Biodiesel Production Using Lithium Metasilicate Synthesized from Non-Conventional Sources.

A facile and versatile process to produce lithium metasilicate (Li2SiO3) from non-conventional silicon sources (two different sand sources from the central area of México) was developed. The synthesis protocol based on a solid-state reaction followed by a hydrothermal treatment resulted in highly pure lithium metasilicate, as corroborated by XRD, SEM-EDS, and XPS analysis. Furthermore, lithium metasilicate was used as a heterogeneous catalyst for biodiesel production from soybean oil, where conversion yields were compared according to the silicon source used (based on chemical purity, stability, and yield efficiency). The best performing metasilicate material displayed a maximum of 95.5% of biodiesel conversion under the following conditions: 180 min, 60 °C, 5% catalyst (wt./wt., catalyst-to-oil), and 18:1 (methanol:oil). This contribution opens up alternatives for the production of lithium metasilicate using non-conventional precursors and its use as an alternative catalyst in biodiesel production, displaying better chemical stability against humidity than conventional heterogeneous catalysts.

Propranolol degradation through processes based on the generation of hydroxyl free radical.

Pharmaceutical substances such as propranolol (PRO) are an emerging class of aquatic contaminants that have increasingly been detected in ground and surface water. For this reason, the aim of this study was to evaluate the efficiency of advanced oxidation systems for the PRO degradation. The tests started with anodic oxidation (AO), using 0.01, 0.05, and 0.1 M Na2SO4 as the supporting electrolyte and 16, 32, 48, and 64 mA cm-2 as current density. Under the best conditions obtained in AO, the electro-Fenton (EF) process was reviewed, where the effect of Fe2+ was analyzed with 5, 10, 15, and 20 mg Fe2+ L-1. The Fenton reaction (FR) was studied using the Fe2+ concentration that promoted the highest percentage of PRO removal and initial concentration of 16 mg L-1 of H2O2, in addition to these conditions, in the photo-Fenton (PF) system, the effect of UV light with wavelengths 254 and 365 nm were evaluated. The results obtained showed that the degradation efficiency of the EF > AO > PF > FR system along with a percent removal of 94.52, 90.4, 25.97, and 4.4%, respectively. The results showed that PRO can be removed through the studied systems, with the EF system being the most efficient.

Enhancement of the electron transfer and ion transport phenomena in microbial fuel cells containing humic acid-modified bioanodes.

Although microbial fuel cells (MFCs) are an attractive alternative to environmental remediation and power generation, there are still significant limitations related to power density and coulombic efficiency. Previous works have shown that the addition of humic acids (HA, a type of organic matter contained in soils and composting-by-products), improves the fuel to electricity conversion at the porous bioanodes (ba)|anolyte junction. In this work, MFCs having HA-modified bioanodes (MFC/baHA) were prepared and electrochemically analyzed utilizing discharge curves (cell potential vs current density plots) and electrochemical impedance spectroscopy (EIS). This investigation was motivated by looking for a deeper understanding of the functional effects of HA molecules on the operation of baHA-containing Microbial Fuel Cells (MFC/baHA). Our results revealed that the modification of bioanodes with HA molecules decreases the activation energy of the acetate ion oxidation, increasing by a factor of three the consumption rate of this fuel at the baHA|anolyte interface, and enhancing the diffusive transport of these ions through the pores of the baHA permeated by the anolyte.

Study of polarized activated carbon filters as simultaneous adsorbent and 3D-type electrode materials for electro-Fenton reactors.

Electro-Fenton (EF) based water treatment processes using activated carbon (AC) packed beds constitute an attractive approach for the development of competitive degradation technology of persistent pollutants in aqueous effluents. In this work, the results of a study aimed to assess the effect on the EF performance of different parameters of the reactor's operation are presented. By means of a factorial experimental design, the influence of the AC source (lignitic or vegetal), AC acid pre-treatment, particle size distribution and the amount of Fe loaded resin in the reactor were analyzed. From the resulting data it was found that the most influential parameter in the EF performance of the reactor is the AC source. Modest effects were observed for AC acid pre-treatment, which limits Fe ion adsorption on the AC substrate. The use of a wide particle distribution of AC particles was also found to improve inter-particle electrical contact, thus favoring the electrochemical processes that take place inside the reactor. An investigation on the effect of the amount of Fe in the reactor as well as its distribution dynamics, also revealed that an excess of Fe ions in the reactor decreases the EF performance of the system since Fe ions efficiently adsorb on the AC substrate, particularly in non- acid treated samples. The best operation conditions consisted on using un-meshed vegetable AC, without acid pretreatment in an EF reactor loaded with 0.25 g of Fe, which allowed to reach full color removal of bright blue FCP model dye in 70 min.

