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Air pollution is considered the world’s most important environmental and public health risk. The annual exposure for particulate matter (PM) in the northern Caribbean region of Colombia between 2011 and 2019 was determined using PM records from 25 monitoring stations located within the area. The impact of exposure to particulate matter was assessed through the updated Global Burden of Disease health risk functions using the AirQ+ model for mortality attributable to acute lower respiratory disease (in children ≤ 4 years); mortality in adults aged > 18 years old attributable to chronic obstructive pulmonary disease, ischaemic heart disease, lung cancer, and stroke; and all-cause post-neonatal infant mortality. The proportions of the prevalence of bronchitis in children and the incidence of chronic bronchitis in adults attributable to PM exposure were also estimated for the population at risk. Weather Research and Forecasting-California PUFF (WRF-CALPUFF) modeling systems were used to estimate the spatiotemporal trends and calculate mortality relative risk due to prolonged PM2.5 exposure. Proportions of mortality attributable to long-term exposure to PM2.5 were estimated to be around 11.6% of ALRI deaths in children ≤ 4 years of age, 16.1% for COPD, and 26.6% for IHD in adults. For LC and stroke, annual proportions attributable to PM exposure were estimated to be 9.1% and 18.9%, respectively. An estimated 738 deaths per year are directly attributed to particulate matter pollution. The highest number of deaths per year is recorded in the adult population over 18 years old with a mean of 401 events. The mean risk in terms of the prevalence of bronchitis attributable to air pollution in children was determined to be 109 per 100,000 inhabitants per year. The maximum RR values for mortality (up 1.95%) from long-term PM2.5 exposure were predicted to correspond to regions downwind to the industrial zone.

El deterioro y agotamiento progresivo de las fuentes de suministro de materiales adecuados para la construcción de infraestructura vial ha llevado al desarrollo de técnicas alternativas de mejoramiento de suelos, dentro de éstas la estabilización química de suelos se presenta como una alternativa técnica, económica y ambientalmente sostenible enfocada al mejoramiento de caminos sin pavimentar de bajo volumen de tránsito. Esta técnica de mejoramiento de suelos consiste en el empleo de productos químicos para mejorar las propiedades ingenieriles de los suelos, reduciendo su plasticidad y haciéndolos más resistentes, ante la acción del tráfico y condiciones ambientales a las que están expuestos. Los estabilizantes químicos que han sido empleados para el mejoramiento de suelos pueden clasificarse, según su naturaleza química, en: polímeros, aceites sulfonados, organosilanos, puzolanas y enzimas. Estas alternativas de mejoramiento de suelos han sido usualmente orientadas a caminos sin pavimentar de mediano y bajo volumen de tránsito, donde el desgaste y la durabilidad de los materiales es debido principalmente a factores climáticos y de intemperismo natural. El intemperismo deteriora los materiales expuestos al exterior produciendo cambios de color, superficies más rugosas, fisuramiento, agrietamiento, pérdida de cohesión y fragmentación, lo que finalmente se traduce en una pérdida de resistencia y efectividad de estos. El intemperismo acelerado es una alternativa que permite evaluar en periodos cortos de tiempo la evolución de las propiedades fisicoquímicas de los materiales y predecir su comportamiento a largo plazo, para ello se cuenta con cámaras de envejecimiento acelerado donde se exponen los materiales a ciclos alternados de luz ultravioleta (UV) y humedad, todo ello a temperaturas elevadas y controladas. The progressive deterioration and depletion of the sources of materials supply suitable for the construction of road infrastructure, the wide variety of soil types and low sustainability and durability of constructive solutions has stimulated the emergence and alternative construction systems evaluation for road sections stabilization, treatment or rehabilitation. Among them, chemical soil stabilization is presented as a technically, economically and environmentally sustainable alternative focused on improving medium and low-volume unpaved roads. This technique involves the use of chemicals to improve the soils engineering properties in order to reduce its plasticity and increase their strength to the action of traffic and environmental conditions to which they are exposed. Chemical stabilizers that have been used for soil improvement can be classified according to their chemical nature, in: polymers, sulfonated oils, silanes, pozzolans and enzymes. These alternatives for soil improvement have been usually aimed over medium and low-volume unpaved roads, where materials wear and durability is mainly due to climatic and natural weathering factors. Natural weathering deteriorates the exposed external materials and it produces color changes, rougher surfaces, fissuring, cracking, fragmentation and loss of cohesion which results in a strength loss, effectiveness and functionality of these materials. The accelerated weathering is a methodology to evaluate the material physicochemical properties evolution in short periods of time and predict long-term behavior by combining the most unfavorable environmental conditions to which the material would be exposed during a relatively long period. For this purpose, tests are performed using a QUV accelerated weathering tester, in which the materials are exposed to alternating cycles ultraviolet light (UV) and moisture. All at high and controlled temperatures. In this research work it intends to evaluate accelerated weathering's effect on the performance and durability of a soil additive with chemical stabilizers of different nature, using a QUV accelerated weathering tester to recreate real environmental conditions, simulating and controlling parameters such as: temperature, humidity (condensation and water spray) and ultraviolet light exposure. This makes it possible to know the behavior and performance of this type of materials over time under weather conditions.

