The water-energy-food nexus and process systems engineering: A new focus

The water-energy-food nexus: a systematic bibliometric analysis

Adequate water, electricity, and food are essential for sustainable development. Regional conflicts intensified by global water, energy, and food shortages necessitate a rethinking of the security and interdependence of these resources. However, most earlier scholars concentrated on the subsystems of the water-energy-food nexus (WEF nexus), lacking holistic studies. Therefore, to understand the history and current state of research on the WEF nexus and predict future research directions, this study analyzed 1313 journal articles from the Web of Science database between 2007 and 2022 using the bibliometric analysis and Citespace software. The findings in this study indicate that (1) the progress of the WEF nexus research can be classified into three stages between 2007 and 2022: the early stage (2007-2010), the fast-developing stage (2011-2015), and the steady and in-depth stage (2016-2022). The WEF nexus has become a hot zone for academic research. (2) Map of the network of countries, institutions, and author collaborations implies tight academic collaboration among countries, institutions, and writers. (3) Climate change, integrated WEF nexus, sustainable development, and security are research hotspots in this field. Meanwhile, energy security, circular economy, and resource allocation are advanced subjects in this field. These key findings can provide managers and researchers with valuable information for decision-making.

Cycling of phosphorus from wastewater to fertilizer using wood ash after energy production

Quercus wood was used for thermal energy production, and wood bottom ash (WDBA) was used as a medium for water purification and soil fertilizer in accordance with the recently proposed food-water-energy nexus concept. The wood contained a gross calorific value of 14.83 MJ kg^-1, and the gas generated during thermal energy production has the advantage of not requiring a desulfurization unit due to its low sulfur content. Wood-fired boilers emit less CO2 and SOX than coal boilers. The WDBA had a Ca content of 66.0%, and Ca existed in the forms of CaCO3 and Ca(OH)2. WDBA absorbed P by reacting with Ca in the form of Ca5(PO4)3OH. Kinetic and isotherm models revealed that the results of the experimental work were in good agreement with the pseudo-second-order and Langmuir models, respectively. The maximum P adsorption capacity of WDBA was 76.8 mg g^-1, and 6.67 g L^-1 of WDBA dose could completely remove P in water. The toxic units of WDBA tested using Daphnia magna were 6.1, and P adsorbed WDBA (P-WDBA) showed no toxicity. P-WDBA was used as an alternative P fertilizer for rice growth. P-WDBA application resulted in significantly greater rice growth in terms of all agronomic values compared to N and K treatments without P. This study proposed the utilization of WDBA, obtained from thermal energy production, to remove P from wastewater and replenish P in the soil for rice growth.

Contribution of the mix renewable energy potentials in delivering parts of the electric energy needs in the west region of Cameroon

The constant supply of energy remains a great challenge in many developing countries and Cameroon is no exception. It is necessary to explore other renewable energy sources that have environmental and energy potential. However, there is limited and sparse literature on the potential of renewable energy sources in Cameroon and its western part in particular. This limits investment and policy design that can lead to the exploitation of renewable energy sources. There is thus a need for more research on renewable energy development to better inform energy policies. This paper investigates the potential and extent to which available renewable energy sources can contribute to the electric power sector in the western part of Cameroon is on estimating the potential of hydroelectric, solar and biomass energy resources. A cross-sectional method, observations and literature review were used to determine the water flow and electrical energy potential of different biomass. The results show that the electrical potential of hydroelectricity is 11.68 GWh/year, for solar represents 44.12 GWh/year, and the energy of biomass 8586.42 GWh/year, 135.53 GWh/year and 13.05 GWh/year for agricultural, animal and forestry residues; they have a rate of access to electricity of 6.64%, 25.08%, 4881.46%, 77.05%, and 7.42% respectively. This potential can satisfy needs of 18 526 464 households. According to results obtained and in order to provide a sustainable solution by improving access to electricity, living standards and socio-economic conditions of populations; two hybrid cogeneration thermal-solar power plants can be installed at the limits of the decentralized areas of Bamboutos-Mifi-Menoua and Noun-Koung Khi, which are nearby areas with high population density. Hydroelectric plants can be installed to electrify villages that are far from the national network.

Optimization of food-energy-water-waste nexus in a sustainable food supply chain under the COVID-19 pandemic: a case study in Iran

Abstract

During the coronavirus epidemic, food supply chains have been affected by disruptions of this epidemic. Having an overview and considering food-related factors such as energy, waste, and water make the design of the supply chain more effective. In this study, a multi-objective model for a sustainable food supply chain is presented based on the prevalence of coronavirus by considering the food-energy-water-waste nexus. There are dual-channel sales including online and in-person channels, which their demand functions depend on products price in every channel, as well as the prevalence of coronavirus in high-risk or low-risk areas. Distribution centers, located in high-risk regions, require the disinfection of products to minimize coronavirus spread. Indeed, the proposed mathematical model has three objective functions that the first objective maximizes the profit of the food supply under COVID-19 conditions. The other two objectives minimize not only the environmental impact of transportation, but also the delivery time. In order to solve this multi-objective model, the epsilon constraint method, as an efficient technique, is employed. To validate the proposed model, the model is finally implemented in a two-channel supply chain in Iran. The results show that the food supply chain has a close relationship with the energy-water-waste nexus COVID-19 and can also affect customers' behavior. Moreover, the model shows when the prevalence of COVID-19 increases, people tend to buy from online shops, affecting product prices that can change by nearly 50%.