Inactivation of helminth eggs in an electro-Fenton reactor: Towards full electrochemical disinfection of human waste using activated carbon.

The disinfection of helminth eggs and Escherichia coli contaminated aqueous solutions, was studied using an electro-Fenton reactor equipped with a polarized activated carbon (AC) packed bed and two chambers loaded with cation exchange resins. Experiments using different arrangements and operation conditions, revealed that effective elimination of Escherichia coli takes place in all electrochemical disinfection tests. For the more resistant helminth eggs however, adsorption, electro-oxidation and electro-Fenton experiments showed retention within the reactor and pathogen inactivation values of 0, 16, and 25%, respectively. Using helminth eggs concentration data in different sections of the reactor, optical microscopy analysis and an exploratory computer simulation, differences in the disinfection performance were explained and new recirculation and flow direction and polarization switching operation schemes were defined. The corresponding experiments revealed that the effective coupling between adsorption and electro-Fenton phenomena, all along the AC packed bed compartment, results in 100% inactivation of helminth eggs.

Evaluation of Yarrowia lipolytica Oil for Biodiesel Production: Land Use Oil Yield, Carbon, and Energy Balance.

Oils from yeasts have emerged as a suitable alternative raw material to produce biodiesel, due to their similar composition to common raw materials such as vegetable oils. Additionally, they have the advantage of not competing with human or animal feed, and, furthermore, they do not compete for arable land. In this work, a carbon and energy balance was evaluated for Yarrowia lipolytica as a model yeast, using crude glycerol from biodiesel as the only carbon source, which improves biodiesel overall yield by 6%. The process presented a positive energy balance. Feasibility of yeast oil as biodiesel substrate was also evaluated by determination of the lipid fatty acid profile and cetane number. Moreover, a comparison of oil yields, in terms of land use, between vegetable, microalgae, and yeast oils is also presented. The results showed that Y. lipolytica oil yield is considerably higher than vegetable oils (767 times) and microalgae (36 times).

Novel arrangement for an electro-Fenton reactor that does not require addition of iron, acid and a final neutralization stage. Towards the development of a cost-effective technology for the treatment of wastewater.

A novel arrangement for an electro-Fenton reactor aimed to treat neutral wastewater is presented. The arrangement consists on three-compartments in series, two of them packed with a cation exchange resin and one positioned between these, containing a polarized activated carbon column where the electrochemical generation of the Fenton reagent takes place. While the hydroxyl radicals electrochemically produced in-situ, react with the pollutant species adsorbed on the activated carbon cathode, the resin compartments administrate and collect the iron cation and the hydrated proton species in alternating flow direction cycles. The resulting process is a system that does not require acid or iron chemical addition to the process while at the same time, renders decontaminated water free of iron-dissolved species at neutral pH. The proposed electrochemical reactor arrangement is therefore the basis for the design of commercially viable electro-Fenton reactors in which the addition and subsequent removal of acid and iron chemicals is avoided; two of the currently most limiting features for the development of electro-Fenton technology for treating wastewater.

Study of different carbon materials for their use as bioanodes in microbial fuel cells.

Microbial fuel cells (MFCs) are capable of removing the organic matter contained in water while generating a certain amount of electrical power at the same time. One of the most important aspects in the operation of MFCs is the formation of biofilms on the anode. Here, we report the characterization of different carbon electrodes and biofilm using a rapid and easy methodology for the growth of biofilms. The biofilms were developed and generated a voltage in less than 4 days, obtaining a maximum of 0.3 V in the cells. Scanning electron microscopy images revealed that growth of the biofilm was only on the surface of the electrode, and consequently both carbon cloth Electrochem and carbon cloth Roe materials showed a greater quantity of volatile solids on the surface of the anode and power density. The results suggested that the best support was carbon cloth Electrochem because it generated a power density of 13.4 mW/m(2) and required only a few hours for the formation of the biofilm.

Chemically pretreating slaughterhouse solid waste to increase the efficiency of anaerobic digestion.