In this work, the global stability of a continuous bioreactor model is studied, with the concentrations of biomass and substrate as state variables, a general non-monotonic function of substrate concentration for the specific growth rate, and constant inlet substrate concentration. Also, the dilution rate is time varying but bounded, thus leading to state convergence to a compact set instead of an equilibrium point. Based on the Lyapunov function theory with dead-zone modification, the convergence of the substrate and biomass concentrations is studied. The main contributions with respect to closely related studies are: i) The convergence regions of the substrate and biomass concentrations are determined as function of the variation region of the dilution rate (D) and the global convergence to these compact sets is proved, considering monotonic and non-monotonic growth functions separately; ii) several improvements are proposed in the stability analysis, including the definition of a new dead zone Lyapunov function and the properties of its gradient. These improvements allow proving convergence of substrate and biomass concentrations to their compact sets, while tackling the interwoven and nonlinear nature of the dynamics of biomass and substrate concentrations, the non-monotonic nature of the specific growth rate, and the time-varying nature of the dilution rate. The proposed modifications are a basis for further global stability analysis of bioreactor models exhibiting convergence to a compact set instead of an equilibrium point. Finally, the theoretical results are illustrated through numerical simulation, showing the convergence of the states under varying dilution rate.

Variations in the carbonaceous aerosol contents, organic carbon (OC) and elemental carbon (EC), in particulate matter less than 10 μm in size (PM

TiO2 doped with nitrogen (N), silicon (Si), or selenium (Se) (N-TiO2, Si-TiO2, and Se-TiO2) were obtained by the integrated sol-gel and solvothermal method with short time of crystallization and low temperature. The UV/visible and visible light absorption and photocatalytic activity of these doped TiO2 materials were improved by a dry-co-grinding process with a short grinding time and low rotational speed (30 min at 200 rpm) to obtain N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 catalysts. The materials were characterized by XRD, Raman, BET surface area and porosity, XRF, SEM, TEM, FTIR-ATR, and UV/vis-DRS analyses. The photocatalytic activity of these materials was evaluated by the degradation of phenol under UV/visible and visible light irradiation. The integrated sol-gel and solvothermal methods with short time of crystallization (2 h) and low temperature (225 °C), and the dry-co-grinding process during 30 min at 200 rpm led to materials (N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2) with higher specific surface area, a reduction in the band gap value, and an enhancement of the absorption in the visible light spectrum. Moreover, N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 exhibited higher photocatalytic activities for degradation of phenol under UV/visible and visible light irradiation than those obtained with the doped TiO2, synthesized TiO2 or TiO2 P25.

This study was designed to evaluate the atmospheric total suspended particle (TSP) and particulate matter (PM10) concentrations and temporal variability in one of the world’s largest open-pit coal mines (El Cerrejon) located in northeast Colombia, during 2012–2016. The results showed overall average TSP and PM10 concentrations of 86 μg m−3 (CI95% 84–88 μg m−3) and 34 μg m−3 (CI95% 33–35 μg m−3), respectively, with the highest concentrations between March and August each year. A time trend analysis of the results revealed that PM10 concentrations in particular have significantly increased between 6.2 and 7.7% per year (CI95% 1.2–12.8% year−1) in several of the monitoring stations. Meteorological parameters were also evaluated. It was observed that NE winds with speeds above 2 m s−1 were significantly correlated with an increase in the concentration of PM10 for selected downwind sites, which suggested that coal mining operations are an important source of atmospheric PM in the area. Regional long-range atmospheric transport scenarios showed potential effects on neighboring municipalities and countries within 72-h transportation events. These highlighted the need to develop new strategies to control the emissions of PM from the local mining industry to comply with local and international guidelines and regulations, particularly when industrial expansion is planned for the near future and relatively large population centers are in the area, of which a high proportion belong to indigenous populations.

