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The world is facing a global sustainability crisis affecting environmental systems and society. Addressing these issues requires a multi-dimensional approach that can integrate energy, water, and environment Systems, as well as provide scientific policy advice. In this study, an updated version of an Integrated Assessment Model (IAM) was used, together with new data compatible with Shared Socioeconomic Pathways (SSPs) projections, to significantly improve the work developed before. SSP climate data (temperature, precipitation, and total radiative forcing) and socioeconomic data (population and GDP) were loaded into the IAM, together with different scenario parameters. By analyzing varying socioeconomic scenarios, mitigation efforts, and adaptation strategies, this study assesses their impact on primary energy demand and, consequently, their impact on hydropower potential production. Our results show diverse energy paths, strongly dependent on the future scenario. Energy demand could increase up to 160%; however, several projections foresee a decline in hydropower production to minus 46% due to both climate change and socioeconomic transformation. Our findings highlight the importance of considering a range of potential future scenarios in energy planning and policy development. The varied outcomes across the considered scenarios emphasize the need for flexibility in strategies to accommodate for uncertainties and address the challenges posed by divergent trajectories in hydropower use and renewable energy shares. [ABSTRACT FROM AUTHOR]

It is often claimed that marine renewable energy alone could meet the electricity demand of current and future human societies. However, such claims are based on highly uncertain estimations of the global potentials of marine renewable energy sources (including tidal, ocean currents, wave, offshore wind and salinity and thermal gradients), and do not take into account the embedded energy of current technologies. To better understand the effective potential of marine energy, we conducted a literature review of its gross, technical, economic and sustainable potentials, as well as the energy return on investment (EROI), and estimated the net energy potential. We found that all marine technologies could provide a maximum energy surplus of 57,000 TWh / yr. This figure goes down to ∼ 5000 TWh / yr when excluding offshore wind. The previous figures do not include the contribution from ocean currents, for which no reliable estimates of global potentials and EROIs could be obtained. Due to its high upfront costs and environmental impacts and low social acceptance, no additional tidal range capacity expansion is envisioned. Similarly, the combination of a low sustainable potential and the low EROI makes the large-scale exploitation of salinity gradients unlikely with current technologies. Including all technologies, the average EROI of marine energy is ∼ 20 , but excluding offshore wind reduces the average EROI to ∼ 8 . While we did consider sustainability constraints for some marine energy sources, our estimation of marine net energy potential primarily relied on technical factors and did not account for economic and legal constraints. Therefore, the results presented here should be interpreted as an upper bound for the actual net energy contribution of marine energy sources to the global energy mix. [ABSTRACT FROM AUTHOR]

In this paper, sensitivity analysis is applied to a mechanistic model developed to simulate microalgae growth. The Morris method of Elementary Effects (EEs) is applied to evaluate the sensitivity of model outputs with respect to a subset of key input parameters. For an easier interpretation, results were plotted as distributions of elementary effects means and standard deviations for each input parameter. The model outputs were very sensitive with respect to the maximum specific growth rate of microalgae ( μ alg ). Results of the sensitivity analysis indicate that the transfer of ammonia ( K a , NH3 ) and carbon dioxide ( K a , CO2 ) have a non-linear relation with nitrogen uptake and carbonate concentrations, respectively. This analysis helped identify the parameters with the greatest impact on simulation outputs. The results indicated that maximum specific growth rate of microalgae ( μ alg ) was the most critical parameter to calibrate properly. [ABSTRACT FROM AUTHOR]

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Constructed wetlands are a widely adopted technology for the treatment of wastewater in small communities. The understanding of their internal functioning has increased at an unprecedented pace over recent years, in part thanks to the use of mathematical models. BIO_PORE model is one of the most recent models developed for constructed wetlands. This model was built in the COMSOL Multiphysics™ software and implements the biokinetic expressions of Constructed Wetlands Model 1 (CWM1) to describe the fate and transport of organic matter, nitrogen and sulphur in horizontal subsurface-flow constructed wetlands. In previous studies, CWM1 was extended with the inclusion of two empirical parameters ( M bio _ max and M cap ) that proved to be essential to provide realistic bacteria growth rates and dynamics. The aim of the current work was to determine the effect of these two parameters on the effluent pollutant concentrations predicted by the model. To that end, nine simulations, each with a different M bio _ max - M cap pair, were launched on a high-end multi-processor computer and the effluent COD and ammonia nitrogen concentrations obtained on each simulation were qualitatively compared among them. Prior to this study, a finite element mesh optimization procedure was carried out to reduce computational cost. Results of the mesh optimization procedure indicated that among the 5 tested meshes of different element size, the mesh utilized for this model in previous studies represented a fair compromise between output accuracy and computation time. Results of the sensitivity analysis showed that the value of M cap has a dramatic effect on the simulated effluent concentrations of COD and ammonia nitrogen, which clearly decreased for increasing values of this parameter. On the other hand, the model output was also sensitive to the values of M bio _ max , but its effects were less important and no clear relation could be established between its value and the simulated effluent concentration of COD and ammonia nitrogen. [ABSTRACT FROM AUTHOR]

