Exploring urban metabolism—Towards an interdisciplinary perspective

© 2017 The Author(s) The discussion on urban metabolism has been long dominated by natural scientists focussing on natural forces shaping the energy and material flows in urban systems. However, in the anthropocene human forces such as industrialization and urbanization are mobilizing people, goods and information at an increasing pace and as such have a large impact on urban energy and material flows. In this white paper, we develop a combined natural and social science perspective on urban metabolism. More specifically, innovative conceptual and methodological interdisciplinary approaches are identified and discussed to enhance the understanding of the forces that shape urban metabolism, and how these forces affect urban living and the environment. A challenging research agenda on urban metabolism is also presented

A reactive barrier to enhance the removal of emerging organic compounds during artificial recharge of aquifers through infiltration basins

Artificial recharge of aquifers through infiltration basins (AR) improves water quality and in- creases groundwater resources, which make of it an appropriate technique for the renaturalization of waters affected directly or indirectly by wastewater effluents. Emerging organic compounds (EOCs), typically present in such waters, are mainly reduced during AR by sorption and biotrans- formation. We installed a reactive barrier in an infiltration basin (5000 m2) to enhance the removal of EOCs in the recharge water. The barrier consisted of sand, vegetable compost, iron oxide and clay. Vegetable compost was aimed at: 1) release organic carbon to be used as a carbon source by the microbial community thus promoting the generation of diverse redox conditions, and 2) to adsorb neutral EOCs. Clay and iron oxides were aimed at increasing sorption sites for cationic and anionic EOCs, respectively. Field application of such a design was tested by comparing the redox indicators and behavior of EOCs prior and after the installation of the reactive barrier. Residence time distributions of the recharge water at the monitoring points were obtained by a pulse tracer test. These distributions were used for calibrating a conservative transport and flow model of the aquifer. Finally, first order rates and retardation factors of several EOCs were estimated by fitting model outputs to observed concentrations. The estimation of the first order decay rates and retardation factors of several EOCs allowed the comparison of such values with values reported from other field sites and column experiments. The reactive barrier succeed in releasing organic carbon and achieving diverse redox condi- tions. The transformation of most EOCs was enhanced after the installation of the reactive barrier. In fact, first order rates and retardation factors were higher in the reactive barrier than in the rest of the aquifer and similar or higher than those from literature. In summary, addition of proposed reactive barrier significantly enhanced the performance of artificial recharge via infiltration basins, thus contributing to the renaturalization of recharged waters.La recarga artificial de acuíferos a través de balsas de infiltración (AR) mejora la calidad del agua y aumenta recursos de aguas subterráneas, convirtiéndola en una técnica apropiada para la renaturalización de las aguas afectadas directa o indirectamente por los efluentes de aguas residuales. En este tipo de aguas la presencia de compuestos orgánicos emergentes (EOCs) es más que frecuente. Durante la recarga artificial este tipo de compuestos es eliminado principalmente debido a la adsorción y a la biotransformación. Para mejorar la eliminación de los EOCs durante la infiltración del agua de recarga se instaló una barrera reactiva en una balsa de infiltración. La barrera consistía en arena, compost vegetal, óxidos de hierro y arcilla. La finalidad del compost vegetal era por un lado la de aportar carbono orgánico disuelto para ser utilizado como principal fuente de carbono por la comunidad microbiana promoviendo así la generación de diversas condiciones redox, y por otro lado la de adsorber EOCs neutros. La Arcilla y los óxidos de hierro se pusieron con la intención de aumentar los sitios de adsorción para los EOCs catiónicos y aniónicos, respectivamente. La efectividad de la barrera en el campo se estudió comparando el comportamiento de los indicadores redox y de los EOCs antes y después de la instalación de la barrera. Mediante un ensayo de trazadores tipo pulso se obtuvieron las distribuciones de los tiempos de residencia del agua de recarga a los puntos de observación. Estas distribuciones se utilizaron para calibrar un modelo de flujo y transporte conservativo del acuífero. Por último, las tasas de degradación de primer orden y los factores de retardo de varios EOCs se estimaron mediante el ajuste de los resultados del modelo con las concentraciones observadas. Las tasas de degradación y los factores de retardo estimados se compararon con valores encontrados en la bibliografía. La barrera reactiva cumple su función aportando carbono orgánico y generando diversas condiciones redox. Muchos de los EOCs estudiados mostraron una mejor transformación cuando la recarga se realizó con la barrera reactiva. Las tasas de degradación y factores de retardo estimados en la barrera son mayores que los estimados para el resto del acuífero, y del mismo orden o superiores a los encontrados en la bibliografía. En resumen, la barrera reactiva propuesta mejora significativamente el rendimiento de la recarga artificial a través de balsas de infiltración, contribuyendo así a la renaturalización de las aguas recargada

