مرکز منطقه ای اطلاع رساني علوم و فناوري - ميزان تأثير رطوبت، بر نرخ توليد آلاينده در لندفيل ها و كنترل آلاينده هاي خروجي با استفاده از سرپوش

چكيده لاتين :

Municipal solid waste (MSW) landfills are generally operated by conventional landfilling methods, where anaerobic conditions are created within the landfill waste. MSW in a landfill undergoes a number of interrelated biological, chemical and physical changes. The most important biological reactions occurring in landfills are those involving the organic material in MSW that lead to the evolution of landfill gas and liquids. The biological decomposition process usually proceeds aerobically for some short period immediately after the deposition of the waste until oxygen initially present is depleted. Carbon dioxide is the principal gas produced during aerobic decomposition. Once the available oxygen has been consumed, the decomposition becomes anaerobic and the organic matter is converted to CQ, CH4 and non-methane volatile organic compounds. In this study, Saravan landfill which is located in Gilan-Iran has been investigated. One of the significant features of Saravan landfill is its high moisture location which causes to heighten the amount of landfill gas. According to data of Saravan Synoptic station, Saravan landfill is located in wet area that annual precipitation is about 1446.5 mm. Moreover its mean Relative Humidity (RH) is greater than %77. For estimating emission landfill gas and pollutions in addition of meteorological parameters, the amount of MSW should be considerate. Saravan landfill opened in 1984 and continues land filling MSW till now in ascending order. According to the statistical data the amount of land filled MSW was 100 and 500 Tons per day in 1984 and 2008 respectively. By considering this growth and received data from recycling organization of Gilan the amount of entering wastes can be estimated. The Landfill Gas Emissions Model (Land GEM) as an automated estimation tool is used to estimate emission rates for total landfill gas, methane, carbon dioxide, non-methane organic compounds, and individual air pollutants from Saravan landfill. For understanding the effect of moisture at landfill gas production, these gases are estimated by Land GEM model in two different conditions. In the first condition the amount of generated gases are estimated with respect to the weather aspect of the location which the landfill is located. In the second condition these gases are estimated in a dry area and with these result the effect of the moisture on the produced gases can be calculated. Land GEM uses the following first-order decomposition rate equation (eq.l) to estimate annual emissions over a time period. n f yt Eq-l QcH4 = £KL0M i=l U"/ Where: Qch4« 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 (year1) Zoqi, M. and Saeedi, M. L0: potential methane generation capacity (m /Mg) Mi: mass of waste accepted in the ith year (Mg) tij.- age of the jth section of waste mass Mi accepted in the ith year The Methane Generation Rate, k, determines the rate of methane generation for the waste mass in the landfill. The higher the value of k, the faster the methane generation rate increases and then decays over time. The value of k is a function of moisture content of the waste mass. In this study, to estimate actual emissions in the absence of site-specific data, the inventory default values is used for, k, value. The k value is 0.7 and 0.04 (year-1) for wet condition (without multilayer cap) and dry condition (with multilayer cap) respectively. The Potential Methane Generation Capacity (L0) depends only on the type and composition of waste placed in the landfill. The higher the cellulose content of the waste, the higher the value of Lo. For the calculation of the biogas generation potential in the landfill, the Intergovernmental Panel on Climate Change (IPCC 1996) methodology equation (eq.2) was used. (—) = MCF x DOC x DOCF x F x 1482.8 Mg Where: MCF: methane correction factor (%) =1.0 for sanitary landfill DOC: degradable organic carbon fraction DOCF: dissolved DOC fraction =0.77 for sanitary landfill F: methane fraction in the landfill gas Degradable organic carbon fraction (DOC) is based on the composition of the waste. DOC is estimated from a weighted average of the carbon content of various components of the waste stream. IPCC guidelines gives default values for the carbon content for various waste types. These values and percentages of the waste compositions in Saravan landfill are presented in Table(l).This