Abstract: Despite the fact that horizontal subsurface flow constructed wetlands have been in operation for several decades now, there is still no clear understanding of some of their most basic internal functioning patterns. To fill this knowledge gap, on this paper we present what we call “The Cartridge Theory”. This theory was derived from simulation results obtained with the BIO_PORE model and explains the functioning of urban wastewater treatment wetlands based on the interaction between bacterial communities and the accumulated solids leading to clogging. In this paper we start by discussing some changes applied to the biokinetic model implemented in BIO_PORE (CWM1) so that the growth of bacterial communities is consistent with a well-known population dynamics models. This discussion, combined with simulation results for a pilot wetland system, led to the introduction of “The Cartridge Theory”, which states that the granular media of horizontal subsurface flow wetlands can be assimilated to a generic cartridge which is progressively consumed (clogged) with inert solids from inlet to outlet. Simulations also revealed that bacterial communities are poorly distributed within the system and that their location is not static but changes over time, moving towards the outlet as a consequence of the progressive clogging of the granular media. According to these findings, the life-span of constructed wetlands corresponds to the time when bacterial communities are pushed as much towards the outlet that their biomass is not anymore sufficient to remove the desirable proportion of the influent pollutants. [Copyright &y& Elsevier]

Abstract: Bacteria communities growing in constructed wetlands play a major role on the removal of pollutants from wastewater and the presence of a stable community is a critical factor affecting their performance. With this work we aimed at finding how long it takes for bacterial communities to stabilise in constructed wetlands and at answering specific questions regarding their abundance, spatial distribution and their relative importance on the treatment processes. To this end the numerical model BIO_PORE was used to simulate the dynamics of 6 functional bacteria groups (heterotrophic, autotrophic nitrifying, fermenting, acetotrophic methanogenic, acetotrophic sulphate reducing and sulphide oxidising bacteria) within a wetland for a period of 3years. Three indicators of bacterial stabilisation were used: 1) total biomass; b) effluent pollutant concentrations and c) Shannon's diversity index. Results indicate that aerobic bacteria dominated the wetland until the 80th day of operation. Anaerobic bacteria dominated the wetland from that moment and until the end of the studied period. Bacteria stability was reached between 400 and 700days after starting operation. Once the wetland reached stability, sulphate reducing bacteria accounted for the highest biomass of all bacterial groups (46%). The distribution of bacterial communities obtained after bacterial stability is consistent with available experimental results, and was clearly controlled by dissolved oxygen (SO) concentrations and H2S toxicity. After stability, the progressive accumulation of inert solids pushed the location of the active bacteria zone towards the outlet section. [Copyright &y& Elsevier]

Abstract: Reactive-transport models have been widely used to describe biogeochemical processes in subsurface environments. Horizontal subsurface-flow constructed wetlands fall in that category, and have experienced an exponential widespreading as an alternative wastewater treatment technique in recent years. As a result, the interest in modelling the processes occurring within these systems has proportionally increased. However, the functioning of wetlands is still poorly understood and the applicability of the available models is still limited. BIO_PORE model was built using COMSOL Multiphysics™ platform to help accelerating the development of constructed wetland models and to shed light on their internal functioning. The biokinetic equations of Constructed Wetlands Model number 1 describe bacteria-induced degradation and transformation processes of organic matter, nitrogen and sulphur. Small changes of such equations were required in order to include attachment and detachment of influent particulate components. Nutrients uptake and oxygen release by plant roots were also simulated. Thanks to the new biofilm sub-model, which prevents unlimited growth of bacteria in areas with high substrate concentrations, BIO_PORE model is able to reproduce the dynamic behaviour of constructed wetlands over long-term scenarios. During calibration, the model was fed with previously measured influent pollutant concentrations, water temperatures and flow rates of the first year of operation of a pilot wetland and simulated effluent concentrations of COD and NH4 good agreement with experimental data. Water temperatures had a great impact on the model output, whereas the inclusion of plants did not cause noticeable differences. [Copyright &y& Elsevier]