A Systematic Literature Review of the Solar Photovoltaic Value Chain for a Circular Economy

As the solar photovoltaic market booms, so will the volume of photovoltaic (PV) systems entering the waste stream. The same is forecast for lithium-ion batteries from electric vehicles, which at the end of their automotive life can be given a second life by serving as stationary energy storage units for renewable energy sources, including solar PV. The main objective of this paper is to systematically review the “state-of-the-art” research on the solar PV value chain (i.e., from product design to product end-of-life), including its main stages, processes, and stakeholder relationships, in order to identify areas along the value chain where circular strategies could be implemented, thereby advancing the transition of the PV industry towards circularity. To achieve this goal, we conducted a systematic literature review of 148 peer-reviewed articles, published in English between 2000 and 2020. Results show the PV value chain has been studied from a forward flow supply chain perspective and mostly from a technological point of view, with little regard for circular design, circular business models, and PV reuse. This article thus takes an integrated value chain perspective, introduces some of the barriers to circularity that industry players face, and argues that these barriers represent future opportunities for incumbent and new entrants to innovate within a circular PV industry

Advances in theory and their application within the field of zeolite chemistry

Zeolites are versatile and fascinating materials which are vital for a wide range of industries, due to their unique structural and chemical properties, which are the basis of applications in gas separation, ion exchange and catalysis. Given their economic impact, there is a powerful incentive for smart design of new materials with enhanced functionalities to obtain the best material for a given application. Over the last decades, theoretical modeling has matured to a level that model guided design has become within reach. Major hurdles have been overcome to reach this point and almost all contemporary methods in computational materials chemistry are actively used in the field of modeling zeolite chemistry and applications. Integration of complementary modeling approaches is necessary to obtain reliable predictions and rationalizations from theory. A close synergy between experimentalists and theoreticians has led to a deep understanding of the complexity of the system at hand, but also allowed the identification of shortcomings in current theoretical approaches. Inspired by the importance of zeolite characterization which can now be performed at the single atom and single molecule level from experiment, computational spectroscopy has grown in importance in the last decade. In this review most of the currently available modeling tools are introduced and illustrated on the most challenging problems in zeolite science. Directions for future model developments will be given

A reactive barrier to enhance the removal of emerging organic compounds during artificial recharge of aquifers through infiltration basins

