Nigerian Journal of Technology (NIJOTECH) Vol. 33. No. 1, January2014, pp. 49-53 Copyright© Faculty of Engineering, University of Nigeria, Nsukka, ISSN: 1115-8443 www.nijotech.com http://dx.doi.Org/10.4314/nit.v33i1.7 METHANE GENERATION POTENTIAL OF MUNICIPAL SOLID WASTE IN IBADAN F. O. Akintayo1- *, O. A. Olonisakin21 2 Department of Civil Engineering, University of Ibadan, Ibadan, NIGERIA E-m ail addresses:1 fo.akintayo@ ui.edu.ng,2 dunsinolonisakin@gmail.comAbstract Energy potential from Municipal Solid Waste (MSW) o f two landfills serving four local government areas in Ibadan metropolis was estimated in this study. The characterization o f the M SW showed that approximately 74% is made up o f organic materials with food wastes constituting the highest portion (35%). The energy content o f the waste is evaluated as 13,022KJ/kg. The methane potential o f the MSW between 2012 and2020 is estimated to be 27,517 tonnes using the Intergovernmental Panel on Climate Change (IPCC) methodology. The gas when collected can be used as alternative energy source for small and medium enterprises in the locality. Keywords: Methane emission, Municipal Solid Waste, Landfills, Energy content, Alternative Energy 1.0 IntroductionThe limited nature of petroleum resources across the globe and the attendant social and environmental effect of its consumption have made many developed and developing nations to explore other energy sources. Recently, renewable energy resources like wind and solar have gained global attention due to their sustainability. Materials such as crop residues, wood residues, biomass from processing industries have all been studied in the past as possible sources of alternative energy as they all possess the ability to reduce our over dependence on fossil fuels [1]. Another of such renewable energy resources is the landfill gas (LFG) which is obtained from the emission of methane and other accompanying gasses from municipal solid waste (MSW) dumpsites. This can be collected and utilized as a green energy source as millions of tons of MSW end up in sanitary landfills (controlled and uncontrolled) daily around the world. Due to the high organic content of municipal solid wastes, biological degradation occurs under anaerobic condition which leads to the production of a combination of gasses collectively called LFG. This process may continue for 20 to 50 years after initial dumping of the MSW. LFG is known to be produced in both managed landfill and open dumpsites. The major constituents of LFG include methane (50% - 60%) and carbon dioxide (40% - 60%) which are also key greenhouse gases with trace concentration of other non-methane organic compounds (NMOCs) such as mercaptans, hydrogen sulphide and other organic compounds[2].The collection and utilization of the methane component of LFG presents a viable and valuable source of renewable energy and an opportunity to reduce the migration of a major greenhouse gas (methane) into the atmosphere thus mitigating the effect of global climate change [3]. Reducing methane emissions by capturing LFG and using it as an energy source can yield substantial energy, economic, and environmental benefits. This is an option that needs to be brought to the fore by relevant stakeholders in the Nigerian energy sector as we continue to witness an upsurge in electricity self-generation which comes with its own environmental and economical implications [4]. In addition, it will address some of the problems associated with solid waste management in a developing country like Nigeria [5].The methane potential of open dumpsites in Ibadan metropolis, Nigeria was therefore investigated in this study. * Corresponding author, Tel: +23-8038310210 UNIV ERSIT Y O F IB ADAN L IB RARY http://www.nijotech.com http://dx.doi.Org/10.4314/nit.v33i1.7 mailto:dunsinolonisakin@gmail.com Methane Generation Potential Of Municipal Solid Waste In Ibadan F. O. Akintayo & O. A. Olonisakin 2.0 Methodology 2.1 Waste characterizationRepresentative samples of MSW were collected randomly from Awotan and Apete dumpsites in Ibadan metropolis in December, 2012. Field visits and preliminary survey revealed that Awotan dumpsite lies on an approximate 25-hectare land while Lapite dumpsite sits on a 20-hectare landmass. However, a large portion of both sites is yet to be put to use as only a fraction (approximately one-quarter) of each site was in use as at the time of this study. The two open dumpsites serve four local government areas: Ido, Ibadan North, Akinyele and Ibadan North­East. The projected total population of the areas in 2012 is approximately 1.2 million people. The amount of waste currently disposed per day at the dumpsites was estimated 171 tonnes using MSW generation rate of 0.71Kg/capital/day [6] and a municipal solid waste factor (MSWf) of 74% (0.74) [7].Characterization was carried out based on ASTMD 5231-92 (Standard Test Method for Determination of the Composition of Unprocessed Municipal Solid Waste) [8]. The MSW sample was homogenized by dividing the total sample into four portions and discarding two portions, then repeating the procedure until a significant weight sample of 100 kg was obtained. The waste was sorted into individual components such as food wastes, paper/cardboard, wood and plastic. The weights of the components were measured and the moisture content determined upon drying at 105oC to a constant weight. 