Graphical abstract

Energy simulation modeling for water-energy-food nexus system: a systematic review

Since essential nexus variables were not considered in the energy subsystem, this study focused on the role of energy in the Water, Energy, and Food nexus (WEF nexus) system. The energy subsystem interacts with water and food on the supply and demand sides. The WEF nexus-based energy model has not been reviewed recently. This study provides a systematic review of 459 articles regarding energy simulation modeling issues relating to the WEF nexus system. The keyword ("energy" AND "simulation" AND "nexus") as well as "water" OR "food" OR "climate" OR "land" OR "carbon" OR "environment" is used for searching WEF nexus documents for energy simulation. The review highlighted that the energy subsystem is modeled online (One-way) and offline (Two-way), and the energy simulation struggles to represent its system boundary with the water and food subsystems in different spatial scales (household to global). The energy subsystem of the WEF nexus did not address return flow from cooling towers and crop energy consumption comprehensively. In the research, the supply and demand section of the energy subsystem demonstrated that a comprehensive simulation model for energy can be developed using the nexus system approach. The energy subsystem's supply, primarily power plants, interacts with the water subsystem, and the energy generation policy is based on water use. The WEF nexus system assesses renewable energy effects to reduce tradeoffs. In addition, energy demand is related to energy consumption, so the energy consumption for each crop can be calculated and explained the appropriate cultivation pattern based on it.

A systematic approach for assessing water, energy and food security during the COVID-19 pandemic: case study of Mexico

Assessing the security of the water-energy-food nexus is a topic of great importance, which allows determining the situation of each resource to implement actions for sustainable management of these resources in today's society. For this reason, a systematic procedure is proposed to evaluate the synergies of the water-energy-food nexus in a large region that is divided into subregions that allow considering their interactions. The new procedure considers the availability, accessibility and regional interdependence of resources while annexing economic and social aspects. A composite index called the WEF Global Index is developed, which involves the WEF nexus index and has nine indicators that evaluate the availability, accessibility and regional interdependence of each resource in the water-energy-food nexus. This new index considers the Gross Domestic Product per capita and the involved population. As a case study, the 32 states of Mexico were considered to assess the effects of the COVID-19 pandemic on the economy and the security of the water-energy-food nexus at the state level. For this, the composite index was evaluated in the years 2019 and 2020. The results show that from 2019 to 2020, the value of the global index increased in 13 states, in 21 states the security index of the WEF nexus increased, and in 9 states the GDP per capita index increased. On the other hand, the results indicate that in 11 states there was no improvement in the nexus security index due to the increase in water demand, which considerably affected the water availability indicator.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10668-022-02671-2.

Domestic plant food loss and waste in the United States: Environmental footprints and mitigation strategies

The United States (U.S.) aims to reduce half of food loss and waste (FLW) by 2030. To achieve this goal, the public, academic, and political attentions on FLW have been increasing, and a series of actions have been implemented. However, the actions lack consideration on the categorical priority of FLW mitigation in relation to environmental footprints. In this article, we compare the FLW of three main plant food categories (i.e., grains, vegetables, and fruits) and their water and carbon footprints during 1970-2017. The vegetable FLW doubled during the period, reaching 3.39 × 10¹⁰ kg in 2017, which was 5- and 2-fold higher than the FLW of grains and fruits, respectively. The FLW of vegetables, grains, and fruits contributed 29%, 47%, and 24% to the total blue water wasted through FLW. The total carbon dioxide emissions generated by plant FLW were contributed by vegetables with 50%, grains with 31%, and fruits with 19%. Canonical correspondence analysis indicates that vegetable FLW had a higher positive correlation with urbanization, household incomes, gross domestic product, and high-income population than grain FLW, whereas fruit FLW was not influenced by these socioeconomic factors. Therefore, we suggest that the FLW mitigation should be prioritized on vegetables. Specific strategies include local food sourcing, shortening food miles, building food belts, and developing controlled-environment agriculture. Our data-based comparisons provide valuable insights into food policy improvement for achieving the 2030 reduction goal of the U.S., but the insights could be improved by considering the influences of foods imported from other nations.

