Reshaping the urban water management paradigm: towards a new decision-support framework for the sustainable design of hybrid systems

几十年来，提供全民覆盖和利用规模经济优势的大型集中式系统一直主导着世界各地的市政供水服务。加拿大大多数城市依赖单一水源，蒙特利尔的88立方米/S污水处理设施可能是世界上最高的最大流量能力，很好地体现了这一范例。然而，今天，许多城市污水系统以最大容量或超过最大容量运行，限制了城市发展，并造成了不利的环境影响。为了避免大规模的系统扩展成本，越来越多的人建议使用完全分散的污水处理系统(如化粪池)来服务于新的城市开发项目，但由于运行条件不佳，这可能会对环境和公众健康造成灾难性的长期影响。在这两个极端之间，小型和中等规模的“卫星”污水处理系统可以纳入大型城市方案。事实上，为了支持城市水系统(UWS)的战略规划，需要用新的替代、多尺度的UWS选项重新审视集中式与完全分散式的范例，并需要新的分析方法和工具来指导未来可持续和有弹性的城市的决策。这项研究考察了UW新的“混合”配置的技术、经济、环境和社会潜力，即在混合规模下运行的UW。为此，将开发未来情景分析、系统建模和综合评估工具的混合方法。将对魁北克省和安大略省现有的城市污水处理厂进行分析，以确定在以下方面影响污水处理厂效率的城市化模式：(I)提供供水服务的成本效益和规模经济；(Ii)废水流出物和污水混合溢流对环境的影响；以及(Iii)不同用途和水质改善带来的最大社会和公共健康效益(O1)。在魁北克南部的一个案例研究城市，将根据可持续发展的三个维度评估利益相关者和社区对未来超大规模杀伤性武器的偏好，形成为超大规模杀伤性武器发展提供信息的情景分析的基础(O2)。将使用废水处理和污水系统建模工具(O3)对满足案例研究城市未来系统能力需求的新混合配置进行建模，并将使用将开发并纳入空间规划工具(O4)的新空间多准则决策分析框架，在可持续性方面与传统备选方案进行比较。这种高度跨学科的方法将加强UWS的科学稳健、创新的空间规划，有可能克服技术锁定和路径依赖。提出这样一种新的城市规划范式是创新的，这种管理模式的实地评估尚未在城市范围内实施，利益攸关方的参与也是具有挑战性的；然而，预期的社会、环境和经济效益是巨大的。

Large centralized systems, providing universal coverage and taking advantage of economies of scale, have dominated municipal water services worldwide for decades. Most cities in Canada rely on a single water source, and Montreal's 88-m3/s wastewater treatment facility, with probably the highest maximal flowrate capacity in the world, exemplifies this paradigm very well. Yet today, many municipal wastewater systems operate at maximum capacity or beyond, limiting urban development and causing adverse environmental impacts. To avoid large system expansion costs, fully decentralized wastewater systems (like septic tanks) are increasingly proposed to serve new urban developments, causing potentially disastrous long-term environmental and public health impacts due to inadequate operating conditions. Between both extremes, small and medium scale 'satellite' wastewater systems can be incorporated into large urban schemes. In fact, to support strategic planning of urban water systems (UWS), the centralized versus fully decentralized paradigm needs to be revisited with novel alternative, multiscale UWS options, and new analytical approaches and tools are needed to guide decision making in designing future sustainable and resilient cities. This study examines the technical, economic, environmental, and social potential of new 'hybrid' configurations of UWS, i.e., that operate at a mix of scales. To this end, a mixed methodology of future scenario analysis, system modelling and integrated assessment tools will be developed. An analysis of existing UWS across the provinces of Québec and Ontario will be performed to identify urbanisation patterns that affect UWS's efficiency in terms of (i) cost-effectiveness in delivering water services and economies of scale; (ii) environmental impacts from wastewater effluents and combined sewer overflows; and (iii) maximal social and public health benefits from different uses and exposure to improved water quality (O1). In a case study city located in Southern Quebec, stakeholder and community preferences for future UWS will be assessed according to the three dimensions of sustainability, forming the basis for a scenario analysis that informs UWS development (O2). New hybrid configurations to meet future system capacity needs in the case study city will be modelled using wastewater treatment and sewage system modelling tools (O3) and will be compared with traditional options in terms of sustainability using a new spatial multicriteria decision analysis framework that will be developed and integrated into a spatial planning tool (O4). This highly interdisciplinary approach will enhance scientifically robust, innovative spatial planning of UWS that has the potential to overcome technology lock-in and path-dependency. Proposing such a new UWS planning paradigm is innovative, field evaluations of such a management model have not yet been implemented at city scale and stakeholder engagement is challenging; yet, the expected social, environmental and economic benefits are huge.