Artificial recharge of aquifers through infiltration basins (AR) improves water quality and in- creases groundwater resources, which make of it an appropriate technique for the renaturalization of waters affected directly or indirectly by wastewater effluents. Emerging organic compounds (EOCs), typically present in such waters, are mainly reduced during AR by sorption and biotrans- formation. We installed a reactive barrier in an infiltration basin (5000 m2) to enhance the removal of EOCs in the recharge water. The barrier consisted of sand, vegetable compost, iron oxide and clay. Vegetable compost was aimed at: 1) release organic carbon to be used as a carbon source by the microbial community thus promoting the generation of diverse redox conditions, and 2) to adsorb neutral EOCs. Clay and iron oxides were aimed at increasing sorption sites for cationic and anionic EOCs, respectively. Field application of such a design was tested by comparing the redox indicators and behavior of EOCs prior and after the installation of the reactive barrier. Residence time distributions of the recharge water at the monitoring points were obtained by a pulse tracer test. These distributions were used for calibrating a conservative transport and flow model of the aquifer. Finally, first order rates and retardation factors of several EOCs were estimated by fitting model outputs to observed concentrations. The estimation of the first order decay rates and retardation factors of several EOCs allowed the comparison of such values with values reported from other field sites and column experiments. The reactive barrier succeed in releasing organic carbon and achieving diverse redox condi- tions. The transformation of most EOCs was enhanced after the installation of the reactive barrier. In fact, first order rates and retardation factors were higher in the reactive barrier than in the rest of the aquifer and similar or higher than those from literature. In summary, addition of proposed reactive barrier significantly enhanced the performance of artificial recharge via infiltration basins, thus contributing to the renaturalization of recharged waters.La recarga artificial de acuíferos a través de balsas de infiltración (AR) mejora la calidad del agua y aumenta recursos de aguas subterráneas, convirtiéndola en una técnica apropiada para la renaturalización de las aguas afectadas directa o indirectamente por los efluentes de aguas residuales. En este tipo de aguas la presencia de compuestos orgánicos emergentes (EOCs) es más que frecuente. Durante la recarga artificial este tipo de compuestos es eliminado principalmente debido a la adsorción y a la biotransformación. Para mejorar la eliminación de los EOCs durante la infiltración del agua de recarga se instaló una barrera reactiva en una balsa de infiltración. La barrera consistía en arena, compost vegetal, óxidos de hierro y arcilla. La finalidad del compost vegetal era por un lado la de aportar carbono orgánico disuelto para ser utilizado como principal fuente de carbono por la comunidad microbiana promoviendo así la generación de diversas condiciones redox, y por otro lado la de adsorber EOCs neutros. La Arcilla y los óxidos de hierro se pusieron con la intención de aumentar los sitios de adsorción para los EOCs catiónicos y aniónicos, respectivamente. La efectividad de la barrera en el campo se estudió comparando el comportamiento de los indicadores redox y de los EOCs antes y después de la instalación de la barrera. Mediante un ensayo de trazadores tipo pulso se obtuvieron las distribuciones de los tiempos de residencia del agua de recarga a los puntos de observación. Estas distribuciones se utilizaron para calibrar un modelo de flujo y transporte conservativo del acuífero. Por último, las tasas de degradación de primer orden y los factores de retardo de varios EOCs se estimaron mediante el ajuste de los resultados del modelo con las concentraciones observadas. Las tasas de degradación y los factores de retardo estimados se compararon con valores encontrados en la bibliografía. La barrera reactiva cumple su función aportando carbono orgánico y generando diversas condiciones redox. Muchos de los EOCs estudiados mostraron una mejor transformación cuando la recarga se realizó con la barrera reactiva. Las tasas de degradación y factores de retardo estimados en la barrera son mayores que los estimados para el resto del acuífero, y del mismo orden o superiores a los encontrados en la bibliografía. En resumen, la barrera reactiva propuesta mejora significativamente el rendimiento de la recarga artificial a través de balsas de infiltración, contribuyendo así a la renaturalización de las aguas recargadasPostprint (published version

