Fresh Perspectives on the Assessment of Sewage Sludge Management

Abstract: Sewage sludge management and its role in closing nutrient cycles have received considerable attention in recent years. This thesis quantified phosphorus flows in Gothenburg, Sweden, under current and possible future waste management practices, and aimed to improve the assessment of wastewater and sludge management from an environmental and human health perspective through blending risk assessment (RA) and life cycle assessment (LCA). A review of previous environmental assessment case studies revealed inconsistent use of terminology regarding what is meant by integration, combination, hybridisation, or integrated use of RA and LCA. To facilitate a better understanding and more transparent communication of the nature of a given case study, this thesis proposed a design space that outlines choices to be made when blending elements of RA and LCA. In particular, this thesis suggests that a case study should only be referred to as a combination or integration of RA and LCA if it addresses two distinct perspectives. For human health effects, these are the perspectives of risks for specific members of a given human population (RA perspective), and of overall impacts for a given human population (LCA perspective). RA and LCA can also be blended by transferring model elements from one framework to the other. This thesis explored the transfer of elements of quantitative microbial risk assessment (QMRA) to an LCA framework in order to account for adverse effects of pathogens on human health. Such practice was found to be adequate, but it is important to ensure that exposure pathways and parameters are chosen in accordance with the principles applied in the LCA study of which the assessment is a part. Also, in the context of sewage sludge management, the consideration of non-routine operation scenarios in LCA may be warranted. This thesis also explored different models to assess human health effects related to chemical contaminants in the context of land application of sewage sludge. The different model variants investigated (i.e. the generic USEtox 1.01 and 2.0 models as well as a context-specific model) provided different burden of disease estimates for individual chemical contaminants, but an aggregate burden of disease estimate of the same order of magnitude. Overall, this thesis emphasises the importance of explicitly contemplating which type of question relevant to sewage sludge management can be answered by quantitative assessment tools such as RA and LCA, and which cannot.