.087 0.788 12
1 12 0.727** 0.007 12 0.730** 0.007 12 −0.921** 0.000 12 −0.976** 0.000 12 0.971** 0.000 12 0.365 0.244 12 0.055 0.864 12
1 12 0.628* 0.029 12 −0.671* 0.017 12 −0.692* 0.013 12 0.547 0.066 12 0.195 0.543 12 0.281 0.376 12
1 12 −0.745** 0.005 12 −0.590* 0.044 12 0.643* 0.024 12 −0.227 0.479 12 −0.186 0.563 12
1 12 0.896** .000 12 −0.892** 0.000 12 −0.190 0.553 12 0.075 0.817 12
Notes: AT = ambient temperature.*Significant at 95% confidence level. **Significant at 99% confidence level.
1 12 −0.963** 0.000 12 −0.488 0.108 12 −0.069 0.832 12
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old landfill being 3.86 ppb. It indicated that H2S generation at site A-1 was decreasing and that at site A-2 was increasing during the study period. Secondly, the correlations between H2S and the major components are significantly positive (r = 0.730 for CH4 and r = 0.628 for CO2) at site A-2, but they exhibited strong correlations (r = 0.125 for CH4 and r = −0.030 for CO2) at site A-1. As pointed out by Kim (2006), no vital correlations were found between H2S and major components (CH4 and CO2) at 5–6-yr-old landfills (stable methane phase). It roughly indicated that H2S acted as a sensitive indicator of LFG emission only in the unstable methane phase. Finally, the CH4/CO2 ratio showed different sensitivities at sites A-1 and A-2. No significant correlation was observed between CH4/ CO2 and major components at site A-1, whereas significant correlation was found at site A-2. The correlation analysis confirmed that it was possible for the operators to judge the characteristics of LFG generation by CH4/CO2.
Conclusions As methane gas can be trapped and used as a green energy source, as is practiced in most of the developed countries, it is important to understand the characteristics, regularities, and mechanisms of the large-scale landfills for power generation applications. In this study, characteristics and annual variations of two sites with different landfill ages were investigated. It was found that the ambient temperature (AT) and rainfall exhibited strong correlations with LFG components at both sites (Table 2). CH4 contents showed excellent correlations with CO2 at both sites. H2 concentrations from both sites showed decreasing trends. In addition, H2S could acted as a sensitive indicator of LFG emission only in unstable methane phase (A-2). Especially, the ratio of CH4/CO2 showed completely different sensitivities to different phases of anaerobic reaction and could act as an excellent indicator for the characteristics of LFG generation. The study of LFG characteristics from sanitary landfills provides information about the field degradation of MSW, which in turn will favor the design and operation of LFG collection and electricity generation facilities.
Funding This work was supported by Program of Natural Science Foundation of China (No. 51278212) and the Fundamental Research Funds for the Central Universities (WUT: 2015IVA026).
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Intergovernmental Panel on Climate Change (IPCC). 2007. Fourth Assessment Report: Climate Change 2007 (AR4). Geneva: IPCC. Kim, K.-H. 2006. Emissions of reduced sulfur compounds (RSC) as a landfill gas (LFG): A comparative study of young and old landfill facilities. Atmos. Environ. 40:6567–6578. doi:10.1016/j.atmosenv.2006.05.063 Kim, K.-H., Y. Choi, E. Jeona, and S. Young. 2005. Characterization of malodorous sulfur compounds in landfill gas. Atmos. Environ. 39:1103– 1112. doi:10.1016/j.atmosenv.2004.09.083 Kim, K.-H., Y.-J. Choi, S.-I. Oh, J.H. Sa, E.-C. Jeon, and Y.S. Koo. 2006. Short-term distributions of reduced sulfur compounds in the ambient air surrounding a large landfill facility. Environ Monit. Assess. 121:343–354. doi:10.1007/s10661-005-9128-y Kumar, S., A.N. Mondal, S.A. Gaikwad, S. Devotta, and R.N. Singh. 