The identification and management of contaminants of emerging concern (CECs) in water systems is crucial for protecting public and environmental health. This paper reports a theoretical approach to studying the adsorption of five CECs: Atrazine (ATZ), Caffeine (CAF), Carbamazepine (CBZ), Sulfamethoxazole (SMX), and Ibuprofen (IBU) - onto Activated Carbon (AC). A set of computational methods, including electrostatic molecular potential maps, conceptual density functional theory, Fukui functions, thermodynamic analysis, and tight-binding molecular dynamics simulations, were employed to analyze the electronic/energetic interactions and mechanisms involved in the adsorption of CECs on AC. The theoretical methodology offered valuable predictions on reactivity sites, stability, and binding mechanisms. Results showed that adsorption primarily occurred through non-covalent interactions like π-π electron donor-acceptor interactions, van der Waals forces, and hydrophobic interactions. Thermodynamic properties suggested the adsorption process was spontaneous and exothermic. However, for the AC/SMX system, the Gibbs free energy reveals that adsorption may be unfavorably compared to the other study systems. Molecular dynamics simulations validated the kinetic stability in the following order CAF (0.13Å)>CBZ (0.23Å)>ATZ (0.75Å)> IBU (1.28Å)>SMX (1.54Å). This exploratory theoretical study provides a deep understanding of the interactions between AC and five CECs, aiding in the rational design and optimization of AC-based treatment systems for environmental and industrial applications.

Between March and June 2020, activity in the major cities of Latin America declined due to containment efforts implemented by local governments to avoid the rapid spread of COVID-19. Our study compared 2020 with the previous year and demonstrated a considerable drop in tropospheric NO2 levels obtained by the SENTINEL 5P satellite in major Latin American cities. Lima (47.5%), Santiago (36.1%), São Paulo (27%), Rio de Janeiro (23%), Quito (18.6%), Bogota (17.5%), Buenos Aires (16.6%), Guayaquil (15.3%), Medellin (14.2%), La Paz (9.5%), Belo Horizonte (7.8%), Mexico (7.6%) and Brasilia (5.9%) registered statistically significant decreases in NO2 concentrations during the study period. In addition, we analyzed mobility data from Google and Apple reports as well as meteorological information from atmospheric reanalysis data along with satellite fields between 2011 and 2020, and performed a refined multivariate analysis (non-negative matrix approximation) to show that this decrease was associated with a reduction in population mobility rather than meteorological factors. Our findings corroborate the argument that confinement scenarios may indicate how air pollutant concentrations can be effectively reduced and managed.

A 3D stationary CFD study was conducted in our previous work, resulting in a novel reactor design methodology oriented to upgrading biogas through CO2 methanation. To enhance our design methodology incorporating relevant power to gas operational conditions, a novel transient 3D CFD modelling methodology is employed to simulate the effect of relevant dynamic disruptions on the behaviour of a tubular fixed bed reactor for biogas upgrading. Unlike 1D/2D models, this contribution implements a full 3D shell cooled methanation reactor considering real-world operational conditions. The reactor’s behaviour was analysed considering the hot-spot temperature and the outlet CH4 mole fraction as the main performance parameters. The reactor start-up and shutdown times were estimated at 330 s and 130 s, respectively. As expected, inlet feed and temperature disruptions prompted “wrong-way” behaviours. A 30 s H2 feed interruption gave rise to a transient low-temperature hot spot, which dissipated after 60 s H2 feed was resumed. A 20 K rise in the inlet temperature (523–543 K) triggered a transient low-temperature hot spot (879 to 850 K). On the contrary, a 20 K inlet temperature drop resulted in a transient high-temperature hot spot (879 to 923 K), which exposed the catalyst to its maximum operational temperature. The maximum idle time, which allowed for a warm start of the reactor, was estimated at three hours in the absence of heat sources. No significant impacts were found on the product gas quality (% CH4) under the considered disruptions. Unlike typical 1D/2D simulation works, a 3D model allowed to identify the relevant design issues like the impact of hot-spot displacement on the reactor cooling efficiency.