This study conducted meteorological simulations in northern Colombia by analyzing different planetary boundary layer (PBL) schemes available in the numerical Weather Research and Forecasting (WRF) model. The study area included three nested domains with horizontal resolutions of 18 km, 6 km, and 2 km, with 38 vertical levels. The evolution and structure of the PBL were analyzed during the driest months (March, April, and May 2016) and in regions with the highest particulate matter concentrations. Sensitivity analysis of the WRF model was performed with two local and two non-local PBL schemes. The results were validated using observations of the surface air temperature, relative humidity, and surface wind speed collected from three meteorological stations in the area. The PBL heights were experimentally determined using radiosonde data provided by a station located in the center of the study area. Variations in PBL heights were estimated using linear regression methods and minimization of statistical errors for the bulk Richardson number, as well as analysis of vertical temperature and wind profiles. The WRF model reliably reproduced the daily values and diurnal cycles of temperature, relative humidity, and wind speed within the PBL and accounted for the influence of topography and sea breezes. Horizontal heat advection dominates the upwelling of air masses when sea breezes are active. The onshore wind direction starts to change from east to northwest, implying a decay in the land breeze regime. All schemes overestimate the mixing height and tend to underestimate surface air temperature values at night. All show wetter conditions and underestimate wind speed. Although the non-local Yonsei University (YSU) scheme shows the best performance, it also shows the largest sources of errors when determining the behavior of the surface layer during stable conditions. Relative humidity and wind speed estimates provided by the local Mellor‐Yamada‐Nakanishi‐Niino (MYNN) scheme were closer to those recorded at the meteorological stations.

Particulate matter (PM) is the main pollutant produced by open-pit mining operations, and its emission into the atmosphere is strongly associated with adverse health effects in the surrounding communities. The objective of this study was to evaluate the effects of the COVID-19-related lockdown on the PM concentrations in the North, Central, and South Zones of Cerrejon, Colombia, the largest open-pit coal mine in Latin America. To compare the levels before and during the emergency shutdown, we analyzed both the ground-based daily PM10 and PM2.5 data and the satellite (Terra/Aqua MODIS)-based daily aerosol optical depth (AOD) values from March 6 through April 13, 2020. The average PM10 concentrations in the North and South Zones, in contrast to those observed at other global monitoring sites, increased by 13–38% and 4–7%, respectively, although they decreased by 26–31% in the Central Zone, between the pre-lockdown and lockdown periods. Furthermore, during the latter, the daily PM2.5 levels in the South Zone rose by up to 43%, and we found higher AOD values (≥ 0.4) over the Central and South Zones as well as significant AOD-contributing loads upwind and downwind of the coal production pits. Finally, the increases in humidity and temperature (≥ 3.5% and ≥ 0.3 K, respectively), decrease in planetary boundary layer height (≥ 0.11 km), wind field variability, and rural biomass burning events shaped the spatial-temporal behavior of the PM in this region, and changes in meteorology and external sources nearly offset the reduction in emissions from mining activities. These results establish a baseline for developing future regulations and mitigation plans.

Intake fraction was determined in this study to provide insight into population exposures to PM10 that is effectively inhaled due to emissions of an opencast coal mine. We applied the CALPUFF model to a coal mine in Northern Colombia, which has 6 active pits with an annual production of 33.7 million tons. We estimated the intake fractions for 7 towns through the integration of dispersion model results over the population data. The resulting average intake fractions were between 6.13 × 10−9 and 3.66 × 10−8 for PM10. 62.4% of the intake fractions in the domain were calculated within a 23 km radius from the coal mine and coved 44.3% of the total population in this area. We calculated an estimate point for morbidity impacts using standard epidemiological assumptions. It is estimated that there were annually 105835 restricted activity days and 336832 respiratory symptom cases due to the direct impact of the opencast coal mining. These data also provide a framework for improved understanding of the effect of coal mining in Colombia.

