Revista Internacional de Contaminación Ambiental
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ANÁLISIS DE CONTAMINANTES AMBIENTALES CON POLÍMEROS DE IMPRONTA MOLECULAR
Get PDFEnvironmental pollutants affect negatively the environment, deteriorating the planet. The analysis of complex mixtures frequently requires several pretreatment steps and if the substance to be analyzed is present in low concentration, it needs to be concentrated so that it can be detected by standard analytical techniques. If it is a complex sample of similar compounds, a step is necessary that involves their cleaning. Solid-phase extraction is a widely used technique for sample pretreatment, since it is flexible and easy to automate. Molecularly imprinted polymers possess selective molecular recognition properties because the recognition sites within the polymer matrix are complementary to the molecule under analysis in the form and position of the functional groups. The molecular imprinting technique is based on the preparation of a highly cross-linked polymer around an analyte used as a template molecule, which is initially contacted with a suitable monomer in order to form a pre-polymerization complex and subsequently adds the cross-linker, the initiator and the solvent with which the polymerization is carried out. Once the polymer is obtained, the template molecule is extracted releasing the specific recognition sites. This paper presents a review of the molecular printing process and its applications in combination with solid phase extraction, to be used as an alternative for the pre-concentration of samples of environmental contaminants.Los contaminantes ambientales afectan negativamente al ambiente, deteriorando el planeta. El análisis de mezclas complejas frecuentemente requiere diversos pasos de pretratamiento, y si la sustancia a analizar está presente en baja concentración, es necesario concentrarla para que sea posible detectarla mediante técnicas analíticas estándares. Si se trata de una muestra compleja de compuestos similares, se requiere un paso que implique su limpieza. La extracción en fase sólida es una técnica ampliamente utilizada para el pretratamiento de muestras, ya que es flexible y fácil de automatizar. Los polímeros de impronta molecular tienen propiedades de reconocimiento molecular selectivo debido a que los sitios de reconocimiento dentro de la matriz del polímero son complementarios de la molécula en análisis en la forma y posición de los grupos funcionales. La técnica de impresión molecular se basa en la preparación de un polímero altamente entrecruzado alrededor de un analito utilizado como molécula molde, el cual inicialmente se pone en contacto con un monómero adecuado para formar un complejo de prepolimerización y posteriormente se le añade el entrecruzante, el iniciador y el disolvente con el que se lleva a cabo la polimerización. Una vez obtenido el polímero, se extrae la molécula molde, liberando los sitios de reconocimiento específico. En este trabajo se presenta una revisión del proceso de impresión molecular y sus aplicaciones en combinación con la extracción en fase sólida, para que pueda emplearse como alternativa a la preconcentración de muestras de contaminantes ambientales
EVALUACIÓN DE UN PROCESO ANÓXICO-AEROBIO-REACTOR BIOLÓGICO DE MEMBRANA CON ALTO CONTENIDO DE NITRÓGENO
Get PDFThe fishmeal processing industry generates wastewater with high content of organic load and nitrogen, therefore it should be treated before its discharge into a receiver body. The objective of this research work was to evaluate a biological treatment system (anoxic-aerobic-membrane biological reactor) operated by a company dedicated to the processing of sardine and tuna meal. This treatment system presents incomplete nitrification and denitrification reactions, which cause deficient removal of nitrogen and non-compliance with the maximum allowable discharge limits. The work was developed with scenarios for evaluation, extension and modification of this process through a simulation with the GPS-X software. The results showed deficient denitrification in the anoxic reactor, therefore increased nitrification is required in the aerobic reactor, and the membrane biological reactor (MBR) only fulfilled the objective of filtration. On this basis, scenarios were simulated for modifications in the process, including the elimination of the MBR and the adequacy of a secondary clarifier, which would help in the denitrification process due to its anoxic conditions. The actual system it has a total effectiveness 49.5 % for nitrogen removal, while the