The catalytic activity of a blast furnace sludge (BFS) with important Fe content, was experimentally evaluated in the methanation of CO2. The effect of temperature (265-320 degrees C), total pressure (1-5 bar), partial pressures of H2 (12-30 kPa), CO2 (0.5-3.0 kPa) and H2/CO2 ratio (4-25) on CO2 conversion and selectivity towards CH4 and CO were studied. The experimental assays were carried out in a laboratory differential reactor. The favorable effect of temperature, total pressure and H2/CO2 ratio on methane formation was demonstrated. In addition, the catalyst exhibited a stable activity during prolonged reaction times, a valuable characteristic for its industrial application. The reaction mechanism of CO2 hydrogenation using this BFS-catalyst was studied under a strict kinetic regime. Different reaction paths were considered, from which kinetic expressions were derived using the Langmuir-Hinshelwood methodology and the Levenberg-Marquardt algorithm. The latter, for evaluation of the resulting kinetic/adsorption parameters. By applying the corrected Akaike information criterion (AICc), the rate controlling step was established. This corresponds to the hydrogenation of adsorbed CH, with surface CO as the main intermediary of methane formation. From the experimental data, an activation energy of 86.5 kJ/mol was calculated. This article can be considered as a first step for future processes of scaling and optimization of CO2 methanation using a waste from the steel production industry.

This research assessed water–energy nexus (WEN) efficiency in Chile's drinking water treatment plants by integrating the life cycle concept and exergy analysis principles. The cumulative exergy consumption (CExC) attributed to freshwater and the energy required by drinking water facilities during the whole life cycle were determined. Water-related indicators, such as the water stress index (WSI) and blue water footprint (BWF), differentiated by region, were used to highlight the critical role of water resources within the nexus. The CExC depicted significant differences between regions (10–30 MJex/m3), depending on the quality of raw water sources, pumping, and drinking water treatment (DWT) configurations. The WSI and the BWF varied spatially across the country due to climatic variability. Regions with a higher WSI (0.4–1) also implied higher CExC. This pattern can be justified by low water availability and poor water quality, which, at the same time, implied more energy-intensive technologies. Improving water and energy efficiency were identified as critical strategies for reducing the water and energy demand in the urban DWT systems.

A tubular reactor based on the disk and doughnut concept was designed as an engineering solution for biogas upgrading via CO2 methanation. CFD (Computational Fluid Dynamics) benchmarks agreed well with experimental and empirical (correlation) data, giving a maximum error of 8.5% and 20% for the chemical reaction and heat transfer models, respectively. Likewise, hot spot position was accurately predicted, with a 5% error. The methodology was used to investigate the effect of two commercially available coolants (thermal oil and molten salts) on overall reactor performance through a parametric study involving four coolant flow rates. Although molten salts did show higher heat transfer coefficients at lower coolant rates, 82% superior, it also increases, by five times, the pumping power. A critical coolant flow rate (3.5 m3/h) was found, which allows both a stable thermal operation and optimum pumping energy consumption. The adopted coolant flow range remains critical to guarantee thermal design validity in correlation-based studies. Due to the disk and doughnut configuration, coolant flow remains uniform, promoting turbulence (Re ≈ 14,000 at doughnut outlet) and maximizing heat transfer at hot spot. Likewise, baffle positioning was found critical to accommodate and reduce stagnant zones, improving the heat transfer. Finally, a reactor design is presented for SNG (Synthetic Natural Gas) production from a 150 Nm3 h−1 biogas plant.

The competition and interlinkages between energy, water, and land resources are increasing globally and are exacerbated by climate change and a rapid increase in the world population. The nexus concept has emerged for a comprehensive understanding related to the management and efficiency of resource use. This paper assesses water–energy–land nexus (WELN) efficiency through integration of the principles of Life Cycle Assessment (LCA) and exergy analysis, using the Chilean energy sector (CES) as a study case. The cumulative exergy consumption (CExC) and cumulative degree of perfection (CDP) are used as indicators for WELN efficiency. The results show the production of 1 MWh of electricity required 17.3 GJex, with the energy component of WELN (fossil and renewable energy sources) being the main contributor (99%). Furthermore, the renewable energy technologies depicted higher CDP of the water–energy–land nexus due to lower CExC and higher technology efficiency concerning non-renewables. The water and land resources contributed slightly to total exergy flow due to low quality in comparison with the energy component. Nevertheless, water availability and competition for land occupation constitute important issues for reducing environmental pressures and local conflicts. This study demonstrated the feasibility of exergy analysis for the evaluation of WELN efficiency through a single indicator, which could facilitate the comparison and integration with different processes and multi-scales.