A Societal Metabolism Approach to Effectively Analyze the Water–Energy–Food Nexus in an Agricultural Transboundary River Basin

We implemented the semantically open conceptual framework ‘Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism’ (MuSIASEM) to deal with nexus challenges in agricultural production systems in transboundary river basins, using the Iranian Aras River Basin as a case study. The performance of the agricultural sector was characterized for relevant typologies of crop production using metabolic profiles, i.e., inputs and outputs per ton of crop produced, per hectare of land use, and per hour of labor. This analysis was contextualized across hierarchical levels of analysis, including the agronomic context at the regional level (rainfed versus irrigated cultivation), the socio-economic and political context at the national level (food sovereignty; urbanization), and the hydro-ecological context of the larger transboundary river basin (water constraints, GHG emissions). We found that the simultaneous use of two different interrelated logics of aggregation—the productivity of land and labor (relevant for the agronomic and socio-economic dimension) and the density of flows under different land uses (relevant for the hydrological and ecological dimension)—allowed for the identification of trade-offs in policy deliberations. In the case of Iran, it showed that striving for strategic autonomy will exacerbate the current water crisis; with the current cropping patterns, agronomic improvements will not suffice to avert a water crisis. It was concluded that the proposed approach fills an important gap in nexus research, but to effectively guide nexus governance in the region, a co-production of the analysis with social actors as well as more complete data sets at the river basin level would be essential.

A decision-making framework for the optimal design of renewable energy systems under energy-water-land nexus considerations

The optimal allocation of land for energy generation is of emergent concern due to an increasing demand for renewable power capacity, land scarcity, and the diminishing supply of water. Therefore, economically, socially and environmentally optimal design of new energy infrastructure systems require the holistic consideration of water, food and land resources. Despite huge efforts on the modeling and optimization of renewable energy systems, studies navigating the multi-faceted and interconnected food-energy-water-land nexus space, identifying opportunities for beneficial improvement, and systematically exploring interactions and trade-offs are still limited. In this work we present the foundations of a systems engineering decision-making framework for the trade-off analysis and optimization of water and land stressed renewable energy systems. The developed framework combines mathematical modeling, optimization, and data analytics to capture the interdependencies of the nexus elements and therefore facilitate informed decision making. The proposed framework has been adopted for a water-stressed region in south-central Texas. The optimal solutions of this case study highlight the significance of geographic factors and resource availability on the transition towards renewable energy generation.

Examining Lebanon's Resilience Through a Water-Energy-Food Nexus Lens

Lebanon faces a mix of underlying political and economic challenges, shocks, and triggering events that threaten the sustainability and resilience of its interconnected resource systems. The complex nature of these pressures begs for a systems approach to better understand the existing interconnections and to support the co-creation of cross-sectoral solutions to address them. This article specifically aims to: 1) conduct a scoping review of the existing literature and current events to identify interconnections between water-, energy-, and food-related challenges as they relate to the underlying conditions and triggering events at play in the context of Lebanon; 2) highlight ways in which the Water-Energy-Food (WEF) Nexus is a useful lens through which to understand and act upon issues at different scales; and 3) identify emergent themes including decentralization and systems thinking and their roles as catalysts toward more resilient resource systems. The examination concludes with two main recommendations: first, to create platforms and opportunities for interactive resource planning and decision making to facilitate systems-thinking for top-down WEF management; and second, to empower decentralized initiatives at the local level to build resilient, bottom-up solutions to WEF challenges.

Governance using the water-food-energy nexus and human-factor measures

Household water food and energy (WFE) expenditures, reflect respective survival needs for which their resources and social welfare are inter-related. We developed a policy driven quantitative decision-making strategy (DMS) to address the domain geospatial entities’ (nodes or administrative districts) of the WFE nexus, assumed to be information linked across the domain nodal-network. As investment in one of the inter-dependent nexus components may cause unexpected shock to the others, we refer to the WFE normalized expenditures product (Volume) as representing the nexus holistic measure. Volume rate conforms to Boltzman entropy suggesting directed information from high to low Volume nodes. Our hypothesis of causality-driven directional information is exemplified by a sharp price increase in wheat and rice, for U.S. and Thailand respectively, that manifests its impact on the temporal trend of Israel’s administrative districts of the WFE expenditures. Welfare mass (WM) represents the node’s Volume combined with its income and population density. Formulation is suggested for the nodal-network WM temporal balance where each node is scaled by a human-factor (HF) for subjective attitude and a superimposed nodal source/sink term manifesting policy decision. Our management tool is based on two sequential governance processes: one starting with historical data mapping the mean temporal nodal Volumes to single out extremes, and the second is followed by WM balance simulation predicting nodal-network outcome of policy driven targeting. In view of the proof of concept by model simulations in in our previous research, here HF extends the model and attention is devoted to emphasize how the current developed decision-making approach categorically differs from existing nexus related methods. The first governance process is exemplified demonstrating illustrations for Israel’s districts. Findings show higher expenditures for water and lower for energy, and maps pointing to extremes in districts’ mean temporal Volume. Illustrations of domain surfaces for that period enable assessment of relative inclination trends of the normalized Water, Food and Energy directions continuum assembled from time stations, and evolution trends for each of the WFE components.