adequacy of the system improved the efficiency to 94.7 %.La industria de elaboración de harinas de pescado genera aguas residuales con alto contenido de carga orgánica y nitrógeno que se deben tratar antes de descargarse a un cuerpo receptor. El objetivo de este trabajo de investigación fue evaluar el sistema de tratamiento biológico (anóxico-aerobio-reactor biológico de membrana) que opera una empresa dedicada a la elaboración de harinas de sardina y atún. Este sistema de tratamiento presenta reacciones de nitrificación y desnitrificación incompletas, lo cual ocasiona que la remoción de nitrógeno sea deficiente e incumpla con los límites máximos permitidos de descarga. El trabajo se desarrolló con escenarios de evaluación, ampliación y modificación del proceso a través de la simulación con el programa GPS-X. Los resultados mostraron desnitrificación deficiente en el reactor anóxico, por lo que se requiere un incremento de nitrificación en el reactor aerobio. El reactor biológico de membrana (MBR, por sus siglas en inglés) cumplió sólo con el objetivo de filtración. Con base en ello se simularon escenarios de cambios en el proceso incluyendo la eliminación del MBR y la adecuación de un clarificador secundario, el cual ayudaría en el proceso de desnitrificación por sus condiciones anóxicas. Con el sistema actual se tiene una remoción de nitrógeno total del 49.5 %, mientras que con la adecuación del sistema se alcanzó una eficiencia del 94.7 %
INFLUENCIA DE LOS PARÁMETROS DE OPERACIÓN EN LA DEGRADACIÓN DE NAFTALENO Y FENANTRENO MEDIANTE ELECTROOXIDACIÓN
Get PDFNaphthalene and phenanthrene are polycyclic aromatic hydrocarbons typically found in the environment. Due to their bio-persistence and toxicity for humans and the environment, their removal has become an important issue. The aim of this work was to evaluate the influence of operating parameters in the electrochemical oxidation of naphthalene, phenanthrene and organic matter in synthetic wastewater using a batch recirculation reactor constituted by a Ti/IrO2 anode and a stainless-steel cathode. By using a factorial design 24 with two central points, the most significant factors for the organic matter removal measured as chemical oxygen demand (COD) were determined. Then, the influence of the operating conditions for the degradation of the studied compounds with an experimental design 23 with one repetition was determined. The highest removal efficiencies for naphthalene and phenanthrene were 91 ± 4 and 95 ± 4.2 %, respectively, at a current density of 50 mA/cm2, electrolysis time of 60 min, pH of 2 and recirculation flow rate of 4 L/min.El naftaleno y el fenantreno son hidrocarburos aromáticos policíclicos típicamente presentes en el ambiente. Estos compuestos persistentes resisten la degradación biológica y provocan efectos tóxicos para la salud humana, organismos acuáticos y el ambiente, por lo que es importante desarrollar tecnologías que permitan degradarlos de manera eficiente. El objetivo de este trabajo fue evaluar la influencia de los parámetros de operación en la electrooxidación de naftaleno, fenantreno y materia orgánica presentes en agua residual sintética utilizando un reactor discontinuo con recirculación constituido por un ánodo Ti/IrO2 y un cátodo de acero inoxidable. Mediante un diseño factorial 24 con dos puntos centrales, se determinaron los factores más significativos en la degradación de materia orgánica medida como demanda química de oxígeno. Posteriormente, se determinó la influencia de las condiciones de operación en la degradación de dichos compuestos aplicando un diseño experimental 23 con una repetición. Se obtuvieron eficiencias de degradación de naftaleno y fenantreno de 91 ± 4 y 95 ± 4.2 %, respectivamente, a una densidad de corriente de 50 mA/cm2, tiempo de electrólisis de 60 min, pH de 2 y caudal de recirculación de 4 L/min
EFFECT OF INOCULUM SOURCE ON THE ANAEROBIC DIGESTION OF MEZCAL VINASSES AT DIFFERENT SUBSTRATE-INOCULUM RATIOS