Sorption and degradation of pesticides in biopurification systems

The increasing use of pesticides in agriculture has given rise to a situation in which countries now have to cope with the problem of residues of these compounds in ground and surface water. 40-90% of surface water contamination is caused by direct losses (e.g. spills during filling operations, leakages of spray equipment, spray leftovers, etc.). Considering the cost of treating water to remove pesticides, contamination should be treated at the source, thus on-farm before discharging. On-farm biopurification systems, developed to treat pesticide contaminated water, consist of a biologically active matrix that retains pesticides into the organic matter and enhances their biodegradation. In order to optimize the efficiency of these systems, the fate of pesticides and the contribution of degradation and retention process needs to be well characterized. In the present work, the intention was to unravel sorption and degradation processes on an increasing spatial scale. The first part of this thesis focused on the sorption of pesticides. The sorption strength of the pesticides appeared to be positively correlated to the Koc-value of the pesticide. Quantification of the sorption capacity with the Freundlich equation led to the following ranking with increasing sorption capacity: sandy loam soil < willow chopping, cow manure < straw, coco chips, compost < peat mix. Finally, it could be observed that the sorption capacity was in this case strongly correlated with the organic carbon content, CaO content and the cation exchange capacity. The second and major part of this thesis was performed with column experiments, thus incorporating transport of pesticides. Sorption and degradation characteristics of linuron, bentazone, metalaxyl and isoproturon were quantified using inverse modeling techniques present in the transport model HYDRUS-1D. The sorption strength of the different pesticides to the organic matrix, increased with decreasing mobility of the pesticides. Concerning increasing degradability of the pesticides, pesticides could be ranked as follows linuron > metalaxyl-isoproturon > bentazone. Delayed degradation could be observed for some pesticides in the micro- and macrocosms and could be fitted by implementing the Monod kinetics into HYDRUS-1D. Moreover, a column study was performed, where metalaxyl or isoproturon primed material was included in the matrix and transport of both pesticides was followed-up. Increased degradation in the presence of metalaxyl primed material was obtained, in contrast to isoproturon. The last part of the studies performed in column experiments were carried out to gain some knowledge on the influence of a variable flux on pesticide degradation and retention. Sorption of pesticides decreased considerably with increasing flux. Degradation of the pesticides was also significantly influenced by the flow in the microcosms. Finally, we explored two strategies to reduce the amount of pesticide residues in the organic matrix after use. Contaminated matrix (bifenthrin, linuron, metalaxyl and bentazone) was treated in an industrial composting plant and in barrel incubation. A decrease in certain pesticide concentrations could be observed in both processes. A removal in extractable pesticide concentration does however not always indicate degradation but could also be attributed to the formation of bound residues. Thus, it could be stated that the treatment of the matrix with the proposed composting process does not offer a decisive solution. In conclusion, the results reported in this thesis have provided insight in the degradation and sorption processes occurring inside the biopurification matrix. These results can be used in future studies to further elaborate the behavior of other pesticides in biopurification systems and to formulate some guidelines for the use of a biopurification system

Advancing Carbon Sequestration through Smart Proxy Modeling: Leveraging Domain Expertise and Machine Learning for Efficient Reservoir Simulation

Geological carbon sequestration (GCS) offers a promising solution to effectively manage extra carbon, mitigating the impact of climate change. This doctoral research introduces a cutting-edge Smart Proxy Modeling-based framework, integrating artificial neural networks (ANNs) and domain expertise, to re-engineer and empower numerical reservoir simulation for efficient modeling of CO2 sequestration and demonstrate predictive conformance and replicative capabilities of smart proxy modeling. Creating well-performing proxy models requires extensive human intervention and trial-and-error processes. Additionally, a large training database is essential to ANN model for complex tasks such as deep saline aquifer CO2 sequestration since it is used as the neural network\u27s input and output data. One major limitation in CCS programs is the lack of real field data due to a lack of field applications and issues with confidentiality. Considering these drawbacks, and due to high-dimensional nonlinearity, heterogeneity, and coupling of multiple physical processes associated with numerical reservoir simulation, novel research to handle these complexities as it allows for the creation of possible CO2 sequestration scenarios that may be used as a training set. This study addresses several types of static and dynamic realistic and practical field-base data augmentation techniques ranging from spatial complexity, spatio-temporal complexity, and heterogeneity of reservoir characteristics. By incorporating domain-expertise-based feature generation, this framework honors precise representation of reservoir overcoming computational challenges associated with numerical reservoir tools. The developed ANN accurately replicated fluid flow behavior, resulting in significant computational savings compared to traditional numerical simulation models. The results showed that all the ML models achieved very good accuracies and high efficiency. The findings revealed that the quality of the path between the focal cell and injection wells emerged as the most crucial factor in both CO2 saturation and pressure estimation models. These insights significantly contribute to our understanding of CO2 plume monitoring, paving the way for breakthroughs in investigating reservoir behavior at a minimal computational cost. The study\u27s commitment to replicating numerical reservoir simulation results underscores the model\u27s potential to contribute valuable insights into the behavior and performance of CO2 sequestration systems, as a complimentary tool to numerical reservoir simulation when there is no measured data available from the field. The transformative nature of this research has vast implications for advancing carbon storage modeling technologies. By addressing the computational limitations of traditional numerical reservoir models and harnessing the synergy between machine learning and domain expertise, this work provides a practical workflow for efficient decision-making in sequestration projects

