Improved methods and practices in life cycle assessment of wastewater and sludge management

Doctoral thesis, 2016

Large amounts of municipal and industrial wastewater are treated each year in order to prevent negative consequences to human health and the environment. The treatment processes, directly or indirectly, give rise to environmental impact, but also offer several possibilities to recover resources. The research presented in this thesis is aimed at improving the relevance of Life Cycle Assessments (LCAs) for the evaluation of the environmental performance of wastewater and sludge management systems, e.g., for process development purposes, or to provide guidance in decision-making on sludge management alternatives. A review of previous studies within the area show that the data inventory practice differs, in terms of which emission and recoverable flows are included and how these flows are quantified, which may have a large influence on results. The review is intended to serve as guidance for future life cycle inventory practice. One area of focus of this research has been systems in which sludge is used in agriculture, partly as this is an issue that attracts stakeholder concern. It was shown that pathogen risk, which historically has not been assessed within the LCA framework, may constitute an important contribution to the overall impact on the endpoint human health. Another important contributor was human toxicity potential. The uncertainties when assessing human toxicity was, however, shown to be high for this type of systems when using currently available assessment methodology, mainly due to uncertainties in the characterisation of heavy metals. Applying a characterisation method adjusted to be more specific for exposure through sludge applied in agriculture did not influence results much. The way resource utilisation from sludge as organic fertiliser is accounted for in LCA studies was also evaluated, and a novel approach to account for the potential benefits of the provision of organic matter to arable land (in addition to the benefits of nutrient provision) was suggested and evaluated. Another focus area has been how to allocate impacts between the different functions provided in a system with simultaneous wastewater treatment and generation of PHA. A novel basis for comparison of the functions was suggested and evaluated, and was shown to be useful.