Get PDFVinasses are a very harmful residue for the environment if no treatment takes place before their discharge. The present study focuses on the anaerobic digestion (AD) of mezcal vinasses for treatment and energy generation. The effect of two inoculum sources, anaerobic sludge and cattle manure, were assessed by biochemical methane potential assays (BMP), testing different substrate to inoculum ratios (SI-ratios). Mathematical modeling was performed using three sigmoidal bacterial growth curves (Gompertz, transference and logistic), in order to understand the kinetics of methane production. Anaerobic sludge was digested with vinasses at SI-ratios of 0.1, 0.3 and 0.4 and cattle manure at 0.3, 0.5 and 0.7. When using a 0.3 SI-ratio, the digestion of vinasses with manure showed the highest results regarding biogas (1025.44 ± 33.80 L/kgVS), methane (up to 81 %) and organic matter removal (54 % volatile solids removal). Manure indicated a higher specific methane yield growth, with a longer lag phase. Concentrations containing low vinasses content resulted in an inefficient AD due to the lack of organic matter, whilst concentrations with high vinasses content resulted in AD inhibition. The present work shows that cattle manure is an alternative inoculum source to achieve a more efficient anaerobic digestion. The optimal SI-ratio to be used for the digestion of vinasses is 0.3, at which the bacterial population has enough substrate to work efficiently.Vinasses are a very harmful residue for the environment if no treatment takes place before their discharge. The present study focuses on the anaerobic digestion (AD) of mezcal vinasses for treatment and energy generation. The effect of two inoculum sources, anaerobic sludge and cattle manure, were assessed by biochemical methane potential assays (BMP), testing different substrate to inoculum ratios (SI-ratios). Mathematical modeling was performed using three sigmoidal bacterial growth curves (Gompertz, transference and logistic), in order to understand the kinetics of methane production. Anaerobic sludge was digested with vinasses at SI-ratios of 0.1, 0.3 and 0.4 and cattle manure at 0.3, 0.5 and 0.7. When using a 0.3 SI-ratio, the digestion of vinasses with manure showed the highest results regarding biogas (1025.44 ± 33.80 L/kgVS), methane (up to 81 %) and organic matter removal (54 % volatile solids removal). Manure indicated a higher specific methane yield growth, with a longer lag phase. Concentrations containing low vinasses content resulted in an inefficient AD due to the lack of organic matter, whilst concentrations with high vinasses content resulted in AD inhibition. The present work shows that cattle manure is an alternative inoculum source to achieve a more efficient anaerobic digestion. The optimal SI-ratio to be used for the digestion of vinasses is 0.3, at which the bacterial population has enough substrate to work efficiently
DISEÑO Y ENSAYO DE FIBRAS PLÁSTICAS RECICLADAS PARA REFUERZO DE MORTERO
Get PDFThe generation increase of solid waste represents a challenge for the development of new forms of recycling and reuse of materials. Plastics make up 10 % of solid waste worldwide and can be used to manufacture fibers for concrete and mortars. The aim of this paper was to design, and test recycled plastic fibers incorporated in cement mortars and compare their behavior with that of commercial fibers. For this, three dosages were elaborated: one standard mix, another mix with the designed fibers and a third one with commercial fibers. Test specimens were constructed and mechanical tests of compressive and flexural strength were carried out. The mixture with the developed fibers achieved more than one and a half times the flexural strength of the standard mixture at 28 days, while only a 25 % increase in the case of commercial fibers mixtures was achieved. The compressive resistance also improved. It was concluded that the performance of the designed fibers was better than that of the commercial fibers, and that the use of fibers improved the properties studied with respect to mortars without fibers.El incremento en la generación de residuos sólidos supone un desafío para el desarrollo de nuevas formas de reciclaje y reaprovechamiento de los materiales. Los plásticos constituyen el 10 % de los residuos sólidos a nivel mundial y pueden emplearse para la fabricación de fibras para hormigones y morteros. El objetivo de este trabajo fue diseñar y ensayar fibras plásticas recicladas incorporadas en mortero de cemento y comparar su comportamiento con el de fibras comerciales. Para ello se elaboraron tres dosificaciones: una mezcla patrón, otra mezcla con las fibras diseñadas y otra con fibras comerciales. Se construyeron probetas y se realizaron ensayos de resistencia a flexión y a compresión. La mezcla con las fibras desarrolladas logró más de una vez y media la resistencia a flexión de la mezcla patrón a 28 días, contra sólo un 25 % de aumento en el caso de la mezcla con fibras comerciales. La resistencia a la compresión también se mejoró. Se concluyó que el desempeño de las fibras diseñadas fue mejor que el de las fibras comerciales y que el uso de fibras mejoró las propiedades estudiadas respecto de morteros sin fibras.
