Reducing the level of greenhouse gas emissions is on the policy agenda in many countries, including Norway. Human settlements draw on resources and cause emissions in many different ways, for example through direct energy use, transportation, water use, wastewater treatment and solid waste handling. The level of impact is influenced by the lifestyle of the inhabitants. Other countries have started both research on and the building of carbon neutral settlements in order to reduce their national carbon footprints. In 2007 an initiative was started with the aim of creating the first Norwegian carbon neutral settlement at Brøset in Trondheim.
Today’s urban infrastructure is the result of centuries of work for healthy city environments. Most developed countries have efficient and highly developed infrastructure for solid waste, water and wastewater. Trondheim has well-functioning waste and water infrastructure, based upon services provided by centralised facilities. These systems draw on resources in the form of energy and material, process resources as nutrients and energy, and result in direct and indirect emissions from treatment and disposal. In the thesis I assess the role of infrastructure in the overall impact from the Brøset settlement, and also whether a new settlement with carbon neutral ambitions should adjust to the conventional infrastructure or implement alternative centralised or decentralised solutions.
To assess the importance of the supporting infrastructure, and to compare alternative systems for the infrastructure, we followed five steps. First, life cycle assessment (LCA) was used to assess the impact of the existing water and wastewater systems in Trondheim and a “business-as-usual” household waste system. Second, the literature was searched for state-of-the art research on innovative new solutions for water, wastewater and solid waste systems that were suitable for the situation at Brøset. Third we used the information from the literature and a parallel commissioning process, and data from Trondheim municipality and from the assessments of the systems in the first step, to build alternative scenarios. Fourth, we used LCA to compare alternative technical solutions for the systems. Finally we interpreted the results of the assessments.
For the waste management system in Trondheim the total impacts in most impact categories were found to be negative, representing a saving in impact due to substitution. Substitution is in this case the replacement of virgin production of materials and energy, and the impacts from this production. When measures such as increased recycling and introduction of food waste sorting and biogas production were assessed, the results showed only small differences among the scenarios, although some benefits from increased source-separation of paper and metal were found. For the water and wastewater system the life cycle global warming impact per person in the city of Trondheim was found to be less than 1 % of the annual total per-capita impact. Around 54% of this was attributed to the operation and discharges from the wastewater treatment plants. The alternative systems for Brøset were few, due to the low total impact. Some improvement in impact could be found when water consumption was reduced and stormwater handled locally, but the gains were small.
Although there is an extensive body of research available in the waste, water and wastewater fields, we found two important areas that have received little attention in the literature. These were analysis in waste management assessments of uncertainty due to differences in waste composition, and the issue of waste prevention. A conceptual study of the consequences of uncertainty in waste composition was performed, and other sources of uncertainty in the assessments carried out for this thesis were discussed. In order to account for waste prevention in environmental assessments we have developed a model that includes the impact from the production of goods in the assessment. This was performed using a hybrid-LCA model, in which the upstream impact was modelled with environmentally extended consumption-based input–output analysis and the downstream waste system was modelled with LCA. The importance of upstream impact became evident, but also the importance of including rebound effects in the calculations.
There are two overall take-home messages from this work. The first is related to the availability and usefulness of existing methods to evaluate environmental impacts from an urban development project in its early phase of planning. Here we conclude that the combination of system analysis and scenario building were helpful in the early stage planning phase for assessing the role of the infrastructure, for including several environmental impact categories, and for comparative assessments of alternative solutions. The second take-home message is related to what kind of strategies and solutions for technologies and management in the waste, water and wastewater subsystems that are to be recommended, in a case such as Brøset in Trondheim. Here we conclude that Brøset should connect to the existing infrastructure systems, but that local stormwater treatment and measures for waste prevention and water saving should be integrated in further planning.