Chapter 5: Sanitary Landfill
Env E 432
Matthew Scott, 1055898
Group: Waste Watchers
March 30, 2007
Introduction
This chapter will prepare a conceptual design for a sanitary landfill facility. The amount of solid waste intended for landfill from 2005 to 2009 at the University of Alberta (UA) will be estimated. The area needed for this amount of waste will also be predicted, with the estimate including space for containment, final cover, water, and equipment areas. The methane generation potential for the sanitary landfill design will be examined, assuming no recovery and that 80% recyclable and 25% composting targets are met. The difference in methane generation with and without recovery will be examined and a carbon credit amount will be estimated, based on the reduced carbon generation when meeting recovery targets. Flaring will also be looked at as a mean to reduce the methane release.
Solid Waste and Population Growth
Waste generation is directly related to population, so it is necessary to examine the population growth when designing a waste management solution that will be used into the future. Based on historical population data (Historical Population Data Appendix 1), Figure 1 shows the projected population growth until the design year of 2029. The current per capita waste generation was found to be 0.096 tonnes, using the current population of 43751 and landfill waste of 4200 tonnes per year. The population in 2029 is expected to be around 71000 people, which corresponds to a waste generation of approximately 6780 tonnes. The total waste generated from 2005 until 2029 is expected to be 135831 tonnes. The waste amounts for each year can be seen in Table 5-1 of Appendix 1.
Figure 1: Projected Population Data
Landfill Area
The landfill volume needed for the projected amount of waste can be calculated using the bulk density for a medium compacted landfill, as shown in Table 5-2 of Appendix 2. A bulk density of 1200lb/yd3 for 135831 tonnes yields a volume of 190503m3 for the waste. An area of 6350m2 will be needed for the landfill, base on a 30m depth. Table 1 shows the different dimensions of the landfill, in addition to the addition areas needed for water storage and ancillary equipment areas. Assumption for these calculations can be found in Table 5-3 of Appendix 2.
Table 1: Landfill Areas
Landfill Height(m) / Length
(m) / Width
(m) / Clay Liner
(m) pg. 134 / Clay Cover
(m) pg. 153 / Total Volume
(m^3) / Ancillary Area (20%, m^2) / Surface Water Area (10%, m^2) / Total Area (m^2)
30.00 / 79.69 / 79.69 / 1.50 / 2.30 / 214632.92 / 1270.02 / 762.01 / 9186.46
Methane Generation
As waste decomposes it generates methane gas. Methane gas is a potent greenhouse gas, and its emissions need to be examined when considering the impact of a landfill. Solid waste can be separated into slowly decomposing (SD) and rapidly decomposing (RD) material, which both contribute to methane generation. Estimating a chemical formula for the SD of C150H223O26N and for the RD of C63H100O46N, the methane generation can be approximated. The calculations to generate these chemical formulas are shown in Appendix 3, Tables 5-5, 5-6 and 5-7. As shown in Tables 5-8 and 5-9 in Appendix 3, SD generates 2368 tonnes-C (tonnes as carbon) of methane, and RD generates 19900 tonnes-C. Assuming that the 80% recycling target, and 25% composting target were met in every year of the study period, the methane generation from SD is 355 tonnes-C while RD generates 2985 tonnes-C of carbon. This is shown in Table 5-10 of Appendix 3.
Carbon Credits
If diversion results in lower methane generation the landfill may qualify for carbon credits. Assuming an average credit amount of $15/tonne-C of CO2 ($0.71/tonne-C methane), and meeting the diversion goals, the 25 year carbon credit would be $13520. If the methane were converted to CO2 using flaring, the credit would be $50102. The assumptions and values are shown in Tables 5-11 and 5-12 of Appendix 4.
It may be possible to increase the number of carbon credits received by altering the treatment technologies. If waste to electricity incineration is used, before landfilling, it is likely that methane will not be generated. Also, the waste burn energy has lower emissions than a coal burning energy facility; therefore using electricity from the waste burn instead of the coal burn should result in even more carbon credits. (Finnveden, 1998)
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Reference
Finnveden, G. 1999. Methodological aspects of life cycle assessment of integrated solid waste management systems. Resources, Conversation and Recycling. 26: 173-187.
Harris, D.C. 2003. Quantitative Chemical Analysis; Sixth Edition. W.H. Freeman and Company. New York USA.
McCartney, D. 2007. Personal correspondence, class/course notes, Solid Waste Management.
Tchobanoglous, G., Theisen, H., Vigil, S. 1993. Integrated Solid Waste Management Enginnering Principles and Management Issues. Irwin McGraw-Hill, Inc. Boston, USA.
Vesiland, P.A., Worrell, W., Reinhart, D. 2002. Solid Waste Engineering. Brooks/Cole. Paciface Grove, CA.
Appendices
Appendix 1: Solid Waste and Population Growth
Appendix 2: Landfill Area
Appendix 3: Methane Generation
Appendix 4: Carbon Credits
Copies of the excel file can be found online
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