LA APLICACIÓN DE LODOS RESIDUALES AFECTA, A CORTO PLAZO, LA BIOMASA MICROBIANA Y SU ACTIVIDAD EN SUELOS SÓDICOS
Get PDFThe effect of applying sewage sludge to sodic soil on C and N mineralization, microbial biomass, microbial enzymatic activity and biological indicators were evaluated. The sodic soil was agricultural, and the incubation experiment was performed at the laboratory level at 56 days with three treatments: control sodic soil group (T1), sodic soil + sewage sludge at 20 Mg/ha (T2) and at 40 Mg/ha (T3). The results obtained for T2 and T3 were: 56.89 and 33.81 % mineralized C, 3.04 and 1.66 % mineralized N, 0.81 and 0.50 % immobilized carbon by microbial biomass in relation to control (T1). The microbial enzymatic activity increased 2.81 and 3.59 times for T2 and T3 with respect to T1. In the biological indicators qCO2, qFDA and Nmin/Cmic, an increase was observed at the beginning of the mineralization dynamics and gradually decreased over time. The application of sewage sludge to sodic soil had a positive effect on the mineralization of C and N, as well as microbial biomass in the short term. The T2 treatment presented a greater efficiency in the mineralization and immobilization of C, but with respect to N mineralization and microbial enzymatic activity no significant differences were found between T2 and T3. It is recommended to evaluate the application doses of the sewage sludge before its application to sodic soils. It is the first time that the use of biological indicators has been reported to evaluate the application of sewage sludge in a sodic soil of Mexico.El efecto de la aplicación de lodos residuales a un suelo sódico sobre la mineralización de C y N, biomasa microbiana, actividad enzimática microbiana e indicadores biológicos fueron evaluados. El suelo sódico fue agrícola y el experimento de incubación se realizó a nivel laboratorio a 56 días con tres tratamientos: suelo sódico testigo (T1), suelo sódico más lodos en 20 Mg/ha (T2) y en 40 Mg/ha (T3). Los resultados obtenidos para T2 y T3 fueron: C mineralizado, 56.89 y 33.81 %; N mineralizado, 3.04 y 1.66 %, y C incorporado a la biomasa microbiana en relación con el testigo (T1), 0.81 y 0.50 %. La actividad enzimática microbiana se incrementó 2.81 y 3.59 veces para T2 y T3 con respecto a T1. Los indicadores biológicos qCO2, qFDA y Nmin/Cmic se incrementaron al inicio de la dinámica de mineralización y disminuyeron paulatinamente. La aplicación de lodos residuales al suelo sódico tuvo un efecto positivo sobre la mineralización de C y N, así como en la biomasa microbiana a corto plazo. El tratamiento T2 presentó una mayor eficiencia en la mineralización e incorporación de C, pero respecto a la mineralización de N y actividad enzimática microbiana no se encontraron diferencias significativas entre los tratamientos T2 y T3. Se recomienda evaluar las dosis de aplicación de los lodos residuales antes de su aplicación a suelos sódicos. Es la primera vez que se reporta el uso de indicadores biológicos para evaluar la aplicación de lodos residuales en un suelo sódico mexicano.