The combined effect of temperature and pretreatment of the substrate on the anaerobic treatment of the organic fraction of slaughterhouse solid waste was studied. The goal of the study was to evaluate the effect of pretreating the waste on the efficiency of anaerobic digestion. The effect was analyzed at two temperature ranges (the psychrophilic and the mesophilic ranges), in order to evaluate the effect of temperature on the performance of the anaerobic digestion process for this residue. The experiments were performed in 6 L batch reactors for 30 days. Two temperature ranges were studied: the psychrophilic range (at room temperature, 18°C average) and the mesophilic range (at 37°C). The waste was pretreated with NaOH before the anaerobic treatment. The result of pretreating with NaOH was a 194% increase in the soluble chemical oxygen demand (COD) with a dose of 0.6 g NaOH per g of volatile suspended solids (VSS). In addition, the soluble chemical oxygen demand/total chemical oxygen demand ratio (sCOD/tCOD) increased from 0.31 to 0.7. For the anaerobic treatment, better results were observed in the mesophilic range, achieving 70.7%, 47% and 47.2% removal efficiencies for tCOD, total solids (TS), and volatile solids (VS), respectively.

Planktonic cyanobacteria of the tropical karstic lake Lagartos from the Yucatan Peninsula, Mexico.

The tropical karstic lakes on the Mexican Caribbean Sea coast are numerous. However, there is an enormous gap of knowledge about their limnological conditions and micro-algae communities. In the present study, surface water samples were collected monthly from November 2007 to September 2008 to provide taxonomical composition and biovolume of planktonic cyanobacteria of the lake Lagartos from State of Quintana Roo, Mexico. Water temperature, pH, conductivity, salinity, soluble reactive phosphorus (SRP), dissolved inorganic nitrogen (DIN), and soluble reactive silica (SRSi) levels were also analyzed. A total of 22 species were identified. Chroococcales and Oscillatoriales dominated the phytoplankton assemblages during the study period. Chroococcus pulcherrimus, Coelosphaerium confertum, Cyanodyction iac, Phormidium pachydermaticum and Planktolyngbya contorta were recorded for the first time in Mexico. A surplus of DIN (mean value of 42.7 microM) and low concentrations of SRP (mean value of 1.0 microM) promoted the enhanced growth and bloom formation of cyanobacteria. The mean biovolume was 3.22 x 10(8) microm3/mL, and two biovolume peaks were observed; the first was dominated by Microcystis panniformis in November 2007 (7.40 x 10(8) microm3/mL), and the second was dominated by Oscillatoriaprinceps in April 2008 (6.55 x 10(8) microm3/mL). Water quality data, nitrates enrichment, and trophic state based on biovolume, indicated that Lagartos is a hyposaline, secondarily phosphorus-limited, and eutrophic lake, where the cyanobacteria flora was composed mainly by non-heterocystous groups.

Planktonic Cyanobacteria of the tropical karstic lake Lagartos from the Yucatan Peninsula, Mexico / Las cianobacterias planctónicas del lago tropical cárstico Lagartos de la Península de Yucatán, México

The tropical karstic lakes on the Mexican Caribbean Sea coast are numerous. However, there is an enormous gap of knowledge about their limnological conditions and micro-algae communities. In the present study, surface water samples were collected monthly from November 2007 to September 2008 to provide taxonomical composition and biovolume of planktonic cyanobacteria of the lake Lagartos from State of Quintana Roo, Mexico. Water temperature, pH, conductivity, salinity, soluble reactive phosphorus (SRP), dissolved inorganic nitrogen (DIN), and soluble reactive silica (SRSi) levels were also analyzed. A total of 22 species were identified. Chroococcales and Oscillatoriales dominated the phytoplankton assemblages during the study period. Chroococcus pulcherrimus, Coelosphaerium confertum, Cyanodyction iac, Phormidium pachydermaticum and Planktolyngbya contorta were recorded for the first time in Mexico. A surplus of DIN (mean value of 42.7µM) and low concentrations of SRP (mean value of 1.0µM) promoted the enhanced growth and bloom formation of cyanobacteria. The mean biovolume was 3.22X10(8)µm³/mL, and two biovolume peaks were observed; the first was dominated by Microcystis panniformis in November 2007 (7.40X10(8)µm³/mL), and the second was dominated by Oscillatoria princeps in April 2008 (6.55X10(8)µm³/mL). Water quality data, nitrates enrichment, and trophic state based on biovolume, indicated that Lagartos is a hyposaline, secondarily phosphorus-limited, and eutrophic lake, where the cyanobacteria flora was composed mainly by non-heterocystous groups.