Photoactive nano-titanium dioxide, as anatase phase, was obtained by the sol–gel method coupled with the solvothermal technique at short crystallization time (2 h) and low temperature (200 °C), using tetraisopropyl orthotitanate as Ti-precursor and 2-propanol as solvent. Precursor ratios were evaluated to determine their influence in the synthesis. Methyl orange was used as model molecule for the photocatalytic degradation. Highest anatase crystallinity was obtained when the water content is close to the stoichiometrically needed to hydrolyze a molecule of TIOT and these materials also showed the highest methyl orange photodegradation.

This study reports the use of excitation-emission matrix (EEM) fluorescence and UV/Vis spectroscopy to monitor the changes in the composition and reactivity of Aldrich humic acids (Aldrich HA) as a model compound for natural organic matter (NOM) during photocatalytic degradation. Degussa P-25 titanium dioxide (TiO(2)) and a solar UV-light simulator (a batch reactor) were used. The photocatalysis shifted the fluorescence maxima of EEMs of Aldrich HA toward shorter wavelengths, which implied that the photocatalytic degradation of commercial Aldrich HA caused the breakdown of high molecular weight components and the formation of lower molecular weight fractions. In addition, the fluorescence intensity of fulvic- and humic-like Aldrich HA presented a strong correlation with dissolved organic carbon (DOC), specific UV absorbance (SUVA) parameters, trihalomethane formation potential (THMFP), and organically bound halogens absorbable on activated carbon formation potential (AOXFP). Fluorescence spectroscopy was shown to be a powerful tool for monitoring of the photocatalytic degradation of HA.

The concentrations of total suspended particles (TSP) and particles with size below 10 and 2.5 micrometers (PM10 and PM2.5) in the urban area of the city of Riohacha in Colombia were determined. The instruments used were a high-volume sampler for TSP and PM10 and a low-volume sampler (Partisol) for PM2.5, all in six monitoring stations. The results showed that the average PM10 concentrations ranged from 43.69 to 19.47 µg/m3, the PST ranged from 86.02 to 27.38 µg/m3 and the average for PM2.5 was 14.57 µg/m3. Relations PM10/PST ranged from 0.50 to 0.68. The six stations showed good correlation PST/PM10 (R=0.795). The PST can imply the presence of PM10 particles in the urban area of this city but PM10 concentrations not necessarily indicate the presence of PM2.5 particles (R=0.035). The results for the correlation PM10/PST are similar to studies conducted in other urban areas of Colombia and of other countries.

Photocatalytic bleaching and mineralization of the dye Cibacron Yellow LS-R using Fe-doped TiO 2 synthesized and Aeroxide TiO 2 P25 have been investigated. The Fe-doped TiO 2 samples were synthesized by sol–gel method combined with solvothermal treatment at short crystallization time (2 h) and low temperature (200 °C), using tetraisopropyl orthotitanate as Ti-precursor, iron (III) nitrate as Fe-precursor and 2-propanol as solvent. Different Fe:Ti molar ratios (0.5%, 1%, 1.5% and 2%) were evaluated. 0.5% Fe-doped TiO 2 had the best photocatalytic performance among Fe doped samples, however it showed a low photocatalytic activity in the dye Cibacron Yellow LS-R photodegradation compared with Aeroxide TiO 2 P25. This result perhaps is due to the poor ability of the Fe-doped TiO 2 to produce hydroxyl radicals under UV irradiation, which was measured using fluorescence method, and its size particle which could be very large for the iron load in the sample, compared with those reported in the literature as appropriate.

This study demonstrated a novel method used to coat polymeric pellets with titanium dioxide (TiO 2 ) using simple and flexible equipment. In this method, TiO 2 catalyst and polymeric pellets were dispersed in glycerine and heated to the melting point of the polymer, and then the system was cooled to room temperature, which resulted in the TiO 2 -embedded polymer. Degussa P-25 TiO 2 was used as the catalyst, and pellets of polypropylene (PP) and low-density polyethylene (PE) were used as the polymeric supporting substrates. The coating adhesion was analyzed using an erosion test, and the photodegradation of the coated polymers was assessed through a photo-degradation test. The characterization of the TiO 2 -embedded polymer was performed using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS), UV/Vis spectroscopy, diffuse reflectance UV–Vis spectra (DR/UV–Vis), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), Fourier transforms infrared spectroscopy (FTIR), and stereomicroscopy. The photocatalytic activity was determined by analyzing the degradation of the model compound, 4-chlorophenol. The results indicated that the controlled-temperature embedding method led to well-TiO 2 -coated polymeric pellets with a high activity and surface area. Thus, the controlled-temperature embedding method is a promising technique for surface engineering in the application of wastewater and drinking water treatment.