PREDICCIÓN DE DRENAJE ÁCIDO DE MINA, JALES DE LA MINA LA PRIETA, CHIHUAHUA, MÉXICO
Get PDFThe La Prieta mine, Chihuahua, Mexico, was intensively exploited (silver, lead and copper) from colonial times until its closure; consequently, large quantities of tailings produced by metallurgical processing accumulated. These tailings can produce acid mine drainage due to oxidation and hydrolysis reactions. With the objective of predicting if tailings can generate acid drainage, tailings samples were characterized and the possibility of generating acidity was investigated. The pH values found were slightly alkaline (7.8-8.4). On the other hand, sulfates and total sulfur were determined by turbidimetric and infrared methods, respectively. It is worth mentioning that total sulfur was below the limit of detection of the Leco S-144DR equipment and sulfur concentrations in the form of sulfates were very low. The mineralogical characterization showed that pyrite was found in only three samples and in low percentages. The calcite and dolomite minerals present in the skarn type deposit were involved in the neutralization of acid mine drainage and the decreased mobility of most toxic metals and metalloids.La mina La Prieta, Chihuahua, México, fue explotada ampliamente (plata, plomo y cobre) desde la época del virreinato hasta su cierre; por consiguiente, se acumularon grandes cantidades de jales o relaves, producto del procesamiento metalúrgico. Estos jales pueden producir drenaje ácido de mina debido a las reacciones de oxidación e hidrólisis. Con el objetivo de predecir si los jales son generadores de drenaje ácido, se realizó la caracterización de las muestras de jales y la determinación de la posibilidad de generar acidez. Los valores de pH hallados fueron ligeramente alcalinos (7.8-8.4). Por otro lado, los sulfatos y el azufre total se determinaron mediante los métodos turbidimétrico e infrarrojo, respectivamente. Cabe mencionar que la concentración de azufre total estuvo por debajo del límite de detección del equipo Leco S-144DR y las concentraciones de azufre en forma de sulfatos fueron mínimas. La caracterización mineralógica mostró que sólo en tres muestras se encontró pirita, y en bajos porcentajes. Los minerales calcita y dolomita presentes en el yacimiento tipo skarn intervienen en la neutralización del drenaje ácido de la mina y disminuyen la movilidad de la mayoría de los metales y metaloides tóxicos
STUDY OF THE DEGRADATION OF CHLORPYRIFOS IN CONTAMINATED SOILS IN THE PRESENCE OF THE RED CALIFORNIA EARTHWORM Eisenia foetida
Get PDFPesticides containing organophosphorus compounds, such as chlorpyrifos (CPF), are frequently used in agricultural activities, and their use has been increasing due to the presence of multiple plant diseases which threaten the production of vegetable food products. As a result of this practice, the soils in question are often found to be contaminated due to the fact that these pesticides do not immediately degrade and hence remain for long periods of time. The objective of this study was to evaluate the degradation of CPF in the presence and absence of the worm Eisenia foetida (EF) in soils contaminated with 40 mg/kg of CPF during a 28-day period. The D group, whose soil was sterilized and in which no EF worms were present, yielded a CPF-degradation result of 33.68 %. The C group, in which the soil was unsterilized and there were no EF worms present, yielded a degradation percentage of 37.16 %. On the other hand, the B group, containing sterilized soil in which the EF worms were present, yielded a degradation percentage of 60.76 %. Finally, with the A group, in which the soil was unsterilized and EF worms were present, degraded in 74.85 %. Pesticides containing organophosphorus compounds, such as chlorpyrifos (CPF), are frequently used in agricultural activities, and their use has been increasing due to the presence of multiple plant diseases which threaten the production of vegetable food products. As a result of this practice, the soils in question are often found to be contaminated due to the fact that these pesticides do not immediately degrade and hence remain for long periods of time. The objective of this study was to evaluate the degradation of CPF in the presence and absence of the worm Eisenia foetida (EF) in soils contaminated with 40 mg/kg of CPF during a 28-day period. The D group, whose soil was sterilized and in which no EF worms were present, yielded a CPF-degradation result of 33.68 %. The C group, in which the soil was unsterilized and there were no EF worms present, yielded a degradation percentage of 37.16 %. On the other hand, the B group, containing sterilized soil in which the EF worms were present, yielded a degradation percentage of 60.76 %. Finally, with the A group, in which the soil was unsterilized and EF worms were present, degraded in 74.85 %.