Los lagos cársticos tropicales en la costa del Caribe mexicano son numerosos. Sin embargo, existe un enorme desconocimiento acerca de sus condiciones limnológicas y de las comunidades de microalgas que se desarrollan en ellos. El objetivo del presente estudio fue estudiar las condiciones limnológicas en las que crecen las poblaciones de cianobacterias planctónicas del lago Lagartos, Quintana Roo, México. Las recolectas se realizaron de forma mensual entre noviembre 2007 y septiembre 2008. Las especies fueron identificadas y su biovolumen determinado. Se midieron in situ la temperatura del agua, pH, conductividad y salinidad. También, se analizaron las concentraciones de fósforo reactivo soluble (SRP), nitrógeno inorgánico disuelto (DIN) y sílice reactivo soluble (SRSi). Se identificaron 22 especies de cianobacterias. Chroococcus pulcherrimus, Coelosphaerium confertum, Cyanodyction iac, Phormidium pachydermaticum y Planktolyngbya contorta fueron nuevos registros para México. Un exceso de DIN (valor promedio de 42.7µM) y bajas concentraciones de PRS (valor promedio de 1.0µM) promovieron la proliferación de cianobacterias. El biovolumen presentó dos picos: el primero en noviembre 2007, dominado por Microcystis panniformis (7.40X10(8)µm³/mL) y el segundo en abril 2008, representado por Oscillatoria princeps (6.55X10(8)µm³/mL). Los datos de calidad del agua, el enriquecimiento por nitratos y el estado trófico basado en el biovolumen, indican que Lagartos es un lago hiposalino, eutrófico, con limitación secundaria por fósforo, donde los crecimientos masivos de cianobacterias sin heterocitos fueron recurrentes.

Assessment of the quality and toxicity of the discharges of a wastewater treatment plant and alternatives to improve its operation.

Wastewater discharges into freshwater bodies represent a serious ecological problem worldwide. In underdeveloped and developing countries wastewater treatment plants (WTP) only count with basic treatment, leading to the pollution of important aquatic reservoirs causing critical situations. In the present work, a one year evaluation of toxicity and main physical and chemical parameters of one of the major WTP of the state of Aguascalientes was conducted fortnightly, and to assess treatment alternatives for this WTP we tested: a) three white rot fungi (WRF), b) a photo-electrochemical process, c) ion-exchangers resins and activated carbon. The 3 WRF exhibited high COD removal from influents (72 - 95 %) but only Phanerochaete chrysosporium reached significant toxicity removals (70 and 55 %, for an influent and an effluent, respectively). Treatments with electrochemical advanced oxidation processes resulted with the highest toxicity and COD removals (96 % for both parameters) in comparison to biological and physicochemical treatments. Adsorption with activated carbon, zeolite and chelex ion-exchange resins removed 60 - 90 % of COD and 60 - 99 % toxicity. These results could be used to improve operation of the Industrial Park WTP and to plan future modifications to the plant.

[Alteplase in acute coronary syndromes]. / Registro de Alteplasa en Síndromes Coronarios Agudos con elevación del ST (REALSICA).

OBJECTIVE: The registry intends to establish the safety and security of one-hour 100 mg alteplase infusion and 50 mg in 30 minutes to facilitate percutaneous coronary intervention (PCI) in a cardiology hospital with primary angioplasty program (24 hours 365 days a year) with current doses of unfractionated heparin and enoxaparin. METHODS AND RESULTS: REALSICA II is a prospective registry that included 103 patients with final diagnosis of ST elevation myocardial infarction in which Alpert's quality criteria were used. Seventy two patients were under one-hour 100 mg alteplase infusion and thirty one under 30 minutes 50 mg alteplase infusion to facilitate PCI. Patients were young and predominantly males. In both groups > 50% had extensive ST elevation myocardial infarction and 68% were Killip & Kimball I. The majority received reperfusion > 3 hours after the onset of symptoms. In-hospital and follow-up treatment were compliant with Mexican Cardiology Society guidelines. ECG reperfusion was observed in 59% and TIMI III flow in 19% of PCI group. Any intracranial hemorrhage was observed. Global cardiovascular mortality was 11%. Patients under PCI had low incidence of recurrent ischemia and reinfarction. CONCLUSION: REALSICA registry showed in non-complicate acute myocardial infarction ST elevation safety and security of one-hour 100 mg alteplase infusion with current recommended unfractionated heparin and enoxaparin doses in ST elevation myocardial infarction. In complicated patients the regimen to facilitate PCI was associated with increased hemorrhagic complications and requires further research.