2004. Qualitative assessment of methane emission inventory from municipal solid waste disposal sites: A case study. Atmos. Environ. 38:4921–4929. doi:10.1016/j.atmosenv.2004.05.052 Mackie, K.R., and C.D. Cooper. 2009. Landfill gas emission prediction using Voronoi diagrams and importance sampling. Environ. Modell. Softw. 24:1223–1232. doi:10.1016/j.envsoft.2009.04.003 Mata-Alvarez, J., S. Mace, and P. Llabres. 2000. Anaerobic digestion of organic solid wastes. An overview of research achievements and perspectives. Bioresour. Technol. 74:3–16. doi:10.1016/S0960-8524(00)00023-7 Niskanen, A., H. Värri, J. Havukainen, V. Uusitalo, and M. Horttanainen. 2013. Enhancing landfill gas recovery. J. Clean. Prod. 55:67–71. doi:10.1016/j. jclepro.2012.05.042 Nwachukwu, A.N., and D. Anonye. 2013. The effect of atmospheric pressure on CH4 and CO2 emission from a closed landfill site in Manchester, UK. Environ. Monit. Assess. 185:5729–5735. doi:10.1007/s10661-0122979-0 Park, S., K.W. Brown, J.C. Thomas, I.-c. Lee, and K. Sung. 2010. Comparison study of methane emissions from landfills with different landfill covers. Environ. Earth Sci. 60:933–941. doi:10.1007/s12665-009-0229-8 Penteado, R., M. Cavalli, E. Magnano, and F. Chiampo. 2012. Application of the IPCC model to a Brazilian landfill: First results. Energy Policy 42:551– 556. doi:10.1016/j.enpol.2011.12.023 Powell, J., P. Jain, H. Kim, T. Townsend, and D. Reinhart. 2006. Changes in landfill gas quality as a result of controlled air injection. Environ. Sci. Technol. 40:1029–1034. doi:10.1021/es051114j Qin, W., F.N. Egolfopoulos, and T.T. Tsotsis. 2001. Fundamental and environmental aspects of landfill gas utilization for power generation. Chem. Eng. J. 82:157–172. doi:10.1016/S1385-8947(00)00366-1
Raga, R., and R. Cossu. 2013. Bioreactor tests preliminary to landfill in situ aeration: A case study. Waste Manage. 33:871–880. doi:10.1016/j. wasman.2012.11.014 Ritzkowski, M., and R. Stegmann. 2007. Controlling greenhouse gas emissions through landfill in situ aeration. Int. J. Greenhouse Gas Control 1:281–288. doi:10.1016/S1750-5836(07)00029-1 Sadasivam, B.Y., and K.R. Reddy. 2014. Landfill methane oxidation in soil and bio-based cover systems: A review. Rev. Environ. Sci. Biotechnol. 13:79– 107. doi:10.1007/s11157-013-9325-z Shin, H.-C., J.-W. Park, H.-S. Kim, and E.-S. Shin. 2005. Environmental and economic assessment of landfill gas electricity generation in Korea using LEAP model. Energy Policy 33:1261–1270. doi:10.1016/j. enpol.2003.12.002 Tecle, D., J. Lee, and S. Hasan. 2009. Quantitative analysis of physical and geotechnical factors affecting methane emission in municipal solid waste landfill. Environ. Geol. 56:1135–1143. doi:10.1007/s00254-008-1214-3 Themelis, N.J., and P.A. Ulloa. 2007. Methane generation in landfills. Renew. Energy 32:1243–1257. doi:10.1016/j.renene.2006.04.020 Uyanik, I., B. Ozkaya, S. Demir, and M. Cakmakci. 2012. Meteorological parameters as an important factor on the energy recovery of landfill gas in landfills. J. Renew. Sustain. Energy 4:063135. doi:10.1063/1.4769202 Valencia, R., W.v.d. Zon, H. Woelders, H.J. Lubberding, and H.J. Gijzen. 2009. The effect of hydraulic conditions on waste stabilisation in bioreactor landfill simulators. Bioresour. Technol. 100: 1754–1761. doi:10.1016/j. biortech.2008.09.055 Zhang, H., X. Yan, Z. Cai, and Y. Zhang. 2013. Effect of rainfall on the diurnal variations of CH4, CO2, and N2O fluxes from a municipal solid waste landfill. Sci. Total Environ. 442:73–76. doi:10.1016/j. scitotenv.2012.10.041
About the Authors Lie Yang and Yanyan Liu are lecturers of School of Resources and Environmental Engineering, Wuhan University of Technology. Zhulei Chen works for the School of Environmental Science & Engineering in the Huazhong University of Science and Technology. Xiong Zhang and Ying Xie are affiliated with the Wuhan Environmental Investment and Development Co., Ltd.
