Life Cycle Assessment (LCA) is useful as an information tool for the examination of alternative future scenarios for strategic planning. Developing a life cycle assessment for a large water and wastewater system involves making methodological decisions about the level of detail which is retained through different stages of the process. In this article we discuss a methodology tailored to strategic planning needs which retains a high degree of model segmentation in order to enhance modeling of a large, complex system. This is illustrated by a case study of Sydney Water, which is Australia's largest water service provider. A prospective LCA was carried out to examine the potential environmental impacts of Sydney Water's total operations in the year 2021. To our knowledge this is the first study to create an LCA model of an integrated water and wastewater system with this degree of complexity. A "base case" system model was constructed to represent current operating assets as augmented and upgraded to 2021. The base case results provided a basis for the comparison of alternative future scenarios and for conclusions to be drawn regarding potential environmental improvements. The scenarios can be roughly classified in two categories: (1) options which improve the environmental performance across all impact categories and (2) options which improve one indicator and worsen others. Overall environmental improvements are achieved in all categories by the scenarios examining increased demand management, energy efficiency, energy generation, and additional energy recovery from biosolids. The scenarios which examined desalination of seawater and the upgrades of major coastal sewage treatment plants to secondary and tertiary treatment produced an improvement in one environmental indicator but deteriorations in all the other impact categories, indicating the environmental tradeoffs within the system. The desalination scenario produced a significant increase in greenhouse gas emissions due to coalfired electricity generation for a small increase in water supply. Assessment of a greenfield scenario incorporating water demand management, on-site treatment, local irrigation, and centralized biosolids treatment indicates significant environmental improvements are possible relative to the assessment of a conventional system of corresponding scale.

Environmental performance of different water recycling technologies is compared on the basis of the associated potential environmental impacts using the technique of Life Cycle Assessment (LCA). The LCA method is used here to support decision making in water recycling in terms of (1) comparison and selection of suitable technology and (2) identification of opportunities to enhance the environmental performance of the water recycling train. In addition to the conventional impact categories used in LCA, a new soil salinisation potential is included. The environmental impact contribution from the construction phase of each technology is estimated using the Missing Inventory Estimation Tool (MIET) approach which relies on the input-output analysis technique. LCA results are reported and discussed in detail in this paper and areas of potential improvement are identified including: (1) sludge quality and quantity, and (2) energy consumption. The suitability of using the LCA technique in the context of water recycling is discussed and the limitations of LCA for this particular purpose are outlined and further research needs identified.

In the wastewater industry, decision-makers lack access to an environmental tool that can assist in further informing the non-financial analysis of a system. Such a tool should incorporate impacts beyond the effluent quality and look at the supporting processes of a plant as well as plant specific operations. Life Cycle Assessment can provide the means to fill a gap in pertinent information towards more sustainable decision-making. The project "Best Practice LCA in the Wastewater Industry" is commissioned by the CRC for Waste Management and Pollution Control at UNSW with representatives from Sydney Water Corporation (SWC), NSW Department of Land and Water Conservation and the NSW Department of Public Works. Two case studies were researched to provide a post-implementation review of changes in wastewater. Case study 1: The conversion from chlorine gas to hypochlorite and UV disinfection has been completed for several inland wastewater plants at SWC. A review of operational data for each of the options has been incorporated into an LCA of each technology. Under efficient dosing conditions, disinfection with the hypochlorite system has the minimum environmental impact. Case study 2 deals with the conversion from anaerobic to aerobic digestion. Aerobic digestion minimises release of nutrients into a sidestream to be further treated in the plant. However conversion results in more biosolids production and higher electricity requirements. This study includes a consideration of the environmental impacts of biosolids production and application. On the basis of the extended boundary including consideration of reflux composition, energy requirements and biosolids quality to potentially offset fertiliser production, anaerobic digestion performs best in 6 out of 9 impact categories. These results suggest that environmental LCA has a role in informing decision-making on unit process and treatment train selection by quantifying aspects on non-financial criteria. Also, improvement potentials are foreshadowed but not detailed.

Sydney Water selected life cycle assessment (LCA) to inform a review of its overall strategic planning document: WaterPlan 21. This assessment covered the entire business and has enabled ecological sustainability to be assessed in terms of quantitative indicators. The LCA was performed by firstly examining a base case which would eventuate if Sydney Water maintained its current operations with only the modifications, augmentations and upgrades planned for implementation between now and 2021. We then performed a number of scenario analyses to examine the benefits of additional demand management, energy efficiency, energy generation, supply augmentation and effluent quality initiatives. The results indicated significant improvements are available and that some of these measures are more desirable than others. We also examined a scenario for the alternative delivery of water and wastewater services in new urban areas. This showed quantitatively that, since connecting new fringe suburbs to the existing system requires significant expenditure on energy for pumping, major improvements in the sustainability of water and wastewater systems can be achieved by using localised, water-saving alternatives.

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