Hydrogenation of CO for methane production was studied using blast furnace sludge (BFS), a Fe-rich residue, as a catalyst. Previously, the raw BFS was subjected to successive leaching stages to reduce some inhibitor compounds. The catalytic runs were carried out in a laboratory scale differential reactor, at 300-350 degrees C, 1 atm, and variable partial pressures of H-2 (10-50 kPa) and CO (0.25-3.0 kPa). Before the reaction, the catalyst was reduced in H-2 at 500 degrees C for 2 h. Product gases were analyzed by gas chromatography. The BFS, reduced (BFS-R), leached (BFS-L) and leached and reduced (BFS-L-R) catalysts were characterized by atomic absorption spectroscopy (AAS), in situ X-ray diffraction (XRD), N-2-physisorption at 77 K and thermogravimetric-mass spectrometry analysis (TG-MS). Some selected samples were also analyzed by X-ray photoelectron spectroscopy (XPS). Iron content in the leached sample was 51.7 wt%, present mostly as hematite (Fe2O3) and magnetite (Fe3O4). Carbon was also detected in the BFS-L-R, although its influence on CH4 formation was found to be negligible. When BFS-L-R was used as a catalyst, at 320 degrees C and H-2/CO = 20:1, rate of methane production and selectivity achieved 2.63 mu molCH(4)/g(cat)/min and 49.5%, respectively. Experimental results demonstrated that, under the studied conditions, CO hydrogenation towards CH4 proceeds through an H-assisted reaction path. Langmuir-Hinshelwood rate laws for both CH4 and the undesired CO2 production were derived, and parameters were adjusted from the obtained data. The activation energy for methane formation was 93.2 kJ/mol. To evaluate the catalyst resistance to poisoning, a BFS-L sample was treated with SO2 prior to the reaction tests. A first-order deactivation model was consistent with the data. The results of this work demonstrate the feasibility of BFS as a low-cost precursor of a methanation catalyst. Although this is a realistic alternative, further research, both experimental and modeling are still required to optimize operating conditions and to explore different reactor configurations.

Reduction of Fe-phases in a slag from the copper smelting process is studied for its use as a catalyst in methanation of carbon oxide (CO). This material contains 36.4 wt% Fe and the main Fe-phases in its fresh and reduced forms were identified and quantified. Chemical analysis and X-ray diffraction (XRD) for crystalline phase detection and determination of Fe dispersion were carried out. Reducibility of Fe-oxides was studied by thermal programmed reduction (TPR) under H-2 at 650 and 800 degrees C using 0.5 and 2 h soak time. In the fresh slag, iron was found to be in the form of Fe3O4 (17.4 wt%) and fayalite, Fe2SiO4 (43.4 wt%). The composition was experimentally determined and verified by stoichiometric balances and thermogravimetric analysis (TGA). Upon reduction at 800 degrees C and 2 h soak time, 87 % of the Fe-phases were reduced, leaving an activated catalyst with a 35.2 % Fe-0, which is the active phase for CO hydrogenation to methane. An expression was derived to determine the Fe-0 concentration in the reduced slag based on the composition of the fresh slag and its reduction degree. The catalytic activity of the reduced slag during CO hydrogenation was evaluated in a fixed bed differential reactor. The selectivity to methane, at 300 degrees C, was 87 %, thus confirming its catalytic activity for the selected reaction.

Novoa, V., Rojas, O., Arumí, J. L., Ulloa, C., Urrutia, R., & Rudolph, A. (marzo-abril, 2016). Variabilidad de la huella hídrica del cultivo de cereales, río Cachapoal, Chile. Tecnología y Ciencias del Agua, 7(2), 35-50. Se evaluaron los efectos de la variabilidad climática en el consumo de agua para la producción agrícola de cereales, a través del cálculo de la huella hídrica, metodología que consideró tres escenarios de precipitación: (a) año húmedo, (b) año normal y (c) año seco, y bajo dos condiciones de rendimiento (constante y disminución de 20%, proyectando el efecto de cambio climático), en tres secciones de la cuenca del río Cachapoal. Además, se calculó el agua virtual y la productividad aparente del agua para evidenciar el efecto de la variabilidad climática en la productividad del consumo del agua en el cultivo de cereales. El análisis de percentiles determinó que el año 2005 correspondió a húmedo, 2006 a normal y 2007 a seco. La huella hídrica de los cereales, bajo un rendimiento constante, fue mayor en el año húmedo con 1 064 m3 /ton; en cambio, con una disminución del rendimiento, fue mayor en el año seco (1 633.9 m3 /ton). Para ambas condiciones, la mayor huella hídrica azul se estimó en un año seco y la mayor huella hídrica verde en un año húmedo. Sin embargo, no se observaron diferencias entre las secciones de la cuenca. En un año húmedo se habría exportado la mayor cantidad de agua virtual con 14 325 000 m3 /año, y se habría producido la menor productividad aparente del agua, 92.8 $/m3 , información fundamental para determinar sistemas agrícolas sustentables.