COMPOSTING SUGAR CANE BAGASSE AT FULL SCALE: ORGANIC MATTER DECAY KINETICS, METAGENOMICS AND PLANT-GROWTH PROMOTING BACTERIA CAPABILITIES
Get PDFThe management difficulties implied at field-scale composting make difficult to perform kinetic studies, leading to a gap in the literature at real enterprise conditions. Although composting has been reported to show a three-phase kinetics regarding the temperature, for organic matter, an exponential decay kinetics has been described. Organic matter decay, internal temperature of sugar-cane bagasse compost windrows along the time at enterprise (field-scale) level and the microbial community of the final product were analyzed. Final compost was achieved at 12-17 weeks with 41-47 % humidity and 31-47 % organic matter content. Kinetics model of organic matter biodegradation showed R2 ≥ 0.6 and no differences between exponential or linear model R2 were observed. Linear biodegradation constant was 2.5 % of organic matter loss/week, ranging from 2.2 to 3.7 %/week. The most abundant bacterial classes were Bacilli and Anaerolineae from metagenomic analysis. Bacterial cultures isolated showed plant-growth promoting and aromatic degradation capabilities. This shed light to future prospection studies on real-world composting for enterprises and scientists. The management difficulties implied at field-scale composting make difficult to perform kinetic studies, leading to a gap in the literature at real enterprise conditions. Although composting has been reported to show a three-phase kinetics regarding the temperature, for organic matter, an exponential decay kinetics has been described. Organic matter decay, internal temperature of sugar-cane bagasse compost windrows along the time at enterprise (field-scale) level and the microbial community of the final product were analyzed. Final compost was achieved at 12-17 weeks with 41-47 % humidity and 31-47 % organic matter content. Kinetics model of organic matter biodegradation showed R2 ≥ 0.6 and no differences between exponential or linear model R2 were observed. Linear biodegradation constant was 2.5 % of organic matter loss/week, ranging from 2.2 to 3.7 %/week. The most abundant bacterial classes were Bacilli and Anaerolineae from metagenomic analysis. Bacterial cultures isolated showed plant-growth promoting and aromatic degradation capabilities. This shed light to future prospection studies on real-world composting for enterprises and scientists.
SYNTHESIS AND CHARACTERIZATION OF TRANSITION ALUMINAS FROM RECYCLED SCRAP ALUMINUM
Get PDFThe aim of this study was to develop an alternative methodology for the synthesis of transition aluminas, in order to reduce ecological costs by using recycled metal scrap as raw material (cans of soft drinks) and generate a product with high added value. The synthesis technique employed yielded a precursor comprised of 55.4 % of bayerite, 41.2 % of boehmite, and ammonium salt, according the characterization performed with X-ray diffraction and quantification by the Rietveld method. The ammonium chloride salt present is not relevant for the process, since given its solubility in water, it could be eliminated by successive washing. Scanning electron microscopy evaluations showed the presence of agglomerates of particles between 50 and 300 μm. A bimodal grain sizes distribution was detected during the laser granulometric test. Thermogravimetric analysis of the precursor indicated a 40.6 % total weight loss at 1000 ºC. The heat treatments at 350 and 750 ºC of precipitates for 1, 2 and 4 h, produced various transition aluminas (γ, η, θ), which are products where value has been added and might have a potential use as binders in monolithic products, catalyst support, or additives for puzzolanic materials, among others.The aim of this study was to develop an alternative methodology for the synthesis of transition aluminas, in order to reduce ecological costs by using recycled metal scrap as raw material (cans of soft drinks) and generate a product with high added value. The synthesis technique employed yielded a precursor comprised of 55.4 % of bayerite, 41.2 % of boehmite, and ammonium salt, according the characterization performed with X-ray diffraction and quantification by the Rietveld method. The ammonium chloride salt present is not relevant for the process, since given its solubility in water, it could be eliminated by successive washing. Scanning electron microscopy evaluations showed the presence of agglomerates of particles between 50 and 300 μm. A bimodal grain sizes distribution was detected during the laser granulometric test. Thermogravimetric analysis of the precursor indicated a 40.6 % total weight loss at 1000 ºC. The heat treatments at 350 and 750 ºC of precipitates for 1, 2 and 4 h, produced various transition aluminas (γ, η, θ), which are products where value has been added and might have a potential use as binders in monolithic products, catalyst support, or additives for puzzolanic materials, among others