ecoinvent : Services Waste Treatment and Assessment of Long-Term Emissions

Goal, Scope and Background. The disposal phase of a product's life cycle in LCA is often neglected or based on coarse indicators like 'kilogram waste'. The goal of report No. 13 of the ecoinvent project (Doka 2003) is to create detailed Life Cycle Inventories of waste disposal processes. The purpose of this paper is to give an overview of the models behind the waste disposal inventories in ecoinvent, to present exemplary results and to discuss the assessment of long-term emissions. This paper does not present a particular LCA study. Inventories are compiled for many different materials and various disposal technologies. Considered disposal technologies are municipal incineration and different landfill types, including sanitary landfills, hazardous waste incineration, waste deposits in deep salt mines, surface spreading of sludges, municipal wastewater treatment, and building dismantling. The inventoried technologies are largely based on Swiss plants. Inventories can be used for assessment of the disposal of common, generic waste materials like paper, plastics, packaging etc. Inventories are also used within the ecoinvent database itself to inventory the disposal of specific wastes generated during the production phase. Inventories relate as far as possible to the specific chemical composition of the waste material (waste-specific burdens). Certain expenditures are not related to the waste composition and are inventoried with average values (process-specific burdens). Methods. The disposal models are based on previous work, partly used in earlier versions of ecoinvent/ETH LCI data. Important improvements were the extension of the number of considered chemical elements to 41 throughout all disposal models and new landfill models based on field data. New inventories are compiled for waste deposits in deep salt mines and building material disposal. Along with the ecoinvent data and the reports, also Excel-based software tools were created, which allow ecoinvent members to calculate waste disposal inventories from arbitrary waste compositions. The modelling of long-term emissions from landfills is a crucial part in any waste disposal process. In ecoinvent long-term emissions are defined as emissions occurring 100 years after present. They are reported in separate emission categories. The landfill inventories include long-term emissions with a time horizon of 60'000 years after present. Results and Discussion. As in earlier studies, the landfills prove to be generally relevant disposal processes, as also incineration and wastewater treatment processes produce landfilled wastes. Heavy metals tend to concentrate in landfills and are washed out to a varying degree over time. Long-term emissions usually represent an important burden from landfills. Comparisons between burdens from production of materials and the burdens from their disposal show that disposal has a certain relevance. 1 Motivation Waste disposal is a somewhat neglected part in life cycle inventories. For production and use phases elaborate data gathering is performed, but the disposal phase receives often comparatively inferior treatment. For example, mere waste masses are summed up into a single figure, or masses of a few waste types are inventoried (see e.g. Boustead 1999). Such parameters pose an unnecessary complication in the valuation step of LCA. Seeing that waste disposal processes are indeed man-made technosphere processes that emit pollutants like any other technosphere process, there seems no need to use extraordinary inventory parameters like 'waste mass' for disposal processes. A comparatively better way to inventory waste disposal is to use average disposal emissions. For example for waste incineration the air emissions, water emissions and auxiliary material inputs during average operation can be inventoried per kilogram of waste treated. However, waste incinerators treat very dissimilar waste materials like paper, plastic, kitchen waste, glass, or cans. These different materials will cause very differServices The ecoinvent Database 78 Int J LCA 10 (1) 2005 ent emissions when incinerated. So, using average incinerator data for all these materials is by comparison as accurate as if the burden from the production of any industrial material (metal, plastic, paper etc.) were inventoried using the emissions of one average industry mix. Disposal emissions should be calculated in a way which is as detailed as the production and use phase. This means to heed the waste-specific burdens generated by a specific waste composition. With data from substance flow analysis in disposal processes, it has become feasible to model the fate of single chemical elements in disposal processes an hence to calculate waste-specific disposal inventories. Such inventories were first calculated in Frischknecht et al. (1994), Zimmermann et al. (1996) and Sundqvist et al. (1997). The aim of this part of the ecoinvent project is to create waste-specific life cycle inventories for different waste compositions, based on the Swiss disposal processes (Doka 2003).