M. B. Beck

The energy-water-food nexus: strategic analysis of technologies for transforming the urban metabolism.

Urban areas are considered net consumers of materials and energy, attracting these from the surrounding hinterland and other parts of the planet. The way these flows are transformed and returned to the environment by the city is important for addressing questions of sustainability and the effect of human behavior on the metabolism of the city. The present work explores these questions with the use of systems analysis, specifically in the form of a Multi-sectoral Systems Analysis (MSA), a tool for research and for supporting decision-making for policy and investment. The application of MSA is illustrated in the context of Greater London, with these three objectives: (a) estimating resource fluxes (nutrients, water and energy) entering, leaving and circulating within the city-watershed system; (b) revealing the synergies and antagonisms resulting from various combinations of water-sector innovations; and (c) estimating the economic benefits associated with implementing these technologies, from the point of view of production of fertilizer and energy, and the reduction of greenhouse gases. Results show that the selection of the best technological innovation depends on which resource is the focus for improvement. Urine separation can potentially recover 47% of the nitrogen in the food consumed in London, with revenue of

On water security, sustainability, and the water-food-energy-climate nexus

33xa0M per annum from fertilizer production. Collecting food waste in sewers together with growing algae in wastewater treatment plants could beneficially increase the amount of carbon release from renewable energy by 66%, with potential annual revenues of

Understanding the metabolism of urban-rural ecosystems

58xa0M from fuel production.

Water — and nutrient and energy — systems in urbanizing watersheds

The role of water security in sustainable development and in the nexus of water, food, energy and climate interactions is examined from the starting point of the definition of water security offered by Grey and Sadoff. Much about the notion of security has to do with the presumption of scarcity in the resources required to meet human needs. The treatment of scarcity in mainstream economics is in turn examined, therefore, in relation to how each of us as individuals reconciles means with ends, a procedure at the core of the idea of sustainable development. According to the Grey-Sadoff definition, attaining water security amounts to achieving basic, single-sector water development as a precursor of more general, self-sustaining, multi-sectoral development. This is consistent with the way in which water is treated as “first among equals”, i.e. privileged, in thinking about what is key in achieving security around the nexus of water, food, energy and climate. Cities, of course, are locations where demands for these multiple resource-energy flows are increasingly being generated. The paper discusses two important facets of security, i.e., diversity of access to resources and services (such as sanitation) and resilience in the behavior of coupled human-built-natural systems. Eight quasi-operational principles, by which to gauge nexus security with respect to city buildings and infrastructure, are developed.

Nexus security: governance, innovation and the resilient city

A Multi-sectoral Systems Analysis (MSA) methodology is presented as a tool for identifying the level of importance of flows of energy and materials (water, nitrogen, phosphorus, and carbon) as they pass through an anthropogenically manipulated system. That system comprises a web of processes, across a total of five industrial sectors: water, forestry, food, energy and waste management. Given the heterogeneous nature and quality of data sources, the propagation of data uncertainty is considered through a Regionalized Sensitivity Analysis (RSA) procedure, based on the Monte Carlo simulation approach. The MSA reveals the advantages of studying different material cycles simultaneously, in addition to interpreting them individually, while gaining insight into the magnitude of the associated flows. The proposed framework is illustrated for a case study of the Upper Chattahoochee Watershed, in which parts of Metro Atlanta are located. Results show that natural flows are predominant in the water and energy cycles. Direct human manipulations of water, i.e., withdrawals for public supply and power generation, are less than 25% of the amount received as precipitation. Solar input is 200 times the total demand for electricity. Apart from sun-light, gasoline for transportation is the flow with the largest content of energy; it is responsible for providing 71% of the total demand of fuels for uses other than power generation. In contrast, cycles of nutrients such as N and C are strongly related to the flows of fuels, mainly coal and natural gas. In a second tier, fertilizer use and the poultry industry in the region are significant for the use of nitrogen. Phosphorus fluxes are similarly dominated by the food sector and, as a consequence, to a lesser extent by the water sector, because of water’s role as a waste-conveyance medium.