ISSN: 1096-2247 (Print) 2162-2906 (Online) Journal homepage: http://www.tandfonline.com/loi/uawm20
Comparison study of landfill gas emissions from subtropical landfill with various phases: A case study in Wuhan, China Lie Yang, Zhulei Chen, Xiong Zhang, Yanyan Liu & Ying Xie To cite this article: Lie Yang, Zhulei Chen, Xiong Zhang, Yanyan Liu & Ying Xie (2015) Comparison study of landfill gas emissions from subtropical landfill with various phases: A case study in Wuhan, China, Journal of the Air & Waste Management Association, 65:8, 980-986, DOI: 10.1080/10962247.2015.1051605 To link to this article: http://dx.doi.org/10.1080/10962247.2015.1051605
Accepted author version posted online: 01 Jun 2015.
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Date: 04 November 2015, At: 00:44
TECHNICAL PAPER
Comparison study of landfill gas emissions from subtropical landfill with various phases: A case study in Wuhan, China Lie Yang,1,⁄ Zhulei Chen,2,⁄ Xiong Zhang,3 Yanyan Liu,1 and Ying Xie3 1
School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan, People’s Republic of China School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, People’s Republic of China 3 Wuhan Environmental Investment and Development Co. Ltd., Wuhan, People’s Republic of China ⁄ Please address correspondence to: Lie Yang, School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, People’s Republic of China; e-mail: [email protected]; or to Zhulei Chen, School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China; e-mail: [email protected]
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The compositions and annual variations of landfill gas (LFG) were studied at two large-scale sites of Chen-Jia-Chong Landfill. Seventy-six wells were built and used for the collection and measurement of LFG. The investigation revealed the similarities and differences of LFG components and variations at two sites with different phases. It was found that ambient temperature and rainfall exhibited strong correlations with LFG components at both sites. Methane (CH4) contents showed excellent correlations with CO2 at both sites. Notable correlations between hydrogen sulfide (H2S) and major components (CH4 and carbon dioxide [CO2]) were only observed in unstable methane phase. Especially, the CH4/CO2 volumetric ratio could act as an excellent indicator for anaerobic reaction stage by judging its phasic variations. The study is beneficial for the efficient operation of LFG collection system and could shed light on gas purification and utilization. Implications: The results in this paper could provide some beneficial information for landfill operators. Especially, the CH4/CO2 volumetric ratio could act as an excellent indicator for anaerobic reaction stage by judging its phasic variations. Moreover, the study could shed light on landfill gas purification and utilization.
Introduction Landfill is the most predominant method for municipal solid waste (MSW) disposal in most countries. However, a number of previous studies in the last two decades have indicated that landfill may impose a threat to the environment and human health due to the generation of landfill gas and leachate. Municipal solid waste (MSW) in landfills decomposes and produces methane (CH4) and carbon dioxide (CO2) gases, trace amount of toxic substances, and bad odor, which are the by-products of the decomposition (Shin et al., 2005). Landfill gas is ranked as the third highest source of global anthropogenic methane emissions, responsible for approximately 9–12% of those emissions in 2005 (Intergovernmental Panel on Climate Change [IPCC], 2007). In particular, the potential contribution of methane to the global warming is 21 times higher than that of carbon dioxide (Gewald et al., 2012). Carbon emission reduction has become a global issue with the increase of methane and carbon dioxide emissions. In recent years, there are generally four approaches for dealing with methane. Firstly, modified-soil covers are applied to promote methane oxidation (Einola et al., 2007; Chiemchaisri et al., 2011; Sadasivam and Reddy, 2014) and aeration is used to reduce
methane production (Ritzkowski and Stegmann, 2007; Raga and Cossu, 2013). Secondly, separate collection of organics before landfilling could efficiently reduce methane emission from landfills (Calabrò, 2009; Bernstad and Jansen, 2012). Thirdly, mechanical biological pretreatment was proven to reduce the gas generation potential and leachate strength of the residue (Bayard et al., 2008; Calabrò et al., 2011). In addition, landfill gas (LFG) is efficiently collected and used as bioenergy for electricity generation (Qin et al., 2001; Bove and Lunghi, 2006; Aguilar-Virgen et al., 2014). Overall, the application of LFG on power generation is more environmentally friendly and sustainable as a potential clean energy. Although varieties of models were applied to estimate the potential energy utilization from landfills (Mackie and Cooper, 2009; Gregg, 2010; Amini and Reinhart, 2011; Penteado et al., 2012), the acknowledgment of the MSW field degradation is indispensable, especially for large-scale landfills. The LFG collection system efficiency varies by the configuration of the system installed (e.g., type, active or passive, number of wells) and by operation management (depression intensity) (Calabrò, 2009). The performance of MSW anaerobic degradation has been investigated using the simulation experiments (MataAlvarez et al., 2000; Agdag and Sponza, 2005; Valencia
980 Journal of the Air & Waste Management Association, 65(8):980–986, 2015. Copyright © 2015 A&WMA. ISSN: 1096-2247 print DOI: 10.1080/10962247.2015.1051605 Submitted January 27, 2015; final version submitted May 6, 2015; accepted May 8, 2015.
