Estimation of product specific emissions from municipal solid waste landfills for the inventory phase in LCA

Life Cycle Assessment (LCA) is an environmental management tool used to examine and evaluate the environmental impactsassociated with the existence of products. The focus of LCA is on the entire life cycle of the product, i.e. from the extraction of theraw materials through the production of materials and components and the manufacture, transportation and use of the product to thefinal disposal and possible recycling of the product. Although LCA has developed significantly during recent years, product specific emissions from disposed waste have only got minorattention in the literature leaving a significant gap in the inventory phase of the LCA. At present, no systematic methods exist fordetermination of emissions from products after disposal meaning that emissions from waste treatment processes are oftendisregarded. Instead, the output from waste treatment processes in the LCA inventory is frequently given as a quantity of solid wasteand possibly some recovered energy from waste incineration.Since product specific emissions can not be calculated or measured directly at the landfills, they must be estimated by modeling oflandfill processes. This paper presents a landfill model based on a large number of assumptions and approximations concerninglandfill properties, waste product properties and characteristics of various kinds of environmental protection systems (e.g. landfill gascombustion units and leachate treatment units). The model is useful for estimation of emissions from waste products disposed inlandfills and it has been made operational in the computer tool LCA-LAND. In the model, waste products are subdivided into fivegroups of components: general organic matter (e.g. paper), specific organic compounds (e.g. organic solvents), inert components(e.g. PVC), metals (e.g. cadmium), and inorganic non-metals (e.g. chlorine,) which are considered individually. The computer toolLCA-LAND is useful for estimation of emissions from specific waste products disposed in municipal solid waste landfills in Europeancountries (for the present Denmark, Germany and The Netherlands). Input data for the model are e.g. distribution of the wasteproduct in different countries, composition of the product and physical/chemical/biological properties of waste product components.Output data of the model are product specific estimates of 1) emissions to atmosphere 2) emissions to aquatic recipients 3) remainsin the landfill after a 100 year period 4) recovered energy from landfill gas combustion. Since waste products considered in LCA are often disposed at different landfills where they are mixed with the general waste, theestimated emissions from specific waste products cannot be compared with measured emissions from true landfills. Hence,LCA-LAND is verified in terms of mass balances and sensitivity analyses. Test mass balances of LCA-LAND agree exactly and thesensitivity analysis show good agreement between the relative proportions of various types of emissions (based on properties of thewaste and properties of landfills) and good agreement with emission levels that would be expected based on a general understandingof landfill processes. The assumptions and approximations used in the model are scientifically based to the extent possible, but where scientificinformation has been missing, qualified estimates have been made to fulfill the aim of a complete tool for estimation of emissions. Itis the belief of the authors that although the model is associated with significant uncertainty in certain areas, the resulting estimatesof emissions from waste products disposed at landfills are much more qualified and useful in LCA than just neglecting theemissions, which is absolutely wrong and misleading.The model is described in Nielsen and Hauschild (1998) and the computer tool LCA-LAND is presented and verified in Nielsen et al.(1998). LCA-LAND is made in Excelâ and will be available for free download (http://www.ipt.dtu.dk/employ/pn.htm.) as soon as thetwo papers are published.