Eco-effectiveness, eco-efficiency, and the metabolism of a city: A multi-sectoral analysis

Driven by considerations of sustainability, it has become increasingly difficult over the past 15–20 years — at least intellectually — to separate out the water infrastructure and water metabolism of cities from their intimately inter-related nutrient and energy metabolisms. Much of the focus of this difficulty settles on the wastewater component of the city’s water infrastructure and its associated fluxes of nutrients (N, P, C, and so on). Indeed, notwithstanding the massive volumes of these materials flowing into and out of the city, the notion of an urban nutrient infrastructure is conspicuous by its absence. Likewise, we do not tend to discuss, or conduct research into, “soilshed” agencies, or soilshed management, or Integrated Nutrient Resources Management (as opposed to its most familiar companion, Integrated Water Resources Management, or IWRM). The paper summarizes some of the benefits (and challenges) deriving from adopting this broader, multi-sectoral “systems” perspective on addressing water-nutrient-energy systems in city-watershed settings. Such a perspective resonates with the growing interest in broader policy circles in what is called the “water-food-energy security nexus”. The benefits and challenges of our Multi-sectoral Systems Analysis (MSA) are illustrated through computational results from two primary case studies: Atlanta, Georgia, USA; and London, UK. Since our work is part of the International Network on Cities as Forces for Good in the Environment (CFG; see www.cfgnet.org), in which other case studies are currently being initiated — for example, on Kathmandu, Nepal — we close by reflecting upon these issues of water-nutrient-energy systems in three urban settings with quite different styles and speeds of development.

New integer representations as the sum of three cubes

Nexus security is a compound mix of ideas: reconciling human needs and wants with access to multiple resources; diversity of access to those resources and services; resilience in the face of weather- and climaterelated variability; resilience likewise in the face of infrastructure failure; and the personal, individual sense of belonging. At the level of Systems Thinking there is a very close relationship between resilience in the behavior of natural (ecological) systems and resilience in the social dynamics of governance within communities, where such resilience establishes the viability of these communities over centuries, which in turn entails successful stewardship of the man-environment relationship. We use insights from this cross-system mapping — across natural, built, and human systems — to assess, first, the role of city governance in achieving nexus security (or not) and, second, the role of technological innovations in serving the same purpose. More specifically, eight principles, covering resilience and diversity of access to resources and services, are used to gauge security-enhancing features of city buildings and infrastructure. Case studies include new designs of resilient office blocks, nutrient (nitrogen and phosphorus) recovery systems for sanitation and wastewater treatment, and the reconstruction of urban parks for the provision of ecosystem services. Throughout the paper, matters of risk in the face of meteorological variability are prominent. We do not conclude, however, that the presence of risk implies nexus insecurity.

Incremental infrastructure transitions towards cities as forces for good in the environment

The vision of Cities as forces for good within the environment is explored herein by proposing a multisectoral analysis that accounts for nutrients, water, energy. The main purpose is to identify those elements in the urban system that can offer more opportunities of improvement with regard to eco-efficiency and eco-effectiveness indicators, and how different sectors, i.e. water, food, forestry, energy, and waste management, interact between each other. For this, (i) a computational model is designed using concepts of Substance Flow Analysis (SFA) together with mass and energy balances, and (ii) a set of indicators are defined to assess the improvement or worsening of the system. (iii) Both model and indicators are simulated under the Regionalized Sensitivity Analysis (RSA) framework to account of uncertainty and test the relevance of prospective technological innovations, i.e. structural changes. The paper presents a case study based on the Upper Chattahoochee Watershed in the south-eastern United States, in which the nitrogen (N) cycle is investigated under two scenarios: 0% and 100% urine source separation implementation. Results reveal that animal feed and fossil fuels are the major flows of N in the system. Urine separation showed to be critical for some aspects of the system as described by the behavior of the set of indicators.

Model Structure Identification and the Growth of Knowledge

We describe a new algorithm for finding integer solutions to x 3 + y 3 + z 3 = k for specific values of k. We use this to find representations for values of k for which no solution was previously known, including k = 30 and k = 52.

Reforming the multilateral export control regimes

As source-separation has been proposed as a sustainable alternative to the current wastewater treatment strategy, the improvement in sustainability associated with such transition needs to be evaluated. However, given the difficulties and uncertainty in both technological and social aspects, such transition will most probably be happening gradually, step by step. Here with a computational case study based on the city of Atlanta within the Upper Chattahoochee watershed in the southeastern United States, we simulated three steps of transition, i.e. 50%, 70%, and 100% ANS-separation (Anthropogenic Nutrient Solution) is reached. The economic sustainability of these transition strategies was evaluated with total annual economic cost (TAEC), and the environmental sustainability was evaluated with three indicators, i.e. ecological footprints (EF), flux of materials passing through the city in its context of global material cycles, and pulse rate in terms of the spectrum of disturbance frequency to which the city is subject. The simulation results showed that compared with the current strategy, the ANS-separation has significantly lower TAEC, lower EF, lower pollutant discharge, higher recovery of nutrient and energy, and more beneficial manipulation of perturbation regimes of the citys environment. These advantages increase with the rate of ANS-separation.