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et al., 2009). There is still a great gap for compositions and collection efficiency between simulation experiments and field studies. This paper aims to investigate the characteristics and annual variations of LFG components (CH4, CO2, H2, H2S, and O2) at two sites with various landfill ages. Meanwhile, climate parameters (ambient temperature and rainfall) are studied to figure out the effects on LFG generation. The emphasis is placed on the similarities and differences between two sites in different phases of anaerobic degradation.
Table 1. The details of the two study areas
Material and Methods
installed in each well for monitoring the gas composition (CH4, CO2, H2, H2S, and O2). The data were transmitted to the control system and stored in the database. The depression of each well was constant. The biogas was collected and pumped into the extraction and purification system. Climate data (ambient temperature and rainfall) were also collected for analyzing their influences on LFG generation. Ambient temperature was measured every day. The rainfall data for each month were obtained from Wuhan Meteorological Bureau, Wuhan, China. Data of ambient temperature and rainfall in 2010 are shown in Figure 2a.
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Site description Chen-Jia-Chong Landfill (30°43′37.03″N, 114°32′35.09″E) is located in Wuhan City of central China. The landfill was opened in 2007 for municipal solid waste (MSW) dumping, acting as one of the biggest sanitary landfill with a high-density polyethylene (HDPE) cap in central China. During the landfilling process, HDPE membrane (1.5 mm) was used as the intermediate cover. Once each landfill cell was finished, the intermediate cover was laid to avoid odor and effects of flies. The average amount of waste disposed at this landfill reaches about 2400 t/day. The landfill is divided into six areas, two of which (A-1 and A-2) were chosen as the study area because of the effective landfill gas collection (Figure 1). The organic matter content of fresh waste ranged from 31% to 47%, and the average moisture content reached 53%. A landfill gas-fired power plant has been in operation based on the biogas from sites A-1 and A-2 since May 2009. The landfill age of site A-1 (from April 2007 to July 2008) was 1.5–3.5 yr and that of site A-2 (from August 2008 to September 2009) was 1–2 yr during the study period of 2010. The details of two sites are presented in Table 1.
Site
Period
A-1
April 2007–July 2008 August 2008– September 2009
A-2
Amount (million ton)
Area Number of (ha) Wells
1.04
6.05
30
1.62
8.65
46
Statistical analysis A number of gas components emitted as LFG were measured, and the emission characteristics of different sites were examined through statistics analysis. Correlation analysis using SPSS (Statistical Product and Service Solutions) 19.0 software (IBM, Armonk, NY, USA) was conducted to analyze the relationship between the gas components (CH4, CO2, H2, H2S, and O2) and the climate parameters (ambient temperature and rainfall). Meanwhile, relationships among gas components were also analyzed. The differences presented were conformed by t test at 95% and 99% confidence levels.
Data collection and pattern There were 30 and 46 wells built for LFG collection at sites A-1 and A-2, respectively. Sensors (biogas sensors; smartGAS, supplied by York Instument Corp., Beijing, China) were
Results and Discussion Comparison of LFG component distribution Shortly after MSW is landfilled, the organic components undergo biochemical reactions. The principal biochemical reaction in landfills is anaerobic degradation, which occurs in three main stages (hydrolysis, acetogenesis, and methanogenesis) that could be divided and extended further to several phases, as shown in Figure 2b (Themelis and Ulloa, 2007; Heyer et al., 2013). In general, LFG concentrations of the same landfill cell were highly variable as a result of the heterogeneity of solid waste in the investigated landfill sites (Chai et al., 2011). The LFG composition (CH4, CO2, H2, and H2S) of two sites with different ages were compared and analyzed in this section.
Variation of CH4 and CO2 contents
Figure 1. Study areas and LFG collection system in Chen-Jia-Chong Landfill.
