School of Chemical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia; Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, United States.
Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, United States; ReNUWIt Engineering Research Center, University of California, Berkeley, CA 94720, United States.
Water Res. 2017 Dec 15;127:139-149. doi: 10.1016/j.watres.2017.10.016. Epub 2017 Oct 9.
In recent years, cities in some water stressed regions have explored alternative water sources such as seawater desalination and potable water recycling in spite of concerns over increasing energy consumption. In this study, we evaluate the current and future life-cycle energy impacts of four alternative water supply strategies introduced during a decade-long drought in South East Queensland (SEQ), Australia. These strategies were: seawater desalination, indirect potable water recycling, network integration, and rainwater tanks. Our work highlights the energy burden of alternative water supply strategies which added approximately 24% life-cycle energy use to the existing supply system (with surface water sources) in SEQ even for a current post-drought low utilisation status. Over half of this additional life-cycle energy use was from the centralised alternative supply strategies. Rainwater tanks contributed an estimated 3% to regional water supply, but added over 10% life-cycle energy use to the existing system. In the future scenario analysis, we compare the life-cycle energy use between "Normal", "Dry", "High water demand" and "Design capacity" scenarios. In the "Normal" scenario, a long-term low utilisation of the desalination system and the water recycling system has greatly reduced the energy burden of these centralised strategies to only 13%. In contrast, higher utilisation in the unlikely "Dry" and "Design capacity" scenarios add 86% and 140% to life-cycle energy use of the existing system respectively. In the "High water demand" scenario, a 20% increase in per capita water use over 20 years "consumes" more energy than is used by the four alternative strategies in the "Normal" scenario. This research provides insight for developing more realistic long-term scenarios to evaluate and compare life-cycle energy impacts of drought-adaptation infrastructure and regional decentralised water sources. Scenario building for life-cycle assessments of water supply systems should consider i) climate variability and, therefore, infrastructure utilisation rate, ii) potential under-utilisation for both installed centralised and decentralised sources, and iii) the potential energy penalty for operating infrastructure well below its design capacity (e.g., the operational energy intensity of the desalination system is three times higher at low utilisation rates). This study illustrates that evaluating the life-cycle energy use and intensity of these type of supply sources without considering their realistic long-term operating scenario(s) can potentially distort and overemphasise their energy implications. To other water stressed regions, this work shows that managing long-term water demand is also important, in addition to acknowledging the energy-intensive nature of some alternative water sources.
近年来，一些水资源紧张地区的城市已经开始探索替代水源，如海水淡化和饮用水再利用，尽管人们担心能源消耗会增加。在这项研究中，我们评估了在澳大利亚东南部（SEQ）长达十年的干旱期间引入的四种替代供水策略的当前和未来生命周期能源影响。这些策略是：海水淡化、间接饮用水再利用、网络整合和雨水池。我们的工作强调了替代供水策略的能源负担，即使在当前干旱后低利用率的情况下，这些策略也使 SEQ 的现有供水系统（采用地表水来源）的生命周期能源使用增加了约 24%。这额外的生命周期能源使用中有一半以上来自集中式替代供应策略。雨水池对区域供水的贡献估计为 3%，但对现有系统的生命周期能源使用增加了 10%以上。在未来情景分析中，我们比较了“正常”、“干旱”、“高需水”和“设计能力”情景之间的生命周期能源使用。在“正常”情景下，海水淡化系统和水再利用系统的长期低利用率大大降低了这些集中式策略的能源负担，仅为 13%。相比之下，在不太可能出现的“干旱”和“设计能力”情景下，现有系统的生命周期能源使用分别增加了 86%和 140%。在“高需水”情景下，20 年内人均用水量增加 20%，消耗的能源比“正常”情景下四种替代策略消耗的能源还要多。这项研究为开发更现实的长期情景提供了见解，以评估和比较适应干旱的基础设施和区域分散式水源的生命周期能源影响。水供应系统生命周期评估的情景构建应考虑：i）气候变异性，因此基础设施利用率；ii）已安装的集中式和分散式水源的潜在未充分利用；以及 iii）以低于设计能力运行基础设施的潜在能源惩罚（例如，海水淡化系统在低利用率下的运行能源强度是其三倍）。本研究表明，如果不考虑这些供应源的现实长期运行情景，评估其生命周期能源使用和强度可能会扭曲并过分强调其能源影响。对于其他水资源紧张地区，这项工作表明，除了承认一些替代水源的能源密集性质外，管理长期水需求也很重要。
