A Research Agenda for the Future of Urban Water Management: Exploring the Potential of Nongrid, Small-Grid, and Hybrid Solutions.

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include nongrid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to coevolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should pursue a transdisciplinary research approach to generating evidence through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experiences from these projects in diverse socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.

The cost of hybrid waste water systems: A systematic framework for specifying minimum cost-connection rates.

To determine the optimal connection rate (CR) for regional waste water treatment is a challenge that has recently gained the attention of academia and professional circles throughout the world. We contribute to this debate by proposing a framework for a total cost assessment of sanitation infrastructures in a given region for the whole range of possible CRs. The total costs comprise the treatment and transportation costs of centralised and on-site waste water management systems relative to specific CRs. We can then identify optimal CRs that either deliver waste water services at the lowest overall regional cost, or alternatively, CRs that result from households freely choosing whether they want to connect or not. We apply the framework to a Swiss region, derive a typology for regional cost curves and discuss whether and by how much the empirically observed CRs differ from the two optimal ones. Both optimal CRs may be reached by introducing specific regulatory incentive structures.

Economies of density for on-site waste water treatment.

Decentralised wastewater treatment is increasingly gaining interest as a means of responding to sustainability challenges. Cost comparisons are a crucial element of any sustainability assessment. While the cost characteristics of centralised waste water management systems (WMS) have been studied extensively, the economics of decentralised WMS are less understood. A key motivation for studying the costs of decentralised WMS is to compare the cost of centralised and decentralised WMS in order to decide on cost-efficient sanitation solutions. This paper outlines a model designed to assess those costs which depend on the spatial density of decentralised wastewater treatment plants in a region. Density-related costs are mostly linked to operation and maintenance activities which depend on transportation, like sludge removal or the visits of professionals to the plants for control, servicing or repairs. We first specify a modelled cost-density relationship for a region in a geometric two-dimensional space by means of heuristic routing algorithms that consider time and load-capacity restrictions. The generic model is then applied to a Swiss case study for which we specify a broad range of modelling parameters. As a result, we identify a 'hockey-stick'-shaped cost curve that is characterised by strong cost reductions at high density values which level out at around 1 to 1.5 plants per km(2). Variations in the cost curves are mostly due to differences in management approaches (scheduled or unscheduled emptying). In addition to the well-known diseconomies of scale in the case of centralised sanitation, we find a similar generic cost behaviour for decentralised sanitation due to economies of density. Low densities in sparsely populated regions thus result in higher costs for both centralised and decentralised system. Policy implications are that efforts to introduce decentralised options in a region should consider the low-density/high-cost problem when comparing centralised and decentralised options.

Emerging solutions to the water challenges of an urbanizing world.

The top priorities for urban water sustainability include the provision of safe drinking water, wastewater handling for public health, and protection against flooding. However, rapidly aging infrastructure, population growth, and increasing urbanization call into question current urban water management strategies, especially in the fast-growing urban areas in Asia and Africa. We review innovative approaches in urban water management with the potential to provide locally adapted, resource-efficient alternative solutions. Promising examples include new concepts for stormwater drainage, increased water productivity, distributed or on-site treatment of wastewater, source separation of human waste, and institutional and organizational reforms. We conclude that there is an urgent need for major transdisciplinary efforts in research, policy, and practice to develop alternatives with implications for cities and aquatic ecosystems alike.

Barriers to Innovation in Urban Wastewater Utilities: Attitudes of Managers in California.

In many regions of the world, urban water systems will need to transition into fundamentally different forms to address current stressors and meet impending challenges-faster innovation will need to be part of these transitions. To assess the innovation deficit in urban water organizations and to identify means for supporting innovation, we surveyed wastewater utility managers in California. Our results reveal insights about the attitudes towards innovation among decision makers, and how perceptions at the level of individual managers might create disincentives for experimentation. Although managers reported feeling relatively unhindered organizationally, they also spend less time on innovation than they feel they should. The most frequently reported barriers to innovation included cost and financing; risk and risk aversion; and regulatory compliance. Considering these results in the context of prior research on innovation systems, we conclude that collective action may be required to address underinvestment in innovation.

To connect or not to connect? Modelling the optimal degree of centralisation for wastewater infrastructures.

The strong reliance of most utility services on centralised network infrastructures is becoming increasingly challenged by new technological advances in decentralised alternatives. However, not enough effort has been made to develop planning tools designed to address the implications of these new opportunities and to determine the optimal degree of centralisation of these infrastructures. We introduce a planning tool for sustainable network infrastructure planning (SNIP), a two-step techno-economic heuristic modelling approach based on shortest path-finding and hierarchical-agglomerative clustering algorithms to determine the optimal degree of centralisation in the field of wastewater management. This SNIP model optimises the distribution of wastewater treatment plants and the sewer network outlay relative to several cost and sewer-design parameters. Moreover, it allows us to construct alternative optimal wastewater system designs taking into account topography, economies of scale as well as the full size range of wastewater treatment plants. We quantify and confirm that the optimal degree of centralisation decreases with increasing terrain complexity and settlement dispersion while showing that the effect of the latter exceeds that of topography. Case study results for a Swiss community indicate that the calculated optimal degree of centralisation is substantially lower than the current level.