Abstract: The aim of this study was to verify under lab conditions the reliability, repeatability and accuracy of the falling head method (FHM) for hydraulic conductivity measurements. The FHM is a reliable procedure that has slight variations (less than 10%) in repeated measurements and turns out to be a reliable technique to record the hydraulic conductivities typically described for clogged and unclogged subsurface-flow constructed wetlands (from 4 to ca. 360m/day). The accuracy of the method is acceptable considering difficulties in the measurement of hydraulic conductivity in highly conductive media. Accordingly, results show measurement deviations of 20% when compared with a laboratory constant head method for highly conductive media (higher than 250m/day), and 80% for media with low hydraulic conductivity (lower than 50m/day). The main conclusion of the present paper is that of the FHM is a reliable and repeatable technique for hydraulic conductivity measurements and it is accurate enough for on-site clogging assessment in full-scale constructed wetlands. [Copyright &y& Elsevier]

In the present study, we compare energy transition scenarios from a new set of integrated assessment models, the suite of MEDEAS models, based on a systems dynamic modeling approach, with scenarios from two already well know structurally and conceptually different integrated assessment models, the Integrated MARKAL-EFOM System (TIMES) and the Long-Range Energy Alternatives Planning system (LEAP). The investigation was carried out to cross-compare and benchmark the response of MEDEAS models with TIMES and LEAP in depicting the energy transition in two different countries, Austria and Bulgaria. The preliminary results show a good agreement across all the models in representing scenarios projecting historical trends, while a major discrepancy is detectable when the rate of implementation of renewable energy is forced to increase to achieve energy system decarbonization. The discrepancy is mainly traceable to the differences in the models' conception and structures rather than in a real mismatch in representing the same scenarios. The present study is put forward as a guideline for validating new modeling approaches that link energy policy decision tools to the global biophysical and socioeconomic constraints. [ABSTRACT FROM AUTHOR]

Europe must move towards a 100% renewable transportation system for climate, energy and sustainability reasons. We estimate the capital and energy required for building and operating a renewable transportation system providing similar services as the EU-28 transport system of 2016. It could be based on: biogas or fuel cell vessels; liquid biogas powered aircrafts; electric railways and fuel cell or electric vehicles between major cities; and car sharing, electric buses and electric two- and three-wheelers, for short journeys. A system of charging posts on the streets and roads for passenger and commercial e-vehicles is studied. Alternatively, a Tracked Electric Vehicle system of continuous power on European roads would improve energy efficiency and the saving of scarce metals (Ni, Li), at a lower cost, if only national roads were electrified. The investment for the construction of the whole system would be 2.3–2.7% of the EU's GDP per year for 30 years. The new system operation would require 16% less energy than that of 2016, with reduction of 70% in road transport. However, shipping and aviation would demand 162% and 149% more energy, respectively, if liquefied biogas were used as fuel. A type of land transport fully based on trains would provide a similar service to that of an electric vehicle fleet, with a 29% lower energy consumption. [ABSTRACT FROM AUTHOR]

Constructed wetlands are currently recognized as an effective environmental biotechnology for wastewater treatment, but the influence of their design parameters on internal functioning and contaminant removal efficiency is still under discussion. In this work, the effect of aspect ratio and water depth on bacteria communities as well as treatment efficiency of horizontal subsurface flow constructed wetlands (HSSF) under the Mediterranean climate was evaluated, using a mathematical model. For this purpose, experimental results from four pilot-scale wetlands of equal surface area but different aspect ratios and water depth were used. The HSSF system was fed with municipal wastewater. The experimental data were simulated using the BIO_PORE model, developed in the COMSOL Multiphysics™ platform. Simulations with the BIO_PORE model fitted well to the experimental results, showing a higher removal efficiency for the shallower HSSF for COD (93.7% removal efficiency) and ammonia nitrogen (73.8%). The aspect ratio had a weak relationship with the bacteria distribution and the removal efficiency. In contrast, the water depth was a factor. The results of the present study confirm a previous hypothesis in which depth has an important impact on the biochemical reactions causing contaminants transformation and degradation. [ABSTRACT FROM AUTHOR]