Registro de Alteplasa en Síndromes Coronarios Agudos con elevación del ST (REALSICA) / Alteplase in acute coronary syndromes

OBJECTIVE: The registry intends to establish the safety and security of one-hour 100 mg alteplase infusion and 50 mg in 30 minutes to facilitate percutaneous coronary intervention (PCI) in a cardiology hospital with primary angioplasty program (24 hours 365 days a year) with current doses of unfractionated heparin and enoxaparin. METHODS AND RESULTS: REALSICA II is a prospective registry that included 103 patients with final diagnosis of ST elevation myocardial infarction in which Alpert's quality criteria were used. Seventy two patients were under one-hour 100 mg alteplase infusion and thirty one under 30 minutes 50 mg alteplase infusion to facilitate PCI. Patients were young and predominantly males. In both groups > 50% had extensive ST elevation myocardial infarction and 68% were Killip & Kimball I. The majority received reperfusion > 3 hours after the onset of symptoms. In-hospital and follow-up treatment were compliant with Mexican Cardiology Society guidelines. ECG reperfusion was observed in 59% and TIMI III flow in 19% of PCI group. Any intracranial hemorrhage was observed. Global cardiovascular mortality was 11%. Patients under PCI had low incidence of recurrent ischemia and reinfarction. CONCLUSION: REALSICA registry showed in non-complicate acute myocardial infarction ST elevation safety and security of one-hour 100 mg alteplase infusion with current recommended unfractionated heparin and enoxaparin doses in ST elevation myocardial infarction. In complicated patients the regimen to facilitate PCI was associated with increased hemorrhagic complications and requires further research.

Electroreduction of Cr(VI) to Cr(III) on reticulated vitreous carbon electrodes in a parallel-plate reactor with recirculation.

The reduction of Cr(VI) to Cr(III) is achieved in a flow-by, parallel-plate reactor equipped with reticulated vitreous carbon (RVC) electrodes;this reduction can be accomplished by the application of relatively small potentials. Treatment of synthetic samples and field samples (from an electrodeposition plant) results in final Cr(VI) concentrations of 0.1 mg/L (i.e., the detection limit of the UV-vis characterization technique used here) in 25 and 43 min, respectively. Such concentrations comply with typical environmental legislation for wastewaters that regulate industrial effluents (at presenttime = 0.5 mg/L for discharges). The results show the influence of the applied potential, pH, electrode porosity, volumetric flow, and solution concentration on the Cr(VI) reduction percentage and on the required electrolysis time. Values for the mass transfer coefficient and current efficiencies are also obtained. Although current efficiencies are not high, the fast kinetics observed make this proposed treatment an appealing alternative. The lower current efficiency obtained in the case of a field sample is attributed to electrochemical activation of impurities. The required times for the reduction of Cr(VI) are significantly lower than those reported elsewhere.

La reacción paradójica a la TRH en la enfermedad de Cushing no es una prueba diagnóstica cinfiable / The paradoxical response to TRH in Cushing's disease is not a reliable diagnostic test

En sólo uno de seis pacientes con enfermedad de Cushing dependiente de un tumor de la hipófisis se obtuvo un incremento paradójico de ACTH y cortisol plasmáticos despúes de la administración de TRH. Por lo contrario, todos los pacientes mostraron un incremento normal de los niveles séricos de TSH y prolactina como reacción a la aplicación de TRH. Se presentan las características clínicas y bioquímicas de cada caso. Los datos obtenidos confirman la impresión general acerca de la inutilidad de la prueba de TRH para el diagnóstico de la enfermedad de Cushingg

La diabetes insípida como complicación de la cirugía de hipófisis / Diabetes insipidus as a complication of pituitary surgery

Se presenta una revisión de 52 pacientes a quienes se diagnosticó un tumor hipofisario y fueron sometidos a cirugía de la hipófisis por abordaje transesfenoidal (n=42) y por vía cranial (n=10). Se investigó la frecuencia de diabetes insípida que resultó ser de 42.3% en la variedad "transitoria" y de 3.8% en la "permanente". Tal diagnóstico se hizo con base en los índices: volumen urinario > 150 ml/hora, osmolaridad sérica 286 + ou - 4 m Osm.Kg H20 y la relación osmolaridad urinaria/osmolaridad sérica. No se encontró relación con la vía de abordaje quirúrgico, extensión del tumor o tipo de secreción endocrina. En el 80% de los casos la poliuria se presentó en las primeras 16 horas poscirugía y en el 20% en las siguientes 40. El manejo se hizo con reposición de volumen y hormona antidiurética acuosa (Pitressin) en las primeras 48 horas después de la cirugía. En los casos en que persistió la poliuria se usó clorpropamida. La diabetes insípida se presenta frecuentemente como complicación temprana de la cirugía de hipófisis pero su evolución es benigna y el tratamiento sencillo