Engineering Resilient Space Systems

Several distinct trends will influence space exploration missions in the next decade. Destinations are becoming more remote and mysterious, science questions more sophisticated, and, as mission experience accumulates, the most accessible targets are visited, advancing the knowledge frontier to more difficult, harsh, and inaccessible environments. This leads to new challenges including: hazardous conditions that limit mission lifetime, such as high radiation levels surrounding interesting destinations like Europa or toxic atmospheres of planetary bodies like Venus; unconstrained environments with navigation hazards, such as free-floating active small bodies; multielement missions required to answer more sophisticated questions, such as Mars Sample Return (MSR); and long-range missions, such as Kuiper belt exploration, that must survive equipment failures over the span of decades. These missions will need to be successful without a priori knowledge of the most efficient data collection techniques for optimum science return. Science objectives will have to be revised ‘on the fly’, with new data collection and navigation decisions on short timescales. Yet, even as science objectives are becoming more ambitious, several critical resources remain unchanged. Since physics imposes insurmountable light-time delays, anticipated improvements to the Deep Space Network (DSN) will only marginally improve the bandwidth and communications cadence to remote spacecraft. Fiscal resources are increasingly limited, resulting in fewer flagship missions, smaller spacecraft, and less subsystem redundancy. As missions visit more distant and formidable locations, the job of the operations team becomes more challenging, seemingly inconsistent with the trend of shrinking mission budgets for operations support. How can we continue to explore challenging new locations without increasing risk or system complexity? These challenges are present, to some degree, for the entire Decadal Survey mission portfolio, as documented in Vision and Voyages for Planetary Science in the Decade 2013–2022 (National Research Council, 2011), but are especially acute for the following mission examples, identified in our recently completed KISS Engineering Resilient Space Systems (ERSS) study: 1. A Venus lander, designed to sample the atmosphere and surface of Venus, would have to perform science operations as components and subsystems degrade and fail; 2. A Trojan asteroid tour spacecraft would spend significant time cruising to its ultimate destination (essentially hibernating to save on operations costs), then upon arrival, would have to act as its own surveyor, finding new objects and targets of opportunity as it approaches each asteroid, requiring response on short notice; and 3. A MSR campaign would not only be required to perform fast reconnaissance over long distances on the surface of Mars, interact with an unknown physical surface, and handle degradations and faults, but would also contain multiple components (launch vehicle, cruise stage, entry and landing vehicle, surface rover, ascent vehicle, orbiting cache, and Earth return vehicle) that dramatically increase the need for resilience to failure across the complex system. The concept of resilience and its relevance and application in various domains was a focus during the study, with several definitions of resilience proposed and discussed. While there was substantial variation in the specifics, there was a common conceptual core that emerged—adaptation in the presence of changing circumstances. These changes were couched in various ways—anomalies, disruptions, discoveries—but they all ultimately had to do with changes in underlying assumptions. Invalid assumptions, whether due to unexpected changes in the environment, or an inadequate understanding of interactions within the system, may cause unexpected or unintended system behavior. A system is resilient if it continues to perform the intended functions in the presence of invalid assumptions. Our study focused on areas of resilience that we felt needed additional exploration and integration, namely system and software architectures and capabilities, and autonomy technologies. (While also an important consideration, resilience in hardware is being addressed in multiple other venues, including 2 other KISS studies.) The study consisted of two workshops, separated by a seven-month focused study period. The first workshop (Workshop #1) explored the ‘problem space’ as an organizing theme, and the second workshop (Workshop #2) explored the ‘solution space’. In each workshop, focused discussions and exercises were interspersed with presentations from participants and invited speakers. The study period between the two workshops was organized as part of the synthesis activity during the first workshop. The study participants, after spending the initial days of the first workshop discussing the nature of resilience and its impact on future science missions, decided to split into three focus groups, each with a particular thrust, to explore specific ideas further and develop material needed for the second workshop. The three focus groups and areas of exploration were: 1. Reference missions: address/refine the resilience needs by exploring