Fixed and Mobile Low-Cost Sensing Approaches for Microclimate Monitoring in Urban Areas: A Preliminary Study in the City of Bolzano (Italy)

In the current scenario of massive urbanization and global climate change, an intelligent monitoring of the environmental variables is becoming fundamental to ensure good living conditions in cities. Indeed, the acquisition of data with high spatiotemporal resolution can enable the assessment of environmental vulnerabilities in urban areas towards the definition of responsive adaptation and mitigation strategies. In this context, the current work presents a two-fold approach based on low-cost cloud-connected sensors for (i) fixed and (ii) mobile monitoring of several environmental parameters. This paper, which focuses on the measurement aspects of the urban micro-climate, describes in detail the hardware and software components of both approaches, and how to exploit them for setting up a field campaign. The methods were tested in the city of Bolzano (Italy), demonstrating their suitability for identifying the spatial variability of the microclimate in relation to the urban morphology, and for highlighting the presence of the urban heat island and estimating its intensity.

Toward Resilient Water-Energy-Food Systems under Shocks: Understanding the Impact of Migration, Pandemics, and Natural Disasters

The historic pandemic faced by the international community today boldly demonstrates the complexity and interconnectedness of the resource challenges we must better understand and address in the future. Further complexity is observed when accounting for the impact of compounded shocks related to natural disasters and forced migration around the world. Effectively addressing these challenges requires the development of research that cuts across disciplines and innovates at their interfaces, in order to develop multifaceted solutions that respond to the social, economic, technological, and policy dimensions of these challenges. Water, energy, and food systems are tightly interconnected. They are faced with pressures of varying natures and levels of urgency which need to be better understood, especially as nations work toward achieving the UN 2030 Agenda’s Sustainable Development Goals by 2030. This paper will review existing models and knowledge gaps related to water-energy-food (WEF) nexus models, as well as models for quantifying the impact of migration, pandemics, and natural disasters on this resource nexus. Specifically, this paper will: (1) explore the WEF nexus literature and identify gaps in current assessment tools and models; (2) explore the literature on tools and models for predicting the shocks of migration, natural disasters, and pandemics; (3) identify interconnections between water, energy, and food systems and the identified shocks; (4) develop a common framework that provides a road map for integrating those shocks in WEF nexus analysis; (5) provide recommendations for future research and policies moving forward.

Paradigm Shift: The Promise of Deep Learning in Molecular Systems Engineering and Design

The application of deep learning to a diverse array of research problems has accelerated progress across many fields, bringing conventional paradigms to a new intelligent era. Just as the roles of instrumentation in the old chemical revolutions, we reinforce the necessity for integrating deep learning in molecular systems engineering and design as a transformative catalyst towards the next chemical revolution. To meet such research needs, we summarize advances and progress across several key elements of molecular systems: molecular representation, property estimation, representation learning, and synthesis planning. We further spotlight recent advances and promising directions for several deep learning architectures, methods, and optimization platforms. Our perspective is of interest to both computational and experimental researchers as it aims to chart a path forward for cross-disciplinary collaborations on synthesizing knowledge from available chemical data and guiding experimental efforts.

The Water–Energy–Food Nexus Discovery Map: Linking Geographic Information Systems, Academic Collaboration, and Large-Scale Data Visualization

The Water–Energy–Food (WEF) Nexus framework for holistic sustainable development has spawned independent and academic communities around the globe that utilize the framework in research, implementation, policy development, and technological advancement. These communities, however, are geographically and topically segmented and lack large-scale databasing that clearly catalogs and classifies their work. Recognizing this need, the WEF Nexus Strategic Initiative program at The Pennsylvania State University has developed the WEF Nexus Discovery Map utilizing the Arc Geographic Information Systems’ (GIS) Online Dashboard creation toolkit. In real time, users are able to select from 5040 different combinations of filters with the ease of a few button pushes and see projects pop up or disappear from the map located on the dashboard. Projects can then be clicked on to view their specific information, such as the institution that produced the work, local collaborators, relevant web page, and point of contact. The WEF Nexus Discovery Map demonstrates the early new-age of data resource management with the intersection of visuals, advanced search with built-in filters, and community-driven data collection to provide users with exact needs and connections to better facilitate and deploy the holistic sustainability framework of the WEF Nexus.

Subcritical water extraction as a circular economy approach to recover energy and agrochemicals from sewage sludge

Global population growth is creating severe pressure on wastewater treatment plants, and specifically on sludge management. Meanwhile, the global challenge of achieving food-security requires the development of green pest control practices that maximize crop productivity. The hydrothermal technology, using subcritical water as the conversion media has been intensively studied, mostly for energy recovery purposes. Here, we focused on the aqueous phase by-product of this process and studied the subcritical water extraction of sewage sludge to recover valuable agrochemicals, with high potential of pre-emergent herbicidal activity. Full characterization of hydrothermal extracts from different reaction temperatures (200-300 °C) and times (30-120 min) highlighted the formation of pyrazine derivatives. Seed germination bioassays with three different species suggested a positive correlation between reaction temperature and extract herbicidal activity. Moreover, differences in seed viability and final root elongation between the tested crop (Trriticum aestivum) and weeds (Lapidium sativum and Amaranthus palmeri) may indicate the competitive abilities that can play a key role in weed management. Our results suggest that subcritical water can be applied as a green solvent for extracting a valuable agrochemical from sewage sludge and improving the circular economy for wastewater treatment.