Beyond User Acceptance: A Legitimacy Framework for Potable Water Reuse in California.

Water resource managers often tout the potential of potable water reuse to provide a reliable, local source of drinking water in water-scarce regions. Despite data documenting the ability of advanced treatment technologies to treat municipal wastewater effluent to meet existing drinking water quality standards, many utilities face skepticism from the public about potable water reuse. Prior research on this topic has mainly focused on marketing strategies for garnering public acceptance of the process. This study takes a broader perspective on the adoption of potable water reuse based on concepts of societal legitimacy, which is the generalized perception or assumption that a technology is desirable or appropriate within its social context. To assess why some potable reuse projects were successfully implemented while others faced fierce public opposition, we performed a series of 20 expert interviews and reviewed in-depth case studies from potable reuse projects in California. Results show that proponents of a legitimated potable water reuse project in Orange County, California engaged in a portfolio of strategies that addressed three main dimensions of legitimacy. In contrast, other proposed projects that faced extensive public opposition relied on a smaller set of legitimation strategies that focused near-exclusively on the development of robust water treatment technology. Widespread legitimation of potable water reuse projects, including direct potable water reuse, may require the establishment of a portfolio of standards, procedures, and possibly new institutions.

Institutional trajectory for diffusing on-site wastewater treatment in urban China.

Urban water scarcity has been an issue for a long time in China while water pollution has attracted more and more attention over the last two decades. Recently, on-site wastewater treatment (OST) has been proposed as a meaningful alternative to deal with both water pollution and water scarcity in cities in a more sustainable way. However, the diffusion of such an OST system is still slow and often hindered by mismatched regulation, city planning and policy interventions. This paper is intended to explore potential solutions from institutional and governance perspectives. Based on expert interviews and in-depth analysis of an OST system in Kunming, an improved trajectory for diffusing OST in urban China is developed, which includes reformed decision-making and operational procedures, role transition of relevant stakeholders, and improved financing mechanisms. The results might give some suggestions for the transition of urban water management in other newly industrializing countries.

The Innovation Deficit in Urban Water: The Need for an Integrated Perspective on Institutions, Organizations, and Technology.

Interaction between institutional change and technological change poses important constraints on transitions of urban water systems to a state that can meet future needs. Research on urban water and other technology-dependent systems provides insights that are valuable to technology researchers interested in assuring that their efforts will have an impact. In the context of research on institutional change, innovation is the development, application, diffusion, and utilization of new knowledge and technology. This definition is intentionally inclusive: technological innovation will play a key role in reinvention of urban water systems, but is only part of what is necessary. Innovation usually depends on context, such that major changes to infrastructure include not only the technological inventions that drive greater efficiencies and physical transformations of water treatment and delivery systems, but also the political, cultural, social, and economic factors that hinder and enable such changes. On the basis of past and present changes in urban water systems, institutional innovation will be of similar importance to technological innovation in urban water reinvention. To solve current urban water infrastructure challenges, technology-focused researchers need to recognize the intertwined nature of technologies and institutions and the social systems that control change.

A compatibility-based procedure designed to generate potential sanitation system alternatives.

Regarding multi-criteria decision analysis (MCDA), the problem of generating alternatives has not received the attention it deserves. Most research is currently devoted to the problem of alternative selection, where it is assumed that a set of appropriate alternatives is already given. This paper addresses the generation of potential alternatives in the domain of sanitation systems planning and decision-making. A compatibility assessment procedure is proposed to determine the set of technically feasible or potential sanitation system alternatives. This is based on a clear definition of such an alternative containing sub-processes that include a user interface, storage, conveyance treatment and reuse/disposal. A newly developed compatibility matrix is applied to identify incompatibilities between the options of the sub-processes. A potential sanitation system alternative is therefore defined by the absence of two-by-two incompatibility between all its options. The compatibility assessment acts as a first filter on the set of sanitation system alternatives to eliminate those that are inoperable before the feasibility assessment. The objective of both steps is to obtain a set of alternatives that are of reasonable and manageable size from which the final solution may be selected.

Future scenarios for a sustainable water sector: a case study from Switzerland.

Uncertainties about the long-term prospects of urban water management systems have increased substantially over the past decade due to an increasing variety of regulations, technologies, and demand structures. In Switzerland, this uncertainty is mirrored by growing difficulties of utility managers and (waste)water scientists to agree on shared strategies: Water professionals demand support for pressing management problems, while researchers fundamentally question the longer-term sustainability of the established water management system. To reestablish shared orientation, we conducted a foresight study for the Swiss (waste)water sector in 2004. Based on interviews with 29 experts from Swiss water management and research to collect 56 drivers of change, a team of 17 experts developed three scenarios: (A) regional mergers of water utilities leading to enhanced professionalism in the sector, (B) consequent material flows management leading to a radically restructured urban water management system, and (C) generalized financial crisis leading to a breakdown of centralized utility services. These scenarios helped identifying shared research priorities. We conclude that scenario analysis is a powerful tool for framing long-term strategies, defining priorities, and integrating different interests in the multidisciplinary contexts of sustainability science, which are marked by high uncertainties and concern a wide range of stakeholder groups.