A new kinetic model for heterogeneous photocatalytic reactions has been developed as an alternative to the Langmuir–Hinshelwood (L–H) and the Direct–Indirect (D–I) models. The L–H model has been widely used to analyze the kinetics of the TiO2-photocatalytic degradation of water-dissolved organic compounds, assuming the adsorption/desorption equilibrium of the reactants (Langmuir isotherm). Nevertheless, it has been reported by some authors that the experimental data on photocatalytic oxidations are incompatible with the behavior predicted by L–H model. The proposed model, unlike the L–H model, considers all the basic steps involved in heterogeneous photocatalysis with TiO2, including the back reaction involved in the process, and it is applicable to organic species non-adsorbed on the TiO2 surface. In the case of phenol photodegradation, the proposed model better describes, mechanistically, the experimental data than L–H and D–I models.

Se presenta una revisión de la literatura sobre la cuantificación y caracterización de partículas suspendidas (PST) y partículas respirables (PM10) producidas en áreas de explotación carbonífera a cielo abierto. El material particulado es un contaminante complejo por sus características físicas (distribución de tamaño de partícula, morfología y densidad) y por sus características químicas (compuestos orgánicos e inorgánicos, metales y contaminantes primarios y secundarios). Estas características son críticas para determinar el tipo y magnitud de los efectos sobre la salud humana. Se encontró que los trabajos realizados, han empleado experimentos de laboratorio y de campo, así como estudios de modelación. Esta revisión bibliográfica contribuye a una mejor comprensión y evaluación de las tecnologías que se deben usar para encontrar soluciones a este problema de contaminación.

The original publication incorrectly presented the names of 3 authors: Richard Toro A., Raul G. E. Morales S., and Manuel A. Leiva G. The initials were written as suffixes and should be corrected to: Richard A. Toro, Raul G. E. S. Morales and Manuel A. G. Leiva.

Degradation of the bacterium E. coli was studied using a rotatory disk photoreactor manufactured in stainless steel to ascertain this photoreaction system’s behavior in different operating conditions. The photoreactor was equipped with 6 black light bulbs (BLB) used as a source of UV light and fitted with 7 removable disks made of common frosted glass impregnated with TiO2 photocatalyzer which were coupled to a rotation system. TiO2 was impregnated on the disks using the sol-gel method varying molar precursor gel ratios. Abrasion resistance, disk adhesion and surface uniformity tests were carried out for selecting the film presenting the best characteristics. Bacterial photodegradation studies were carried out using the following variable parameters: the disks’ rotation speed, radiation intensity and the number of discs which were directly related to the concentration of photocatalyzer in the system. Up to 64.3% degradation was achieved in 4 hours using 7 disks, low intensity and low rotation speed.

RESUMEN: El comportamiento viscoso de pulpas de cuarzo provenientes de moliendas fue caracterizado midiendo su viscosidad a diferentes tiempos de molienda y para varias concentraciones de sólidos, utilizando un viscosímetro Brookfield. Se usó el modificador reológico hidroxietilcelulosa (HEC) para preparar las suspensiones, evitar el problema de la sedimentación y evaluar la influencia de la concentración de sólidos en la pulpa y la diferencia en la granulometría. Los resultados indican que la característica newtoniana de una solución de HEC al 0.3% se ve afectado con el incremento de sólidos en la suspensión, siendo este efecto más marcado para una concentración de sólidos de 60%. Se observó también que para una misma concentración de sólidos la disminución del parámetro de tamaño de la muestra no produce cambios significativos en el comportamiento reológico de la pulpa, para porcentajes bajos de sólidos (menor a 40%). ABSTRACT: The viscous behavior of quartz pulp from mills was characterized by measuring their viscosities at different times for several grinding times and solid concentrations, using a Brookfield viscometer. The rheology modifier hydroxyethylcellulose (HEC) was used for preparing the suspensions, for avoiding the problem of sedimentation and for evaluating the influence of the concentration of solids on the pulp as well as on the difference in particle size. The results indicate that the Newtonian characteristic of a solution of 0.3% HEC is affected by the increase of solids in the suspension. This effect is more notorious for a solid concentration of 60%. It was also observed that for the same concentration, the solid size reduction parameter of the sample does not produce significant changes in the rheological behavior of the pulp, for low percentages (lower than 40%). COL0014897