Improving Energy Efficiency of Irrigation Wells by Using an IoT-Based Platform

The irrigation sector has undergone a remarkable transformation in recent decades due to the application of pressurized water distribution technologies, improving the management of limited water resources. As a result of this transformation, irrigation has become, together with agricultural machinery, the primary consumer of energy within the agri-food sector. Furthermore, the energy cost of operating pumping equipment during a farming season represents 30–40% of the crop’s total cost. For this reason, one of the most interesting challenges in this scope is that of improving energy efficiency and reducing economic costs so that productive work become more and more competitive. Energy audit makes possible to determine the efficiency of installations, and enables to determine energy saving protocols (requirements), for this reason the aim of this article is to carry out these by using IoT-based systems. The proposed system improves decision-making on agricultural pumping management by classifying wells’ efficiency and integrating the data sets that determine their efficiency into a single information model. The system monitors energy efficiency according to different parameters such as: infrastructure, energy consumption, electric rates, manometric height or type of installation, making it possible to enhance each pumping operation’s decisions. This solution has been deployed in an irrigation community in southeast Spain whose results have warned about the lack of efficiency in two of its wells: in one of them it is proposed that they be replaced, due to the high cost of pumping water, and in the other, hydraulic mechanisms are implemented to improve the water-energy binomial.

Simulations of the Water Food Energy Nexus for policy driven intervention

Water-Food-Energy (WFE) resources exert mutual influences upon each other and thus cannot be managed separately. Information on household WFE expenditures addresses knowledge that distinguishes between geospatial districts' social welfare. Social welfare and investment in districts' WFE resources are interconnected. District (node) product of WFE normalized expenditures (Volume) is considered as a representative WFE Nexus holistic quantity. This Volume is assumed to be a function of residents' knowledge of welfare level across districts. We prove that the Volume rate conforms to Boltzmann entropy, and this is the premise of our hypothesis for directed information from high to low welfare between network nodes. Welfare mass (WM) represents the district's Volume combined with its income and population density. This WM is used as input into a model balancing between all domain nodes that allows policymakers to simulate the effects of potential quantifiable policy decisions targeted to individual districts at a domain level while also considering influences between districts. Based on existing historic data, the established tool exemplifies its potential by providing outcomes for Israel districts showing the influence of imposing different temporal allocation/deallocation actions as managerial regulations to prescribed districts. It is found that districts with a high WM do not suffer when a defund is applied, but districts that have a low WM gain from subsidies.

Continuous Technological Improvement Using Systems Engineering Principles to Achieve Sustainability

The design of a continuous plan would benefit society, as seen in systems engineering. To understand complex systems and to uphold the principles of stability, systems engineering has shown that it is a discipline of great importance. The principle of continuous technological improvement has augmented this idea, as the quality improvement of the design to meet inherent objectives would be the focus. This study aims to present the necessity of continuous technological improvement through systems engineering principles for socioeconomic and community-oriented growth. Thus, the context that would tackle global concerns and facilitate humanity's growth toward knowledge would be the application of technology. The context at hand, the design of systems thinking, and the overall approach taken to promote deeper perspectives has been illustrated in various literature. Healthcare, chemical production and organizational development are various fields of distinction that have shown evidence from the investigation into related literature. To streamline quality, as well as to maintain high quantities of production, all employed systems engineering have focused on technological improvements. In the field of industrial engineering, for a stable industry in which the system operates, this line of thinking is crucial.

A Complex Systems Analysis of the Water-Energy Nexus in Malaysia

Water security plays a crucial role in maintaining livelihoods, especially emerging economies. In Malaysia, understanding the inter-relationships of water within the water-energy-food (WEF) nexus is at its infancy. This paper investigates the interactions of the water sector with energy sector in Malaysia, through the lenses of WEF nexus, using system dynamics. The first part of the research involves qualitative interviews with key stakeholders in the water sectors, which provides validation for the initial causal loop relationships built and qualitative inputs of the water-energy nexus through the lenses of the water sector. The second part of the research is a quantitative simulation of stock and flow based on four carefully designed scenarios revolving around Malaysian water security. Key findings include an apparent disconnect between the states and federal governments in managing water supply, poor economic sustainability of the water supply and services industry, and significant energy use in the water sector. On the other hand, environmental impacts stemming from the water sector is minimal. Streamlining water governance and revising water tariffs have thus been suggested as policy recommendations, where their implementation could propagate into downstream benefits for the energy sector.