The variations of CH4 and CO2 at site A-1 and site A-2 are presented in Figure 2c. The CH4 contents ranged from 45.48% to 62.91% and from 14.54% to 65.59% for site A-1 and site A-2, respectively. Both methane contents from A-1 and A-2
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Figure 2. (a) Temperature data and rainfall data during the year 2010. (b) Gas quality during the “life time” of a landfill (Heyer et al., 2013). (c) Annual variations of CH4, CO2, and CH4/CO2 from both sites. (d) Annual variations of H2S, H2, and O2 from both sites.
were in accordance with the data of Figure 2b and kept increasing. Moreover, it is observed that CH4 content of A-2 showed a higher growing rate of 3.51 times than that of A-1 for 36.69% during 2010. As for carbon dioxide, the contents of CO2 ranged from 21.74% to 31.60% and from 22.29% to 31.62% for site A-1 and site A-2, respectively. Both CO2 contents of A-1 and A-2 showed slightly increasing trends. CO2 content of A-1 displayed a more stable curve with smaller fluctuation values (26.03 ± 4.29%). There may be several potential causes that may explain the differences between A-1 and A-2 for CH4 and CO2 variations. A lot of variations in the LFG emission are observed due to hydrogeology of the site and the methods of landfilling (i.e., open dumping or sanitary landfill) (Frid et al., 2010; Kumar et al., 2004). Chen et al. (2008) found that CH4 and CO2 emission rates depended on soil pH, moisture content, pressure, total organic carbon, type and age of the burial waste, type and depth of soil cover, and methane oxidation. In addition, it is reported that 2–3-yr-old landfill had the highest methane and carbon dioxide emission rates, whereas 5-yr-old landfill was the least (Hegde et al., 2003). As for Chen-Jia-Chong Landfill, hydrogeology, pressure, waste composition, and landfilling
method were nearly the same for sites A-1 and A-2. HDPE cover was employed as the temporary and final caps, whereas methane oxidation was only effective in conventional soil covers (Einola et al., 2007; Park et al., 2010; Capaccioni et al., 2011; Chiemchaisri et al., 2011). Accordingly, soil characteristics were unlikely to be the key impact factors. Hence, landfill age could explain the phenomenon above and the differences may be attributed to the different stages of anaerobic reactions. Differences of oxygen concentrations may also explain the above phenomenon. CH4/CO2 of A-2 was found to be lower than that of A-1 from January to June (Figure 2c). MSW in A-2 with higher oxygen concentrations may be attributed to the shorter landfill age. Powell et al. (2006) found that air injection could cause a decrease of CH4/CO2. In other words, lower oxygen concentrations are favorable for higher CH4/CO2. In addition, no similarity of variations was observed between rainfall and CH4/CO2, which should be attributed to the isolation function of HDPE membrane covers (Zhang et al., 2013). In conclusion, site A-1 could be inferred in a stable methane phase and site A-2 was in an unstable methane phase (Figure 2b) approximately. In addition, the CH4/CO2 ratio showed different sensitivities at A-1 and A-2. As reported by
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Capaccioni et al. (2011), the total emission rate appeared well correlated with the CH4/CO2 volumetric ratio. Precisely, the CH4/CO2 volumetric ratio increases up to typical values for a mature LFG (Capaccioni et al., 2011). In this study, CH4/CO2 at A-1 kept a stable value of about 2.00, whereas that at A-2 increased up to nearly 2.00 and then got into a stable state, as shown in Figure 2c. The phenomenon observed in Figure 2c showed great accordance with related literatures. Accordingly, the CH4/CO2 volumetric ratio could act as an excellent indicator for the characteristics of LFG generation.