2 2 Ultimate analysisThe ultimate analysis involves determination of mass percentage of carbon (C), nitrogen (N), hydrogen (H), oxygen (0), sulphur (S) and ash content of the individual components of the MSW. This was carried out using methods stated in ASTMD 3174-3176 (StandardTest Method for Ash in the Analysis Sample of Coal and Coke from Coal) [9]. Chemical composition of the MSW resulting from the ultimate analysis was obtained and recorded. 2.3 Energy contentThe energy content of MSW was evaluated using the modified Dulong formula [10] given in Equation (1). This is the high heating value (HHV) from the total combustion of the waste. Kl = 337N + 1428Op - R T + 95U (1)In (1), Qh is the energy content (KJ/Kg), C is the percentage carbon, H is the percentage hydrogen, 0 is the percentage oxygen and S the percentage sulphur.The low heating value (LHV) which has been suggested a better measure of heat released by the waste under actual operating conditions [11], is evaluated using Equation (2) [12].WPX = P P X - 0.0244(Y + 9P) (2)Where LHV is the low heating value (MJ/kg), HHV is the high heating value (MJ/kg).M and H represent the percentages of moisture and hydrogen on dry basis respectively. 2.4 Methane generationThe methane potential was estimated using the Intergovernmental Panel on Climate Change (IPCC) methodology [13] expressed in Equation(3):CPZ = MUWr x M S[C x MCF x DOC x DOCP x1612 (3)Where CH4 is the emissions in tonnes, MSWt is the total MSW generated in tonnes, MSWf is the fraction of MSW disposed off to landfills and MCF is the Methane Correction Factor. The default values (0.4 to 1.0) for MCF are dependent on the types of MSW landfill practices. If most of the landfills under consideration are unmanaged, a value of about 0.6 can be used [14].D0C =Fraction of degradable organic carbon which is based on the waste composition. It is obtained from Equation (4).DOCf =Fraction of total D0C that actually degrades and is converted to LFG. IPCC default value of 0.77 is usually used.F = Fraction of methane in LFG.'O C = 0.4C + 0.15d + 0 .3 [ (4)In (4), P is the fraction of paper in MSW, K is the fraction of kitchen garbage in MSW, W is the fraction of woods/leaves in MSW and MSWt is the waste generation rate by population.The total Municipal Solid Waste (MSWt) was estimated by multiplying the solid waste generation rate in Ibadan, 0.71Kg/capita/day, [6] by the population of the local governments served by each dumpsite. The 2006 Census population figures were used and the current Nigerian Journal of Technology Vol. 33, No. 1, January 2014 50 UNIV ERSIT Y O F IB ADAN L IB RARY Methane Generation Potential Of Municipal Solid Waste In Ibadan F. O. Akintayo & O. A. Olonisakinpopulation was estimated using a population growth rate of 3.2% [15]. The population was estimated using Equation (5).c e fg h ijk e l(mnopqrsqt)(Cefghijken Grewjh R ije { Cresenj Cefghijken) + Cresenj Cefghijken (5)A value of 0.74 was adopted as the Municipal Solid Waste factor (MSWf) as about 74% of MSWt end up in landfills [7]. The default values of 0.6, 0.77 and 0.5 were adopted as MCF, DOCf and F respectively [16]. 3. Results and discussion 3.1 Solid waste compositionTypical compositions of the MSW at the two dumpsites are presented in Table 1. Over 30% of the solid waste materials are organics; 20% is paper and cardboard; tin cans constitute 9%; ashes and other constituents of the waste account for 6%. The moisture content of the organic fraction of the waste is 44.6% which contributes to the high heating value (HHV) of the MSW. The moisture content of the MSW is evaluated as 28.7%. The MSW composition is a reflection of the socio-economic and socio-cultural lifestyles of the people in the four local government areas (a mixture of rural, semi-urban and urban dwellers). 