Resource recovery and waste-to-energy from wastewater sludge via thermochemical conversion technologies in support of circular economy: a comprehensive review

With the rapid rise in global population over the past decades, there has been a corresponding surge in demand for resources such as food and energy. As a consequence, the rate of waste generation and resultant pollution levels have risen drastically. Currently, most organic solid wastes are either land applied or sent to landfills, with the remaining fraction incinerated or anaerobically digested. However, with the current emphasis on the reduction of emissions, nutrient recovery, clean energy production and circular economy, it is important to revisit some of the conventional methods of treating these wastes and tap into their largely unrealized potential in terms of environmental and economic benefits. Wastewater sludge, with its high organic content and fairly constant supply, provides a great opportunity to implement some of these strategies using thermochemical conversion technologies, which are considered as one of the alternatives for upcycling such waste streams. This paper summarizes the results of prominent studies for valorizing wastewater sludge through thermochemical conversion technologies while drawing inferences and identifying relationships between different technical and operating parameters involved. This is followed by sections emphasizing the environmental and economic implications of these technologies, and their corresponding products in context of the broader fields of waste-to-energy, nutrient recycling and the progress towards a circular economy.

Contamination of N-poor wastewater with emerging pollutants does not affect the performance of purple phototrophic bacteria and the subsequent resource recovery potential

Propagation of emerging pollutants (EPs) in wastewater treatment plants has become a warning sign, especially for novel resource-recovery concepts. The fate of EPs on purple phototrophic bacteria (PPB)-based systems has not yet been determined. This work analyzes the performance of a photo-anaerobic membrane bioreactor treating a low-N wastewater contaminated with 25 EPs. The chemical oxygen demand (COD), N and P removal efficiencies were stable (76 ± 8, 62 ± 15 and 36 ± 8 %, respectively) for EPs loading rate ranging from 50 to 200 ng L^-1 d^-1. The PPB community adapted to changes in both the EPs concentration and the organic loading rate (OLR) and maintained dominance with >85 % of total 16S gene copies. Indeed, an increment of the OLR caused an increase of the biomass growth and activity concomitantly with a higher EPs removal efficiency (30 ± 13 vs 54 ± 11 % removal for OLR of 307 ± 4 and 590 ± 8 mgCOD L^-1 d^-1, respectively). Biodegradation is the main mechanism of EPs removal due to low EPs accumulation on the biomass, the membrane or the reactor walls. Low EPs adsorption avoided biomass contamination, resulting in no effect on its biological methane potential. These results support the use of PPB technologies for resource recovery with low EPs contamination of the products.

Exploring interactions in the local water-energy-food nexus (WEF-Nexus) using a simultaneous equations model

Exploring interactions between factors is a critical step to understand, quantify and govern the WEF-Nexus. However, current research mainly focuses on mapping causal loops and the hierarchy structure; equations in interaction exploration have been largely ignored. Using the panel data of China's 30 provinces from 2005 to 2016, this paper adopts a simultaneous equations model (SEM) to evaluate intensities between related factors in the local WEF-Nexus. We define a local WEF-Nexus as containing core, peripheral and interactive sub-nexuses, and decouple the core sub-nexus from the supply, consumption and waste disposal processes. Results show that effective irrigated area, secondary industry rate and crop sown area are key positive influencing factors in the WEF subsystem, with positive impact coefficients of 1.0426, 0.6986 and 1.149, respectively. Food production (-0.303) and chemical fertilizer used per sown area unit (-0.3129) are key negative factors in the WEF subsystem. Additionally, urban green land (0.4436) and total population (0.5815) exert specific influences on the water and energy subsystems, with a 1% increase in urban green land resulting in a 0.4436% increase in water consumption. The system boundary, two positive feedback loops and seven nexus points are identified, with total groundwater pumping being the only nexus point exerting an holistic impact across the WEF equations. The results in this paper complement recent nexus modeling work, and give a better understand of interaction mechanism in China's local WEF nexus, with useful implications for future policy development.

Structuring an integrated water-energy-food nexus assessment of a local wind energy desalination system for irrigation

Desalination is increasingly put forward as a sustainable local solution to water scarcity in combination with the exploitation of renewable energy sources. However, the complexity of the resource nexus entails the unavoidable existence of pros and cons across its various dimensions that can only be assessed at different scales of analysis. In turn, these pros and cons entail different winners and losers among the different social actors linked through the nexus. To address these challenges, a novel approach to resource nexus assessment is put forward, based on multi-scale integrated analysis of societal and ecosystem metabolism (MuSIASEM) and recognizing the resource nexus as a wicked problem. The integrated representation identifies the existence of biophysical constraints determined by processes both under human control (in the technosphere) and beyond human control (in the biosphere). The approach is illustrated with a local case study of desalination in the Canary Islands, Spain. The material presented has been generated in the context of the project "Moving towards adaptive governance in complexity: Informing nexus security" (MAGIC) for use in participatory processes of co-production of knowledge claims about desalination, a prerequisite for informed policy deliberation.