composition was used to estimate the degradable organic fraction of the landfill waste (Table 1). Waste type Percentage Percent DOC by Weigh DOC Wood 6/6 30 0/02 Paper fl\X 40 0/05 Organic compounds 76/3 16 1220 Textiles 407 40 0190 Total 100 0/211 According to Table (1), the amount of DOC will be 0.211. By considering the DOC amount and the Eq.2 the potential methane generation capacity (L0) will be 96.4 (m3/Mg) in Land GEM model. The amount of methane and carbon dioxide emission have been estimated by Land GEM model in wet condition which is shown in figure 1. The maximum of methane and carbon dioxide emission were occurred in 2008 with the amount of 11700 and 32110 tons respectively. The most generation of Non-methane volatile organic compounds (NMVOCs) have been occurred in 2009 with the amount of 500 tones (figure 2). By considering the danger of these compounds for environment, according to the U.S environmental protection agency if the amount of these compounds exceeds 50 tons per year methane gases should be flared. The amount of methane and carbon dioxide emission that have been shown in figure3 are estimated in a dry area. The maximum amount for methane emission is 3043 tons per year and this amount is 8349 tons per year for carbon dioxide emission. The amount of NMVOC generating in the landfill in dry condition has been shown in figure4 and its maximum production is 130 tons per year. Zoqi, M. and Saeedi, M. L0: potential methane generation capacity (m /Mg) Mi: mass of waste accepted in the ith year (Mg) tij.- age of the jth section of waste mass Mi accepted in the ith year The Methane Generation Rate, k, determines the rate of methane generation for the waste mass in the landfill. The higher the value of k, the faster the methane generation rate increases and then decays over time. The value of k is a function of moisture content of the waste mass. In this study, to estimate actual emissions in the absence of site-specific data, the inventory default values is used for, k, value. The k value is 0.7 and 0.04 (year-1) for wet condition (without multilayer cap) and dry condition (with multilayer cap) respectively. The Potential Methane Generation Capacity (L0) depends only on the type and composition of waste placed in the landfill. The higher the cellulose content of the waste, the higher the value of Lo. For the calculation of the biogas generation potential in the landfill, the Intergovernmental Panel on Climate Change (IPCC 1996) methodology equation (eq.2) was used. (—) = MCF x DOC x DOCF x F x 1482.8 Mg Where: MCF: methane correction factor (%) =1.0 for sanitary landfill DOC: degradable organic carbon fraction DOCF: dissolved DOC fraction =0.77 for sanitary landfill F: methane fraction in the landfill gas Degradable organic carbon fraction (DOC) is based on the composition of the waste. DOC is estimated from a weighted average of the carbon content of various components of the waste stream. IPCC guidelines gives default values for the carbon content for various waste types. These values and percentages of the waste compositions in Saravan landfill are presented in Table(l).This composition was used to estimate the degradable organic fraction of the landfill waste (Table 1). Waste type Percentage Percent DOC by Weigh DOC Wood 6/6 30 0/02 Paper fl\X 40 0/05 Organic compounds 76/3 16 1220 Textiles 407 40 0190 Total 100 0/211 According to Table (1), the amount of DOC will be 0.211. By considering the DOC amount and the Eq.2 the potential methane generation capacity (L0) will be 96.4 (m3/Mg) in Land GEM model. The amount of methane and carbon dioxide emission have been estimated by Land GEM model in wet condition which is shown in figure 1. The maximum of methane and carbon dioxide emission were occurred in 2008 with the amount of 11700 and 32110 tons respectively. The most generation of Non-methane volatile organic compounds (NMVOCs) have been occurred in 2009 with the amount of 500 tones (figure 2). By considering the danger of these compounds for environment, according to the U.S environmental protection agency if the amount of these compounds exceeds 50 tons per year methane gases should be flared. The amount of methane and carbon dioxide emission that have been shown in figure3 are estimated in a dry area. The maximum amount for methane emission is 3043 tons per year and this amount is 8349 tons per year for carbon dioxide emission. The amount of NMVOC generating in the landfill in dry condition has been shown in figure4 and its maximum production is 130 tons per year.