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Variation of H2S, H2, and O2 contents The variations of H2S, H2, and O2 at site A-1 and site A-2 are illustrated in Figure 2d. The concentrations of H2S ranged from 47.08 to 120.01 ppm and from 81.22 to 215.27 ppm for sites A-1 and A-2, respectively. It was observed that H2S of A-2 presented lower concentrations than that of A-1 from January to June, but higher concentrations from July to December. Overall, H2S of A-2 presented an increasing trend, whereas that of A-1 showed a decreasing trend. In general, H2S concentration is remarkably higher than all the other sulfur compounds and therefore chosen as one of the typical LFG components for investigation (Kim et al., 2005, 2006; Kim, 2006). H2S is produced by sulfate-reducing microorganisms, with a sulfate ion acting as a terminal acceptor and the reaction proceeds at neutral or slightly alkaline pH (Farquhar and Rovers, 1973). As shown in Figure 2d, H2S concentration at A-2 presented an increasing trend with low O2 concentrations, on account of H2S generation in the anaerobic stage reasonably. Moreover, landfill age of MSW could also affect H2S generation. Kim (2006) compared emissions of reduced sulfur compounds from young and old landfill facilities. The results showed that H2S generation had an evident correlation with the landfill age. For H2 concentration, H2 concentrations from both of site A-1 and site A-2 showed decreasing trends. It is obvious that H2 concentration of A-2 was significantly higher than that of A-1 during the whole year. H2 is a typical product of the hydrolytic process in acid phase, as shown in Figure 2b, and forms CH4 and H2O with the addition of CO2 (Farquhar and Rovers, 1973), that is, H2 is produced during the nonmethanogenic stage but consumed during the methanogenic stage. This could explain the downtrend of H2 in the study period for A-1 and A-2. The differences of H2 concentration between A-1 and A-2 could be resulted from the landfill ages and the stages of anaerobic reaction. In addition, O2 of A-2 presented higher concentrations than that of A-1 from January to June, but lower concentrations from July to December. As shown in Figure 2b, O2 would be gradually consumed over time; therefore, the O2 concentrations presented a decreasing trend in both sites. Higher concentrations of O2 at site A-2 from January to June could be attributed to shorter landfill age, whereas lower concentrations at site A-2 from July to December may be explained by fractional air leakage at site A-1, which was caused by the sealing property. Chen et al. (2011) found that the sealing property of the HDPE layer would affect the test results at a landfill of Ningbo, China. Usually, the
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HDPE leakage aggravated with time, and site A-1 had longer landfill age. Hence, It is necessary to keep the maintenance of HDPE to guarantee the sealing property in the long run.
Relationships among LFG components and the external factors As a simple means to investigate the factors affecting LFG emissions, we conducted a correlation analysis of LFG components with the measurement of other parameters (including climate conditions) concurrently. The results of this analysis made for the A-1 and A-2 sites are shown in Table 2, respectively. Both similarities and differences were observed between the two sites. It indicated that the climate parameters (ambient temperature and rainfall) exhibited strong correlations (all of P values were over 0.05) with LFG components at both site A-1 and site A-2. There have been several literatures about climate effects on LFG emissions (Tecle et al., 2009; Uyanik et al., 2012). The influences of atmospheric pressure on landfill methane emissions at landfills with soil covers have been investigated, and notable effects were pointed out by some researchers (Czepiel et al., 2003; Nwachukwu and Anonye, 2013). For 36 hr following a rainfall event, both CH4 and N2O emissions were significantly correlated with moisture content of the cover soil at the two landfill sites without HDPE membrane cover (Zhang et al., 2013). However, the correlations between LFG components and climate parameters were poor in this study, which should be attributed to the isolation function of HDPE membrane covers. It is critical because HDPE can reduce heat loss and injection of water and oxygen into landfills. Chen et al. (2011) found that after welding the HDPE geomembranes together to form a whole airtight layer upon a larger area of landfill, the gas flow in the general pipe increased 25% comparing with the design where the HDPE geomembranes were not welded together, which means that the gas extraction ability improved. Moreover, CH4 contents showed excellent correlations with CO2 at both sites (r = 0.952 and 0.727). The similar phenomenon was also observed in other landfills (Uyanik et al., 2012). The reaction in the anaerobic decomposition releases a very small amount of heat and the product gas mainly contains about 54% methane and 46% carbon dioxide (Themelis and Ulloa, 2007), which could reasonably explain the