Towards Productive Cities: Environmental Assessment of the Food-Energy-Water Nexus of the Urban Roof Mosaic

Cities are rapidly growing and need to look for ways to optimize resource consumption. Metropolises are especially vulnerable in three main systems, often referred to as the FEW (i.e., food, energy, and water) nexus. In this context, urban rooftops are underutilized areas that might be used for the production of these resources. We developed the Roof Mosaic approach, which combines life cycle assessment with two rooftop guidelines, to analyze the technical feasibility and environmental implications of producing food and energy, and harvesting rainwater on rooftops through different combinations at different scales. To illustrate, we apply the Roof Mosaic approach to a densely populated neighborhood in a Mediterranean city. The building-scale results show that integrating rainwater harvesting and food production would avoid relatively insignificant emissions (13.9-18.6 kg CO₂ eq/inhabitant/year) in the use stage, but their construction would have low environmental impacts. In contrast, the application of energy systems (photovoltaic or solar thermal systems) combined with rainwater harvesting could potentially avoid higher CO₂ eq emissions (177-196 kg CO₂ eq/inhabitant/year) but generate higher environmental burdens in the construction phase. When applied at the neighborhood scale, the approach can be optimized to meet between 7% and 50% of FEW demands and avoid up to 157 tons CO₂ eq/year. This approach is a useful guide to optimize the FEW nexus providing a range of options for the exploitation of rooftops at the local scale, which can aid cities in becoming self-sufficient, optimizing resources, and reducing CO₂ eq emissions.

Requirements Based Design of Environmental System of Systems: Development and Application of a Nexus Design Framework

Social, technological, and environmental systems have become increasingly interconnected. Integrated problems arising between embedded water, energy, and food systems, require political and strategic cooperation between the actors involved at multiple governance levels. A holistic design approach is needed to guide the inherent decision-making processes. In this article, we developed a normative decision-making framework based on System of Systems Engineering (SoSE) and demonstrated how it can help to foster the cross-sectoral design of solutions to these interlinked water, energy, and food issues. The actors involved in our case study demonstrated a strong interest in collaborating across sectors and participating in the transition to cross-sectoral and sustainable resource management practices. However, experts from science and practice face a high degree of uncertainty when they design solutions to cope with the existing regional problems. As almost all regions of the world are highly integrated in national and global markets, future research might consider conducting larger research projects that also link the design approaches to inter-regional, national, and international levels. Our methodological approach illustrates how such a project could be structured on a regional level and identifies the processes that are important to consider.

Coupling and Coordination Degrees of the Core Water⁻Energy⁻Food Nexus in China

Achieving sustainable development in the water–energy–food (WEF) nexus is gaining global attention. The coupling and coordination degrees are a way to measure sustainable development levels of a complex system. This study assessed the coupling and coordination degrees of the core WEF nexus and identified key factors that affect sustainable development. First, an index system for assessing coupling and coordination degrees of the core WEF nexus was built. Second, the development levels of three subsystems as well as the coupling and coordination degrees of the core WEF nexus in China were calculated. The results showed that from 2007 to 2016, the mean value of the coupling degree was 0.746 (range (0.01, 1)), which was a high level. This proved that the three resources were interdependent. Hence, it was necessary to study their relationship. However, the mean value of the coordination degree was 0.395 (range (0, 1)), which was a low level. This showed that the coordination development of the core WEF nexus in China was low. It is necessary to take some measures to improve the situation. According to the key factors that affect the development levels of water, energy, and food subsystems, the authors put forward some suggestions to improve the coordination development of the WEF system in China.

A Review of the 21st Century Challenges in the Food-Energy-Water Security in the Middle East

Developing countries have experienced significant challenges in meeting their needs for food, energy, and water security. This paper presents a country-level review of the current issues associated with Food-Energy-Water (FEW) security in the Middle East. In this study, sixteen countries in the Middle East are studied, namely Iraq, Iran, Syria, Lebanon, Israel, Palestine, Egypt, Turkey, and the Arabian Peninsula (Bahrain, Kuwait, Oman, Qatar, Saudi Arabia (KSA), United Arab Emirates (UAE), and Yemen). Here, we conduct a comprehensive assessment to study and evaluate the emerging drivers of FEW systems in the region. The investigated drivers include water security, extreme events, economic growth, urbanization, population growth, poverty, and political stability. The results suggest that most of the studied countries are facing FEW resource insecurity or weak planning/management strategies. Our evaluation further revealed the current status of each country with respect to each factor, and suggested that climatic and socioeconomic factors have contributed to the subsequent stress on FEW resources, specifically on the water sector. In general, and with respect to the water-energy security, it was found that energy production in the Middle East is highly constrained by water deficiency, drought, and/or economic growth. The water-food security in the region is mainly affected by drought, water scarcity, population growth, urbanization, and/or political unrest.