a set of reference missions 2. Capability survey: collect, document, and assess current efforts to develop capabilities and technology that could be used to address the documented needs, both inside and outside NASA 3. Architecture: analyze the impact of architecture on system resilience, and provide principles and guidance for architecting greater resilience in our future systems The key product of the second workshop was a set of capability roadmaps pertaining to the three reference missions selected for their representative coverage of the types of space missions envisioned for the future. From these three roadmaps, we have extracted several common capability patterns that would be appropriate targets for near-term technical development: one focused on graceful degradation of system functionality, a second focused on data understanding for science and engineering applications, and a third focused on hazard avoidance and environmental uncertainty. Continuing work is extending these roadmaps to identify candidate enablers of the capabilities from the following three categories: architecture solutions, technology solutions, and process solutions. The KISS study allowed a collection of diverse and engaged engineers, researchers, and scientists to think deeply about the theory, approaches, and technical issues involved in developing and applying resilience capabilities. The conclusions summarize the varied and disparate discussions that occurred during the study, and include new insights about the nature of the challenge and potential solutions: 1. There is a clear and definitive need for more resilient space systems. During our study period, the key scientists/engineers we engaged to understand potential future missions confirmed the scientific and risk reduction value of greater resilience in the systems used to perform these missions. 2. Resilience can be quantified in measurable terms—project cost, mission risk, and quality of science return. In order to consider resilience properly in the set of engineering trades performed during the design, integration, and operation of space systems, the benefits and costs of resilience need to be quantified. We believe, based on the work done during the study, that appropriate metrics to measure resilience must relate to risk, cost, and science quality/opportunity. Additional work is required to explicitly tie design decisions to these first-order concerns. 3. There are many existing basic technologies that can be applied to engineering resilient space systems. Through the discussions during the study, we found many varied approaches and research that address the various facets of resilience, some within NASA, and many more beyond. Examples from civil architecture, Department of Defense (DoD) / Defense Advanced Research Projects Agency (DARPA) initiatives, ‘smart’ power grid control, cyber-physical systems, software architecture, and application of formal verification methods for software were identified and discussed. The variety and scope of related efforts is encouraging and presents many opportunities for collaboration and development, and we expect many collaborative proposals and joint research as a result of the study. 4. Use of principled architectural approaches is key to managing complexity and integrating disparate technologies. The main challenge inherent in considering highly resilient space systems is that the increase in capability can result in an increase in complexity with all of the 3 risks and costs associated with more complex systems. What is needed is a better way of conceiving space systems that enables incorporation of capabilities without increasing complexity. We believe principled architecting approaches provide the needed means to convey a unified understanding of the system to primary stakeholders, thereby controlling complexity in the conception and development of resilient systems, and enabling the integration of disparate approaches and technologies. A representative architectural example is included in Appendix F. 5. Developing trusted resilience capabilities will require a diverse yet strategically directed research program. Despite the interest in, and benefits of, deploying resilience space systems, to date, there has been a notable lack of meaningful demonstrated progress in systems capable of working in hazardous uncertain situations. The roadmaps completed during the study, and documented in this report, provide the basis for a real funded plan that considers the required fundamental work and evolution of needed capabilities. Exploring space is a challenging and difficult endeavor. Future space missions will require more resilience in order to perform the desired science in new environments under constraints of development and operations cost, acceptable risk, and communications delays. Development of space systems with resilient capabilities has the potential to expand the limits of possibility, revolutionizing space science by enabling as yet unforeseen missions and breakthrough science observations. Our KISS study provided an essential venue for the consideration of these challenges and goals. Additional work and future steps are needed to realize the potential of resilient systems—this study provided the necessary catalyst to begin this process