3 2 Ultimate analysisFollowing the ultimate analysis of the MSW, recorded results are presented in Table 2. The data revealed that carbon was dominant in each of the components of the MSW ranging between 46.24 % (wood) and 64.28% (plastic). The least dominant was sulphur ranging between 0.03% (wood) and 1.24% (food waste).The results from Table 2 were used to evaluate the chemical composition (dry mass basis) of the MSW and the results are presented in Table 3.The main chemical component of the MSW was carbon (30.4%) ranging from 1.1% (wood) to 10.1% (food waste); oxygen constitutes 20.8%, hydrogen 3%, ash 3.4%, nitrogen 0.6% and sulphur 0.3%. This resulted in the formula for the volatile fraction given as C250H610O290N5S. 3.3 Energy contentThe HHV and LHV of the MSW are evaluated as 13,022KJ/kg (13.02 MJ/kg) and 11.66 MJ/kg respectively. The energy content of the water vapour in the MSW accounts for the difference between the two values.The value of LHV obtained is higher than 7 MJ/kg suggested by the World Bank [11] in the criteria for efficient applicability of MSW incineration projects Table 1: Typical composition o f Ibadan MSWComponent (%) Wet Mass Dry Mass, Moisture ContentFood Waste 35 19.40 44.60Paper & Cardboard 20 14.60 27.00Plastic 5 4.10 18.00T extile 6 4.10 31.70Rubber 9 7.60 15.60Wood 3 2.30 23.30Glass 7 6.80 2.90Tin Container 9 8.91 1.00Miscellaneous (Dirts, Ashes, e.t.c) 6 3.50 41.70 Table 2: Ultimate analysis o f the combustible components o f Ibadan MSWComponent (%) Carbon Hydrogen Oxygen Nitrogen Sulphur AshFood Waste 51.85 3.79 40.23 2.39 1.24 9.75Paper & Cardboard 56.34 6.13 36.59 0.34 0.21 4.38Plastic 64.28 6.89 27.44 0.96 0.39 3.04T extile 53.26 5.76 40.07 0.69 0.18 2.43Rubber 51.28 5.96 36.22 0.24 0.12 6.13Wood 46.24 6.08 44.42 0.17 0.03 2.97Miscellaneous (Dirts, Ashes, etc.) 59.78 2.76 41.79 0.42 0.25 3.79 Nigerian Journal of Technology Vol. 33, No. 1, January 2014 51 UNIV ERSIT Y O F IB ADAN L IB RARY Methane Generation Potential Of Municipal Solid Waste In Ibadan F. O. Akintayo & O. A. Olonisakin Table 3: Chemical composition o f Ibadan M SW (dry mass basis)Component (%) WetMass, DryMass Carbon Hydrogen Oxygen Nitrogen Sulphur AshFood Waste 35 19.40 10.10 0.74 7.80 0.50 0.24 1.90Paper &Cardbo. 20 14.60 8.23 0.90 5.34 0.05 0.03 0.64Plastic 5 4.10 2.64 0.30 1.13 0.04 0.02 0.12Textile 6 4.10 2.20 0.24 1.64 0.03 0.01 0.10Rubber 9 7.60 3.90 0.50 2.80 0.02 0.01 0.50Wood 3 2.30 1.10 0.14 1.02 - - 0.10Miscellaneous(Dirts,Ashes,etc.) 6 3.50 2.20 0.20 1.11 - - -Total 84 55.60 30.40 3.02 20.84 0.64 0.31 3.40 Table 4: Methane generation potential o f Ibadan MSWYear MSWttonnes MSWf MCF d o c DOCf F 16/12 Methane,tonnes2012 84,407 0.74 0.6 0.14 0.77 0.5 1.33 2,6872103 87,108 0.74 0.6 0.14 0.77 0.5 1.33 2,7732014 89,895 0.74 0.6 0.14 0.77 0.5 1.33 2,8612015 92,772 0.74 0.6 0.14 0.77 0.5 1.33 2,9532016 95,741 0.74 0.6 0.14 0.77 0.5 1.33 3,0472017 98,804 0.74 0.6 0.14 0.77 0.5 1.33 3,1452018 101,966 0.74 0.6 0.14 0.77 0.5 1.33 3,2452019 105,229 0.74 0.6 0.14 0.77 0.5 1.33 3,3492020 108,596 0.74 0.6 0.14 0.77 0.5 1.33 3,457 Figure 1: Expected Methane Generation between 2012 and2020 3.4 Methane generation potential Relevant values from Table 1 are substituted into Equation (4) to give DOC of 0.14. The obtained values were used in estimating the total CH4 generated in the dumpsites in 2012. The total methane generation potential of the MSW from 2012 to 2020is presented in Table 4 and the trend shown in Figure 1. Nigerian Journal of Technology It is projected that 27,517 tonnes of methane will be generated from the MSW during the period. This value will be affected by the quantity and composition of waste generated, which depend on how developed the community is and state of its economy. Vol. 33, No. 1, January 2014 52 UNIV ERSIT Y O F IB ADAN L IB RARY Methane Generation Potential Of Municipal Solid Waste In Ibadan F. O. Akintayo & O. A. Olonisakin 3. ConclusionThe study revealed that the Ibadan MSW is predominantly organic (35%) with other recyclables such as paper and cardboard, plastic, glass accounting for up to 50%. The general formula for Ibadan MSW resulting from the ultimate analysis carried out is C250H610O290N5S (% dry mass basis) with ash content of 3.4%. The MSW was adjudged to have energy content value of 13.02 MJ/kg and 11.66 MJ/kg representing the HHV and LHV of the MSW respectively. Based on the study, the MSW is expected to produce a total of 27,517 tonnes of methane between 2012 and 2020. The gas can be used as alternative energy source for small and medium enterprises in the community. References[1] Ezeike, G. 0. I. Determination of Calorific Values ofSome Nigerian Bio-Mass Solid Materials. Nigerian Journal o f Technology, Vol. 7, Number 1, 1983, pp 21-33.[2] Amini H. R. and Reinhart D. R. Regional predictionof long-term landfill gas to energy potential. Waste Management, Vol. 31, 2011, pp 2020­2026.[3] Spokas, K., Bogner, J., Chanton, J. P., Morcet, M., Aran, C., Graff, C., Golvan, Y. M. and Hebe I. Methane Mass Balance at Three Landfill Sites: What is the Efficiency of Capture by Gas Collection Systems? Waste Management, Vol. 26, 2006, pp 516-525.[4] Ugwu, H. U., Nwankwojike, B. N., Ogbonnaya, E. A.,Ekoi, E. J. 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