There is growing interest in obtaining compounds with photocatalytic activity in the solar spectrum, and this has led to intense research on the topic. In our laboratory, Fe-doped TiO

The photocatalytic efficiency of pure and 0.5‐20 wt.% Fe-containing ZrO 2 samples, prepared by a sol‐gel technique, was tested in the transformation of environmentally important substrates, such as nitrite, EDTA and Cr(VI) and compared with that of TiO2 (Degussa P-25). All samples were active, although the efficiency was lower than that of TiO 2. Nevertheless, the presence of iron increased the activity for nitrite photooxidation, with the maximum efficiency at 5 wt.% Fe content. At higher Fe content, the efficiency decreased but it was always higher than that of the undoped sample. For EDTA oxidation and Cr(VI) reduction, the same trend was observed. Remarkably, Cr(VI) reduction in the presence of EDTA was strongly accelerated, all zirconia samples being as active as P-25, although initial rates were lower and somewhat detrimentally affected by the presence of iron. The photocatalytic activity depends on the structural, surface and optical properties of the sample, on the preparation conditions and on the nature of the photocatalytic reaction. ©1999 Elsevier Science S.A. All rights reserved.

This study shows the changes of natural organic matter (NOM) from Lake Hohloh, (Black Forest, Germany) during heterogeneous photocatalysis with TiO2 (TiO2/UV). The effect of pH on the adsorption of NOM onto TiO2 in the dark and TiO2/UV degradation of NOM was followed using three-dimensional excitation–emission matrix (EEM) fluorescence. At pH values between 4 and 9, the NOM was adsorbed onto TiO2 in the dark with a greater decrease in the fluorescence intensity and in the spectral shapes, especially under acidic pH conditions. However, at pH = 10 there was not adsorption on NOM which led to a negligible changes the fluorescence intensity. A significant high linear correlation was observed between the DOC adsorption onto TiO2 and the maximum fluorescence intensity. Additionally, the NOM adsorption onto TiO2 and its TiO2/UV degradation shifted the fluorescence maxima toward shorter wavelengths in the EEM contour plots, with a decrease in aromaticity. These changes were accompanied by a substantial decrease in the organically bound halogens adsorbable on activated carbon (AOXFP) and the trihalomethane formation potential (THMFP). Thus, the decrease in maximum fluorescence intensity can be used as an indicator of AOXFP and TTHMFP removal efficiency. Therefore, fluorescence spectroscopy is a robust analytical technique for evaluate TiO2/UV removal of NOM.

RESUMEN: Se presentan los resultados del diseño y evaluación de dos sistemas de molienda en circuito cerrado, para un clasificador tipo ciclón neumático y uno tipo harnero vibratorio. Se comparan las eficiencias energéticas bajo similares condiciones de granulometrías a la entrada del molino, conservando el mismo tamaño de corte en el clasificador. El material se caracterizó mediante: fluorescencia de rayos X, area superficial por el método Brunauer-Emmet-Teller y análisis granulométrico por tamizado. Los resultados indican que la velocidad de giro del molino no tiene significancia estadística sobre la eficiencia mecánica de molienda. A partir de un análisis de superficies de respuestas se determinó que el ciclón favorece la eficiencia (valor óptimo 30%) comparado con el harnero (valor óptimo 18%). Los modelos encontrados para la determinación de la eficiencia mecánica del sistema molino-ciclón y molino-harnero, muestran correlaciones del 85 y 83 % respectivamente. ABSTRACT: The design and experimental evaluation of two grinding systems in closed circuit which use two types of classifiers, a pneumatic cyclone and a sieve vibratory, were carried out. The energetic efficiencies under similar conditions in material particle sizes at the mill entrance and keeping the same classifier were compared. The material was characterized by: X-ray fluorescence (XRF), surface area by the method Brunauer-Emmet-Teller and granulometry analysis by sieving. Results show that the mill speed does not have statistical significance over the grinding mechanical efficiency and using a response surface analysis was determined that the cyclone favors the milling (optimum value 30%) against the sieve vibratory type (optimum 18%). Models found for mechanical efficiency determination of the systems mill-cyclone and mill-sieve vibratory, show correlations of 85 % and 83%, respectively. COL0014897