strong correlations observed above. The significant correlations between oxygen and major components (CH4 and CO2) at both sites are obvious during anaerobic reaction. Landfilled organic waste generates landfill gas (LFG) when it degrades in anaerobic environment (Niskanen et al., 2013). Nevertheless, there were still several differences for composition variations between the two sites. Firstly, H2S and H2 variations showed positive correlations at site A-1, but negative correlations at site A-2. Hydrogen was consumed during the methanogenic stage (Themelis and Ulloa, 2007) and showed a downtrend at both sites (Figure 2d). H2S was produced in the methanogenic stage and reached a peak at a time, then the concentration would get into a slow downward trend (Kim, 2006). Kim (2006) found that the mean value of H2S from a young landfill was 139.07 ppm, whereas its counterparts in an
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Yang et al. / Journal of the Air & Waste Management Association 65 (2015) 980–986 Table 2. Correlation matrix between different parameters at site A-1
Parameter Site A-1 CH4 CO2 H 2S
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H2 O2 CH4/CO2 AT Rainfall Site A-2 CH4 CO2 H 2S H2 O2 CH4/CO2 AT Rainfall
CH4 r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N r P N
CO2
H2S
H2
O2
1 12 0.952** 0.000 12 0.125 0.699 12 −0.315 0.319 12 −0.922** 0.000 12 −0.180 0.575 12 −0.297 0.348 12 −0.351 0.264 12
1 12 −0.030 0.925 12 −0.459 0.134 12 −0.935** 0.000 12 −0.472 0.122 12 −0.127 0.693 12 −0.307 0.332 12
1 12 0.798** 0.002 12 0.133 0.679 12 0.570 0.053 12 −0.327 0.228 12 −0.129 0.690 12
1 12 0.512 0.089 12 0.444 0.149 12 −0.395 0.204 12 −0.003 0.993 12
1 12 0.359 0.252 12 −0.084 0.795 12 0.087 0.788 12
1 12 0.727** 0.007 12 0.730** 0.007 12 −0.921** 0.000 12 −0.976** 0.000 12 0.971** 0.000 12 0.365 0.244 12 0.055 0.864 12
1 12 0.628* 0.029 12 −0.671* 0.017 12 −0.692* 0.013 12 0.547 0.066 12 0.195 0.543 12 0.281 0.376 12
1 12 −0.745** 0.005 12 −0.590* 0.044 12 0.643* 0.024 12 −0.227 0.479 12 −0.186 0.563 12
1 12 0.896** .000 12 −0.892** 0.000 12 −0.190 0.553 12 0.075 0.817 12
Notes: AT = ambient temperature.*Significant at 95% confidence level. **Significant at 99% confidence level.
1 12 −0.963** 0.000 12 −0.488 0.108 12 −0.069 0.832 12
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old landfill being 3.86 ppb. It indicated that H2S generation at site A-1 was decreasing and that at site A-2 was increasing during the study period. Secondly, the correlations between H2S and the major components are significantly positive (r = 0.730 for CH4 and r = 0.628 for CO2) at site A-2, but they exhibited strong correlations (r = 0.125 for CH4 and r = −0.030 for CO2) at site A-1. As pointed out by Kim (2006), no vital correlations were found between H2S and major components (CH4 and CO2) at 5–6-yr-old landfills (stable methane phase). It roughly indicated that H2S acted as a sensitive indicator of LFG emission only in the unstable methane phase. Finally, the CH4/CO2 ratio showed different sensitivities at sites A-1 and A-2. No significant correlation was observed between CH4/ CO2 and major components at site A-1, whereas significant correlation was found at site A-2. The correlation analysis confirmed that it was possible for the operators to judge the characteristics of LFG generation by CH4/CO2.
Conclusions As methane gas can be trapped and used as a green energy source, as is practiced in most of the developed countries, it is important to understand the characteristics, regularities, and mechanisms of the large-scale landfills for power generation applications. In this study, characteristics and annual variations of two sites with different landfill ages were investigated. It was found that the ambient temperature (AT) and rainfall exhibited strong correlations with LFG components at both sites (Table 2). CH4 contents showed excellent correlations with CO2 at both sites. H2 concentrations from both sites showed decreasing trends. In addition, H2S could acted as a sensitive indicator of LFG emission only in unstable methane phase (A-2). Especially, the ratio of CH4/CO2 showed completely different sensitivities to different phases of anaerobic reaction and could act as an excellent indicator for the characteristics of LFG generation. The study of LFG characteristics from sanitary landfills provides information about the field degradation of MSW, which in turn will favor the design and operation of LFG collection and electricity generation facilities.
Funding This work was supported by Program of Natural Science Foundation of China (No. 51278212) and the Fundamental Research Funds for the Central Universities (WUT: 2015IVA026).
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About the Authors Lie Yang and Yanyan Liu are lecturers of School of Resources and Environmental Engineering, Wuhan University of Technology. Zhulei Chen works for the School of Environmental Science & Engineering in the Huazhong University of Science and Technology. Xiong Zhang and Ying Xie are affiliated with the Wuhan Environmental Investment and Development Co., Ltd.