A Food-Energy-Water Nexus approach for land use optimization

Allocation and management of agricultural land is of emergent concern due to land scarcity, diminishing supply of energy and water, and the increasing demand of food globally. To achieve social, economic and environmental goals in a specific agricultural land area, people and society must make decisions subject to the demand and supply of food, energy and water (FEW). Interdependence among these three elements, the Food-Energy-Water Nexus (FEW-N), requires that they be addressed concertedly. Despite global efforts on data, models and techniques, studies navigating the multi-faceted FEW-N space, identifying opportunities for synergistic benefits, and exploring interactions and trade-offs in agricultural land use system are still limited. Taking an experimental station in China as a model system, we present the foundations of a systematic engineering framework and quantitative decision-making tools for the trade-off analysis and optimization of stressed interconnected FEW-N networks. The framework combines data analytics and mixed-integer nonlinear modeling and optimization methods establishing the interdependencies and potentially competing interests among the FEW elements in the system, along with policy, sustainability, and feedback from various stakeholders. A multi-objective optimization strategy is followed for the trade-off analysis empowered by the introduction of composite FEW-N metrics as means to facilitate decision-making and compare alternative process and technological options. We found the framework works effectively to balance multiple objectives and benchmark the competitions for systematic decisions. The optimal solutions tend to promote the food production with reduced consumption of water and energy, and have a robust performance with alternative pathways under different climate scenarios.

Toward Sustainable Chemical Engineering: The Role of Process Systems Engineering

Products from chemical engineering are essential for human well-being, but they also contribute to the degradation of ecosystem goods and services that are essential for sustaining all human activities. To contribute to sustainability, chemical engineering needs to address this paradox by developing chemical products and processes that meet the needs of present and future generations. Unintended harm of chemical engineering has usually appeared outside the discipline's traditional system boundary due to shifting of impacts across space, time, flows, or disciplines, and exceeding nature's capacity to supply goods and services. Being a subdiscipline of chemical engineering, process systems engineering (PSE) is best suited for ensuring that chemical engineering makes net positive contributions to sustainable development. This article reviews the role of PSE in the quest toward a sustainable chemical engineering. It focuses on advances in metrics, process design, product design, and process dynamics and control toward sustainability. Efforts toward contributing to this quest have already expanded the boundary of PSE to consider economic, environmental, and societal aspects of processes, products, and their life cycles. Future efforts need to account for the role of ecosystems in supporting industrial activities, and the effects of human behavior and markets on the environmental impacts of chemical products. Close interaction is needed between the reductionism of chemical engineering science and the holism of process systems engineering, along with a shift in the engineering paradigm from wanting to dominate nature to learning from it and respecting its limits.

Developing interpretive structural modeling based on factor analysis for the water-energy-food nexus conundrum

Factor identification and analysis are effective ways to explain and quantify complex relationships in the water-energy-food nexus (WEF-nexus). It has been acknowledged that factors in the WEF-nexus vary by time, level and location, but the hierarchy between factors has been largely ignored. Taking advantage of the interpretive structural modeling (ISM) method, this paper presents an identification and analysis on the interwoven factors in an urban WEF-nexus in Beijing. As a result, 87 representative factors have been identified and classified, with a hierarchy structure established by ISM. Based on the relative importance of given factors, factor hierarchy structure shows that the energy system in the core nexus is the essential system and is critical to promoting the WEF-nexus in Beijing; factors from peripheral nexuses - such as population and vehicle volume - also have a significant influence on nexus governance. Furthermore, integrated policies from subsystems within the core nexus or between the core and peripheral nexuses are critical to secure WEF in Beijing. Factor analysis suggests that the portrayed nexus structure could provide valuable references for further quantification and decision making.

Exploring synergistic benefits of Water-Food-Energy Nexus through multi-objective reservoir optimization schemes

This study proposed a holistic three-fold scheme that synergistically optimizes the benefits of the Water-Food-Energy (WFE) Nexus by integrating the short/long-term joint operation of a multi-objective reservoir with irrigation ponds in response to urbanization. The three-fold scheme was implemented step by step: (1) optimizing short-term (daily scale) reservoir operation for maximizing hydropower output and final reservoir storage during typhoon seasons; (2) simulating long-term (ten-day scale) water shortage rates in consideration of the availability of irrigation ponds for both agricultural and public sectors during non-typhoon seasons; and (3) promoting the synergistic benefits of the WFE Nexus in a year-round perspective by integrating the short-term optimization and long-term simulation of reservoir operations. The pivotal Shihmen Reservoir and 745 irrigation ponds located in Taoyuan City of Taiwan together with the surrounding urban areas formed the study case. The results indicated that the optimal short-term reservoir operation obtained from the non-dominated sorting genetic algorithm II (NSGA-II) could largely increase hydropower output but just slightly affected water supply. The simulation results of the reservoir coupled with irrigation ponds indicated that such joint operation could significantly reduce agricultural and public water shortage rates by 22.2% and 23.7% in average, respectively, as compared to those of reservoir operation excluding irrigation ponds. The results of year-round short/long-term joint operation showed that water shortage rates could be reduced by 10% at most, the food production rate could be increased by up to 47%, and the hydropower benefit could increase up to 9.33 million USD per year, respectively, in a wet year. Consequently, the proposed methodology could be a viable approach to promoting the synergistic benefits of the WFE Nexus, and the results provided unique insights for stakeholders and policymakers to pursue sustainable urban development plans.