Indicators for Measuring the Sustainability of Urban Water Systems - A Life Cycle Approach
Infrastructure for the provision of drinking water and the treatment of wastewater and stormwater, is essential for an urban society. In this project methods are developed which measure and assess the sustainability of urban water systems. A first set of environmental sustainability indicators (ESIs) was constructed, covering technical and environmental aspects, with a division within traditional water resources and process boundaries. The ESIs were applied in case studies in Göteborg, Sweden and King William's Town, South Africa. The ESIs demonstrated that the urban water system in Göteborg has moved towards environmental sustainability, but that recycling of nutrients to agriculture remains a major concern. The situation in King's Williams Town was quite different due to an increasing population and an increasing pressure on water resources. One of the findings from the case studies was that a more rational procedure for the selection of ESIs is required. Further, consideration of system boundary extensions is essential for the provision of a relevant assessment. At this point an iterative ESI selection procedure based on life cycle assessment (LCA) was developed.
The strength of LCA was demonstrated in two studies comparing technical options. First, LCA was used to compare projected wastewater systems with increased recycling of plant nutrients. Urine separation in combination with existing large-scale treatment was demonstrated to be a promising option that improves the opportunities for recycling of nutrients. Thereby water emissions are lowered, as well as energy use since the production of mineral fertilisers can be decreased. The benefits of separation systems were first revealed when the system boundaries were expanded to include fertiliser production. LCA combined with a cost analysis provided an assessment of four sewage sludge options. It was shown that incineration and agricultural use have respectively economic and environmental restrictions. The development of relatively low cost phosphorus recovery technologies has the potential to reconcile the environmental and economic aspects of sustainability.
Finally, the iterative procedure for ESI selection was applied and evaluated in a cooperative study with Stockholm Water to ensure indicator user interaction. A number of assessment tools (including LCA) were used as an input to rank technical options for handling sludge in a multi criteria analysis and led to the selection of indicators that reflect the economic, environmental and social aspects of sustainability for wastewater and sludge handling systems.
environmental systems analysis
life cycle assessment
urban water systems