Resumen Sistemas Oxido de Titanio/Oxido de Silicio (TiO 2 /SiO 2 ) fueron obtenidos por anclaje de TiO 2 en SiO 2. El fotocatalizador TiO 2 se obtuvo por alcoholisis del TiCl 4 con 2-propanol y posterior cristalizacion a presion autogena a 200 °C, excluyendo etapas de calcinacion a altas temperaturas. Se emplearon diferentes relaciones SiO 2 /TiCl 4 para determinar su influencia en la estabilidad, propiedades y fotoactividad de los sistemas TiO 2 /SiO 2 . La actividad fotocatalitica fue evaluada por la fotodegradacion de metanol en fase gaseosa. El TiO 2 cristalizo como fase anatasa o como una mezcla rutilo/anatasa, dependiendo por la relacion SiO 2 /TiCl 4 inicial. Los resultados muestran que se producen materiales compuestos con alta cristalinidad del TiO 2 . Se encontro tambien que hay una fuerte relacion entre la actividad fotocatalitica con las propiedades fisicoquimicas y de estas con las composiciones iniciales de sintesis. Palabras clave: sistemas TiO 2 /SiO 2 , fotocatalisis, metodo solvotermico, materiales compuestos

This work reports on the changes in compositions of humic acids (HAs) and fulvic acids (FAs) during photocatalytic degradation. The HAs and FAs were obtained from the XAD-resin fractionation of natural-organic matter (NOM) from a bog lake (Lake Hohloh, Black Forest, Germany). Degussa P-25 titanium dioxide (TiO2) in a suspension and a solar UV simulator (batch reactor) were used in the experiments. The photocatalytic degradation of the HAs and FAs were monitored using size-exclusion chromatography (SEC) equipped with dissolved organic carbon (DOC) and ultraviolet (UV254) detection (SEC-DOC and SEC-UV254) and UV–Vis spectrophotometry. The evolutions of the photocatalytic degradations of the HA and FA fractions were selective. The photocatalytic degradation started with the degradations of high molecular weight compounds with relatively high UV254 absorbances in the HA and FA fractions to yield low molecular weight compounds showing less specific UV254 absorbances. Observance of the same tendency for the original NOM from Lake Hohloh indicates that these XAD-fractions still having complex compound mixtures. However, the larger molecular weight fractions of the FAs showed higher preferential adsorptions onto TiO2, which caused their faster degradation rates. Furthermore, FAs showed a greater reduction of the total THM formation potential (TTHMFP) and the organic halogen compounds adsorbable on activated carbon formation potential (AOXFP), in comparison with the HAs.

Biodiesel production is a very modern and technological area for researchers due to the relevance that it is winning every day because of the increase in the petroleum price and the environmental advantages (Mustafa, 2011). Biodiesel is a mixture of mono-alkyl esters of long chain fatty acids, is an alternative fuel made from renewable sources as vegetable oils and animal fats. It is biodegradable, nontoxic, show low emission profiles and also is beneficial environmentally. (Fangrui and Milford, 1999). Biodiesel is quite similar to petroleum-derived diesel in its main characteristics such as cetane number, energy content, viscosity, and phase changes. Biodiesel contains no petroleum products, but it is compatible with conventional diesel and can be blended in any proportion with fossil-based diesel to create a stable biodiesel blend. Therefore, biodiesel has become one of the most common biofuels in the world (Lin et al., 2011). There are four primary techniques for biodiesel production: direct use and blending of raw oils, microemulsions, thermal cracking and trans-esterification (Siddiquee and Rohani, 2011). Direct use of vegetable oil and animal fats as combustible fuel is not suitable due to their high kinematic viscosity and low volatility. Furthermore, its long term use posed serious problems such as deposition, ring sticking and injector chocking in engine. Microemulsions with alcohols have been prepared to overcome the problem of high viscosity of vegetable oils. Another alternative way to produce biodiesel is through thermal cracking or pyrolysis. However, this process is rather complicated to operate and produce side products that have not commercial value. The most commonly used method for biodiesel production is transesterification (also known as alcoholysis) reaction in presence of a catalyst. Transesterification is the process of exchanging the alkoxy group of an ester compound with another alcohol (Lam et al., 2010). Esterification is the sub category of trans-esterification. This requires two reactants, carboxylic acids (fatty acids) and alcohols. Esterification reactions are acid-catalyzed and proceed slowly in the absence of strong acids such as sulfuric, phosphoric, sulfonic-organic acids and hydrochloric acid (Vyas et al., 2010). The fatty acid methyl esters (FAME) are more used because of its facility of production, however, presents operating problems at low temperatures for its high content of saturated