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.

wastewater treatment

Life cycle assessment

decision basis


sewage sludge

environmental impact

KA-salen, Kemigården 4, Göteborg
Opponent: Accociate Professor Ulf Sonesson, Swedish University of Agricultural Sciences and SP Technical Research Institute of Sweden


Sara Heimersson

Chemical Environmental Science

Avloppsvatten behandlas för att undvika påverkan på mänsklig hälsa och vår miljö. Avloppsreningen kräver insatsvaror i form av energi och kemikalier, och genererar utsläpp, både från reningsverket och slamhanteringen och då insatsvarorna produceras. Resursutvinning ur avlopp och slam, t.ex. i form av energi, näringsämnen eller organiskt material, kan ge miljömässiga vinster men är också kopplat till miljöpåverkan, i form av utsläpp kopplade till användningen av slammet eller slambehandlingen som föregår den. Livscykelanalys (LCA) är en metod som kan användas för att bedöma miljöprestandan hos avloppsrening och slamhantering, t.ex. för att se var den största miljöpåverkan uppstår, eller om en förändring i processen är miljömässigt motiverad eller riskerar att skapa andra miljöproblem, eller flytta problemen någon annanstans. Forskningen i denna avhandling visar hur man kan förbättra kvantifieringen av resursuttag och utsläpp och hur dessa bedöms i LCA. Forskningen visar också att miljöpåverkan som inte tidigare kvantifierats i liknande LCA-studier, som risker kopplade till patogena mikroorganismer, är viktiga att inkludera. Dessutom har användbarheten av LCA-resultaten för beslutsfattande varit i fokus.

Municipal wastewater is collected and treated in order to avoid impacts on human health and the environment. The treatment requires inputs in the form of energy and consumables, and creates emissions; from the wastewater treatment plant and during the handling of the sewage sludge, as well as during production of the consumables. Resource recovery from wastewater and sludge in the form of e.g. energy, nutrients or organic material (recoverable flows), can give environmental benefits but are also connected to environmental impact. Examples of such impact are emissions during the required sludge treatment or during the use of the sludge. Life cycle assessment (LCA) is a method that can be used to assess the environmental performance of wastewater and sludge management systems by e.g., identifying where the major impact originates from, or evaluate if a change in the process is environmentally motivated or likely to create other environmental problems, or move the problem elsewhere. The research presented in this thesis shows how to improve LCA methods and practices for quantifying and accounting for recoverable flows and emission flows. The results also show, e.g., that formerly neglected pathogen risk is relevant to assess in LCA. In addition, the usefulness of the LCA results for decision-making have been in focus.

Driving Forces

Sustainable development

Subject Categories

Other Chemical Engineering



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4037

KA-salen, Kemigården 4, Göteborg

Opponent: Accociate Professor Ulf Sonesson, Swedish University of Agricultural Sciences and SP Technical Research Institute of Sweden

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