The water footprint was calculated to evaluate the effects of climate variability on the water consumed during the production of cereals. This methodology considered three precipitation scenarios: a) rainy year, b) normal year and c) dry year. It also included two yield conditions - constant and a 20% reduction (projecting for the effect of climate change)- for three sections of the Cachapoal River basin. In addition, virtual and apparent water productivity were calculated to demonstrate the effect of climate variability on water productivity of cereal crops. The analysis of percentiles found that the year 2005 corresponded to a rainy year, 2006 to a normal year and 2007 to a dry year. Under constant yield conditions, the water footprint of the cereals was larger during the rainy year (1 064 m3/ton), while under reduced yield conditions it was larger during the dry year (1 633.9 m3/ton). For both conditions, the largest blue water footprint estimated corresponded to a dry year and the largest green water footprint to a rainy year. Nevertheless, no differences among the sections of the basin were observed. During a rainy year, the largest amount of virtual water (14 325 000 m3/year) would be exported and the lowest apparent water productivity (92.8 $/m3) would be produced. This information is crucial to develop sustainable agricultural systems.

The co-firing of coal and biomass was studied using DTG assays. Blends of coal of different ranks and pine charcoal (obtained through pyrolysis of biomass at 1000 degrees C) were prepared. Combustion profiles and characteristic temperatures (IT, PT and BT) were obtained and compared. To detect deviations, the experimental burnout curves for each blend were compared with weighted averages calculated from the conversion profiles obtained for the individual fuel samples and the blend composition. Positive and negative deviations were obtained which can be predicted from the differences in the reactivity of the blend components and their relative proportions.

The energy system in the Region of Aysén, Chile, is characterized by a strong dependence on fossil fuels, which account for up to 51% of the installed capacity. Although the implementation of waste-to-energy concepts in municipal waste management systems could support the establishment of a more fossil-independent energy system for the region, previous studies have concluded that energy recovery systems are not suitable from an economic perspective in Chile. Therefore, this work intends to evaluate these technical options from an environmental perspective, using life cycle assessment as a tool for a comparative analysis, considering Coyhaique city as a case study. Three technical alternatives were evaluated: (i) landfill gas recovery and flaring without energy recovery; (ii) landfill gas recovery and energy use; and (iii) the implementation of an anaerobic digestion system for the organic waste fraction coupled with energy recovery from the biogas produced. Mass and energy balances of the three analyzed alternatives have been modeled. The comparative LCA considered global warming potential, abiotic depletion and ozone layer depletion as impact categories, as well as required raw energy and produced energy as comparative regional-specific indicators. According to the results, the use of the recovered landfill gas as an energy source can be identified as the most environmentally appropriate solution for Coyhaique, especially when taking into consideration the global impact categories.

The co-pyrolysis of coal-biomass blends were studied by using thermogravimetric analysis to look for thermal events indicating interactions that could cause synergic or inhibitory effects during the first stage in the co-combustion of these materials. Two coals from different rank were selected for the study and combined with radiata pine sawdust, the selected biomass compound. Pyrolysis assays were carried out on the individual components and the binary coal-sawdust blends (50% p/p) at different heating rates (10, 30, 50 °C/min) until reaching a maximum temperature of 1200 °C. The individual components behaved as expected and as is widely described in the specialized literature. Interactions detected in the blends resulted in greater-than-expected volatile yield values. These interactions were produced at pyrolysis temperatures over 400 °C, when most of the components in the blend are devolatilized, and are attributed to secondary reactions that inhibit the formation of char.